Friday, June 30, 2017

1899: Is asthma simply a "Nerve Storm?"

Nerve Storm: Seizure, as in seizure of the entire body (epilepsy), seizure of the muscles of a certain joint (gout) or seizure of the respiratory bronchi (asthma). The seizure is caused by some imbalance either internal (emotion) or external that triggers the abnormal response of the brain.

I've read about asthma being described this way in many older journals, yet Dr. Joe Shoemaker, in his 1899 book, "The Monthly Encyclopedia of Practical Medicine" (Philadelphia, Vol. XIII), uses this term with force.

He further describes asthma as:
  • A disease essentially due to some nervous change (this was the accepted dogma of the time)
  • Partial hereditary (so we still think this)
  • It's occurrence is largely in "neurotic" subjects
  • It's occurrence in families subject to migraine (hmmm, where does this come from?)
  • Attacks are characteristic of asthma (dyspnea due to bronchospasm)
  • Pt inclined to hold to a chair or bed railing firmly to help expiratory muscles of expiration
  • And all this is caused by a "nervous storm"
  • Triggered by some unknown cause
  • The cause of who has such a "nervous change" also remains a mystery
  • It's seen in children and some adults
  • It's rare
  • Sudden in onset
  • Occurs between 2-4 a.m. (remember, this is based on his observations)
  • Accessory and natural muscles of respiration are contracting vigorously
  • Dusky face shows embarrassment to circulation and deficient oxygen in the blood
  • Sweating skin shows muscular exertion
  • Lungs enlarged during paroxysm
  • Yet auscultation shows little to no air entering them
  • No normal respiratory murmur, instead expiratory whistle is heard upon austultation
  • Sonorous rhonchi often heard (which is what we now call a wheeze)
  • Duration of attack is variable, yet is often over by morning
  • Duration may last 24 hours or longer
  • Attack ends with expulsion of mucus
  • No continued cough or expectoration
This is all part of the nervous storm we call asthma. What do you think?

Wednesday, June 28, 2017

1950s: The first peak flow meter

Wrights original peak flow meters (circa 1950s)
If you're an asthmatic you may not be familiar with Dr. Martin Wright, but you probably are familiar with an instrument he invented:  the peak flow meter.  It was a convenient, inexpensive, hand held tool that could be used by patients at home or in the hospital setting to assess the effects of bronchitis and asthma.  

It was first introduced in the 1950s by London physician, Dr. Martin Wright, of the Clinical Research Center at Northwick Park Hospital.  It was an instrument specifically designed to measure 'peak flow,' or the amount of air that can be forced out of a patient's lungs after a maximum inhalation.  

The original Wright Peak Flow Meter was a large, heavy, clock shaped device that was too expensive for the common person to have at home. It was generally used in hospitals to assess patients. It worked by the patient blowing air into the meter, and this air rotated a pointer on a dial against the resistance of a spring. The device gave the first accurate readings of a peak flow.

Mini Wrights Peak Flow Meters (circa 1970s)
In the 1970s, Dr. Wright invented a new device that was inexpensive and portable.  It's basically just a "tube with a spring inside and a calibrated scale along the outside.  The puff from the patient under test pushes the spring back.  A pointer registers the furthest point reached.  The meter comes complete with a set of cardboard mouthpieces.  Doctors recon that the instrument could be useful in home treatment. Patient's could monitor their own lung power in a simple and cheap way of determining recovery from lung ailments." (1, page 675)

This instrument was called a "Mini Wright," although ultimately it became known as the peak flow meter. The devices were ultimately manufactured by various companies, and now you can get an array of different types. The first ones were not disposable, although they were soon thereafter manufactured for single patient use only, and the separate cardboard mouthpieces are no longer needed  

Many peak flow meters available today
I remember the "Mini Wright" from when I was an asthma patient back in the late 1970s and throughout the 1980s. Gone are the days of the Mini Wright, replaced by the even cheaper plastic models.

Can you guess how many peak flow meter brands are on the market today?  I couldn't even fathom a guess, although I've had over 20 in my grasp at one point or another.

  1. "Hot Air Invention," New Scientist, March 1, 1979, page 675
Further reading and another picture:

1980-2000: Evolution of Artificial Respiration

So we must continue on our journey through the evolution of artificial resuscitation or respiration. This journey made it's way from simple mouth to mouth breathing all the way to volume ventilators. That pretty much takes us to the 1980's.

Figure 1 -- Drawing of Down's Flow Generator
Face Mask CPAP
1980sDown's Flow Generator:
Continuous Positive Airway Pressure (CPAP) was something that was researched in the 1930's and 40's and then dropped. This research was picked up again as it was believed a continuous flow of pressure during inspiration and expiration might be helpful to patients with sleep apnea and chronic lung diseases.

The most common mode of delivery was by using a Down's Flow Generator. The generator was connected to a 50 PSI source and corrugated tubing. The opposite end of the tubing was connected to a mask with a Positive End Expiratory Pressure (PEEP) valve. (Keep in m;ind here that PEEP and CPAP are basically the same thing.)  The mask was securely strapped to the patient's face.

A pressure manometer was sometimes attached to the mask and an oxygen analyzer was sometimes added to the circuit using a T-piece to monitor how much oxygen the patient was receiving. A venturi-system allowed the caregiver to determine the percentage of oxygen allowed to the patient.

Ideally, a CPAP of 7.5 was supposed to increase the partial pressure of oxygen of alveolar air (PaO2) by one percent, just enough to force more oxygen into the blood to make a clinical difference. It is in this way that CPAP or PEEP were determined to improve oxygenation. (1)

A nice thing about these generators is they were completely pneumatic, meaning no electricity was needed. A downside to these generators is that they did not have alarms, meaning there was no way of knowing for sure that the patient was getting in the dialed in CPAP.

This system was used until the mid 1990s when electronic noninvasive positive pressure breathing machines entered the scene. We had one of these units at Memorial Medical Center when I started working, although I never had the good fortune of using one.

While rarely used in hospitals today, they are still used by Paramedics in the field.

1980s: Pressure Support Ventilation:

1980s: Pressure Controlled Ventilation:

1980s:  Airway Pressure Release Ventilation:  here is a good article.

1980s: Inverse Ratio Ventilation:

Puritan Bennete 7200
1983:  Puritan Bennett 7200 Micro-processor Ventilator:  This was the first microprocessor volume ventilator to hit the market. The machine was very durable and simple to use.  The settings were set by scrolling through an LED screen, and alarms were set in the same way.

It was easily used, portable, and worked well for the patient.  It quickly became the "most widely used ventilator around the world, capturing a 60 percent share of the international market by the end of the decade. (2)

This was the most common ventilator when I entered the respiratory therapy scene in 1995. It was in a majority of hospitals I worked as a student.

Bird 6400 ST
1986:   The Bird 6400 ST:   This ventilator was the first of the new generation of volume ventilators to hit the market. It was a rectangular shaped ventilator with all your basic knobs on the front, including volume control, assist control, SIMV, PS and CPAP modes. It also had a PEEP valve that was easily adjusted by a dial, and a full set of alarms.

The only knock on this simple device was the expiratory valves needed to be cleaned between each use and were a pain in the butt to put back together and keep in functioning order. It was a very compact ventilator for its time. We had two of these ventilators at Memorial Medical Center (MMC) when I started in November of 1997.

After purchasing a Servo 300 Ventilator around 2000, we kept one Bird in circulation until 2008.

1988: Respironics BiPAP:  It was introduced to provide noninvasive positive pressure ventilation to spontaneously breathing patients in the hospital setting using a mask. It could be set in ST mode to deliver IPAP and EPAP, or it could be set in CPAP mode to deliver CPAP.

Servo 300
1991: Seimen's Servo 300 Ventilator. This was a replacement ventilator for the Servo 900 and was generally created to complete with the the Puritan Bennett 7200.  It was much simpler to use than the old 900 version, and therefore was less intimidating. It included some very nice features, and some new modes, as noted below.

1991:  Pressure Regulated Volume Control: It had a new mode called Pressure Regulated Volume Control (PRVC) which made it so the patient could get a guaranteed volume, yet a sensor in the machine sensed changes in patient lung compliance to make sure the lowest pressure possible was given.

