1920-1980: The evolution of oxygen delivery devices

By the mid 1920s many of the challenges of oxygen therapy had been tackled.  Oxygen could be easily produced, stored in tanks, and delivered to the patient.  There also existed the means of confirming oxygenation status of patients, and the effects of oxygen therapy.  So the stage was set for oxygen to be introduced to hospitals.

In 1922 John Haldane wrote about his research in "The Therapeutic Administration of Oxygen."
Soon thereafter oxygen tanks became more and more common at the patient bedside.  The tanks were stored in closets, and when needed were strapped by the patient bedside.

There were various devices available for providing oxygen, which included a metal nasal cannula, a nasal catheter, the oxygen chamber, the Haldane Apparatus, and the oxygen rebreather mask or mouthpiece and an oxygen tent.  For patients that were comatose, any device needed to provide therapeutic oxygenation could be used.  For awake and alert patients, the mask posed a claustrophobic feeling, and it was also hot.  The same was true with the oxygen tent.  So the physician would basically have to base what oxygen device he used on the patient.

One of my readers at my Respiratory Therapy Cave blog informed me that, the first practical oxygen tent was invented by Doctor Benjamin Eliasoph in 1921, at The Mount Sinai Hospital,New York, with rubberized fabric from the Goodyear Rubber Company, Aeronautical Division used for balloons such as the widely known Goodyear Blimp." 

This information is confirmed in a New York Times obituary for Dr. Benjamin Eliasoph, which notes: "Dr. Benjamin Eliasoph, a physician at Mount Sinai Hospital who was a pioneer in the design of the oxygen tent, died Sunday at the hospital. He was 70 years old."

The first mass producible oxygen tent was invented by Doctor Leonard Hill.  It consisted of a canopy with slots so the patient could see out that was placed over the bed and patient, and a machine was set at the bedside that blew oxygen into the tent and over the patient.

Dennis Glover, in his 2010 book "A History of Respiratory Therapy," said there was no means of cooling the atmosphere inside these tents, and being inside was almost unbearably hot and uncomfortable for many patients.

Glover said that the most common use for the oxygen tent was for patients presenting with cyanosis due to heart failure or pneumonia.  Some patients would beg to get out of the tents, Glover explained, yet once out they would became short of breath and they'd beg to get back in.  So it was sort of a double edged sword for the patient until the patient got better, if they got better.  Some critics complained such tents basically provided a tortuous method of ending a person's life, and petitioned for their demise.

In 1926 Alvin Barach invented an oxygen tent that blew air over ice chips to cool the temperature inside the tent.  This made it so being inside the tents was much more bearable.  Usually these they were reserved for patients with pneumonia and heart failure. (2)

In 1931 John Emerson invented an oxygen tent that had a cooling system.  Previous devices were prone to rust and failure.  (7)

The metal cannula was another device that was used.  It was a narrow metal pipe that was secured to the forehead by a strap that wrapped around the head, and at the lower end of the pipe were two prongs that were inserted into the nares.  I can imagine this may have felt awkward for the patient, but it may have been much nicer than having to lie inside an oxygen tent or having a rubber mask on your face.

The nasal catheter was introduced to the world by Lane in 1907, and introduced to the United States in 1931 by Waters and Wineland. (3)  Between 1920 and 1960 the nasal catheter was the most widely used method of delivering oxygen to patients. (8)

Glover explained that by the 1960s vinyl had been invented and this technology spread to the medical profession.  Masks, catheters, nasal cannulas and tubing were then made of this new material, and were much more comfortable for patients.  (2)
l
Another benefit was the material was see through, and this allowed the caregivers to see right away if the mask was filling with secretions, vomit or pulmonary edema. This made the masks much safer. They were also disposable, so it removed the need to clean and sterilize between patients.

Vinyl nasal cannulas quickly became the preferred basic oxygenation device, and this slowly caused the demise of the nasal catheter.

The nonrebreather was also introduced during the 1920s.  For those not familiar with these, they involve placing a mask tightly over the patients face to prevent the entry of room air. A one way valve on the mask allows the patient to exhale, but it closes on inhalation. This forces the patient to inhale only oxygen, which enters the airway from tubing which is connected from the mask to an oxygen flow meter. A bag connected to the mask collects oxygen while the patient is exhaling. When the patient inhale, inhales oxygen that is stored in the bag.

