Vagal cooling and positive end-expiratory pressure reduce systemic to pulmonary bronchial blood flow in dogs.
Positive end-expiratory pressure (PEEP) reduces systemic to pulmonary bronchial blood flow [Qbr(s-p)] presumably because it increases bronchial vascular resistance. Since PEEP increases lung volume and thus could stimulate pulmonary stretch receptors, we investigated the hypothesis that the PEEP-related decrease in bronchial blood flow was due to a reflex mediated by the vagus. In open-chest dogs the left lower lobe (LLL) was isolated, independently ventilated, perfused in situ with a closed pulmonary vascular circuit and weighed continuously. Qbr(s-p) was measured as LLL vascular circuit overflow and changes in LLL weight. When LLL PEEP was increased from 5 to 15 cm H2O in a group of 11 dogs Qbr(s-p) was reduced by half from 60.8 +/- 10.5 to 31.6 +/- 6.1 ml/min/100 g dry lobe weight. In another group of 7 dogs Qbr(s-p) was 46.5 +/- 6.9 with PEEP = 5 cm H2O; it decreased to 28.3 +/- 6.8 with bilateral cervical vagal cooling (0-1.5 degrees C) and did not decrease further after increasing PEEP to 15 cm H2O. We conclude that the effect of resting vagal tone is to increase Qbr(s-p) and that the effect of PEEP on Qbr(s-p) may be mediated at least partially by vagal influences.
Lakshminarayan
S
S
Department of Medicine, University of Washington, Seattle.
Agostoni
P G
PG
Kirk
W
W
D000818:Animals; D001980:Bronchi / Q000098:blood supply*; D003080:Cold Temperature; D004285:Dogs; D006439:Hemodynamics; D011175:Positive-Pressure Respiration; D012039:Regional Blood Flow; D014630:Vagus Nerve / Q000502:physiology*; D014655:Vascular Resistance