1991:  Volume Support:  Similar to pressure support, although it guaranteed the patient achieved a certain tidal volume with each breath. It was basically a pressure support breath that guaranteed tidal volumes. When weaning a patient.

1991: Automode: The Servo 300 had an option called automode. The caregiver would set the patient up in a control mode. As the patient began spontaneously breathing, the machine would sense this and switch over to a support mode. For instance, if PRVC was the set mode, the machine would switch to volume support (VS). If Pressure Control was the set mode, the machine would switch to pressure support (PS).

Servo 300 A Control Panel
This was nice because it allowed patients to control the ventilator rather than the other way around. This was another mode that made mechanical ventilation more comfortable for patients.

It could also be useful as a tool to see if patients were ready to be weaned. For instance, a post operative patient would be started in PRVC mode with automode. When the patient began to wake up and spontaneously breathe, the machine would sense this and switch over to volume support.

Of course, if the patient stopped spontaneously breathing, the machine would sense this and switch back to PRVC.

1991:  Flowby:  Another neat feature of this machine was that it allowed caregivers to choose between pressure sensitivity or flow sensitivity. Prior to the Servo 300, most ventilators used pressure sensitivity, meaning the patient had to make an effort to draw in a set pressure, usually 2-3cwp.

Flowby actually made machines more sensitive to the needs of the patient. A constant flow was maintained throughout the circuit. As the patient drew some of this flow, a breath was given.

Therapists had a choice between setting the sensitivity between 2-14 cwp, or in the green flowby range. As therapists became educated on the benefits of flowby it became the preferred choice. I believe most newer ventilator models do not even offer pressure sensitivity as a choice, and simply go with flowby.

1991:  Ventilator Graphics:  Another neat feature of this ventilator is that it also allowed for a graphics screen to be added. I think our machine did not have the graphics screen initially, but it was eventually added. This was nice because you could use graphics to adjust settings to improve patient comfort. Graphics also helped determine if suctioning was needed, or if there was a leak in the system. This was all part of improving patient comfort.

And that's not all.  It was also the first ventilator that could be adjusted for use by adults, pediatrics, and neonates. This made it a more universal device. Safety valves were in place, whereby neonates could not receive a tidal volume higher than 40, and pediatrics could not receive a tidal volume higher than 400.

Alarms were all red knobs. The LED showing dialed in settings were green. The LED showing what the patient was doing were all red. This made it easy to know what the machine was doing and what the patient was doing. We would often tell nurses, "Red bed, Green machine."   (d)

 This ventilator was used at MMC until the purchase of a Servo i made it no longer relevant. It continued to be a back-up ventilator until taken out of service in 2015.

1992:  V.I.P. Bird Infant Pediatric System

It was referred to as the T-Bird ventilator. At the time it was also the first and only ventilator that was mobile.

1988:  Noninvasive Positive Pressure Ventilation (NIPPV): Providing positive pressure breaths using a ventilator hooked up to an endotracheal tube was nice, although it was associated with a host of complications, and this was mainly due to the fact that it was invasive. Invasive ventilation essentially entails providing mechanical breaths through an endotracheal tube.

It was linked with an increased risk for nosocomial pneumonia. It was also difficult to get patients with end stage lung diseases weaned from ventilators. This created an ideal market for NIPPV.

NIPPV is essentially mechanical ventilation without the use of an endotracheal tube. It generally entails using applying a mask to the patient's face. In the hospital setting a full face mask is used, or a mask that covers the mouth and nose. However, a nasal mask or full

Now, technically speaking, IPPB was a form of NIPPV before NIPPV became a common acronym for CPAP and BiPAP machines. Electronic CPAP machines became common for the treatment of sleep apnea. A constant flow of pressure during inspiration and expiration helped to keep airways open. This assured the upper airway did not collapse while sleeping, and made sure that apnea episodes did not happen. It also kept alveoli open to assure adequate oxygenation.

Electronic CPAP machines were produced by a variety of manufacturers for use at home. These machines have become smaller, quieter, and more convenient over the years.

BiPAP is an acronym for Bilevel Positive Airway Pressure. It was first used in 1988 by professor Benzer of Innsbruck. It refers to a machine that delivers PEEP/ CPAP during expiration, and Pressure Support during inspiration.

When BiPAP is used, different acronyms are used as follows
  • Inspiratory Positive Airway Pressure (IPAP): This refers to pressure support, or a flow of positive pressure during inspiration to assist with inspiration. This basically helps to control ventilation, or to assure adequate tidal volumes. This is adjusted to blow off carbon dioxide. However, increases in tidal volume may also improve oxygenation. 
  • Expiratory Positive Airway Pressure (EPAP): This refers to a constant flow of pressure on expiration, also known as CPAP or PEEP. This keeps airways open. It increases the partial pressure of oxygen in the alveoli to force more oxygen into the blood stream. This is adjusted to improve oxygenation. 
Machines used in the hospital setting tended to be larger than home machines. This was due to the need for alarms in the hospital setting to monitor tidal volume, pressure, and oxygen levels. 

BiPAP machines became increasingly popular during the 1990s. Most were capable of providing patients with either CPAP or BiPAP, and this made it so that Downs Flow Generators were no longer needed and were phased out. This was about the phase I entered into. As a matter of fact, when I was in RT school BiPAP was covered vaguely. When I started as an RT it was only occasionally used. 

Early machines were were electric although not connected to oxygen. This meant that oxygen had to be bleed into the circuit from an external source. This sometimes made it difficult to meet oxygen demands of patients, and resulted in some patients being intubated. This problem was solved by later BiPAP models, such as the Vision. 

Regardless, early BiPAP macines gave physicians another option for helping patients. They were increasingly used for who were in respiratory failure or impending respiratory failure. This basically offered physicians a noninvasive method of treating hypoxia and ventilatory failure in patients who had a spontaneous drive to breathe, and who were capable of ripping the mask off if necessary. These machines prevented many patients from needing a ventilator, and they are still used to this day. 

1996: Respironics Vision:  

 Some of the initial models were crude and called for supplemental oxygen to be connected into the system, but new systems, such as the Vision, are touch screen, have flow and pressure waveforms, and allow the machines to be used pretty much like a ventilator.  The advantage is you can ventilate a patient and improve oxygenation without having to intubate the patient.  Masks can be removed for eating and drinking and taking medicine, and also oral care.  Studies show these machines work great for COPD, CHF and even some asthma patients.  They also work well for home use for patients with obstructive sleep apnea. Modern BiPAP machines are also more effective than the aforementioned down's flow generator in delivering CPAP, and the machines also allow for alarms and patient monitoring. 

2000:  Servo i, 840, Avea Ventilators

It has all the same features as the Sero 300 except that the flaws of the 300 have been corrected.  Instead of having all the dials on the front the settings are set by an easy to use touch screen.  The basic settings of rate, tital volume, and FiO2 could be set either this way or by quick access dials on the bottom of the screen.  The ventilator was also connected to a graphics screen for easy to see ventilator graphics.  (d)  Other similar ventilators include the Puritan-Bennett 840 and the Avea Ventilator.  These newer vents are microprocessor vents that include a variety of modes to improve patient comfort.  They also include waveforms to monitor the patient, and a variety of alarms.  Modern vents are also upgradeable. 

The future:  What will the future bring?  


