Physiological effects of positive pressure breathing with pure oxygen and a low oxygen gas mixture

Positive pressure breathing (PPB) can cause circulatory dysfunction due to peripheral pooling of blood. This study explored a better way at ground level to simulate pure oxygen PPB at 59,055 ft (18,000 m) by comparing the physiological changes during PPB with pure oxygen and low oxygen at ground level.

Six subjects were exposed to 3 min of 69-mmHg PPB and 3 min of 59-mmHg PPB with pure oxygen and low oxygen while wearing the thoracic counterpressure jerkin inflated to 1× breathing pressure and G-suit inflated to 3 and 4× breathing pressure. Stroke volume (SV), cardiac output (CO), heart rate (HR), and peripheral oxygen saturation (Spo2) were measured. Subjects completed a simulating flying task (SFT) during 3-min PPB and scores were recorded.

HR and SV responses differed significantly between breathing pure oxygen and low oxygen. CO response was not significantly different for pure oxygen and low oxygen, the two levels of PPB, and the two levels of G-suit pressure. Spo2 declined as a linear function of time during low-oxygen PPB and there was a significant difference in Spo2 response for the two levels of PPB. The average score of SFT during pure oxygen PPB was 3970.5 ± 1050.4, which was significantly higher than 2708.0 ± 702.7 with low oxygen PPB.

Hypoxia and PPB have a synergistic negative effect on both the cardiovascular system and SFT performance. PPB with low oxygen was more appropriate at ground level to investigate physiological responses during PPB and evaluate the protective performance of garments. Liu X, Xiao H, Shi W, Wen D, Yu L, Chen J. Physiological effects of positive pressure breathing with pure oxygen and a low oxygen gas mixture.