Cardiac afferent control of bronchial flow in awake dog

Resting bronchovascular constrictor tone is determined by α-adrenergic andcholinoceptor activity. Since baroreceptor afferents do not control this autonomic activity (White et al, Proc. Aust. Phys. Phann Soc., 28(2), 107P, 1997), the question was raised concerning cardiac afferents. In 10 dogs (27±3.2kg, mean ± SD) at right thoracotomy (02/N20/halothane 1.5%), pulsed Doppler flow probes were mounted on right bronchoesophageal artery to measure bronchial blood flow (Q_BR), and intrapericardial (IPC) catheters were placed in pericardial sac for drug infusion. Arterial and central venous catheters were placed in omocervical vessels for measurement of blood pressures. IPC infusion of 2% procaine (16 mgkg^-1) significantly (all P<0.05) raised resting heart rate (HR, to 210% of control), aortic pressure (P_a, 115%), Q_BR (146%) and bronchial flow conductance (C_BR, 125%). In 6 dogs, IPC nicotine (0.5-16μgkg^-1) produced transient bradycardia and hypotension, characteristic of vagal afferent stimulation in anesthetised dogs, before significantly (all P<0.05) raising HR (114%), P_a (121%), Q_BR (142%) and C_BR(126%) 80 seconds after injection. IPC veratridine (2-20μg) significantly (all P<0.05) raised HR (134%), P_a(108%), Q_BR (164%) and C_BR (155%) at 65 seconds. Responses to both stimuli were blocked by prior IPC application of procaine. The results suggest that cardiac sympathetic afferents tonically constrict the bronchial circulation at rest in the awake dog. Further, the chemical stimuli used cause non-specific activation of both sympathetic and vagal afferents to evoke a mixed cardiovascular response where a dilator mechanism prevails in the bronchial circulation, and a sympathoexcitatory effect in the systemic circulation. The findings are relevant to pulmonary congestion in heart failure syndromes