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The effect of haemorrhage on venous return and regional blood flow in the anaesthetized cat
Insights
This study measured feline venous return and found that hemorrhage shifts blood flow distribution. Blood flow to the head and liver is prioritized over kidneys and hind limbs during shock.
Area of Science:
- Physiology
- Cardiovascular System
Background:
- Understanding venous return is crucial for managing circulatory shock.
- Hemorrhage significantly impacts blood flow distribution and organ perfusion.
Purpose of the Study:
- To quantify venous return in cats under anesthesia.
- To investigate the effects of hemorrhage on regional blood flow distribution.
Main Methods:
- Utilized a venous long-circuit technique in anesthetized cats.
- Measured blood flow in the superior and inferior vena cava segments (hepatic, renal, iliac).
Main Results:
- Mean venous return was 130 ml/kg, with specific contributions from different vena cava segments.
- Hemorrhage decreased overall venous return, altering regional flow distribution.
- Increased proportion of flow from superior and hepatic vena cava, decreased from renal and iliac.
- Significant vasoconstriction observed in kidneys and hind limbs, preserving flow to head and liver.
- Renal blood flow autoregulation was impaired by vasoconstriction during hemorrhage.
Conclusions:
- Hemorrhage leads to a redistribution of blood flow in cats.
- The body prioritizes perfusion to vital organs like the head and liver during hypovolemia.
- Renal vasoconstriction plays a key role in this compensatory mechanism, affecting autoregulation.
Abstract:
1. In cats under pentobarbitone anaesthesia, a venous long-circuit technique was used to measure the blood flows in the superior vena cava and the hepatic, renal and iliac segments of the inferior vena cava. The sum of these flows gave the venous return (minus coronary and bronchial flows).2. In these preparations, the mean venous return was 130 ml./kg. Of this 28% came from the superior vena cava and 37% from the hepatic, 23% from the renal and 12% from the iliac segments of the inferior vena cava.3. After haemorrhage, the flows from all the venae cavae segments decreased. The quantitative changes varied with the particular cat, the degree and duration of the haemorrhage and whether the animal had been subjected to a previous haemorrhage.4. The proportion of the reduced venous return draining from the superior vena cava and the hepatic segment increased, that draining from the renal and iliac segments decreased. Vasoconstriction occurred in all vascular beds, but was greatest in the kidney and hind limbs. Thus the blood flow through the head and liver was partially maintained at the expense of that through the kidneys and hind limbs.5. Autoregulation of blood flow in the kidneys was usually seen immediately after the first removal of blood but with the onset of renal vasoconstriction it was reduced or abolished for the remainder of the experiment.