It is called a nonrebreather because the patient is not rebreathing any exhaled air. The idea here is that, if there is that if the mask is sealed tightly around the patient's face, and the one way valves are working, then the patient should be inhaling 100% oxygen.

Of course a problem with this system is that there were no surefire methods of knowing how much oxygen was left in an oxygen tank. So when a tank became empty, the patient had not oxygen to inhale, and would die of asphyxia. Learning this the hard way must have given quite a fright to some early orderlies, nurses and doctors.

The remedy to this problem was to remove one of the one way valves to assure that, if the oxygen tanks to run empty, that the patient can still inhale some room air. This is how most nonrebreather masks are produced today. So, while some people still report that nonrebreathers give patients 100% oxygen, the actual percentage is estimated to be between

Nonrebreathers of today aren't even nonrebreathers at all: they are partial rebreathers. Still, it is very common for them to be called nonrebreathers. They aren't generally referred to as partial nonrebreathers until both one way flaps are removed. With both flaps removed, the patient's estimated FiO2 is about 50-60%.

This represents one of the medical conundrums in medicine.

Early masks were also not see through, so if a patient vomited you might not know right away. Newer masks are made of disposable material that is see through, eliminating some of the older complications from these masks.

Regardless, nonrebreathers were good devices for oxygenating patients suffering from acute anoxia.

The next evolutionary breakthrough in oxygen delivery devices came as a result of observations made during the 1950s that some patients given 100% oxygen were becoming lethargic. It was soon realized that these were patients with emphysema and chronic bronchitis, or what we now refer to as chronic obstructive pulmonary disease (COPD).

This was where the hypoxic drive theory was derived from. You can learn about this theory in my post, "Hypoxic Drive Theory: A History of the Myth."  Essentially, this theory postulates that giving too much oxygen to some COPD patients might blunt their drive to breathe. So this resulted in the market for a better oxygen delivery device, and the invention of the Venturi Mask.

The new masks were based on the Venturi Principle, and allowed physicians the opportunity to provide accurate oxygen levels up to 50%. Nasal catheters, and later cannulas, were the preferred method of oxygenating these patients. However, because these devices are low flow devices, changes in the rate and depth of breathing make these less effective. Venturi masks were nice because they guaranteed the patient would get the desired oxygen level.

This was because the masks were based on the Venturi Principle. An adjustable opening allowed the caregiver to determine how much air was being inhaled. The larger the opening, the more air was inhaled and the less oxygen inhaled. The smaller the opening the less air was inhaled and the more oxygen was inhaled. So oxygen could now be set at between 28 and 50%, and this would not be affected by changes in rate or depth of breathing. It was a nice concept, especially for COPD patients.

These masks are still used today as a nice option for patients who are in respiratory distress, or who need a little more oxygen than a nasal cannula can provide, but don't quite need anything higher than 50%. They are generally only made as a temporary oxygen device, although some patients with terminal lung diseases (such as lung cancer) may occasionally use one at home.

By the 1980s plastic had been invented, and during this decade most respiratory therapy devices were slowly replaced by plastic.  Plastic nasal cannulas, masks, and nebulizers were introduced in the early 1980s and slowly phased into various hospitals through assimilation.

The earliest oxygen humidifiers were either made of metal or glass.  Until plastic was invented, none of the equipment here was disposable, and needed to be washed, sterilized, dried, and restocked on the shelves before being set up on the patient. So cleaning respiratory therapy equipment became sort of a secondary job for therapists until this aspect was phased out by turn of the 21st century.

