DIFFERENTIAL SPINAL BLOCK. II. THE REACTION OF SUDOMOTOR AND VASOMOTOR FIBERS 1

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Abstract
The sympathetic preganglionic fibers and the sensory fibers associated with the appreciation of pin-prick were blocked without affecting fibers concerned with touch, position sense, vibratory sense or motor power. This was done by introducing quantities of a 0.2% soln. of procaine HC1 into the subarachnoid space. The initial injn. was 15 ml. followed by 0.6 ml./min. of the same soln. The soln. was delivered from an elevated leveling bulb through a calibrated dripper via non-distensible rubber tubing to an indwelling needle in the 3d-lumbar interspace. This resulted in a maximal rise in skin temp., rise in skin resistance and loss of the appreciation of pin-prick without loss of touch, vibratory sense, position sense or motor power. The cutaneous and stretch reflexes were abolished. The basis for the differential susceptibility is thought to be the fiber size and degree of myelination. The results indicate that the fall in blood pressure observed with spinal anesthesia is due not to muscular paralysis and venular stasis but rather due to the block of sympathetic vasoconstrictor impulses. The usefulness of this technique in studying intestinal dyskinesia, the mechanics of pulmonary edema, peripheral vascular disease, amputation stump and phantom limb pain, and in predicting the fall in blood pressure to be achieved with sympathectomy in hypertensive patients was indicated.