THE EFFECT OF VARYING PULMONARY PRESSURE ON THE ARTERIAL PRESSURES IN MAN AND ANESTHETIZED CATS 1

Abstract

In the anesthetized cat, an increased intrapulmonary pressure (+20 mm. Hg.) produced a fall in the mean arterial pressure. The observed fall was greater in the feet downward position than when tilted feet upward. Negative pulmonary pressure ( - 30 mm. Hg) produced a rise in arterial pressure, independently of body position. However, in man (unanesthetized) systolic and diastolic pressures, measured by recording sphygmomanome-ter, fall with negative and rise with positive pulmonary pressures (range of +30 to -30 mm. Hg.) by an amount equal to the estimated change in intrathoracic pressure. Pulse pressures showed minor variations, consistently decreasing only with positive pressure in the supine position. Heart rates were variable. If circulatory failure occurs, it is only with positive pressure in the sitting position, but arterial pressure and heart rate are maintained until just before collapse. The effect of altered pulmonary pressure on venous return and blood pressure regulatory receptors is discussed.