RESPIRATORY AND CIRCULATORY RESPONSES TO SUSTAINED POSITIVE-PRESSURE BREATHING AND EXERCISE IN MAN

To investigate the effects of sustained positive-pressure breathing (PPB) on the adaptation of respiration and hemodynamics exercise, 8 healthy volunteers were exposed to PPB of air at 15 and 30 cm H2O in the supine position at rest and during leg exercise at 50% of individual maximal working capacity. PPB was subjectively and objectively better tolerated when combined with exercise than at rest. PPB at 30 cm H2O resulted in marked hyperventilation with alkalosis in the resting condition, but did not significantly affect respiratory minute volume, blood gases or acid-base balance during exercise. Cardiac output and left ventricular work were reduced by .apprx. 1/5 and 1/3, respectively, at rest and during exercise. Compared with normal airway pressure, exercise-induced increase pressure (relative to atmospheric) was elevated by PPB at rest and during exercise, the driving pressure in systemic circuits (arterial minus central venous pressure) was reduced in both conditions. Dynamic exercise counteracts deleterious effects of PPB by normalizing respiratory function and by improving cardiac filling by activation of the leg muscle and abdominal pumps.