Effect of cold air on the bronchial response to inhaled histamine in patients with asthma.

We measured the concentration of inhaled histamine required to reduce the FEV1 by 20% (PC20) in seven asthmatic patients immediately following the inhalation of warm air (mean temperature +/- 1 SD, 21.1 +/- 1.1 degrees C) and following cold air inhalation (-10.2 +/- 5.0 degrees C). Patients breathed either warm or cold air for 10 min before 30-s challenges with doubling concentrations of aerosolized histamine that were nebulized while the subject breathed warm air. Before histamine inhalation minute ventilation (VI) was 8.41 +/- 1.38 L/min breathing warm air and 7.86 +/- 0.97 L/min breathing cold air. Respiratory heat exchange (RHE) was 0.25 +/- 0.05 kcal/min with warm air and 0.24 +/- 0.03 kcal/min with cold air. The PC20 obtained following cold air breathing (0.48 +/- 4.63 mg/ml) was lower than that following warm air breathing (0.85 +/- 4.60 mg/ml; p less than 0.02). We conclude that breathing cold air increases the bronchial reactivity to inhaled histamine in asthmatic patients.