COMPARISON OF CHANGES IN INFERIOR CAVA FLOW AFTER HEMORRHAGE AND CIRCULATORY FAILURE FOLLOWING TRANSFUSION

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Abstract
The inferior cava flow recorded by a differential pressure flow meter decreases during sudden hemorrhage and remains low during the 50 and 30 mm. Hg periods of hypotension maintained in standard expts. A blood flow of about 150 rnl./min. is ap-prox. the lowest critical level which sustains the heart and circulation in a 10 to 12 kg. dog. The decrease in flow rate is accompanied by a significant reduction in venous pressure gradient between the lower end of the inferior cava, and the right atrium. It also causes a decline of a trial pressure. However, when the flow is reduced for an hr. or more and when it approaches the critical rate, central venous pressures tend to increase somewhat, while flow decreases. These effects of simple hemorrhage on inferior cava flow were contrasted in the same animal with changes which supervene after reinfu-sion of all withdrawn blood and subsequent spontaneous circulatory failure. Reinfusion immediately restored inferior cava flow to normal values as a. result of a. high peripheral venous pressure. This increased flow plus a tremendous augmentation of coronary flow raises right atrial pressure, augments cardiac output, and improves the form of central arterial pressure pulses, as well as restored arterial pressures. However, flow rate in the inferior cava progressively diminishes, as does the differential venous pressure; indeed, a 50% reduction may occur before central arterial pressure pulses show significant changes in form or quantitative values. This clearly indicates that reduction of inferior cava flow is an antecedent factor in circulatory failure after transfusion. Contrary to effects following simple reduction of blood vol. by hemorrhage, the reduction in inferior cava flow does not eventuate in as great a reduction of right atrial pressure; indeed, right atrial pressure was often as high at the end as at the start. In short, in hemorrhagic shock reduction in inferior cava flow correlated with decrease in pressure gradient, but not with changes in right atrial pressure. This may be due to compensated flow from other venous sources including the coronary veins, but is more probably due to myocardial depression which is a subsidiary factor causing the circulatory failure.

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