Physiologic factors in the use of the body respirator for impaired respiratory function.

Summary In normal breathing the respiratory muscles change the configuration of the thorax in such a way that air inflates the lungs on each inspiration and is expelled by elastic recoil of the lungs on each expiration. These movements not only effect gas exchange but affect the circulation of blood through the thorax. If the respiratory muscles are for any reason inadequate, their efforts must be assisted or replaced by mechanical means. The pulmonary effects of normal breathing can be very nearly simulated by intermittent elevation of airway pressure (obtained by raising pulmonic pressure with the body at atmospheric pressure, or by lowering pressure around the body with the lungs remaining at atmospheric pressure). The effects of intermittent positive pressure breathing on the circulation are very different from those of normal breathing; the impeding effect on cardiac output is beneficial in some conditions (pulmonary edema) and detrimental in others (shock). The advantages of alternative methods of pressure breathing are presented. A device which permits the patient to cycle a body respirator is described.