Differential pattern of sympathetic outflow during upper airway stimulation with smoke

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Abstract
The possibility that sympathetic discharge to the heart is decreased while it is increased to other organs during upper respiratory perfusion with cigarette smoke was tested. Blood pressure (BP), heart rate, ECG and respiratory movements were monitored in urethane-anesthetized rabbits. Insertion of 2 cannulas allowed respiration of room air while passing smoke across the upper respiratory irritant receptors and out through the nares. Through a retroplural incision, the left stellate ganglion was exposed and a cardiac branch isolated. A left renal nerve was isolated. Multiunit nerve recordings were obtained from both nerves. In 4 control animals, cigarette smoke (50 ml) caused apnea, bradycardia (-116 beats/min) and increased BP (33 mmHg). Activity in the renal nerve increased (248% of control [C]) and activity in the cardiac nerve was reduced (62% C). In these animals after flaxedil and artificial respiration, nerve activity responses were still pronounced (renal, 178% C; cardiac, 66% C). In 4 other barodenervated animals neural responses to smoke were similar to those observed with baroreceptors intact (renal, 211% C; cardiac, 51% C). In these animals after artificial ventilation and flaxedil, responses were not significantly changed. Apparently, smoke stimulation causes a differential pattern of sympathetic discharge. The responses observed cannot be accounted for by secondary adjustments through arterial baroreceptors, chemoreceptors or pulmonary stretch receptors.