Autoregulation of the Total Systemic Circulation Following Destruction of the Central Nervous System in the Dog

Abstract

The quantitative importance of total systemic autoregulation in the whole body was studied in dogs in which the cardiovascular control loops of the central nervous system were eliminated by decapitation and alcohol destruction of the spinal cord. Transient changes in cardiac output, right atrial pressure, oxygen consumption, arteriovenous oxygen difference, and hematocrit that occurred immediately after single-step changes of 25 to 50 mm Hg in arterial pressure were followed by gradual return of the variables toward control values. The time required to reach a new steady state ranged from 13 to 75 minutes with an average of 35 minutes. The calculated open-loop gain of the autoregulation control system ranged from 0.93 to 9.5 with an average gain of 3.32±0.7 (SE) indicating more than 75% compensation. In a second group of animals the arterial pressure was increased from 50 mm Hg to as high as 150 mm Hg in small steps of 10 to 15 mm Hg allowing 5 to 20 minutes on each step for the autoregulation response to occur. The pressure-flow curves showed significant total systemic autoregulation. The return of arteriovenous oxygen difference and oxygen consumption toward control values is consistent with a metabolic mechanism of autoregulation. The absence of significant transcapillary fluid flux in autoregulating preparations indicates (a) that the locus of autoregulatory resistance changes is completely or almost completely in the precapillary vessels of the circulatory system and (b) that autoregulation is important in maintaining capillary pressure at a normal level as well as in maintaining blood flow at the level required by the tissues.