Response of capacity vessels in human limbs to head-up tilt and suction on lower body.

Abstract

The "occluded" limb technique was used for continuous monitoring of reflexly mediated changes in venous tone in 10 normal subjects. Tilting to 70[degree] head up and exposure of the lower part of the body to subatmospheric pressure (60 mm Hg) caused a transient increase in venous pressure in the hand, foot, and forearm whose circulation was arrested, in contrast to a maintained decrease in forearm blood flow. On return to the horizontal or release of suction, another transient rise in venous pressure often occurred in association with an increase in forearm blood flow. The transient venous responses could not be related to the redistribution of blood caused by these procedures. It seems that reflex changes in tone of the capacity vessels in the limbs are not an essential part of the compensatory vascular responses for maintenance of systemic arterial blood pressure in the upright position, although the transient increase in tension of the walls of the capacity vessels may aid the resistance vessels in reducing the rate of pooling of blood in dependent parts.