The Collapse Factor in the Measurement of Venous Pressure Tbe Flow Offluidthroughcollapsibletubes~

If veins were rigid tubes, then a change in mean right auricular pressure would cause a corresponding change in the peripheral venous pressure, provided the velocity of blood flowing along the veins remained constant. However, veins are not rigid, but collapsible, and it has been shown by Lyon, Kennedy and Burwell (1938), and by Holt (1940), that peripheral venous pressure, referred to the level of the heart as zero, is increased when the vein is above heart level because the veins collapse. Carrier and Rehburg (1923) have also shown that the collapse of peripheral veins and capillaries may maintain capillary pressure at a high level when the capillary is above heartlevel. Since veins are collapsible tubes, and the pressure in the right auricle is generally agreed to be subatmospheric, and there is a small positive tissue space pressure around the veins tending to collapse them, it was thought that changes in mean right auricular pressure might not affect peripheral venous pressure because the veins just before entering the chest might be partially collapsed. METHODSAND RESULTS. When the veins entering the upper end of the thoracic cage were dissected out in the living dog, they were seen to be normally partially collapsed or to dilate and collapse synchronously with respiration. When the animal breathed air which was under a negative pressure the veins were seen to collapse more completely, and when air under a positive pressure was breathed the veins became dilated. The inferior vena cava was seen to collapse, after dissecting the liver away from it, when air under a negative pressure was breathed, but was not seen to collapse with normal respiration. In ten barbitalized dogs with the chest closed, and placed in the supine position, mean peripheral venous pressure was measured in the femoral,