Angelo Mosso's Experiments at Very Low Barometric Pressures

Paul Bert (1833–1886) is often regarded as the father of high altitude physiology. His monumental book La Pression Barométrique (Bert, 1878) is essential reading and includes extensive accounts of his experiments using low-pressure chambers. Bert himself never went to high altitude and much of the stimulus of his research came from Denis Jourdanet (1815–1892), a Parisian doctor who spent 19 years in Mexico, much of it exploring remote areas at high altitude. He had the distinction of climbing the volcano Popocatépetl. Jourdanet strongly influenced Bert's ideas and in fact may have been the original proponent of the view that low Po₂ in the blood was the critical factor at high altitude. Jourdanet also provided the financial support for Bert's experiments using his sophisticated low-pressure chambers in the Sorbonne. Much of Jourdanet's work was published in a lavishly illustrated two-volume book (Jourdanet, 1875).

Among Bert's experiments was one in 1874 when he decompressed two balloonists, Crocé-Spinelli and Sivel, to a barometric pressure of 304 mm Hg, which was noted to cause impairment of vision and hearing. Tragically these two aeronauts were later to lose their lives as a result of acute hypoxia in the flight of the balloon “Zenith.” Oxygen had been provided on the advice of Bert, but it was insufficient. In another experiment in 1874, Bert himself was in the chamber, and the pressure was reduced to as low as 248 mm Hg which he had correctly predicted was about the pressure on the Everest summit. Of course Bert could only remain conscious at this simulated altitude by breathing oxygen.

Although we now accept Bert's view that the reduced Po₂ was responsible for the deleterious effects of high altitude, there was great controversy at the time, and many eminent scientists including Sechenov, Cyon, Frankel, Geppert, and Kronecker criticized the findings. A full description of the sometimes vituperative discussions can be found in Kellogg (1978). Among those who disagreed with Bert's conclusion was Mosso.

Angelo Mosso (1846–1910) was professor of physiology in Turin and is well known for being responsible for building the physiological laboratory in the Capanna Margherita at an altitude of 4559 m on Monte Rosa. Most of Mosso's work was done in the Capanna and indeed the first edition of his influential book Fisiologia dell' Uomo sulle Alpi: Studi Fatti sul Monte Rosa (Mosso, 1897) does not mention his experiments using low-pressure chambers. However, these are described in the second edition of his book which was published in 1898 and was translated into English as Life of Man on the High Alps (Mosso, 1898).

Mosso's low-pressure chamber experiments make entertaining reading. Many were carried out using his faithful technician, Giorgio Mondo, as the subject. Mosso exposed Mondo to a series of simulated altitudes and collected expired gas samples that were later analyzed for oxygen and carbon dioxide. He also arranged for Mondo to inspire samples of gas containing different concentrations of oxygen and carbon dioxide. His conclusion from these experiments was that, as indicated above, the deleterious effects of high altitude could be ascribed to the low carbon dioxide levels rather than the hypoxia. He reached this conclusion because he believed that his studies showed a closer correlation between the reduced Pco₂ rather than the reduced Po₂, and the symptoms caused by exposure to low pressures. An extensive description of Mosso's many scientific interests is available (West, 1998).

One of Mosso's assertions was that carbon dioxide was eliminated from the body by exposure to low pressures rather as the gas can be removed from the blood by a mercury pump in a blood-gas apparatus. However this notion was criticized by Barcroft who stated in his typical English manner “I speak with all deference, but Mosso seems to have overlooked the fact that the body is exposed to what is practically a vacuum of CO₂, whether it be at the Capanna Margherita or in his own laboratory at Turin” (Barcroft, 1925).

Because Mosso was focused on high altitude and carbon dioxide, he was less interested in the oxygen levels in the chamber, and in some experiments added oxygen to the chamber air as the pressure was reduced. He became intrigued by the extent to which the pressure could be lowered. In one remarkable experiment, Mosso himself was decompressed to the extraordinary barometric pressure of 192 mm Hg, though of course the chamber was enriched with oxygen. Mosso made the observation that he could cover the height of the mercury column in the barometer in the chamber with the palm of his hand and this gave him great satisfaction. He also exposed an orangutan, Slabi, to a pressure of 126 mm Hg with no apparent ill effects. Experiments like this emphasize that one of Mosso's primary interests was extreme hypobaria.

An interesting sidelight on Mosso's experiments in his low-pressure chamber has recently emerged. Mosso had a daughter named Emilia Mimí (1890–1937) who wrote several books including I Tempi del Cuore (The Tming of the Heart), Segno le Ore Serene (Sign of the Quiet Hours), and L'Uomo del Viale (The Man in the Street). In one of her books, Un Cercatore d'Ignoto (A Seeker of the Unknown), dedicated to her father's life, there is a chapter titled Himalaya at the Valentine. Valentine refers to a park alongside the river Po where Mosso's laboratory was located. Here is a translation of part of this chapter. “When instead of a guinea pig or a frog, Angelo Mosso subjected himself to the pneumatic room… an assistant closed the bolted door, he was alone on his frightening slope… A manometer marked the degree of air rarefaction… An assistant read the altitude out aloud… 4800 m Mont Blanc… On the other side of the big glass, my father smiled and lifted his shoulders nonchalantly. Little height in truth. It's the beginning of the slope… after about 20 minutes another figure appeared 5100 m… Kilimanjaro, the African peak of 5800 m.… Now he was climbing slower because it was dangerous. All the eyes were intent on the face of the man who by now had touched the zone where few living beings had ever risked: 6100 m and then 6500 m… White in face he kept on climbing. He reached 8000 m on the peak of Everest, the tallest mountain of the world, he beckoned to stop. With a sigh of relief, his assistant started to slowly input external air and the altitude started to descend, they opened the door… and my father came out of his diving bell, staggering, he had to lean against the wall in order not to fall.”

In summary, Mosso was one of the giants of high altitude physiology at the turn of the century and he made many important contributions. In particular, he was responsible for setting up the physiology laboratory in the Capanna Margherita, and this is still in use over 100 years later. However, his belief that the symptoms of high altitude were best explained by the low partial pressure of CO₂ rather than Po₂ was eventually shown to be erroneous. His extraordinary experiments where he exposed himself to extremely low barometric pressures in his chamber are one of the highlights of the history of high altitude physiology.