THE EFFECTS OF SPINAL ANESTHESIA ON THE CIRCULATION IN NORMAL, UNOPERATED MAN WITH REFERENCE TO THE AUTONOMY OF THE ARTERIOLES, AND ESPECIALLY THOSE OF THE RENAL CIRCULATION

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Abstract
21 normal unanesthetized subjects were observed before and during spinal anesthesia. In 18 of these subjects sensory anesthesia was established up to T5 and in 3 subjects above T1. That the vasomotor pathways were effectively blocked was demonstrated by the abolition of typical reflex responses to hypercapnia, anoxemia, and gravity. The tone of the renal arterioles is normally maintained by autonomous intrinsic activity of the peripheral vascular apparatus and is not dependent upon tonic activity of the central nervous system. Changes in blood pressure attending spinal anesthesia, and other evidence cited in the paper, showed that the arterioles of the body generally (with the exception of those of the skin) are autonomous in their activity and that in the resting basal condition and the supine position there is negligible tonic activity in the sympathetic vasomotor paths. The fall in blood pressure which may attend high spinal anesthesia is attributed to decreased cardiac output, due to stagnation of blood in the capillaries, veins, and venules of the flaccid skeletal muscles, and to other subsidiary factors decreasing venous return. The exptl. evidence bearing on the tonic activity of the vasomotor system is reviewed and it is pointed out that most of this evidence suffers from having been obtained from anesthetized animals. Reasons are given for its inadequacy.