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 car diovascular 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 pres sures than the traditional 4:1 ratio. Nine experienced subjects were e xposed to 2 min of 70 mm Hg PPB while wearing either the COMBAT EDGE ( CE) and Tactical Life Support System (TLSS) garments with the C-suit i nflated to 4 X breathing pressure, and the Advanced Tactical Anti-G-Su it (ATAGS) at 4, 3, 2, and 1 x the breathing pressure. All subjects we re measured with impedance cardiography (IC), and six were measured si multaneously with both IC and the Cardioscint(TM) nuclear probe. IC-es timated stroke volume, relative left ventricular (LV) end-diastolic vo lume, LV ejection fraction, and peak filling rate were depressed most in the CE and ATAGS 1 conditions (p < 0.001). Heart rate and mean arte rial blood pressure changes were highest and lowest, respectively, usi ng 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, pr otection against the PPB-induced fall in LV preload and cardiovascular function may still be adequately afforded by lower G-suit inflation p ressures when using full-coverage anti-G suits during PPB intended for high altitude-protection.