Eight persons with asthma were exposed to seven air conditions varying in temperature (37°C to 49°C [98.6°F to 120.2°F]) and water content (44 mg H2O per liter to 79 mg H2O per liter). Normocapnic hyperventilation for three minutes at 40% maximal voluntary ventilation was carried out for each condition. A constant-volume body plethysmograph measured the functional residual capacity and specific airway conductance (SG(aw)), followed by two forced expiratory maneuvers. Measurements were taken before and 1, 5, 10, and 20 minutes after each challenge. Air conditions with 100% relative humidity caused a fall in the SG(aw) that was maximal in 1 minute. Air conditions at 100% relative humidity caused a greater fall in both the forced expiratory volume in 1 second (FEV1) (P < .05) and the SG(aw) (P < .005) than did conditions of the same temperature but less water content. At 44°C and 100% relative humidity, the mean percent change in FEV1 and SG(aw) was -2% and -40%, respectively, at 1 minute after challenge. Of the conditions examined, the optimal temperature was 44°C, and we speculate that the optimal water content is less than 44 mg H2O per liter. Inhaled water concentrations exceeding 44 mg H2O per liter should probably not be used in patients with asthma.
|Original language||English (US)|
|Number of pages||5|
|Journal||Western Journal of Medicine|
|State||Published - Jan 1 1988|