Role of the Autonomic Nervous System in Minimizing Acceleration-Induced Pressure Fluctuations in Intact Dog

David C. Randall ； Charles F. Knapp ； Joyce M. Evans ； Mao Wang

中華民國航空醫學會刊 12 卷 1 期 (1998 / 12 / 01) P66-74

Low frequency accelerations during flight maneuvers can destabilize a pilot's arterial blood pressure. This experiment used a centrifuge to evaluate the autonomic control of arterial blood pressure during sinusoidal acceleration. Blood pressure, left ventricular stroke volume, heart rate and total peripheral resistance were recorded or calculated in intact dogs. The animals were sedated and positioned horizontally on a platform mounted on the arm of the centrifuge. Rotation of the centrifuge produced a radially outward acceleration of ±2G. The platform on which the dog was positioned was turned at each of 12 different rates while the centrifuge was rotating to produce sinusoidal, ±2G accelerations along the dog's z (spinal) axis. The platform rotation periods ranged from 125 sec. to 4.3 sec. The resulting changes in the dog's cardiovascular function were tested in 5 control dogs, in 5 dogs subject to complete cardiac denervation, and in 6 dogs whose hearts were paced at 120 bpm. The blood pressure fluctuations were smaller in the control animals than in the cardiac denervated subjects. Large increases and decreases in blood pressure in the denervated dogs at frequencies between ≈0.02-0.07 Hz were caused primarily be lack of well-timed changes in heart rate and in total peripheral resistance and by failure to minimize inappropriate changes in stroke volume. Fixing the heart rate by pacing significantly diminished the otherwise normal dog's ability to minimize acceleration-induced blood pressure changes. We concluded that (1) the regulation of blood pressure in the lowest frequency range (0.005-0.012 Hz) in neurally intact dogs was primarily by appropriately timed adjustments in total peripheral resistance and stroke volume: (2) reflex regulation of heart rate as important for minimizing blood pressure fluctuations within the range from 0.032-0.077 Hz; and (3) blood pressure oscillation at frequencies >0.1 Hz was minimized primarily by the low-pass filter characteristics of the cardiovascular system.