Circulational heat dissipation of upper airway: Canine model of inhalational thermal injury

BackgroundThe upper airway has powerful heat-absorbing ability, in which the blood circulation may play an important role.ObjectiveThis study aimed to explore the circulational heat-dissipating ability, and to investigate the contribution of blood circulation to the heat-absorbing ability of upper airway.Methods18 adult, male Beagle dogs were divided into three groups to inhale thermal dry air of 70–80 °C, 150–160 °C or 310–320 °C for 20 min. Blood temperatures and blood flow rates of bilateral common jugular veins (CJVs) were measured. Dogs’ breathing rates and air temperatures in middle trachea were also measured. According to the formula “Q = c·m·ΔT”, the heat dissipated by blood (Q-blood) and the heat release by air (Q-air) were calculated out. The contribution of circulational heat dissipation to the heat-absorbing ability of upper airway was defined as “C-blood”.ResultsThe blood temperature rise of CJV was 2.24 ± 0.60 °C. The blood flow rate of CJV was 44.5 ± 5.9 ml/min. The air temperature in middle trachea was 63.5 ± 18.9 °C. The mean breathing rate was 51.8 ± 7.5/min. The calculated “Q-blood” and “Q-air” were 13197.3 ± 4408.6 J and 33540.2 ± 24578.7 J, and the “C-blood” was 55.2 ± 25.0% (21.7–88.8%).ConclusionCirculational heat dissipation plays an important role in the heat-absorbing process of upper airway when inhaled air is less than 160 °C. However, for air higher than 160 °C, some other mechanism might be dominant in the upper airway's heat-absorbing ability.