References:

1. Hess, Dean,  Neil MacIntyre, Shelley Misha,"Respiratory Care:  Principles and Practice," page 281
2. Glover, Dennis, "History of Respiratory therapy: discovery and evolution, ," 2010, Indiana, page 94
3. Wyka, Kenneth A., Paul J. Mathews, John Rutkowski, editors, "Foundations of Respiratory Care," 2012, U.S., Delmar, page 9
4. Hess, Dean,  Neil MacIntyre, Shelley Misha,"Respiratory Care:  Principles and Practice," page 281
5. Barach, Alvin L., "The Therapeutic Use of Oxygen," The Journal of the American Medical Association, Vol 79, No. 9, Chicago, October 26, 1922, page 693-699
6. Barach, Alvin L, Margaret Woodwell, "Studies in oxygen therapy with determinations of blood gases," Archives of Internal Medicine, Vol. 28, 1921, Chicago, American Medical Association, pages 367-393
7. 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

Further Reading:

1. Use of oxygen in pneumonia in an oxygen chamber, page 466
2. RT Cave: Oxygen Therapy Made Easy
3. RT Cave: ypoxic Drive Theory: A history of the myth
4. RT Cave: The Physics Lexicon

1910-1920: The oxygen revolution

Joseph Barcroft (1872-1947)
In 1886 he received his M.D. from Cambridge,
and began his study of hemoglobin.
He exposed himself to different environments
to determine their effects on the human body.
.

Three significant events occurred at the dawn of the 20th century that resulted in increased interest in supplemental oxygen therapy. The first was the invention of a means of measuring oxygen saturation. The second was an experiment that Dr. Joseph Barcroft performed on himself. The third were experiments by WWI physicians to find a treatment for pulmonary edema caused by gas poisoning.

The ability to draw arterial blood was a significant discovery. It was hurter in 1912 who introduced the method. (2, page 693)

Yet even more significant was the machine blood could be inserted into that would determine the how saturated hemoglobin molecules in the blood were with oxygen molecules. This is referred to as oxygen saturation. Once inserted into the machine, the saturation was reported as a percentage.

John Scott Haldane (1850-1936)
He graduated from Edinburgh University in 1884,
and worked with his uncle at Oxford,
where he became interested in air,
its composition, and effects on humans.

Adolf Fick of Germany and Paul Bert of France described oxygen tensions as units of partial pressure, and it was these units that made it possible to describe the difference between arterial and venous blood. Since the partial pressure of oxygen in arterial blood is higher than the partial pressure of oxygen in venous blood. Or at least this is the case in a healthy individual. (1, page 4) (2) (6)

Donald Dexter Van Slyke (1883-1971) and John Scott Haldane (1892-1964) of Scotland developed effective means of measuring these differences. (1, page 94) (2) (6)

Further studies by various experts determined the normal levels and critical levels of oxygenation. It was determined that a normal arterial saturation of hemoglobin is between 95 and 98 percent, and a normal venous saturation is between 70 and 75 percent. These new values allowed physicians to monitor a patient's oxygenation status, and the effectiveness of oxygenation therapy. (2)(3, page 369)

Among the first to prove the significance of this discovery was Sir Joseph Barcroft, who lived for six days in an atmosphere that had 18 percent oxygen in the air, as opposed to the normal 21 percent that's in roomair. Alvin L. Barach, a pioneer in oxygen therapy, liked to use Barcroft's experiment as an example to prove the significance of oxygenation.

Barach explained:

"On the last day, the oxygen saturation of his arterial blood was 88 per cent., and after the performance of work 83.8 per cent. He lay in the chamber racked with headache, with occasional vomiting, and at times able to see clearly only as an effort of concentration. He became faint on exertion. His pulse, normally 56, had risen to 86. These effects were apparently due purely to oxygen want. The degree of anoxemia that produced them has frequently been found in pneumonia and heart disease by the investigators mentioned above. In many instances, the saturation of the arterial blood falls to far lower levels. It would, therefore, seem likely that lack of oxygen in the degree often found in disease would produce bodily discomfort, disturbances in function and damage to living structure." (3, page 369)

The effects on Barcroft were similar to the effects of pneumonia and heart failure for some patients. Studies showed that the oxygen saturation could range from 75-95 percent in cases of cardiac insufficiency, and 60-95 percent in cases of pneumonia. (2, page 693)

So it became apparent these diseases, as they progress, decrease the amount of oxygen that gets to the blood and to hemoglobin.  

