Relationship between stroke volume and pneumocardiogram.

The intratracheal pressure oscillations produced by the heartbeat, called the pneumocardiogram, were recorded in 15 dogs. It was found that a linear relationship existed between the amplitude of the major negative deflection of the pneumocardiogram and the cardiac stroke volume, the latter determined either by indicator dilution (avg r = 0.94) or by use of an electromagnetic flow probe (avg r = 0.95). This relationship existed in animals with both an open and a closed chest. The vector of left ventricular wall motion directed toward the lungs, determined by high-speed cineradiography of the motion of a tantalum marker inserted in the wall of the left ventricle, looked very similar to the pneumocardiogram. This study showed that the pneumocardiogram can be used as a noninvasive technique to measure changes in stroke volume and is caused primarily by the motion of the cardiac walls.