Effects of Tetra-ethyl-ammonium Chloride on the Cardiovascular Reactions in Man to Changes in Posture and Exposure to Centrifugal Force

Abstract

Studies of man''s reactions to the effects of gravity produced by tilting erect to 70[degree] from the supine position or by exposure to positive acceleration (centrifugal force) reveal that a fall in arterial blood pressure and an increase in heart rate result. These physiol. effects are quickly compensated for by reflex mechanisms mediated by the autonomic nervous system which produce an increase in arterial pressure at heart level and a subsequent slowing in heart rate. The intraven. injn. of 5.5 to 7.7 mg. of tetra-ethyl-ammonium chloride per kg. of body wt. has been found to block these reactions for periods of 5-15 min. so that arterial pressure continues to fall often to levels that produce symptoms of cerebral anoxemia. The marked decreases in arterial pressure fail under these circumstances to produce compensatory alterations in heart rate. The compensatory cardiovascular reactions induced by tilting to an upright position of 70[degree] or exposure to centrifugal force are gradually recovered in a period of 10-45 min. after injn. of the drug. Simultaneous studies of arterial pressure, heart rate, venous pressure and vol. of the leg indicate that these compensatory reactions which determine man''s tolerance to the upright position or positive acceleration are chiefly concerned with the arterial rather than the venous side of the circulation. The failure of reflex vaso-constriction to compensate for the increased hydrostatic pressure in the dependent parts of the body and thus to prevent an increase in blood flow through these parts, rather than reduced venous return to the heart, is the primary factor accounting for the reduction of man''s tolerance to positive acceleration after the admn. of tetra-ethyl-ammonium chloride.