Asystolic Gradient, Intrinsic Blood Pressure and Critical Closing Pressure in the Human Forearm

¹ From the Cardio-Pulmonary Physiology Laboratory, National Jewish Hospital at Denver, Denver, Colorado

The rate of pressure fall after occlusion (asystolic gradient) in the vascular bed of the arm of 82 patients without cardiovascular disease and in 9 hypertensive patients were studied as a measure of peripheral resistance. The time of pressure fall between 60 and 50 mm Hg (standard decrement time—SDT) shows little scattering in normal subjects. SDT decreases with intra-arterial injections of acetylcholine and reactive hyperemia and increases with intra-arterial norepinephrine and reflex vasoconstriction. In hypertensive patients, SDT was significantly prolonged. The arterial pressure after 25 seconds of occlusion was 26 ± 7 mm Hg and showed an increase with acetylcholine and norepinephrine. This value is elevated in hypertensives. When the arterial and venous pressures did not equilibrate after 25 seconds of interruption of the circulation, the existence of a ‘critical closing pressure’ was assumed. Thirty-six per cent of the patients showed critical closing pressures, the other 64% equilibrated their venous and arterial pressures at 23.6 ± 5 mm Hg (intrinsic blood pressure).