  1. n l Need Reference
  2. "Puritan Bennett Corporation History,",, accessed 4/8/16

  1. (d)"About us:  History of Ventilation,",, accessed February 27, 2012
  2. "Face Mask CPAP," 

Monday, June 26, 2017

1950: Life for polio victims inside an iron lung

This is Richard Daggett in an iron lung. The photo was
added by Dagett at
There were various versions of the Emerson Lung, and the Drinker and Shaw Respirator, that were available in hospitals around the United States and Europe by the 1950s. Richard Daggett, in his 2010 book "Not just polio: my life," explains that the machines made a whooshing sound as air entered and exited the patient's lungs. He explained that he was placed in a Drinker Collins Iron Lung in the early 1950s, and he described waking up in the machine: (4, page 30, 31)
There was a mirror over my head and, in the mirror, I could see a row of large black bellows across the room.  They were going up and down.  I didn't know much about respirators, but I figured one of them must be making me breathe.  I tried to figure which one it was by timing my breathing with the motion of each bellows.  None of them seemed to match my breathing pattern. It wasn't until later in the day, when my mirror was adjusted upward, that I realized that those bellows were all attached to the underside of other respirators.  I couldn't see mine because it was beneath me.... I was in a Drinker Collins Iron Lung."  (4, page 29)
Daggett and his parents during his first trip home from the hospital
in December of 1953.  Photos added by Daggett at
Daggett said that as a child it was difficult to grasp the seriousness of having bulbospinal polio and, ultimately, pneumonia.  He wrote: "I was very naive. I had no understanding of how serious my condition was.  Oh, I knew I was completely paralyzed, but the long-term impact did not sink in.  My greatest concern was that I might miss the first day of school." (4, page 33)

It must have been common for these patients to develop pneumonia, as their would have been constant secretions forming in the upper air passages that needed to be cleared, or they would be inhaled, thus causing respiratory infections such as pneumonia.  Daggett mentions the constant urge to blow his nose, which he often did "without even using a tissue." (4, page 31, 33)

Daggett during a trip home in 1954.  He is wearing
metal hand sprints, and sitting in his first wheel chair.
Photo added by Daggett at
The desire to clear secretions would be a constant concern for caregivers because due to paralyzed muscles they did not have the ability to swallow, and therefore these patients lost the ability to control their airway.  This would have posed a greater serious problem back when the Drinker Respiratory was first used on polio victims, as a patient may survive because of the respirator only to later drown in his own secretions a few days later.

To treat this problem the patient's bed had to be slid out from iron lung, and the patient had to be turned by one attendant, while another used rags to wipe away secretions.  This probably would have been necessary often for some patients, further compounding the workload of the staff and the stress of the patient.

However, this problem was remedied somewhat with the invention of a suction device in 1937. By the 1950s caregivers could simply apply suction to the nose and mouth and suck out secretions.  Many such patients had a tracheostomy in place for just this reason.  And this brings me back to Daggett.

Daggett describes being awake when the tracheostomy was inserted into his neck.  He was later put inside an iron lung, which proceeded to breathe or him.  He notes that it was by means of his tracheostomy that his caregivers, all of whom wore cloth gowns (some wore masks), would clear his air passages, probably with one of these original suction devices.  (4, page 30, 33)  Of the tracheostomy, he wrote:
Those of us with significant paralysis of our breathing muscles also had additional air forced into our lungs through a tracheostomy.  The tracheostomy can also be used to suction mucous from our lungs.  I'm sure the tracheostomy saved my life." (4, page 30)
While iron lungs gave medical professionals an opportunity to save lives, they were also viewed as a terrible way to spend the end of ones life, although, thankfully, they allowed many children, such as Daggett, an opportunity to live to tell about it.

Iron lungs were ultimately replaced by other more complicated machines, such as intermittent positive pressure breathing (IPPB) machines, the Monaghan Ventalung Respirator, and the Bird Mark 7 Respirator. All of these newer ventilators were among a new breed of respirators that applied positive pressure to the lungs, as opposed to negative pressure.

So the iron lung has a significant place in the history of respiratory therapy.  It was an idea created to save the lives of millions of children who would have otherwise met an early demise due to a disease called infantile poliomyelitis.  To all the children saved from a dreaded diseases they were simply a Godsend.

Daggett was ultimately transferred to Rancho Los Amigos Hospital (now Rancho Los Amigos National Rehabilitation Center) where he could be rehabilitated.  He went on to become an "active journalist" who lives in Southern California who has "written extensively on disability and the human condition."  (1, last page)

  1. Daggett, Richard Lloyd, "Not just polio: my life story," 2010, Bloomington, IN, iUniverse

Friday, June 23, 2017

1940-1970: The decline and return of tuberculosis

By the 1940s there were a variety of antibiotics that allowed physicians to control most cases of tuberculosis. For patients that seek medical attention and follow the prescription of their physician, tuberculosis can be controlled and even cured. By 1969 it seemed that the disease had been conquered, and attention was diverted from it.

It seems to be normal for human beings to forget that of which they do not see. When we don't have a war for a while, we tend to assume one will never occur again and we cut our military spending. When a war occurs, we usually aren't prepared. The same can be said of disease. When we go years without a plague, we assume the disease is cured. When the plague strikes, we aren't prepared. A perfect example of this is the Spanish Flu of 1918.  

There was a friend of mine who often said that we ought to have a war every ten years so we don't forget that freedom comes with a price. We should have a plague every so often so that we don't take these diseases for granted. Surely we don't want wars or plagues, but my friend had a valid point.

By the 1930s and 40s sulfa drugs and antibiotics were discovered as a means of treating infection. These and other medicines allowed physicians to effectively treat and even cure tuberculosis. This decade saw a rapid decline in the number of tuberculosis patients.  

According to Elaine Landau, in her 1995 book "Tuberculosis:"
As late as 1969, the federal government was still channeling annually more than $20 million in TB project grants to local clinics and hospitals throughout the nation. But the declining TB rate made people feel that the crisis was over. So when the government began giving blocks of aid to states and municipalities to be used at the areas' discretion, the funding generally was not expended for TB controll. 
As time passed,countless successful TB programs were dismantled. In New York City alone, more than one thousand beds formerly reserved for TB patients were eliminated from municipal hospitals. Although outpatient services were supposed to be established to ensure the disease's continued decline, these were never made available. Instead, funding was diverted to meet more immediate needs. As one physician who's treated numerous TB victims described the situation, "We knew how to cure it. We had it in our hands. But we dropped the ball. (1, page 3, 4)
Once the "ball was dropped" it was difficult to pick it up again. Organizations with the ability to provide methods of preventing the spread of such diseases, such as the Centers for Disease Control and Prevention (CDC), were not provided with enough funds to effectively perform this task. (1, page 34)

In 1989 a plan was made to provide the CDC with $30 to $34 million dollars to create a TB control plan. Yet the plan was never made "because each year that it was proposed, the White House eliminated its funding from the budget." A similar plan was proposed in 1993 to offer $484 million for TB prevention, but the budget was cut by the Clinton administration to $124 million before it was sent to Congress. So the return of a disease that once ravaged a nation was greatly ignored by Reagan, Bush and Clinton. (1, page 35)

What may have opened the eyes of the government was the AIDS epidemic that struck during the 1980s. Studies showed that with weakened immune systems, up to 50 percent of AIDS victims were developing tuberculosis, and were unable to fight it off. This is one reason tuberculosis spread through prisons and homeless shelters rather fast, particularly in cities like New York "where nearly one-fifth of prison inmates have TB, but none of the jails have separately ventilated cells for contagious cases." (1, page 35-37)

To make matters worse the TB bacteria has the ability to mutate to create drug resistant strains. This occurs when people who are given antibiotics, which are proven to cure TB if used properly, were not taking the antibiotics once they started feeling better. Effective treatment usually takes 6-9 months, but many would stop taking it within weeks.

Landau also said that "this is actually worse than not taking any medication at all, because over a period of time the illness no longer responds to any form of medication, and they have, in fact, dissipated the drug's effectiveness... Unfortunately, significant numbers of people have misused their medication this way. The tendency to do so appears to cut across racial, class, and economic lines." (1, page 39)

Studies show that up to 50 percent of TB patients do not take their medicine as prescribed, and that 14.1 percent of TB cases responded poorly to TB medicines. Studies also showed that TB resistant strains have a 50 percent mortality rate. (1, page 39-40)

  1. Landau, Elaine, "Tuberculosis," 1995, New York, Chicago, London, Toronto and Sydney, Franklin Watts 

Wednesday, June 21, 2017

1956: The A-B-Cs of CPR are born

In 1949,  Dr. James Elam, an anesthesiologist, investigated old records of how mouth to mouth breathing was used on newborn infants.  While trying to save the life of a boy, he used this method and it worked.  This was the beginning of the re-birth of mouth to mouth resuscitation.  (1)

I say re-birth because when the Royal Humane Society was established in 1773, mouth to mouth resuscitation was recommended as one of many options for reanimating victims of near drownings. It as later removed from the list due to complaints that it was gross and unhygienic. The Sylvester and Shaefer methods of reanimation were added in its place.

