Assisted positive pressure breathing for augmentation of acceleration tolerance time

The addition of assisted (chest counterpressure), positive pressure breathing (APPB) at 50 mm Hg (PPB50) and 70 mm Hg (PPB70) was compared to the current operational support of the G-suit and the anti-G straining maneuver (AGSM) without PPB (PPB0), during acceleration exposures of sustained 9 +Gz for 45 s and a 5-9 +Gz simulated aerial combat maneuver (SACM) to exhaustion. We selected 7 highly motivated male centrifuge subjects from a group of 31 volunteers. Positive pressure breathing was applied to the oronasal cavity with a Royal Air Force P/Q mask. Mask pressure was monitored continuously. Counterpressure was applied to the chest with a Canadian counterpressure garment at the same pressure as the mask. Lower body pressure was provided by a standard USAF G-suit inflated with the standard pressure schedule of 1.5 psi/G after 2.0 G. Positive pressure breathing was provided linearly in proportion to the +Gz level beginning at about 1.2 +Gz and reaching a peak of either 50 or 70 mm Hg (6.7 and 9.3 kPa, respectively) at 9 +Gz. Prepressurization (ready pressure) was used for both PPB (2.1 mm Hg) and G-suit (10.3 mm Hg) inflation. All subjects were monitored for heart rate and rhythm, SaO2 with an ear oximeter, inspired air flow, and rectus femoris electromyogram (EMG). Assisted positive pressure breathing provided a significant (p less than 0.01) increase in mean tolerance time at PPB50 (108%) and PPB70 (88%) compared to PPB0 during the 5-9 SACM.(ABSTRACT TRUNCATED AT 250 WORDS)