Various studies, including the Barcroft study, proved that a low level of oxygen stimulates the central nervous system to stimulate various changes within the body in an attempt to return oxygenation back to normal: heart rate increases, respiratory rate increases in rate but decreases in depth, patient may become delirious and may have hallucinations  If not treated, death may result.  (2, page 694)

So these studies proved to the medical community the significance of observing the signs and symptoms of poor oxygenation and speedily treating them with oxygen. (2, page 694)

Oxygen was not meant to cure, but to treat the symptom of low oxygenation long enough to allow the physician to remedy the underlying condition, which may include: (2, page 694)

• Pneumonia
• Acute Cardiac Failure
• Severe Hemorrhage
• Epidemic Encephalitis
• Ascent to high altitudes
• Complications of chronic cardiac insufficiency
• Pulmonary Edema
• Acute Bronchitis
• Carbon Monoxide Poisoning
• Nitrous Oxide Poisoning
• Other anesthesia

Further studies also allowed physicians the opportunity to determine that a therapeutic percent of oxygen for most diseases was between 40 and 60 percent, and it's for this reason the oxygen chamber, oxygen catheter, and nasal cannula generally are not effective for oxygenating patients with severe oxygen deprivation. (2, page 696)

Studies likewise showed greater than 70 percent could cause pneumonia, and did so in rabbits. (3, page 373)

It was probably based on these and similar studies that John Haldane, another pioneer of oxygen therapy, would recommend 41% oxygen administration continuously for patients suffering from anoxemia (Haldane would coin a new term to describe this: hypoxemia). (6) (7) (8)

In fact, it is said Haldane once mused:

Intermittent oxygen therapy is like bringing a drowning man to the surface of the water—occasionally. (7) (8)

Yet even while he and other physicians proved the usefulness of continuous oxygen therapy during WWI, it would take a few more years for it to catch on. (6)

Oxygen mask designed by Haldane in 1917

A third significant event was the gas poisonings that occurred during WWI. Phosgene was used by the enemy on the war front because, when it combines with water in the lungs, it creates hydrochloric acid, which damages lung tissue. If inhaled in high enough doses it may cause pulmonary edema within 6-10 hours, leading to acute respiratory distress syndrome (ARDS).  As the illness progresses, the lungs lose their ability to pass oxygen to pulmonary capillaries, therefore causing anoxemia or hypoxemia. (6)

While oxygen was not thought to cure these patients, it was believed that it would treat the symptoms caused by anoxemia, particularly cyanosis and dyspnea.

Sometimes patients who presented with pulmonary edema due to gas poisoning were treated in oxygen chambers, which could be supplied with 40-60 percent oxygen. These chambers were found to be effective in treating cases of chronic gas poisoning. Some patients would spend up to 16 hours a day inside one with good results. (3, page 360)

However, this therapy wasn't practical for common use.

Another means of providing these patients oxygen was to use a tube or funnel to aim the oxygen at their faces, although studies showed this provided no more than a 2 percent increase in oxygenation of inspired air.

So this opened the door for an improved oxygenation apparatus that was easily portable by medics, comfortable to wear, could be used long term for chronic cases, and provided a therapeutic dose of oxygen. John Haldane invented such a device, and it was called the "Haldane Apparatus." (3, page 370)

Alvin Barach said Haldane's apparatus provided oxygen blended into the air the patient inspired, and by doing this the amount of oxygen making it to the alveoli was greatly increased. By this means, the patient was supplied with a therapeutic level of oxygen. (3, page 370)

Barach described the device as consisting of an oxygen tank, a reducing valve, and a face mask. He said:  (3, page 370)

"The mask was connected with a connecting bag which received oxygen from the tank, and with the outside air, from which the patient breathed. Oxygen was added to the inspired air in amounts of from one to four liters per minute. This was largely used in acute cases with generally good results." (3, page 370)

The problem with the Haldane apparatus was the only patients who tolerated it were those who were comatose. It worked great for these patients. Yet for others, for those who were awake and alert, it was not comfortable. Patient's complained that having the mask over their faces created a feeling of claustrophobia, and the mask was also hot and stuffy. This was especially a problem on hot days. Some patients simply didn't tolerate the mask, and some even ripped it off, refusing to wear it. (3, page 370)

Another problem, a pretty severe one actually, was it was impossible for clinicians to see through the opaque rubber masks. Clinicians learned to be vigilant, although this sometimes didn't prevent them from getting busy and not recognizing a patient was vomiting or expectorating foaming pulmonary edema. When not recognized, secretions occluded airways resulting in worsening anoxemia.

