Abstract

Numerous observations of the effects of pres-sure breathing on the arterial blood pressure of anesthetized animals are available in the literature (1-7). In all cases an increase in the pulmonary pressure results in a fall of the arterial pressure (mean pressure as measured on a mercury ma-nometer), with an occasional secondary compensa-tory rise. With negative pulmonary pressures the effects are less regular, according to Schaefer and Bain (2), but usually the arterial pressure rises (7). Bruns (8) showed an increased stroke volume in a plethysmographic record of a rabbit heart during negative pressure breathing and B6ger, Cobet, and Stepp (9) found an increased cardiac output of 15 to 162 per cent, and an increased oxygen con-sumption (37 per cent) with a negative pulmonary pressure of 5 cm. H2O in a rabbit. Since these experiments were done on anesthetized animals it is difficult to apply them directly to the human problem. Most measurements previously made on men are confined to brief periods of increased positive pressure such as may be obtained by the Valsalva experiments (5, 6, 10-14). It has been generally found that with such an increase of intrapulmonary pressure the systemic arterial pressure rises briefly and then falls. This is followed by a secondary rise above the initial level. The secondary rise does not occur if the intrapulmonary pressure is too high. The heart rate usually accelerates. Ac-cording to Burger (13), only 3 out of 145 cases