Dr. Elam and Dr. Peter Safar would prove that neither the Sylvester nor Shaefer method provided enough tidal volume, although mouth to mouth breathing did. So this brought back the method once thought to be gross and unhygienic.

Also recommended by the Humane Society back in 1773 were chest compressions and abdominal thrusts, and these were ultimately phased out.

By the 1890s chloroform was a common anaesthetic during operations. Occasionally a patient would go into what was then referred to as "chloroform syncopy." This was a term used to describe patient's who stopped breathing and ceased to have a heartbeat, or who were in cardiac arrest. Physicians had no treatment for this, and so it was almost always fatal. (3, page 6)

However, in his 1891 book, "General Surgery," Dr. Franz Koenig of Germany described using "external cardiac massage" to treat such a patient at the University of Goettingen. He recommended compression of the chest over the heart at a rate the person would spontaneously breathe. He later settled on a rate of 30-40 per minute, and recommended chest compressions during "chloroform sycopy" instead of one of the other methods of resuscitation.  (3, page 6) (4, page 2968)

A search was ongoing to determine the optimal rate to perform chest compressions. The first official recommendation was to perform 60 compressions per minute. (3, page 6) (4, page 2968)

A year later, a resident at the University of Goettingen, Dr. Fredrick Maass, and a student to Dr. Koenig, published a paper in the Berlin Clinical Weekly called "Resuscitation technique following cardiac death after inhalation of chloroform." Here he described the first successful use of external cardiac massage. He observed a clinical response from the patient at a compression rate of 120 per minute.  (3, page 6) (4, page 2968)

Ever since then the rate of chest compressions has been the subject of much debate and many studies. The recommendation as of March 28, 2010, by the American Heart Association is 100 per minute. The main reason for choosing this number is seems to be effective and easy to remember.

Studies during the 1940s showed that chest compressions stimulated blood to circulate through the body, and this was essential during artificial resuscitation.  This revolutionary idea transformed artificial respiration to cardiopulmonary resuscitation, otherwise known as CPR.

In 1956, while having a conversation with Dr. Elam, Dr. Peter Safar came up with the following anagram for artificial resuscitation: (1)
  • A (Airway)
  • B (Breathing)
Although the anagram was later changed to:
  • A (Airway)
  • B (Breathing)
  • C (Circulation)
Thus was the beginning of the modern A-B-C's of artificial resuscitation, now more commonly referred to as cardiopulmonary resuscitation, or CPR). It was taught to all the citizens of the world who aspired, or were required by their employers, to save lives.

The American Heart Association officially endorsed CPR in 1963, and in 1966 adapted their first guidelines for performing CPR. These guidelines are reviewed every five years and updated.

A most significant change came on October 8, 2010. Here the decision was made to change A-B-C to C-A-B. The reason for the change was noted in the "2010 Guidelines for CPR and ECC: "
There are many reasons for this change. First, this change allows rescuers to begin chest compressions right away. As we know, most victims of sudden cardiac arrest (SCA) receive no bystander CPR. One of the reasons for this may be that the A-B-C CPR sequence began with opening the airway, the most difficult and daunting task for the rescuer. This change attempts to decrease the barriers to performing CPR by allowing the rescuer to start with chest compressions. Also, the vast majority of SCAs occur in adults who suffer a witnessed arrest and ventricular fibrillation or pulseless ventricular tachycardia. In these victims, critical elements of resuscitation are chest compressions and early defibrillation, which can begin earlier if there is no delay to open the airway and provide breaths. The process of opening the airway (which may involve getting a barrier device or setting up ventilation equipment) takes time and delays the start of CPR. Using the C-A-B sequence lessens this delay. 
For those not familiar with the terms "ventricular fibrillation" or "pulseless ventricular tachycardia," these are names for life threatening cardiac arrhythmias, or ineffective heart rhythms. This change included adults, children and infants, but not newborn infants. The ABC algorithm should be used for newborns, because "newborn cardiac arrest is most often respiratory."

The American Heart Association made one other change to increase the chances that CPR would be performed by bystanders: it removed the recommendation to perform mouth to mouth breathing. Once coming upon a witnessed or non-witnessed cardiac arrest, and once confirming that the person is non-responsive, the recommendation is now to perform effective chest compressions until emergency responders are on the scene. 

Modern studies also proved the following: 
  • Mouth to mouth breathing provided enough positive pressure, coupled with the natural recoil of the chest after a compression, to allow for enough ventilation to occur. 
  • That circulation was far more important than breathing (It may also be underestood that chest compressions causes pressure changes within the chest to allow for ventilation to occur, thus eliminating the need for mouth to mouth breathing.) 
  • That bystanders were more likely to do CPR when all they had to do was chest compressions
That's all I'm going to write about CPR. 

  1. Donahue, Mary, "History of Lifesaving," DeAnza Collegge,, accessed 8/10/13
  2. "2010 AHA Guidelines for CPR & ECC," American Heart Association, 2010,, accessed March 28, 2010
  3. Figl, Marcus,  et al., "Resuscitation Great: Franz Koenig and Friedrich Maass," Resuscitation, July, 2006, 70, pages 6-9
  4. Nolan, Jerry P., et al, "Editorials: Chest Compression Rate: Where Is The Sweet Spot?" Circulation, 2012, 125, pages 2968-2970)

Monday, June 19, 2017

1937-80: The evolution of mechanical ventilation

Inventor Holger Hess
Note: Here is my attempt to piece the history of mechanical ventilation together. If you have access to information or pictures to help tell this history please contact me. This is all done pro bono. As you can see there are no adds on this blog.

Non-invasive negative pressure ventilators (iron lungs) were a godsend in intensive care units during the first half of the 20th century. Yet their day in the sun was about to end, mainly due to two medical developments.
  1. The realization that iron lungs made it very challenging to clear secretions from airways. The patient's bed had to be pulled from the tank by one person, another person had to provide manual artificial respiration to the patient, a third had to rotate the patient, while another wiped away secretions. Considering there were sometimes copious secretions, caregivers sometimes had trouble keeping up. Since excessive secretions obstructed airways, caregivers yearned for a better system. 
  2. Improved anesthetics made it possible to perform complicated operating procedures, particularly upper abdominal surgeries. This made it necessary to develop an apparatus that would provide artificial respiration without covering the patient.  
These two developments lead to a paradigm shift away from noninvasive ventilation and toward invasive ventilation. They also lead to a shift away from negative pressure ventilation and towards positive pressure ventilation. These transitions were made possible due to the following innovations.

1923: Waters to and fro bag and canister:  This is not a history of anesthesia, although at times our history intertwines with theirs. Roger Waters devised a system that includes a canister filled with sodalime. The canister is placed between a rubber mask and a rebreather bag.  A gas flow (possibly oxygen with anesthesia) entered the system between the canister and the mask. Inspiration and expiration then went through the canister (to and fro). The soda lime would collect CO2 and create moist heat. The bag would collect exhaled gas flow. During inhalation the patient would get humidified gas. (28, page 433) (29, page 49)

This created a closed circuit system whereby the anesthesia gas used would not leak into the atmosphere. This was important because surgeons, anesthesiologists, nurses and other operating room attendants did not want to inhale the gas, but also because some anesthetics were flammable. So it made sense to make sure the gas was delivered to the patient in a closed loop system. This system was also nice because it was cheap, sterile, and easy to operate. (28, page 433) (29, page 49)

The anesthetic Waters created this system to deliver was Cyclopropane, a gas that is explosive when it comes into contact with oxygen. Other anesthetics are also flammable, so the system allowed them to be contained. (30, page 147)

I just mention this device here because it is used in 1952 as part of a study that is pertinent to our own history.