This concern opened the door for a more comfortable and safer oxygenation device.

One such device was the nasal cannula or prongs devised by Captain Adrian Stokes, M.D., in 1917. Stokes created the device while triaging patients on the war front who were suffocating due to pulmonary edema, and to which the tight fitting rubber mask of Dr. Haldane was not feasible. The metal cannula provided less oxygen than Haldane's device, although it helped medics keep pulmonary fluid from re-entering and blocking the airway. (1, page 38) (3, page 370)  (5, page 8) (6)

Stoke's cannula was a device similar in design to what we use today, although it was supplied by rubber tubing and the prongs were made of metal, and therefore was not very comfortable. However, patients tolerated it much better than the rubber mask, and of course it was safer. (1, page 38) (3, page 370)  (5, page 8) (6)

A similar device was the rubber nasal catheter, which was initially invented by Arbuthnot Lane in 1907, although re-introduced by Stokes in 1917. The catheter was introduced into the United States in 1931 by Waters and Wineland.  (1, page 17) (5, pages 8-9) (7, page 20)

The soft, rubber catheter (later made of pliable plastic) was a 12 inch long tube that was blindly inserted into one of the nostrils and then secured to the forehead. The patient would then open his mouth, depress his tongue to the bottom of his mouth, and the physician or nurse would check to see that the catheter was in place at the back of the airway. (4)

The end that remained outside the patient had a fitting to which oxygen supply tubing was connected.  On the distal side of the catheter, the side inside the patient's airway, were a series of small holes to allow oxygen to enter the patient's airway.  (4)

Catheters were designed for adults and pediatrics, the flow was set at 1- 5 lpm, and the the delivered oxygen was 22-35%.  The catheters would stay in the nose for a day or two.  If it was needed longer a new catheter had to be inserted. (4)

Most experts recommended changing the catheter every 24 hours to prevent tissue breakdown, and most hospital protocols eventually called for changing it every eight hours.

So you can see that while it was more convenient for the patient, there was some risk to the patient too.  It also provided some inconvenience for those taking care of patients requiring it.

While nasal catheters were simple to insert and manage, and while they were generally well accepted by patients, they did not provide enough oxygen in patients presenting with acute pulmonary edema or worsening pneumonia to eliminate cyanosis.  (3, page 370)

The nasal catheter was the most commonly used device for supplying supplemental oxygen prior to the invention of the modern nasal cannula in the 1960s.

Figure 2 --Apparatus for giving oxygen.(3, page 374)

Another option was a device similar to the one in figure 2.  The apparatus works this way: 

"The patient breathes through the rubber mouthpiece M (or a mask could be used) through the can of soda-lime C into a rebreathing bag B. The carbon dioxide exhaled is removed by the soda-lime, and oxygen is admitted from the tank O at a sufficient rate to keep B inflated.In this way the patient rebreathes pure oxygenfrom the apparatus,but since his nose is left open he dilutes this with a certain proportion of atmospheric air. In practice this results in the inhalation of from 40 to 60 per cent, oxygen." (3, page 374)

Yet another option was the oxygen tent. These were clear canopies that were made to cover the entire bed. A machine at the bedside provided an environment inside the tent of about 30 percent oxygen. These were effective as far as oxygenating some patients, although the original oxygen tents were hot and stuffy, and this particularly posed a problem on hot days.

Patients would generally go inside one long enough to catch their breath, and then they'd return to breathing room air. (1, page 94)

Barach recommended to physicians that the best means of measuring oxygenation status was by monitoring the heart rate, respiratory rate, and especially the level of cyanosis (bluish skin color). This was much more logical than an invasive blood draw. (3, page 370)

Caregivers would ultimately learn to monitor these signs, along with level of consciousness, before, during and after therapy.  This, they found, was the best means of monitoring the effectiveness of oxygenation therapy, and whether or not it was still needed.  (2)

What equipment to use to supply oxygen depended on what equipment was available, the physician taking care of the patient, and the independent oxygenation requirements of patient.

How long oxygen therapy was used primarily depended on the patient and how quickly, or slowly, the underlying condition resolved. (2)

Still, by 1922, when Barach wrote many of his papers, he explained that...

