Respiratory Augmentation of Inferior Vena Caval Flow Demonstrated by a Low-Resistance Phasic Flowmeter

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Abstract
A new flow-meter is described, and its applicability vena caval flow studies is presented. By simultaneously recording flow rates from the thoracic and abdominal portions of the inferior cavae of anestheized dogs, the following basic observations were made: Inspiration, under physiological circumstances, causes significant augmentation of return flow to the heart via the inferior cava. Two forces are commonly involved: abdominal compression and thoracic suction. These forces ordinarily supplement one another in maintaining venous return but either one is capable of acting separately. The forces governing extrathoracic venous collapse previously described for the superior cava obtain as well in the inferior cava. In addition, elevation of abdominal pressure tends to enhance the tendency toward collapse.

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