Protection against the physiological effects of positive pressure breathing

The degree of protection afforded by three jerkin G-suit systems (British, Canadian and Swedish) using different pressures against the adverse physiological effects produced by high levels (50 mm Hg and 70 mm Hg) of positive pressure breathing (PPB) was investigated at ground level in 10 male subjects. The British and Canadian systems were evaluated with G-suit pressure equal to breathing pressure and 3.2 times breathing pressure, whereas the Swedish system was studied only with 3.2 times breathing pressure in the G suit. The experimental design was a 10 X 10 Latin swuare. PPB produced significant increases in heart rate, peripheral resistance, and systolic, diastolic and mean arterial blood pressures, and significant decreases in stroke volume and cardiac output. These effects were directly related to the level of PPB. Our results show that the British system provides the highestdegree of protection against PPB, followed by the Swedish and the Canadian systems. It was also found that a G-suit pressure of 3.2 times breathing pressure significantly increases the degree of protection afforded by the British and Canadian systems.