NEURAL REGULATION OF THE PULMONARY CIRCULATION FOLLOWING SYSTEMIC HYPOTENSION IN CONSCIOUS DOGS

Abstract

To investigate autonomic nervous system (ANS) regulation of the pulmonary vascular response to increasing cardiac index (CI:ml/min/kg) following systemic hypotension (H), the pulmonary vascular pressure gradient (pulmonary arterial-pulmonary capillary wedge pressure: ΔP) was measured at multiple levels of CI during stepwise inflation and deflation of an inferior vena cava (IVC) occluder. In intact dogs, maximum IVC constriction decreased (p<0.01) CI from 139±9 to 46±3, and systemic arterial pressure from 108±2 to 55±3 mmHg. Following 15 minutes of H, CI was gradually increased by deflation of the IVC occluder. Surprisingly, ΔP was not significantly changed at any level of CI following H in intact dogs or after cholinergic block (atropine 0.1 mg/kg). In contrast, β adrenergic block (propranolol 1 mg/kg) increased ΔP at every level of CI following H, e.g. at CI = 100, ΔP was increased (p<0.01) 16±2% from 10.2±0.5 mmHg. Pulmonary vasoconstriction following H was not observed during total autonomic ganglionic block (hexamethoniura 30 mg/kg), i.e. AP at CI - 100 was slightly decreased (p<0.05) 6±2% from 9.7±0.8 mmHg following H. These results suggest that the pulmonary circulation is actively modulated by the ANS following H. ANS-mediated vasodilator and vasoconstrictor influences appear to offset one another in the intact and cholinergic blocked conscious dog.