Cardiovascular effects of varying G-suit pressure and coverage during +1 Gz positive pressure breathing

With the continued evolution of anti-G suits, used to counter the cardiovascular dysfunction arising from +1 Gz hypoxia protection positive pressure breathing (PPB), it was hypothesized that full-coverage anti-G-suits would offer equal protection while using lower inflation pressures than the traditional 4:1 ratio. Nine experienced subjects were exposed to 2 min of 70 mm Hg PPB while wearing either the COMBAT EDGE (CE) and Tactical Life Support System (TLSS) garments with the G-suit inflated to 4 x breathing pressure, and the Advanced Tactical Anti-G-Suit (ATAGS) at 4, 3, 2, and 1 x the breathing pressure. All subjects were measured with impedance cardiography (IC), and six were measured simultaneously with both IC and the Cardioscint nuclear probe. IC-estimated stroke volume, relative left ventricular (LV) end-diastolic volume, LV ejection fraction, and peak filling rate were depressed most in the CE and ATAGS 1 conditions (p < 0.001). Heart rate and mean arterial blood pressure changes were highest and lowest, respectively, using the CE and ATAGS 1 garments (p < 0.001). There were no differences in these variables between the TLSS and ATAGS 2-4 conditions. Thus, protection against the PPB-induced fall in LV preload and cardiovascular function may still be adequately afforded by lower G-suit inflation pressures when using full-coverage anti-G suits during PPB intended for high altitude-protection.