Wednesday, June 28, 2017

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," 

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