1930s: First use of Positive End Expiratory Pressure (PEEP). Applying a constant pressure during expiration was first used during open chest surgeries to prevent lung collapse. A circle system anesthesia apparatus was used, where the exhalation outlet was connected with rubber tubing to a glass tube. The tube was inserted into a glass of water. The deeper the tube was inserted the higher the PEEP. This could usually generate 3-5 cwp of PEEP.  (24, page 91)

1937:  Suction pump invented:  Iron lungs were nice in that they gave caregivers the ability to keep children infected with paralytic poliomyelitis alive. Yet caregivers could not prevent some of these kids from drowning in the copious secretions they produced, secretions that obstructed their airways. This challenge was met in 1935 by Dr.  Hess, who said he had "a dream of developing products to save lives." (17) (18)

In 1937 he formed Testa Laboratories.  He invented a suction pump so secretions could easily be cleared (or sucked) from the patient's airway.  The pump was connected to rubber tubing. The distal end of the tubing was connected to a catheter that was inserted into the patient's airway. The pump acted like a vacuum and sucked secretions from the airway.  (17) (18)

One end of a rubber tube was attached to the pump, and the opposite end was inserted into the patient's airway.  When the pump was turned on a negative pressure was created, and any loose secretions in the patient's oral cavity would be sucked up.  This was a significant improvement over manually clearing the airway or feeling helpless as a patient suffocated on his own phlegm. (17) (18)

1945?: Bennett Clinical Research Model X2 Respirator (Bennett Valve):  During WWII, Dr. V. Ray Bennett worked with Dr. Cournand and Dr. Motley to invent the BRx2 Resuscitator for the United States Aeromedical Laboratory. (25, page 1)

According to The Journal of the American Association of Nurse Anesthetists, "This device featured the Bennett clinical research model (Ben X-2, or the Bennet Valve) valve and was used for administration of intermittent pressurized oxygen inhalation during high-altitude flights in unpressurized aircraft."  (24, page 90)

The system was connected to rubber corrugated tubing and a comfortable mask created by Bennett for other breathing units he invented. It was meant to control breathing, or assist breathing, for pilots at high altitudes. Yet as the war ended soon after it was invented, it was never used by the military.  (25, page 1) (26, AARC Virtual Museum).

A picture and write up on the device used here can be viewed at the AARC Virtual Museum. (

The device was then used medically to supply positive pressure ventilation, with or without PEEP, to patients in respiratory failure. (25, page 1) (26, AARC Virtual Museum).

John Dillon, of Los Angeles County Hospital, writing for the Anesthesia History Association Newsletter in July of 1990, explained how Bennett came to his office in the autumn of 1976 with his "gadget." Dr. Dillon said:
I took it into an operating room, along with Ray (Bennett), where a patient was under general anesthesia, and we slipped it into the circuit as an assistor; it worked very nicely. The depth of ventilation was readily controllable. Our outstanding characteristic, which was important at that time, was that it was not controlled by electricity and hence not a danger with ethyl ether. (26, page 1)
They then decided to try out the device on patients in the "infectious disease" section of the hospital where there was several poliomyelitis patients in Drinker Collin's Respirators, or iron lungs. The received the permission from a patient who was paralyzed due to the disease to try out the device. Dillon said:
We told him that we were going to put a mask on his face, and that it was connected to a device that would breathe for him while he was in the lung, and for him when the lung was opened. I assured him that we would not let him become distressed and that, if he were uncomfortable, he should blink his eyes rapidly, which was about all he could do, and we would put him back in the lung immediately."  (25, page 1,9)
We put a mask on and connected the "Valve" to a cylinder of compressed air. The unit synchronized with the lung. We then had the lung shut off and cracked open. The unit now provided "Controlled Respiration" to the patient at the rate and depth which had been set by the lung. The patient showed no sign of distress. His chest moved freely. As soon as it was evident that respiration was adequate, a couple of nurses, or attendants, gave the patient a sponge bath and some passive exercise on his limbs." (25, page 9)
We were all impressed by the action of the "Bennett Valve" as a ventilator. The patient was kept out of the lung for almost a half hour, and when he was returned to the lung and could talk, told us that he had been perfectly comfortable." (25, page 9)
The Bennett Valve, later known as the Puritan Bennett Valve, was therefore the first such device to supply controlled respiration with positive pressure on both a patient under anesthesia and paralyzed due to poliomyelitis.

1946: First Positive Pressure Inhalation Device:  Dr. Forrest Bird was an experienced pilot by the time WWII started. A week after the bombing of Pearl Harbor he signed up for the Army Air Corp. He was responsible for transporting many of the planes used in the war from factories to aircraft carriers, and was in an ideal position to study aerodynamics. (21)

He studied high altitude breathing problems that prevented pilots at this time from flying higher than 28,000 feet. He obtained a German regulator and made adjustments to it that allowed pilots to receive intermittent positive pressure breaths, allowing them to travel as high as 37,000 feet by the end of the war. This was important because it allowed American pilots to fly higher than enemy planes, giving them an advantage over enemy pilots.  (21)

The device he invented was effectively the first prototype of an intermittent positive pressure breathing machine, and would prove "invaluable" when he later worked on devising respirators for medical purposes. (21) (23)

1948:  Continuous Positive Airway Pressure (CPAP):  The first studies using crude CPAP devices were done during the 1930s. Alvin Barach performed the first modern studies on CPAP. This is a continuous flow of pressure applied to the airway by a mask. During WWII Alvin Barach supervised experiments whereby CPAP was used on a variety of pilots who traveled to high altitudes.

After the war he studied the use of CPAP on a variety of patients, although his work was relatively ignored until the 1980s when studies would confirm CPAP was was useful in treating patients with sleep apnea or lung diseases. CPAP was studied during the 1980s as a means of preventing patients from needing intubation.  (v2)

1948: Bennett Flow-Sensing Pressure Breathing Unit TV-2P: V. Ray Bennett's valve (The Bennett Valve) was featured in the Bennett TV-2P Respirator.   It was flow sensing, and time cycled, meaning a breath ended after a set time was met. It could provide controlled mechanical breaths to treat patients in respiratory failure. (24, page 90) (7, page 1318)

Patient's could also control the rate, making it also an ideal device for delivering intermittent positive pressure breathing. A nebulizer could be added to the circuit for the delivery of bronchodilators during IPPB therapy. It was run by electricity, batter, hand pump, or air. (22, page 94)

1948:  First Study Using IPPB:  Dr. Albert Bower noted a near epidemic number of cases of respiratory failure among bulbar poliomyelitis patients using Drinker Collin's Respirators at Los Angeles County Hospital. Several TV-2P's were used to provide assisted ventilation to several of these patients with noted respiratory failure. However, they proved less than ideal for long term IPPB.

Dr. Bower worked with Biomedical engineer V. Ray Bennett, who used his attachments (BR X2 valves) to make the Drinker-Collin's Respirators...
...capable of supplying "intratracheal" intermittent positive pressure ventilation (IPPV), supplementary to its NPV (negative pressure ventilation). Together with their teams, Bower and Bennett used this attachment for 73 of 1949's 130 "respirator cases", to establish the first-ever large-scale long-term success of IPPV for respiratory failure in acute polio. (22, page 91)
The device was powered by the motor of the negative pressure ventilator. Positive pressure could be supplied to these patients by a mask that covered both the mouth and nose, or a tracheotomy adapter created by Bower. "The special exhalation was installed adjacent to the mask or tracheotomy connector." A bellows adapter was also added to the system. A humidifier could also be added. Likewise, supplemental oxygen or helium could also be added to the system.  (22, page 94-95)

Now, these negative pressure ventilators were still negative pressure ventilators, although positive pressure breaths could be applied to patients when needed. While the study did not report how often ventilation was augmented by IPPB, "The authors do describe IPPV as providing more effective AV, so presumably, they would favour it."

