title: Physiological effects of positive pressure breathing with pure oxygen and a low oxygen gas mixture.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Beihang University, Beijing, P. R. China; the Institute of Aviation Medicine, Air Force of P. R. China, Beijing, P. R. China;
authors.forename: Xiaopeng
authors.initials: X
authors.lastname: Liu
authors.forename: Huajun
authors.initials: H
authors.lastname: Xiao
authors.forename: Weiru
authors.initials: W
authors.lastname: Shi
authors.forename: Dongqing
authors.initials: D
authors.lastname: Wen
authors.forename: Lihua
authors.initials: L
authors.lastname: Yu
authors.forename: Jianzhang
authors.initials: J
authors.lastname: Chen
mesh_terms: D000293:Adolescent; D000337:Aerospace Medicine; D000531:Altitude; D005676:Gravity Suits; D006339:Heart Rate; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D010100:Oxygen / Q000008:administration & dosage* / Q000097:blood / Q000502:physiology*; D011175:Positive-Pressure Respiration / Q000009:adverse effects; D019442:Space Suits; D013318:Stroke Volume; D013647:Task Performance and Analysis; D055815:Young Adult
chemical_list: D010100:Oxygen