Effect of positive pressure breathing on hemodynamics in patients with borderline arterial hypertension during water immersion

Patients with borderline hypertension were exposed, while being immersed, to positive pressure breathing. During exposure cardiac output (CO), heart rate (HR), mean arterial pressure (MAP), total peripheral resistance (TPR), left ventricle work (W), blood content of head vessels (Qh), upper and lower lung lobes (Qu1 and Q11), liver (Q1) were measured. During immersion CO and MAD decreased, HR and TPR increased slightly, and W diminished. Simultaneously Qh, Qu1 and Q11 increased significantly while Q1 decreased considerably, indicating blood "centralization" during simulated microgravity. Courses of positive pressure breathing led to decreases in Qh, Qu1, Q11 and increase in Q1, i. e., they caused blood to be displaced from the head and lungs to the liver. Thus, the liver plays the role of a physiological pool which accumulates blood removed from the upper body by positive pressure.