Ventilatory control characteristics of the exercise hyperpnea as discerned from dynamic forcing techniques.

were the carotid chemoreceptors also excluded from the circulation of the remainder of the body? Dr. Levine: In the head perfused animal preparation (Ic third preparation), both the carotid chemoreceptors and the brain were excluded from the circulation to the remainder of the body. the effect of acute cord transection on blood pressure? Dr. Levine: My dogs were anesthetized with chioralose (not barbiturate) ; mean arterial blood pressure following L2 spinal transection was 145 mm Hg. Your question raises the possibility that decreases in arterial blood pressure during exercise may have accounted for the increases in VE noted in my experiments. In fact, a decrement in mean arterial blood pressure of 13 mm Hg accompanied muscular exercise. However, the literature (as well as my own experience) indicates that this small decrement in blood pressure is not adequate to elicit twofold increments in 7E#{149} Moreover, conventional arterial baroreceptors (Ic, carotid sinus and aortic baro-receptors) were denervated in the chemodenervated animal experiments; nonetheless, this preparation still responded to exercise of the hindlimbs with twofold increases in VE. There is a discrepancy between Dr. Le-vine's findings and those of Kao who observed that venous blood from the exercising hind limbs of a donor dog produced an increase in ventilation in a recipient dog which was bess than proportional to the increased ;; co2 in this dog so that its PaCO2 rose. Since the thoracic receptors postulated by Dr. Levine were intact in this dog and were exposed to " exercise blood, " it should have responded with an isocapnic hyperpnea, but it did not. Its response resembled that of CO, inhalation. Dr. Levine: Dr. Kao's experiments with his triad preparation failed to demonstrate that venous blood from the exercising hindlimbs of one dog will stimulate E a second dog (Ic, recipient dog). However, since he failed to demonstrate that the recipient dog in his triad preparation was capable of responding to any ventilatory stimulus, these experiments of Dr. Kao do not permit definitive conclusions regarding humoral exercise stimuli. I '' the steady-state of moderate intensity exercise, mean arterial Pco9, Po, and pH are precisely regu-bated, leaving no apparent stimulus for the marked venti-latory increase. We have looked for clues to the underlying mechanisms in the transient state, hoping that the timing of events leading to this " errorless " state would provide information which might help solve this enigma. The first systematic look …