Physiological Observations on Hyperventilation at Altitude with Intermittent Pressure Breathing by the Pneumolator

Abstract

The pneumolator is an automatic instrument which causes pressure to rise within the lungs. A valve releases this pressure periodically so that the lungs are periodically inflated and deflated at any desired rate and at any desired pressure. Expts. with the pneumolator on human subjects showed that there results a hyperventilation and lowered CO2 tension. This hyperventilation is greater at altitude than at ground level because of the decreased resistance to air flow and because a larger tidal volume is necessary to produce the same peak pressure at the lower ambient pressure. The expansion of the chest during the inflation with the pneumolator is not entirely passive. As acapnia developed the chest seems to have expanded less for the same pulmonary pressure. In simulated flights to 46,000 ft. comparisons were made between continuous pressure breathing and intermittent pressure breathing. It was found that the higher O2 tension and arterial saturation which resulted from the greater ventilation obtained in the latter system were not sufficiently advantageous to compensate for the lower mean pressure in the lungs, so that under the conditions of these expts. the subjects preferred continuous to intermittent pressure breathing. There is, however, a possibility that an intermediate system might be better than either. During these one-hour periods of hyperventilation at high altitudes, the alveolar CO2 tension fell to 20 mm., the alkaline reserve of the blood fell 1.3 meq./l. and the lactic acid concn. of the blood rose in an approx. equivalent amt. The pH of the urine and the excretion of base also increased, but the absolute amt. of base lost in this way was not sufficient to have a significant effect on the alkaline reserve of the blood.