Bronchial temperature reflects transcapillary heat transport of isolated blood-perfused rabbit lungs

The pulmonary capillaries are in such close proximity to the terminal airways that changes in capillary blood temperature should also cause changes in bronchial wall temperature. Therefore, we hypothesized that injection of cold solutions into the pulmonary artery would yield bronchial temperature-time curves similar to those in the pulmonary artery and left atrium. These bronchial curves should mainly represent the capillary bed. Isolated rabbit lungs (n=8) were ventilated (5% CO2 in air) and perfused (autologous blood, 37 degrees C) at various flow rates (50-200 mL x min[-1]). Thermistor probes (diameter 0.46 mm) registered temperature changes in the pulmonary artery, at the bronchial wall (wedge position) and in the left atrium after injection of 0.8 mL Ringer's lactate (0 degrees C) into the pulmonary artery. Bronchial temperature-time curves were found to resemble "dilution" curves located between pulmonary arterial and left atrial curves. Independent of flow rate, their appearance times, peaks and calculated mean transit times were between those from the pulmonary artery and the left atrium. We conclude that bronchial temperature-time curves reflect transcapillary heat transport and that this approach might be useful in gaining further information about vascular transport processes in the interior of the lung.