A year later, Bower and Bennett "demonstrated the superiority of (supplemental) IPPV over (negative pressure ventilation) alone, achieving a survival rate of 83.7 (108/129)-- compared with the 21.1% survival rate in 1946 among the 38 patients ventilated that year. (22, page 91)

This study was the first that used positive pressure ventilation, and the first to study the long term effects of intermittent positive pressure breathing. The study showed that use of IPPV lowered the incidence of mortality among those inflicted with paralytic bulbar poliomyelitis. It was essential to the transition from negative pressure ventilators to positive pressure ventilators. According to Critical Care Resuscitation, "Bower and Bennett deserve greater recognition of their pioneering merit than they currently receive in the written history of intensive care medicine."   (22, page 91, 99)

The lack of success of the TV-2P for long term ventilation and the success of this study highlighted the need for a more effective IPPB machine for general patient care. (22, page 94)

The Bennett Valve was also featured in the Bennett BA-2 Anesthesia Ventilator. It too was used by Los Angeles County Hospital during the 1948 polio epidemic.  (7, page 1318)

1950s-1970s:  Rubber masks:  Positive pressure breaths were often provided by using a rubber mask over the patient's mouth and nose. One of the major complications of the rubber masks used at this time was that they were opaque and concealed aspiration or foaming pulmonary edema, and this was noted as a major disadvantage of such masks.

Another disadvantage was prolonged use caused facial skin breakdown. And yet another disadvantage was that air would often leak around the masks. Masks also required persons to hold them onto the face, and this could get very tiresome for both the patient and the caregiver.

 When used on polio patients, nursing assistants or respiratory therapists would often work in two hour shifts. The disadvantages of these masks could be compensated for by tracheotomies and inserting a catheter, and later by intubation (see below).  (v3)

Mark 4 Resuscitator
Introduced by Dr. Forrest Bird
in 1958? as an anesthesia ventilator.

1952: The Bird Mark I:  Pressure ventilation was found useful during operations to prevent respiratory failure, although they posed two pretty significant problems.
  • There was no way to monitor accurate pressures and tidal volumes delivered to patients, and so uncuffed endotracheal tubes were needed to prevent barotrauma from excessive pressures and tidal volumes. This left airways unprotected and subject to aspiration of stomach contents.
  • Some early anesthesia ventilators were powered by electricity. This posed a problem because sparks from them could trigger an explosion due to flammable gases present in operating rooms at the time.   (24, page 91)
This created a need for a pneumatic respirator, or one that was powered by air instead of electricity. 

Roger Manley was an anesthesiologist from Westminster, London. He worked with Dr. Forrest Bird, who incorporated the technology he
invented in 1946 into an anesthesia ventilator. The first Bird Medical Universal Respirator prototype was introduced in 1950, and a second was introduced in 1951.

All that was needed to operate it was a 50 PSI source. By this time most operating rooms had piped in oxygen, so this should not have been a problem. It was pressure triggered and cycled, meaning breaths began when the patient generated a negative pressure, and ended when a preset pressure was met.

It was marketed in 1952 as the Manley Respiratory, although it was later refined and re-branded as the Mark II. It was used by anesthesiologists for the next 40 years.

The machine provided some clear advantages to older ventilators. Patients were given anesthesia, and once the paralyzing effect occurred, patients were intubated. Tubing from the machine was connected to an endotracheal tube. The tube made it easy to keep airways patent and free from secretions. The ventilator provided a hands free method of providing artificial respiration until the anesthetic was withdrawn and patients were spontaneously breathing.

Previous anesthesia ventilators only provided the preset rate and inspiratory time, what was referred to as "controlled ventilation." This meant that the patient could not trigger a breath. This worked fine in operating rooms where patients were paralyzed and sedated due to anesthesia. But it was not acceptable for the general population, particularly patients who were awake and alert who could fight the machine, thereby creating what is referred to as patient-ventilator asynchrony.

So, while initially made as an anesthesia ventilator, the Mark 1 was also found to be a useful ventilator by physicians in emergency rooms and critical care units. This was because it sensed a patient's inspiratory effort, and then provided a positive pressure breath to "assist" ventilation. This became known as "assisted ventilation."

And, of course, when used outside operating rooms, they were operated by inhalation therapists. This created a new market for pneumatic positive pressure ventilators, a market that Bird would tap into with a later model.

Bennett PR II
( gallary of ICU Ventilators.)
Check out this link for pictures
of most ventilators on this page.
One of the pictures shows
external PEEP with the MA1. 
1952:  Bennett Pressure Breathing Unit:  After the BR X2 Respirator attachment was successfully studied in 1948, Dr. V. Ray Bennett incorporated into the PR I and later the PR II.  Like the Mark I and Mark II, it was a pressure cycled ventilator. It had a nebulizer cup for the nebulizatiion of Isuprel and Alevaire. It could be used as a ventilator or for IPPB treatments.

Pneumatic positive pressure machines were increasingly used as ventilators instead of iron lungs when suctioning of the airway was required. These units were also increasingly used for IPPB therapy, and often referred to as IPPB machines.

Iron Lungs and IPPB machines were used as ventilators until the 1960s when volume ventilators (such as the Emerson and MAI ventilators below) were proven to be safer and more effective as ventilators. However, IPPB units remained a viable ventilator option when called upon.

Bennett later refined this machine and re-branded it as the Bennett Bennett PR 2 in 1963. Both of these machines (the BR1 and BR2) ) were still mentioned in respiratory therapy texts through the 1990s.

1952-1953: Second Study of Long Term IPPB:  Dr. Bjorn Aage, an anesthesiologist, Ibsen performed a large scale study using intermittent positive pressure ventilation in Copenhagen, Denmark. During the polio epidemic of 1952-1953, Ibsen was called to an emergency meeting, where he recommended providing ventilation manually using a bag when polio patients. Despite criticism, Ibsen's idea went on to become the largest study up to that time using Intermittent positive pressure breaths. (24, page 97) (27, page 398)

Isben was met with criticism because the hospital had access to an Emerson Tank (iron lung) and six cuirass respirators. And here came along an anesthesiologist who proposed "ventilating patients with breathing failure, somehow without respirators." (27, page 399)

Waters to and fro system (
His first patient was a "moribund 12 year old, Vivi Ebert (her name has been in the public domain). Per Ibsen's request, she had a tracheotomy, and then she was ventilated with manual positive pressure ventilation. The device used was a "Waters to and fro bag and (soda lime packed) canister." This was an early anesthesia device for providing positive pressure ventilation to patients while anesthesia was administered. (27, page 399)

It should be noted that "The treatment succeeded, and she lived until 1971." This success garnished the excitement of all involved, and this lead to a two year study of other similar patients with poliomyelitis, and the hospital had plenty of trainees, students, nurses, and anesthesiologists to perform the duties. About 277 patients were provided IPPV with the device, and this was about four times as many patients that were trialed with IPPV in Los Angeles a in 1948. (24, page 97)(37, page 399)

This study showed that IPPV could prove useful when used on a large scale for poliomyelitis patients in respiratory failure.

For the record here, Ibsen is often referred to as the father of intensive care for his work in this study, and for his work in establishing the first intensive care unit in the world in 1953 at Copenhagen. (27, page 398)

1953:  Bag-valve mask (self inflating resuscitator) invented. Surgeons are unable to perform surgeries in the upper abdominal region mainly due to the inability to provide artificial resuscitation. They were also faced with the daunting challenge of performing artificial resuscitation for kids infected with paralytic poliomyelitis when they were outside their iron lungs. Surely there were a few mechanical or pneumatic devices, although these were all new and relatively primitive at this time. Plus they wouldn't have been available at many hospitals. To tackle these challenges, Holger Hess joined forces with anesthesiologist Henning Ruben.

AMBU resuscitator
Also shows opaque rubber mask.
This Hess invented the bag valve mask (BVM), or what is also known as the first self inflating resuscitator. Now it is most commonly referred to as an AMBU-bag. There has often been speculation as to what the  acronym A-M-B-U stands for, although no one knows for sure. There are a couple accepted ones, such as ambulatory manual breathing unit, or air mask breathing unit. Either way, the device gave anesthesiologists the ability to give paralytics during complicated surgeries, allowing surgeons to save lives.

The device was a lightweight black rubber bag. On one end was rubber tubing that connected to an air or oxygen tank (preferably oxygen). The other end of the bag was connected to a rubber mask that was placed over the patient's face. Once the flow was turned on, the caregiver would squeeze the bag to provide a breath. Once the caregiver released the bag, it self inflated. This was an evolutionary breakthrough that quickly gained in popularity throughout the hospital.

