Circulatory Responses to Baroreflexes, Valsalva Maneuver, Coughing, Swallowing, and Nasal Stimulation during Acute Cardiac Sympathectomy by Epidural Blockade in Awake Humans

Abstract

Reflex circulatory responses are chiefly governed by the integrated functions of both sympathetic and parasympathetic nervous systems at any moment. To examine how sympathetic denervation of the important effector organ, the heart, modifies such reflex responses, the authors compared circulatory responses to arterial baroreflexes, the Valsalva maneuver (VM), coughing (C), swallowing (S), and nasal stimulation (NS) before and after cervical epidural blockade using 10 ml of 1.5% lidocaine in awake, healthy humans. The cervico-thoracic sympathetic denervation (sensory block of C4-T7) caused a slight suppression of the baroreflex sensitivity assessed by increases in RR intervals to increased systolic blood pressure with a pressor test (phenylephrine) in all eight subjects studied; the mean slopes of the regression lines were 29.1 .+-. 9.8 ms .cntdot. mmHg-1 before the blockade and 17.2 .+-. 6.3 ms .cntdot. mmHg-1 after the blockade (P < 0.05). However, the baroreflex sensitivity to a depressor test (nitroglycerin) remained unchanged following the blockade. Furthermore, the responses in heart rate and blood pressure to VM (Phases II and IV) and the responses in heart rate to C, S, and NS were partially suppressed after the blockade (P < 0.05). Despite these suppressions, the overall responses to VM, C, S, and NS remained unchanged after the blockade. No predominant parasympathetic responses such as profound hypotension and bradycardia were observed during any maneuver after the blockade. Since the vagus nerves were kept intact, these results indicate that acute sympathetic denervation of the central organs appears to preserve reflex circulatory responses to physical maneuvers such as producing high intrathoracic pressure, moderate changes in blood pressure or swallowing, though with some suppression of the cardiac acceleratory response. The results suggest that sypathetic control of heart rate functions as an inhibitor of the vagus rather than an active cardiac accelerator.