Davis M S, Freed A N
Division of Physiology, Department of Environmental Health Sciences, The Johns Hopkins School of Public Health, Baltimore, Maryland, USA.
Am J Respir Crit Care Med. 2001 Sep 1;164(5):785-9. doi: 10.1164/ajrccm.164.5.2003081.
Winter athletes have an increased incidence of asthma, suggesting that repetitive hyperventilation with cold air may predispose individuals to airways disease. We used a canine model of exercise-induced hyperpnea to examine the effects of repeated hyperventilation with cool, dry air (i.e., dry air challenge [DAC]) on peripheral airway resistance (Rp), reactivity, and inflammation. Specific bronchi were exposed to a single DAC on five consecutive days. Rp and Delta Rp to aerosolized histamine, intravenous histamine, or hypocapnia were measured daily. Bronchoalveolar lavage fluid (BALF) was obtained on the fifth day. Rp increased from 0.70 +/- 0.08 to 1.13 +/- 0.22 cm H(2)O/ml/s (n = 25) 24 h after the first DAC, rose to 1.49 +/- 0.24 cm H(2)O/ml/s by Day 3, and remained elevated throughout the remainder of the protocol. Repeated DAC increased reactivity to hypocapnia and intravenous histamine. Intravenous salbutamol failed to reduce Rp as effectively in challenged airways (111% of Day 1 baseline) as in naive airways (54% of baseline). Repeated DAC caused increased BALF neutrophils, eosinophils, and sulfidopeptide leukotrienes. We conclude that repeated DAC causes peripheral airways inflammation, obstruction, hyperreactivity, and impaired beta-agonist-induced relaxation. This suggests that other mechanisms in addition to increased smooth muscle tone may contribute to the development of repetitive hyperventilation-induced bronchial obstruction and hyperreactivity.
