BALLISTOCARDIOGRAPHIC STUDY OF CHANGES IN CARDIAC OUTPUT DUE TO RESPIRATION 1

Abstract

Circulatory effects of positive pressure breathing, of variations in the alveolar CO2 tension, and of pure O2 inhalation were studied in human subjects by means of a ballistocardiograph. Breathing against a continuously elevated pulmonary pressure decreased the stroke vol. but in- creased the heart rate. In some individuals, compensation was complete; others showed a net reduction in cardiac output. Breathing from a pneumolator which elevated the pulmonary pressure only during inspiration produced a decrease of both stroke volume and heart rate. When the mean pulmonary pressure was about 10 cm. of water, cardiac output was reduced to about 85% of normal. Voluntary hyper-ventilation of about the same volume as that produced by the pneumolator decreased the stroke volume and increased the heart rate so that the cardiac output was 95% of the normal. Elevation of alveolar pCO2 by increased dead space produced no consistent effect on cardiac output. Substitution of pure O2 for air in normal breathing resulted in an increase of 5% in the volume of ventilation and a decrease of 8.5% in the heart rate and cardiac output.