Physiological studies of the effects of intermittent positive pressure breathing on cardiac output in man.

Three types of positive pressure breathing have been differentiated : a) continuous positive pressure breathing where a pressure above atmospheric is maintained in the lungs throughout the respiratory cycle, b) expiratory positive pressure breathing in which a pressure above atmospheric is present during the expiratory phase of breathing, and c) intermittent positive pressure breathing (IPPB), provided by automatic respirators, which consists in an active inflation of the lungs under an increasing positive (above atmospheric) pressure; while after cycling of the respirator, deflation of the lungs occurs almost to or to atmospheric pressure as a passive process engendered by the elasticity of the lungs and chest-wall structures. Only the latter type of pressure breathing (IPPB) is suitable for maintaining artificial respiration in the apneic subject. Moreover, IPPB as produced by automatic respirators is more comfortable and less exhausting fur the conscious subjects when compared to continuous or expiratory positive pressure l