Tibial nerve and deep fibular nerve effects on venous and extravascular volumes.

The innervation of the vasculature of the dog hindpaw separately controls the series and parallel coupled vessels by means of the tibial, deep fibular, and superficial fibular nerves. The latter primarily affects veins. The venous effects of the tibial and deep fibular nerves have not been adequately defined. The right hindpaw of anesthetized dogs was vascularly and neurally isolated in a volume recorder. The animals were heparinized and the preparation autoperfused (constant pressure). Total tissue volume changes were determined by the volume recorder. Total vascular volume changes were calculated from changes in paw 51Cr-red blood cell radioactivity measured by a scintillation detector. Arterial pressure and paw blood flow were monitored. The tibial and deep fibular nerves were each separately stimulated at 1, 5, and 15 Hz. Deep fibular nerve stimulations resulted in progressively significant increases in precapillary flow resistance. Vascular and tissue volumes decreased with stimulation frequency but vascular volume decreased significantly less than tissue volume change. Tibial nerve stimulation resulted in significant precapillary resistance increases. Vascular and tissue volumes decreased by similar amounts. Thus, deep fibular nerve stimulation causes passive decrease in venous volume, reduced capillary pressure, and fluid absorption. Tibial nerve stimulation causes active arterial and venous constriction maintaining capillary pressure with minimal fluid transfer.