"the use of oxygen in medical therapy occupies at present an uncertain role." 

Despite Barach's doubts, the 1920s was an oxygen revolution of sorts.

Barach would go on to study the effects of oxygen therapy on a variety of respiratory diseases, including pneumonia and cor pulmonale. He would also study the effects of oxygen therapy on respiratory failure. For his work, he is often considered the father of modern oxygen therapy.

References:

1. Glover, Dennis, "History of Respiratory therapy," 2010, Indiana, page 94.
2. Barach, Alvin L., "The Therapeutic Use of Oxygen," The Journal of the American Medical Association, Vol 79, No. 9, Chicago, October 26, 1922, page 693-699
3. Barach, Alvin L, Margaret Woodwell, "Studies in oxygen therapy with determinations of blood gases," Archives of Internal Medicine, Vol. 28, 1921, Chicago, American Medical Association, pages 367-393
4. Hess, Dean,  Neil MacIntyre, Shelley Misha,"Respiratory Care:  Principles and Practice," page 281
5. Wyka, Kenneth A.,  Paul Joseph Mathews, William F. Clark, editors, "Fundamentals of Respiratory Care," 2002
6. Grainge, CP, "Breath of Life: the evolution of oxygen therapy," Journal of the Royal Society of Medicine, October, 2004, 97 (10), pages 489-493
7. Heffner, JE, "The story of oxygen," Respiratory Care, January, 2013, volume 58, number 1, pages 18-30
8. Sekhar, KC., "John Haldane: The Father of Oxygen Therapy," Indian Journal of Anesthesia, May-June, 2014, 58 (3), pages 350-352

1836: The beginning of pressure therapy and Tabarie's Sphere

G

Galileo (1564-1642) was perhaps the first to consider the idea that air had weight.  Yet it was his pupil, Evangelista Toricelli (1608-1647), who proved the existence of atmospheric pressure.  From there, it didn't take long for ideas to evolve for using changes in atmospheric pressure as therapy for various diseases, such as lung ailments  (3, page 52)

Tabarie's Sphere (3, page )

The major question Toricelli set out to answer was:  Why is it that water is prevented from being pumped up higher than 32 feet?  He performed a test, and proved the answer was due to the weight of the air, or atmospheric pressure.

Apparently influenced by folks who described the benefits of climate change or high altitudes, Nathaniel Henshaw (1628-1673) was the first to create a chamber for artificially raising or lowering atmospheric pressure so that it could be used to help people feel better.  Henshaw's called his chamber the "Domicilium," which was basically a "sealed room," that was attached to a "pair of large organ bellows."  This chamber is now considered the first hyperbaric chamber.  (5, page 1)

According to Tissier, the "chamber was built of masonry and supplied with doors and windows that could be closed hermetically.  It communicated with two bellows (the organ bellows) provided with valves, which worked in opposite directions, in such a way that it was possible, at will, to obtain compression or rarification of air." (3, page 55)  

Here we require a couple definitions:

1.  Compressed Air:  This was the original term used to describe increases in atmospheric pressure.  It's air with a larger volume of oxygen than ordinary air.  It is positive pressure. 

2.  Rarified Air:  This was the original term used to describe decreases in atmospheric pressure.  This is air that contains less oxygen that normal room air.  It is negative pressure. 

So, basically, Henshaw's organ bellows, when pressed, forced air into the chamber, and therefore increased the atmospheric pressure inside.  When the bellows were relaxed, pressure was decreased inside the chamber.  Future chambers, and portable apparatus's, would apply a similar technique to compress and rarify air.  

Other than Henshaw's work, there's little evidence pressure changes were considered for therapeutic use for diseases until the 1750s.  Yet by 1800 there was such strong speculation for the therapeutic use of pressure therapy that the Royal Society of Haarlem opened the idea up to a competition to determine "The influence of condensed air on animal and vegetable life."  Yet it was to no avail. (1, page 43)

However, the idea continued to circle the profession, and Sir John Sinclair suggested, based on his observations of the effects of pressure on animals, that changes in pressure may have therapeutic benefits for humans.  (1, page 43) 

Among the first to come to the challenge were Emile Tabarie and Junod.  In 1833 Tabarie discussed the topic with the Parisian Academy of Science, (2, page 19) and in 1835 Tabarie performed the first experiments.

