Instantaneous femoral artery pressure-flow relations in supine anesthetized dogs and the effect of femoral venous pressure

Abstract

Instantaneous femoral artery pressure-flow (P/Q̇) relations were evaluated in consecutive 50-msec intervals of the pulseless flow changes during cardiac arrest in six anesthetized dogs and in two anesthetized dogs with α-adrenergic blockade. In all 245 P/Q̇ graphs obtained under conditions of normal or elevated venous pressure, either with or without α blockade, the pressure-flow relations are linear, and the zero-flow intercept on the pressure axis - reached in less than 3 seconds after the onset of cardiac arrest - is markedly higher than the simultaneous venous pressure. We believe that the zero-flow intercept is the effective downstream pressure to arterial flow and that the reciprocal of the slope of the pressure-flow line indicates the arterial resistance. The elevation of femoral venous pressure raises the effective downstream pressure and the resistance to arterial flow in the same leg. The effective downstream pressure in the contralateral leg is raised also. α-Adrenergic blockade abolishes the reflex change in the contralateral leg, but a change in P/Q̇ relations in the manipulated leg remains. We believe that the central reflex change could be triggered by stretch receptors in the wall of the small veins transmitted to the arterioles through α-adrenergic receptors. The encroachment on the smallest arterioles by distended small veins and by the rise in interstitial fluid pressure might be the local mechanism by which venous pressure elevation directly changes arterial P/Q̇ relations in the manipulated leg.