Postural Changes in Plasma Volume in Hypoalbuminemia

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Abstract
Egress and ingress of intravascular fluid are governed largely by the net pressure gradient of the opposing forces of hydrostatic pressure and plasma oncotic pressure. Although the concept of "volume receptors" is gaining wide acceptance,1-3 their role in the moment-to-moment regulation of the blood volume is uncertain. It is generally agreed that in normal subjects the blood volume decreases with standing.4-6 There are few studies, however, concerned with the magnitude of this change under circumstances of a disturbance in the forces controlling movements of fluid across the capillary membrane. In the present study, alterations in plasma volume on standing were observed in subjects with hypoalbuminemia in order to assess the role of lowered oncotic pressure in this reaction. Materials and Methods Radiochromium was employed as a reference for the determination of red cell mass; plasma volume was then estimated from this value and the venous hematocrit. This procedure