MECHANISM OF THE POSTURAL REDUCTION IN VITAL CAPACITY IN RELATION TO ORTHOPNEA AND STORAGE OF BLOOD IN THE LUNGS

Abstract

Many determinations of vital capacity were made on 5 subjects, standing, lying down, and supine on an inverted T shaped scaffold, of which the cross bar supported the hips and the upright the spines of the dorsal vertebrae. The evidence showed that, while vital capacity decreases in the recumbent posture, the residual air remains constant. In the completely inspired position the size of the chest may increase in the recumbent posture. In the completely expired position the size of the chest usually increases in the recumbent posture. Hence it would seem that the lungs serve as storage for blood which is poured out of the dependent veins when one lies down. This conception is substantiated by the fact that when blood pressure cuffs are applied to the 4 extremities, and blood trapped in the arms and legs by raising the pressure in the cuffs to diastolic, there is a prompt and marked increase in the recumbent vital capacity, so that it may equal or exceed the vital capacity in the standing posture.