Control of Total Vascular Resistance in Hemorrhagic Shock in the Dog

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Abstract
Cardiac output in the dog was measured by indocyanine green dilution in 24 hemorrhagic shock experiments. Total peripheral resistance (TPR) was calculated from the cardiac output and systemic arterial blood pressure. Early in the hypotensive phase resulting from hemorrhage to 50 mm Hg blood pressure, the cardiac output was 19.3±6.6 (SD) % of control and the total peripheral resistance was 199 ±73 (SD) % of control. During the hypotensive phase the peripheral resistance declined significantly. This decline in TPR was associated with a significant decrease in respiration and heart rates, indicating a partial failure of the neurogenic control of the cardiovascular system. Following transfusions of the shed blood, the TPR decreased to the control value, but during subsequent progressive decline in blood pressure, vascular resistance again increased. Occasionally, TPR again fell terminally as the blood pressure decreased below 60 mm Hg. Although there is evidence for partial failure of peripheral resistance vessel tone during severe hypotension and some evidence for this following reinfusion of the shed blood, this failure, when observed, is a minor component of the progressive cardiovascular failure and is not the cause of irreversibility.