Impairment during marked hypotension of the plasma volume control in hemorrhage.

During hypovolemia extravascular fluid is transferred across the capillaries into the circulation in order to restore blood volume. Several studies have shown that this process, which mainly occurs in skeletal muscle, effectively can compensate for the blood loss. The preset investigation performed in the cat strongly indicates, however, that this vital compensatory mechanism is inactivated in situations of pronounced hypovolemia leading to hypotension levels of 30-40 mmHg, i.e. when the need for refill of the circulatory system is most in demand. It is suggested that the cessation of fluid transfer from skeletal muscle to blood during marked hypotension is causally linked to the evoked pronounced reduction of blood flow, due partly to the much reduced perfusion pressure and partly to the marked vasoconstriction. Pronounced vasoconstriction in the hemodynamically important vascular bed of skeletal muscle is obviously an essential part of the necessary resistance response evoked in the systemic circulation in order to avoid circulatory collapse already in the early phase of a large blood loss. However, the chances for the organism to survive is minimized if the vasoconstriction leads to impairment of the mechanisms for plasma volume regulation.