BRONCHIAL TEMPERATURE AS A KEY TO THE INTERIOR PULMONARY CAPILLARY BED OF ANESTHETIZED DOGS

The terminal airways are separated from the surrounding pulmonary capi llaries by a tissue layer of a few micrometers in thickness only. Ther efore, it should be possible to gain information about in vivo transca pillary heat transport of the interior pulmonary vascular bed by recor ding the terminal bronchial temperature. For this purpose, we studied temperature-time curves in the pulmonary artery, bronchial system and the aorta of six anaesthetized dogs permanently instrumented for measu ring pulmonary blood flow. Thermistors recorded temperature changes at the three locations after injection of 5 mi cold solution into the ri ght atrium. From the observed temperature-time curves mean transit tim es between the three recording sites were calculated for various pulmo nary blood flows (integral Delta Ttdt/integral Delta Tdt) (range 1.1-3 .5 l/min). We found that the temperature-time curves of the bronchial system resemble typical ''dilution'' curves and are interspaced betwee n those in the pulmonary artery and those in the aorta. Regardless of pulmonary blood flow, mean transit times from the pulmonary artery to the distal bronchial system and from there to the aorta were about equ al. We conclude that transcapillary heat transfer generates bronchial temperature-time curves which permit an estimation of the relation of precapillary to postcapillary mean transit times in the interior of th e lung.