Initially mailed in wooden boxes out of a small factory in Copenhagen, the company soon had to move to larger facilities. It even changed its name to AMBU.  While initially used only by anesthesiologists, when other physicians learned of the product they wanted one. Soon one was available in nearly every corner of every hospital, particularly in operating rooms, emergency rooms, and critical care units.

Anesthesiologists now had the means of providing  providing artificial resuscitation during operations. Physician, anesthesiologists, nurses aides, orderlies and inhalation therapists would take turns providing artificial respiration to kids infected with polio until an iron lung was available.
A picture of the Bird Mark 7,
sometimes referred to
simply as "The Bird."

1958:  Bird Mark 7 Universal Respirator:
Dr. Bird continued working on positive pressure technology, and in 1955 came up with a prototype of the Bird Mark 7.

Dr. Bird showcased it at various teaching hospitals, allowing it to be used in the most critically ill patients who were suffering from respiratory failure where other accepted therapies had failed to work. The Bird Mark 7 Respirator was quickly accepted by the medical community, and in 1958 it was introduced to the market.

This respirator was ideal for inhalation therapists, as it was portable, durable, and easy to operate. It was connected to a 50 PSI source and was operated by a flow of air. It could be used to provide controlled positive pressure breaths long term by connecting it to an endotracheal or tracheotomy tube. It was one of the first respirators to provide continuous controlled mechanical breaths for patients who were unable to spontaneously breathe. (20, pages 66-67).

Dr. Forrest Bird demonstrating
the Bird prototype introduced in 1950,
and the Bird Mark 7 introduced in 1958.
Like the Mark I and Bennett respirators, it was pressure cycled. Like the other pressure breathing machines. Likewise, tidal volumes were determined by resistance, meaning they were variable from breath to breath, patient to patient. When set to "air-mix" the fraction of inspired oxygen was 40%, although could also get as high as 80%. (20, page 67)

It was also easy to repair and maintain, and for this reason, Dr. Bird once quipped that it was the Model T of respirators.

It was initially intended to be used as a ventilator. Yet two problems were observed:
  1. No manometers or devices to indicate how much of a tidal volume was being delivered. 
  2. No alarms to indicate when too much pressure was being given, or if the patient became disconnected (20, page 67)
These disadvantages required patients ventilated with these machines to be located close to nurses stations, where they could be frequently monitored by nurses, doctors, and inhalation therapists. The machines made a distinct sound during inhalations, so it would be easy to hear if they were working.

The conveniences offered by these machines made them ideal for IPPB therapy. So, while IPPB therapy was first described in 1947, and while there were other pressure machines that did the same thing, the Bird Mark 7 made it famous. It would become the most commonly used IPPB machine, and was generally responsible for the IPPB Revolution that followed.

They were very commonly found in hospitals during the 1960s and 1970s, although some hung around until the 2000s.  Some of these machines can still be found in respiratory therapy equipment storage rooms collecting dust, although most have been discarded or sent to Africa.

A Bird Mark 7 service manual can be viewed here.

John "Jack" Haven Emerson
1964:  Emerson Volume Ventilator The Bennett and Bird Respirators were the two main ventilators used in the first decade after the decline of negative pressure ventilators. Yet their weaknesses soon became apparent. This particularly became evident during the 1960s as critical care units were on the rise. So this made apparent the need for volume ventilators, the first of which to enter the scene was created by the already famous Dr. John Emerson.

According to a 1998 article by Richard Branson in Respiratory Care, "Jack Emerson: Notes on his life and contributions to respiratory care," John Emerson was the second person to come up with a volume ventilator. Branson described this ventilator.
"This simple devise resembled a green washing machine and used a piston to deliver precise volumes. Oxygen was added into a ‘trombone-shaped’ accumulator connected to the intake of the piston for delivery of elevated FIO2. The tidal volume was changed by a crank on the front of the machine, which controlled the stroke of the piston. Respiratory rate and inspiratory-to-expiratory-time ratio (I:E) were adjustable. The humidifier was a modified pressure cooker and was known as the Emerson Hot Pot. A belt, connected to a DC motor and pulley wheel, served to move the piston. In case of failure of the existing belt, a spare was hung inside each cabinet. The belts were similar to those used to circulate air in forced air gas furnaces in homes. On numerous occasions I have heard the story of the belt becoming loose or breaking and the spare found to be missing. Under these circumstances, the resourceful respiratory therapist would run to the parking lot and obtain the belt from a Volkswagen Beetle (the old one) and place it in the Emerson to restore it to working order. I’ve never looked to see whether the two belt sizes are compatible because it’s such a good story. In any event, the Emerson Post op Volume Ventilator was reliable and would allow ventilation of patients when other devices failed. Emerson’s device was not the first of the piston ventilators (M¨orch and Engstrom preceded him), but it was the first device to allow independent control of I:E." (9, page 568)
This was the first volume ventilator.  Unlike the IPPB units that could be used with either an endotracheal tube, trach tube, mask or mouthpiece, volume ventilators required that the patient either be intubated or have a tracheotomy tube.

1967:  The Puritan Bennett MA1 Ventilator:  In 1940 Ray Bennet produced a gas delivery system that involved a "jewled pneumatic valve - the 'valve that breathes with the patient." It was this concept that allowed the Puritan Bennett company to create the the MA1. (a10) (b11)

It was a compact unit that could easily be carted to the patient's bedside. Knobs on the machine allowed the therapist to set in a desired rate, tidal volume, sigh depth, sigh rate, and maximum pressure.

The machine also added a feature from the IPPB machines called sensitivity. This allowed the therapist to control how hard or easy it was for patients to trigger breaths. When set high, such as 10cwp, patients would have to work very hard to start a breath. This was ideal for patients who were not breathing on their own. It would be a fright show as the patient started to wake up and breathe spontaneously. This resulted in patient anxiety and stress and patient-ventilator assynchrony.

When the sensitivity was set to 2-3 cwp the patient could easily trigger a breath. This was an ideal feature, making mechanical ventilation much more comfortable for patients. This feature combined "controlled ventilation" with "assist ventilation, and it became known as "assist-control mode." This made it so the patient would receive the dialed in rate, although could trigger spontaneous breaths in between machine breaths.

Once the patient was intubated, tubing from the machine could easily be hooked up to the ETT (it could also be hooked up to a trach tube). It gave caregivers much better control compared to negative pressure and positive pressure breathing units.

Most therapists who were familiar with these machines say they were very durable. Even after other ventilators were purchased and broke down, the MA1s continued to function. Even after the MA2s were introduced, most facilities preferred to stick with their reliable MA1. This tended to be the case until more reliable volume ventilators hit the market.

One problem with the MA1 is that it didn't come with much needed alarms. This was my problem in my brief experience with the ventilator. Most alarms were external alarms, and were complicated to work, or at least I thought so. External alarms included high rate, low rate, high pressure, and low pressure.

Another knock on the MA1 was that it had no way showing rate and tidal volume. To assure that these were adequate, an external manometer was needed.

Still, even with these annoying alarms, the machine was relatively easy to operate. If you needed to make a change all you did was turn a knob.

When I was an RT student in 1995 there was an old MA1 in the classroom. We were vaguely educated on this machine, mainly because most hospitals that still had one were phasing them out. When I was first hired at Memorial Medical Center we had one that sat in the storage room. I only had to use it one time before it was taken out of circulation sometime around the year 2000.

Another neat thing about these machines is that they were so durable, and lasted so long, that nearly every time a ventilator was featured on TV, or in a movie, it was an MA1. This continued to be the case for years after they weren't even in circulation.

In fact, when I took my registry test back in 1997, nearly all the ventilator questions were regarding the MA1. So, in preparing for the test, we had to become pseudo MA1 experts.  But that was in an era before computers, back when it wasn't easy to update a test with the click of a keystroke.

