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Impairment during marked hypotension of the plasma volume control in hemorrhage
Insights
During severe hypovolemia, the body
Area of Science:
- Physiology
- Cardiovascular Science
Background:
- Hypovolemia triggers extravascular fluid transfer to circulation, primarily from skeletal muscle, to restore blood volume.
- This compensatory mechanism is crucial for maintaining blood volume during blood loss.
Purpose of the Study:
- To investigate the efficacy of the compensatory fluid transfer mechanism during pronounced hypovolemia and hypotension in cats.
Main Methods:
- The study was conducted in cats under conditions of induced hypovolemia and hypotension.
- Hemodynamic parameters and fluid shifts were monitored.
Main Results:
- The investigation indicated that the compensatory fluid transfer mechanism is inactivated during severe hypovolemia with hypotension (30-40 mmHg).
- This inactivation is linked to reduced blood flow in skeletal muscle due to decreased perfusion pressure and vasoconstriction.
- Marked vasoconstriction, while preventing circulatory collapse, may impair plasma volume regulation.
Conclusions:
- The vital compensatory fluid transfer from skeletal muscle is shut down during profound hypotension.
- This shutdown compromises plasma volume regulation, potentially reducing survival chances despite necessary vasoconstriction to prevent circulatory collapse.
Abstract:
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.