Volume (compression)

Abstract: The measurement of volume changes in the limbs or in portions of the limbs of man is now recognized as a valuable technique in many physiological and clinical investigations. The various methods employed in the measurement have been recently reviewed (Potter, 1948). Volume plethysmography has proved particularly useful in investigations on vasomotor response and, combined with the venous occlusion procedure, has become the standard method for estimating peripheral blood flow in man. Although there have been many refinements to the technique of volume plethysmography during the past 20 or 30 years, the current procedure is still based essentially on the system originally devised by Schaifer & Moore (1896) and subsequently adapted to human limb measurements by Hewlett & van Zwaluwenburg (1909). In this system, the limb, or a segment of it, is sealed in a rigid jacket so that volume changes of the enclosed part will cause corresponding volume displacements of the fluid filling the space between the limb and the jacket. The sealed space, filled with either water or air, is connected to a volume recorder by an airor water-line. It is apparent, from the extensive literature which now exists on the application of this technique, that it must always suffer from some of the following disadvantages and limitations: (a) The apparatus tends to be cumbersome. (b) The sealing of the limb within the jacket gives rise to problems, for a perfect wateror air-tight seal must be achieved without appreciable constriction of the tissues and the seal must be arranged so that the volume change of the limb enclosed results in an equivalent volume displacement of the fluid filling the jacket. (c) During any continuous record of volume change there must be no relative movement between the limb and its jacket. The subject is, therefore, largely immobilized, and the possibilities of recording volume changes in relation to normal muscular activity are very limited. (d) The airor water-