Junod reported that when the "natural pressure of the atmosphere is augmented by one-half, the following effects will be observed:"

1. Disagreeable sensation of pressure in the ears, subsiding as equilibrium is re-established
2. Respiration is Facilitated.  The inspiration becomes deeper and less frequent
3. Circulatory changes occur
4. Functions of digestive apparatus are stimulated
5. Secretions of salivary glands and kidneys are very profuse

There were various theories to account to the perceived benefits of pressure changes on breathing. The pressure seems to open and keep the alveoli open to better receive the next breath.  The vessels of the body appear to be compressed, which stimulates the pulse to increase so it is "full and easily compressible. the caliber of the superficial veins is diminished, and the lumen may even become completely obliterated, so that the blood on its way back to the heart courses through the deeper veins."  (3, page 72)

If this is true, it was determined that the same effect must occur to the pulmonary vessels, and this results in "the quantity of venous blood contained in the lungs (to) diminish; and this probably explains why a much greater quantity of air can be drawn into the lungs at each inspiration that is possible under normal pressure. (3, page 72)

"Further, if an increase in the density of the air tends to diminish the caliber of the veins, it follows necessarily that a greater quantity of blood will enter the arterial system and more blood will also reach the principal nerve-centers; especially those in the brain, because the latter is protected from the direct pressure of the atmosphere by the resistant bony calvarium. The cerebral functions are accordingly enhanced, the imagination becomes more active, and in some persons there is a peculiar exaltation which stimulates drunkeness." (3, page 72)

By 1838 Tabarie had performed a variety of tests to study the effects on pressure changes on the various parts of the body, all except for the head. He studied the effects of both condensed and rarified air. By his experiments Tabarie determined that condensed air "retards the action of the heart and steadies the rhythm. This effect is very slight and may not be noticeable under normal conditions, but becomes quite evident in disease." (3, page 72)

Tabarie ultimately devised a chamber, or sphere, that was made of iron that allowed up to twelve people to enjoy the benefits of pressure changes.  "He advised sittings of two hours duration with an increased pressure of from one-half to two-thirds of an atmosphere.  Bertin, who used the spheres, reported the cure of fifteen cases of uncomplicated emphysema, and ninety-two cases of nervous and catarrhal asthma with associated emphysema.  Air chambers, cumbrous, expensive and not portable, were thus far used." (1, page 44)

Various pneumatic chambers were devised and used around this time, with a variety of shapes being used. However, they were all based on the design of Tabarie's Chamber. They contained two pipes, one for for supplying the air and connected to a hydraulic compressor operated by steam.  The other pipe was for ventilation.  

References:

1. Minnesota State Medical Society, "Transaction of the Minnesota State Medical Society," 1886, St. Paul, H. M. Smyth Printing Co.
2. Foster, Frank, editor, "Practical Therapeutics," Volume I, 1897, New York, Appleton and Co., page 19
3. Tissier,Paul Lewis Alexandre, edited by Solomon Solis Cohen, "Pneumotherapy: Including Aerotherapy and inhalation methods," volume X, 1903, Philadelphia, P. Blakiston's Sons and Co., pages 296-224.  If the profession of respiratory therapy existed in their era, we would be reading their books.  However, as it was, their books were written for the medical profession. All of the material from this post is from Tissier's book unless otherwise noted in the above paragraphs. Tissier page 72
4. Rose, A., "Treatment of Disease of Respiration and Circulation by the Pneumatic Method," New York, The Medical Record: A Weekly Journal of Medicine and Surgery, Edited by George F. Shrady, M.D., Volume 10, Jan. 2, 1875 to Dec. 25, 1875, New York, William Good and Co., page 577
5. Clarke, Dick, "History of Hyperbaric Therapy," Chapter 1 of the book, "Physiology and Medicine of Hyperbaric Oxygen Therapy," 2008, Philadelphia, Saunders, page 1-2
6. Picture is from an advertisement placed in the Medical Press of Western New York, volume II, No. 6, June, 1887, Roswell Park M.D., editor, New York, Bigelow Brothers, page 338