Abstract
Summary
The effect of the composition of the fluid in the manometer system on tissue pressure was examined. Needles were introduced into the ventricular wall of isolated, non-beating hearts. The pressure registered by manometers attached to the needles varied with the composition of the fluid in the manometer system. When distilled water was in the manometer, the pressure fell slowly to values less than atmospheric pressures; when the manometer fluid was normal saline, a positive pressure usually developed. The results are interpreted by considering that the liquid in the manometer is separated from the tissue fluids by membranes such as the walls of cells, capillaries, and connective tissue sheaths. The diffusion of water from regions of higher to lower concentrations becomes manifest in the slow development of a pressure gradient. This virtual diffusion or osmotic pressure must be differentiated from the hydrodynamic pressure which becomes manifest immediately as a pressure wave is transmitted from one compartment to another. Because the concentration of water in the tissue differs from that in the manometer, pressure recordings will represent the sum of the actual hydrodynamic pressure and the virtual osmotic pressure. Such sums may be negative with respect to the atmosphere. The manometer system thus becomes a part of the experimental design for measurement of tissue pressure.
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