Tracheobronchial Constriction in Asthmatics Induced by Isocapnic Hyperventilation With Dry Cold Air

¹ From The Tri-Hospital Pulmonary Function Laboratories, Department of Medicine, University of Toronto, Toronto, Ontario, Canada

Although it is well known that isocapnic hyperventilation (IHV) with dry cold air produces airway constriction in asthmatic subjects, the site of airway narrowing is unclear. To address this issue, we have quantified the tracheal and bronchial response to IHV with dry cold air in 15 patients with mild asthma and 7 healthy control subjects. We employed the acoustic reflection technique to evaluate changes in airway cross-sectional areas caused by IHV with dry cold air. Airway areas were measured during tidal breathing before and 5 to 10,30,60, and 90 min following cold air challenge. For analysis purposes, airway areas were divided into three anatomic segments: extrathoracic tracheal segment, intrathoracic tracheal segment, and main bronchial segment. These segments were assessed at a fixed volume below total lung capacity. Maximal and partial expiratory flow-volume curves were also obtained before each set of area measurements. In normal subjects, IHV with dry cold air caused no significant changes in FEV₁, flow at 30% of the vital capacity in the partial curve (V_30p), or airway areas. In asthmatics, at 5 to 10 min after challenge, we found that FEV₁ decreased by 22±5% (mean±SEM) (p<0.0001), V_30p by 33±8% (p<0.003), intrathoracic tracheal area by 10.7%±2% (p<0.03), and main bronchial area by 14±3% (p<0.003). At 30 min, tracheal and main bronchial areas were returned to baseline levels; however, FEV₁ and V_30p were still significantly decreased, by 13±3% and 16±4%, respectively. We conclude that in asthmatics, IHV with dry cold air causes both tracheal and bronchial constriction, and that recovery seems to occur first in the central airways.

Key Words: acoustic reflections • asthma • bronchi • cold air • trachea

Submitted on February 8, 1995
Accepted on April 9, 1996