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.