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 H20 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 H20; it decreased to 28.6.8 with bilateral cervical vagal cooling (0-1.5°C) and did not decrease further after increasing PEEP to 15 cm H20. 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.
- Bronchial blood flow
- Positive end-expiratory pressure
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine