Changes in blood flow distribution and capillary function after deep hypothermia in rat.

The present experiments were carried out in the rat to investigate the peripheral vascular function prior to the development of posthypothermic circulatory collapse. In the first study, mean arterial blood pressure, heart rate, cardiac output, regional blood flow, and plasma volume of hypothermic (4 h, 15-13 degrees C) and rewarmed rats were compared with normothermic controls. In response to hypothermia, arterial blood pressure, heart rate, and cardiac output declined markedly. After rewarming, arterial blood pressure and heart rate recovered fully, whereas cardiac output was only 33 +/- 7% of the control value (p < 0.025). Tissue blood flow was markedly depressed during hypothermia (p < 0.025), except for the abdominal skin. After rewarming, blood flow in skeletal muscle returned to within control levels, whereas blood flow in internal organs remained low (p < 0.025 vs. control). Posthypothermic plasma volume was 77 +/- 3% of control (p < 0.05). In the second study, the transcapillary colloid osmotic pressure gradient (COPp - COPi) was calculated following measurement of colloid osmotic pressure in plasma (COPp) and interstitium (COPi) in prehypothermic, hypothermic, and posthypothermic rats. The posthypothermic value of COPp - COPi was 76 +/- 4% of the prehypothermic value (p < 0.05). In conclusion this study demonstrates that the reduced cardiac output in rewarmed rats is associated with an altered regional blood flow distribution compared with that of normal rats. Capillary integrity also seemed perturbed. Thus, changes in both control and function of the peripheral vasculature are important mechanisms in the development of a posthypothermic circulatory collapse.