Plasma colloid osmotic pressure in venous blood from the human foot in orthostasis

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Abstract
Several theories could explain the slow rate of edema formation in the feet of sitting or standing man. One possible mechanism is a rise in local plasma colloid osmotic pressure (πp). We measured πpin blood from superficial veins of warm and cold feet during ortho-stasis. The difference in venous (πp) between the foot and the arm averaged 12.8 mmHg (range 9.4–16.1 mmHg) in subjects sitting in a cold room. Hemoconcentration was also reflected as increased hematocrit. These findings support the view that a local increase of (πp) in foot capillaries contributes considerably to edema prevention during orthostasis.