Comparison of intraairway temperatures in normal and asthmatic subjects after hyperpnea with hot, cold, and ambient air.

To determine how the inhalation of hot dry, frigid, and room temperature air influences airway heat transfers, we obtained single-breath temperature washout curves in eight asthmatic and eight normal subjects before and during periods of hyperpnea. The order of study was randomly determined, and the thermal events with each inspirate were correlated with their effects on lung function. Each inspired air condition produced significant airway cooling in both groups. Cold air evoked the greatest response, followed thereafter by hot dry and then room air. Only the asthmatic subjects developed airway obstruction. These data demonstrate that hot dry gases facilitate evaporative cooling and do not keep the airways warm as has been previously suggested. It appears the airway cooling is a normal part of respiration and develops whenever air is inhaled that requires the transfer of heat and/or water to bring the inspirate to body conditions.