Abstract
According to Pbiseuille's law the volume of fluid flowing through a rigid tube is proportional to the fall in pressure along the tube. It seems possible, therefore, that if the peripheral fall in blood pressure could be increased the total amount of blood flowing past an arterial obstruction in unit time would be greater. The fall in pressure through the arterial tree may be increased physically in two ways, (a) by elevating aortic blood pressure or (b) by reducing peripheral blood pressure to a negative value. The first method is impracticable for numerous reasons but it is possible temporarily to reduce capillary and venous pressure by applying suction to the extremities.
An aluminium box was built large enough to accommodate the lower extremity to a point about 6 inches above the kne.e and strong enough to withstand pressures of —120 to + 120 mm. Hg. A mercury manometer, communicating with the interior of the box, was equipped with electrodes so arranged that the one-half horse power motor operating an air pump was stopped through an electrical relay, whenever the pressure in the box exceeded or fell below atmospheric pressure by 120 mm. Hg. A valve was inserted between the pump and the box so that for 25 seconds the pump evacuated air from the box while for 5 seconds the pump expelled cooled air into the box.
The effects of alternate suction and pressure were first studied by using a circulation schema in which a rubber bag simulated the distensible capillary and venous bed. The rate at which water flowed through the system under a pressure of 80 mm. Hg. was measured first without external pressure variations and then for a like period with alternate suction and pressure.
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