1967: Positive End Expiratory Pressure (PEEP): This feature was added to ventilators as a feature in order to keep airways open, or to prevent airways from collapsing at end expiration. It was initially used to improve oxygenation in patients suffering from Acute Respiratory Distress Syndrome (ARDS). This was initially added as an external feature, although newer ventilators came with PEEP capabilities. (31, page 9)

1971: Intermittent Mandatory Ventilation:

Servo 900C set up and ready to go.
1971:  Servo 900 Ventilator:  It was small, slightly larger than two shoe boxes, and all the knobs were on the front. It became known as a minute ventilation ventilator because the respiratory therapist would set the minute ventilation and the tidal volume and respiratory rate would be secondary. In this way, in volume control mode, the tidal volume could be set.

This machine had a sensor to make sure the tidal volume was adjusted with changes in patient compliance so the patient was guaranteed to get the set tidal volume. This was the first ventilator to have this function.

In order to set tidal volume, though, you had to do a little math. I know because when I did my clinical rotation in 1996 at Blodgett Hospital, in Grand Rapids Michigan, they still used this ventilator on a regular basis. It was also commonly used on cardiac patients at Mott's Children's Hospital at the University of Michigan when I did a rotation.

Many students were afraid to use it, and so was I at first. Yet once you were used to it, it was a very nice ventilator. However, students were thankful when it was ultimately replaced by the Servo 300 Ventilator.

It was the first ventilator to have all the alarms you needed right on the machine, and it was also the first ventilator to allow for the addition of a device so you could see pressure and flow curves. This was nice because you could see what you were doing and make changes based on the needs of the patient. (d12)

It was also the first ventilator to provide both volume control and intermittent positive ventilation (IMV), which was later improved to synchronized intermittent positive ventilation. These new modes improved the physician's ability to wean patients from the ventilator. (e13)

There were some features added to the servo 900 series that most respiratory therapists would understand, but probably not the lay person.  The first addition came in 1978, and this was the ability to measure exhaled carbon dioxide (CO2).  This was nice because, prior to this, the only way to determine CO2 was by drawing an arterial blood gas (ABG), which is an invasive blood draw.

This was nice because it allowed clinicians the ability to change settings based on a noninvasive number, as opposed to having to do an invasive blood draw. It meant that a change could be made right now, as opposed to waiging up to 30 minutes for the results of the ABG. (e14)

A couple other features may be a bit more complicated to explain. Positive End Expiratory Pressure (PEEP) is essentially the same thing as CPAP, and is a continuous flow during expiration. It works to keep airways patent to ensure adequate oxygenation.

Prior to 1981 various devices were used to provide PEEP. One was by placing the expiratory circuit in a bottle of water. Today this system is still used in neonatal units and is referred to as bubble CPAP. Non-electronic PEEP was fine, although there was not way to know how much you were giving, and it sometimes applied external resistance to breathing. These problems were solved in 1981 as PEEP was introduced to the Servo 900 series.  Now all you had to do was dial it in.

Most initial modes of ventilating patients gave mandatory breaths to patients. This essentially means that the caregiver dialed in a rate and tidal volume, and this is what was given to the patient. It is called control ventilation, meaning that the ventilator controls everything. The patient can try to take in a breath, but nothing will come.

This was fine when patients were sedated and paralyzed, but once they started to wake up, you can imagine this would be quite uncomfortable. This often resulted in patient-ventilator asynchrony, where the machine would try to force a breath into the patient when the patient wasn't ready for it, and the patient would want to take a breath and no breath would come.

A new mode called Pressure Support solved this dilemma. PS means that the patient's spontaneous inspirations were supported with a small amount of pressure. This would assure that the breath was adequate, and was important for those patients who were too week, or too sick, to take in an adequate tidal volume. It was also a useful tool as far as weaning patients off the ventilator.

Pressure Control mode was also later added. This essentially means that the patient is guaranteed a certain pressure, while the tidal volume may vary with each breath. There are certain disease conditions that benefit from this mode. Neonates who use uncuffed ETTs also benefit from pressure control mode.  (e15)

1975: Synchronized Intermittent Mandatory Ventilation:

1977: Mandatory Minute Volume Ventilation:

  1. Szmuk, et al, "A brief history of tracheostomy and tracheal intubation, from the Bronze Age to the Space Age," Intensive Care Medicine, 2008, 34, pages 222-228, reference to page 227
  2. Wyka, Kenneth A., Paul J. Mathews, William F. Clark, ed., "Fundamentals of Respiratory Care," 2002, . page 630, Section IV, Essential Therapeutics
  3. Wyka, ibid
  4. Sills, J.R.,  "Modifying IPPB Therapy," Respiratory Care Certification Guide1994, second edition, St. Lois, Mosby.
  5. Stephen, Phyllis Jean, "Nebulization Under Intermittent Positive Pressure," The American Journal of Nursing," 1957, Sept., vol. 57, No. 9, pages 1158-1160
  6. Stephen, ibid
  7. Hess, Dean R., et al, "Respiratory Care:  Principles and Practice," 2012, "Intermittent Positive Pressure Breathing," chapter 18, page 370
  8. Wyka, op cit
  9. Branson, Richard,  Branson, Richard D, "Jack Emerson:  Notes on his life and contributions to Respiratory Care," Respiratory Care, July 1998, vol. 43, no. 7, pages 567-71
  10. "Company History," Puritan Bennett Corporation,, accessed February 27, 2012
  11. "About us:  Respiratory Products for nearly a century,",, accessed February 27, 2012
  12. "About us:  History of Ventilation,",, accessed February 27, 2012
  13. "The Servo Story:  Thirty Years of Thechnological Innovation Evolving with Clinical Development of Ventilatory Treatment Strategies,",, accessed February 27, 2012
  14. "The Servo Story...," ibid
  15. "The Servo Story...," ibid
  16. Vogel, Virgil J., "American Indian Medicine," 1970, London, Oklahoma University Press
  17. "AMBU History,",, accessed 6/29/13
  18. "AMBU History," a slide show presentation,, accessed 7/5/13
  19. Garrison, "An introduction to the history of medicine," 1921, 3rd edition, Philadelphia and London, W.B. Saunders Company
  20. Glover, Dennis, "History of Respiratory Therapy," 
  21. McFadden, Robert, "Dr. Forrest Bird, Inventor of Mechanical Respirators and Ventilators, Dies at 94," New York Times, August 3, , 2015,; accessed April 3, 2016
  22. Trubuhovich, RV, "On the very first, successful, long-term, large-scale use of IPPV. Albert Bower and V Ray Bennett: Los Angeles, 1948-1949," Critical Care Resuscitation, 2007, March 9, (1), pages 91-100,, accessed 4/10/16
  23. Obituary, Dr. Forrest Bird, file:///home/chronos/u-48b0af7d8a6e832f841243beb1bf56db699d3e12/Downloads/forrest_bird_obituary.pdf, accessed 4/
  24. Somerson, Steven J., Michael R. Sicilia, "Historical perspectives on the developmentand use of mechanical ventilation," The Journal of the American Association of Nurse Anesthetists, February, 1992, Vol. 60, no. 1, pages 83-94,, accessed April 10, 2016
  25. Dillon, John Bartley, "The Beginning of Mechanical Intermittent Positive Pressure Ventilation," Anesthesia History Association Newsletter, July, 1990, Vol. 8, No. 3, pages 1,9,, accessed 4/11/16
  26. AARC Virtual Museum, "What is IPPB?", accessed 4/11/16
  27. Obituaries: "Bjorn Ibsen: commemorating his life, 1915-2007," Critical Care and Resuscitatjion, December, 2007, Volume 9, No. 4, pages 398-403,, accessed 4/11/16
  28. Agasti, TK, "Textbook of Anesthesia for Postgraduates," 2011, Jaypee Brothers, London, page 433
  29. Paul, Uran Kumar, "Essentials of Anesthesiology," 2006, 7th edition, Jaypee Brothers, New Delhi, page 49
  30. Vacanti, Charles, Scott Segal, Pankaj Sikka, Richard Urman, editors, "Essential Clinical Anesthesia," 2011, New York, Cambridge University Press, page 147
  31.  Kacmarek, Robert M, James K. Stoller, Albert J. Heuer, editors, "Egan's Fundamentals of Respiratory Care," 2017, St. Louis, Elsevier, inc.