Circulatory heat sources for canine respiratory heat exchange.

Abstract

We assessed the roles of the pulmonary and bronchial circulations as potential heat sources to the pulmonary airways during respiratory heat loss, by observing the changes in airstream temperature that accompanied temporary occlusion of the pulmonary or bronchial circulations. Baseline end-expiratory and end-inspiratory airstream temperatures were 35A±0.20C (SEM) and 30.9±0.30C, respectively, among all trials. With occlusion of the lower lobe pulmonary arteries for 3 min ipsilateral endexpiratory and end-inspiratory airstream temperatures fell by 2.8±0.2 and 1.1±0.20C, respectively, during hyperpnea with room temperature air, and by 3.5±0.5 and 1.8±0.20C, respectively, during hyperpnea with frigid air. In marked contrast, interruption of the bronchial circulation for 3 min had no effect on airstream temperatures. These data indicate that under these conditions, the pulmonary circulation, but not the bronchial circulation, serves as an important local heat source for respiratory heat exchange within the pulmonary airways.

Modeling bronchial circulation with application to soluble gas exchange: description and sensitivity analysis

“…In particular, the pulmonary circulation is in close proximity to the airways, beginning at approximately the 4th generation, and, due to its large volumetric flow rate (two orders of magnitude larger than the bronchial circulation), represents an enormous source of ethanol and heat. In addition, the pulmonary circulation has been previously shown experimentally to have a large impact on intra-airway heat exchange (33). Hence, the pulmonary circulation dictates the thickness of the body layer in the model and, thus, has a larger impact on ethanol exchange than does the bronchial circulation.…”

Determinants of the difference between expired and core temperatures: effect of a breath-hold

“…This is probably the reason why T E reached, on average, core temperature after 2 min of apnea preceded by hyperventilation, as the time constants observed in the second and third series of experiments indicated that a longer duration would have been needed. The role of tracheo-bronchial blood flow in respiratory heat exchange is a matter of debate; some studies have shown alterations in expired or intra-airway temperatures after challenges in asthmatics or after inhalation of vasoconstrictors [7], but in dogs occlusion of bronchial circulation was found to have no effect on air stream temperature [15].…”

“…Two one-way passive valves prevented the subject inspiring from the expiratory circuit or expiring into the inspiratory circuit. In order to determine the relationship between T E and the temperature of the inspired gas (T I ), which is linear for a given inspired humidity [5,15], the inspired gas was either cooled or heated by passing it through copper tubing immersed in a temperature-controlled bath set at 10°C or 34°C. However, owing to further heat exchange along the circuit, subjects' inspired temperatures were 15±2°C and 30±2°C respectively.…”

Vocal Function and Upper Airway Thermoregulation in Five Different Environmental Conditions

“…These studies provide evidence of laryngeal epithelial viscosity maintenance in the ovine and canine larynx. Translation of laryngeal epithelial research conducted with canine and ovine models to human laryngeal epithelial physiology may not be optimal because, unlike humans (Robertshaw, 2006), these panting species employ the respiratory mechanism as a primary means of thermoregulation (Fayez, Marai, Alnaimy, & Habeeb, 1994; Hales & Brown, 1974; Ingram & Legge, 1972; Ray, Ingenito, Strek, Schumacker, & Solway, 1989; Solway et al, 1986). This primary physiologic difference for thermoregulation may signal key differences in respiratory epithelial physiology that are yet to be described in the human larynx.…”