SOME CIRCULATORY RESPONSES TO HEMORRHAGE IN THE DOG

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Abstract
37 dogs were subjected to repeated small hemorrhages, continued until death was inevitable. Arterial and central venous pressures were recorded continuously. Cardiac output and resistance were calculated from the pulse contours. Ecg. changes, heart volume and oxygen consumption and transport were detd. at selected intervals. The responses of the animals could be divided into 3 phases: In phase I there was no significant change in heart rate, with a decline in arterial pressure and cardiac output, with a slight rise in resistance; in II, the heart accelerated, with a temporary interruption of the decline in pressure and flow, venous pressure was lowered, and the heart volume decreased rapidly; in III, compensation failed, with arterial pressure, flow and resistance all falling, oxygen transport was curtailed, venous oxygen content fell to low levels, the heart volume was small, and venous pressure remained the same or was elevated. Ecg. changes were often present. In early hemorrhage, cardiac output and resistance seemed reciprocally related. In late hemorrhage, this was not true. Possible causes of the late flow failure are discussed.
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