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

Abstract

The terminal airways are separated from the surrounding pulmonary capillaries by a tissue layer only a few micrometers thick. Therefore, they could be interesting targets for gaining information about transcapillary heat transport. Their particular anatomy should favour a rapid equilibration of heat diffusion between the capillary bed and the distal bronchial walls, especially since significant indicator transfer to the intrabronchial space after injection of cold solutions into the pulmonary artery has been observed [1]. Therefore, it should be possible to trace temperature changes of the capillary blood by recording bronchial temperature. These temperature-time curves after injection of cold solutions into the pulmonary artery should allow calculation of mean transit times from the pulmonary artery to the bronchial system and from there to the left heart and, thus, provide information about transcapillary transport in the interior of the lung.To study this new approach under controlled experimental conditions, we recorded thermodilution curves in the pulmonary artery, at the wall of small bronchioles and in the left atrium of isolated rabbit lungs perfused with their own blood. This experimental procedure allowed a huge range of alterations to be made to pulmonary blood flow as the major variable for pulmonary mean transit times. Materials and methods Animals and isolation of the lungsTemperature-time curves were recorded at the wall of small bronchioles, in the pulmonary artery and in the left atrium of isolated lungs of New Zealand white rabbits treated in accordance with the Helsinki convention for the use and care of animals and with approval of the governmental animal care and use commission. Adult rabbits (mean(±SD) body weight 3.3±0.3 kg) of either sex were anaesthetized with pentobarbital sodium (30 mg·kg -1 i.v.). After tracheotomy, the animals' lungs were mechanically ventilated with air at a tidal volume (VT) of 10 mL·kg -1 and a frequency of 30 breaths·min -1 (Harvard Respirator, model 683; Harvard Apparatus, South Natick, MA, USA). Heparin (1,000 IU·kg -1 ) was injected 3 min before the rabbits were exsanguinated through the carotid artery. After midline sternotomy, the trachea, heart and lungs were removed en bloc and perfusion cannulas tied into the pulmonary artery and left atrium via the left ventricle with meticulous care to avoid air embolism. These cannulas had separate lumina allowing pressure as well as temperature (thermistor) measurements at their tips. The pulmonary arterial catheter had an additional injection port 1.8 cm proximal to the thermistor for the injection of the tracer. The rabbits' own blood was used to fill the extracorporeal perfusion circuit with a capacity of 35 mL.The time from excision of the lungs to the start of the in vitro perfusion was less than 12 min. The lungs were suspended via the trachea from a force transducer and inflated up to 15 cmH 2 O until any visible atelectasis had resolved. Thereafter, the lungs were covered with a thin plastic foil to conserve h...

Does bronchial thermodilution allow estimation of cardiac output?

“…After injections of cold solution into the right atrium or into the pulmonary artery, bronchial temperature-time curves can be recorded which conform to those recorded in the pulmonary artery and in the ascending aorta [1,2]. Stimulated by a recent editorial [3], we wondered whether these bronchial thermodilution curves allow estimations of cardiac output using the Stewart-Hamilton approach.…”