The Effects of Temperature and of Tissue Pressure on the Movement of Fluid Through the Human Capillary Wall

Abstract

The various physical factors concerned in transporting fluid through the human capillary wall have received relatively little attention in spite of the value that such information might have in clarifying the complicated mechanism of fluid balance and the even more involved mechanism of edema formation. The present lack of information is to be ascribed, in all probability, to the difficulty of obtaining quantitative data concerning the filtration and absorption of small amounts of tissue fluid. At present the plethysmograph offers the only available means of detecting small changes in the volume of extravascular fluid.The ordinary plethysmograph was found by Krogh, Landis and Turner (1) to be quite unsuitable for measuring the volume of tissue fluid accumulating during short periods of slight or moderate venous congestion. Therefore, a so-called "pressure plethysmograph " was devised to exclude spontaneous variations in arm volume referable to changing vasomotor tone. Pressure was exerted on the surface of the segment of forearm within the plethysmograph in order to collapse the blood vessels before the final volume was measured. Under these conditions the state of contraction or dilatation of the blood vessels did not, within certain limits, interfere with the reasonably accurate measurement of changes in the volume of tissue fluid.It was found in normal subjects that fluid was filtered into the tissues of the forearm when the venous pressure exceeded 15 cm. water. Above an average venous pressure of 17 cm. water the rate of filtration was directly proportional to the increase in venous pressure. WVhen the subject stood motionless the colloid osmotic pressure of the blood rose and the rate of filtration produced by given grades of venous congestion fell. Thus changes in capillary pressure and in the colloid osmotic pressure of the blood influenced the movement of fluid through the capillary walls of normal human subjects in a manner conforming to the Starling hypothesis.If capillary blood pressure and the colloid osmotic pressure of the blood were the sole factors involved in fluid balance it would be difficult to explain how it is possible for the human being to avoid dependent 105

The Effect of Local Cooling on the Filtration and Absorption of Fluid in the Human Forearm

“…This was done in order to insure complete absorption (by the capillaries) or drainage (by the lymn-phatics) of any extravascular fluid that might have accumulated as a result of previous activity or dependency of the forearm. This prolonged preparation increased the accuracy of the method and also led to modification of certain conclusions reached by Landis and Gibbon (7).…”

“…in the water surrounding the arm in the plethysmograph, on the skin of the forearm within the plethysmograph, on the skin of the wrist just outside the plethysmograph, and in room air near the plethysmograph. Water from a cool or warm reservoir was circulated at a rate of 5 liters per minute through the space between the inner and outer walls of the plethysmograph and through a jacket surrounding an accessory vessel between the plethysmograph and the burette (7). This (7) observed a significant decline in reduced forearm volume during control observations at this and other temperatures.…”

“…The pressure plethysmograph of Landis and Gibbon (7,8) was used throughout. The particular advantage of this method is that the volume of a segment of forearm can be measured very precisely while it is exposed intermittently for brief periods to an external pressure of 200 mm.…”

“…The effect of temperature on the rate at which recently filtered extravascular fluid is reabsorbed after congestion Landis and Gibbon (7) observed that small amounts of excess tissue fluid sometimes were removed from the forearm less rapidly during cooling (140 to 15°C.) than at higher temperatures.…”

“…To obtain more quantitative information, the pressure plethysmograph of Landis and Gibbon (7) was used to measure changes in the volume of extravascular fluid in the forearm during exposure to external temperatures ranging from 44.50 to 4.50 C. It was found that moderate cooling (a) increased the extravascular volume of the forearm even when venous pressure was normal, (b) decreased the rate of filtration produced by a given increase of venous pressure and (c) decreased the rate at which extravascular fluid was reabsorbed. The evidence is consistent with the view that the human capillary wall becomes increasingly permeable to protein and fluid as environmental temperature falls below 250 C., but it also appears that other factors influence the rate at which edema develops during exposure to cold.…”