Temperature dependence of intraparenchymal bronchial blood flow.

Previous studies suggested that bronchial vascular resistance, like that of the skin, changes with the temperature of the surrounding tissue. To investigate this phenomenon, we recorded anastomotic (systemic to pulmonary) (Qbrs-p) and total (Qbr) bronchial blood flow over a temperature range centered on normal. In 7 open-chested dogs the in situ left lower lobe (LLL) was separately ventilated (30 degrees C, 5% CO2 in humidified air) and was suspended in a fabric net from a strain gauge for continuous recording of weight. The pulmonary circulation of the LLL was pump-perfused at 255 +/- 69 ml/min in a closed circuit with temperature set at 30, 33, 36, 39 and 42 degrees C. Qbrs-p was measured as overflow from the LLL vascular circuit corrected for LLL weight changes. Qbr, tracheal, mid-esophageal and coronary flow were measured with 15 mu radiolabelled microspheres injected in the left atrium. The animal's core temperature and that of the humidified air around the LLL were held constant. Qbr and Qbrs-p were equal and reached a peak at 36 degrees C with lower levels of flow at higher and lower temperatures. Esophageal, tracheal and coronary flow and cardiac output did not change nor did pressures in the systemic and LLL pulmonary artery and in the LLL airways. An intralobar change in temperature above or below 36 degrees C decreases only the lobar bronchial blood flow and does not influence blood flow to other nearby tissues including those vascularized by the bronchial circulation.