No influence of airway heat flux on airflow-induced bronchospasm.

We used a canine model of airway reactivity to examine the role of airway heat flux in the response to dry air challenge. Airflow-induced bronchospasm (AIB) was assessed by measuring collateral system resistance (Rcs) with a wedged bronchoscope technique in anaesthetized mechanically ventilated dogs. We manipulate post-challenge airway heat flux by exposing peripheral airways to cool dry air (23.9 +/- 0.3 degrees C, 0.8 +/- 0.2 mgH2O.l-1), cool humid air (24.2 +/- 0.2 degrees C, 21.5 +/- 0.3 mgH2O.l-1), or warm humid air (35.3 +/- 0.4 degrees C, 40.6 +/- 0.3 mgH2O.l-1) during the recovery period (n = 14) following a high flow challenge (1,500 ml.min-1 for 2 min) with cool dry air. In a second series of experiments (n = 6), we attempted to further exaggerate airway heat flux during challenge by exposing peripheral airways to warm humid air during both baseline and recovery periods. In comparison to control (i.e. treatment with cool dry air before and after challenge), treatment with warm humid air during recovery period produced a small but significant attenuation (p less than 0.01) in Rcs. Cool humid air during recovery had no affect on Rcs following challenge. Warm humid air during both baseline and recovery tended to attenuate Rcs after challenge (p less than 0.05). We conclude that airway heat flux in itself has no significant physiological affect on AIB in the canine lung periphery.