Effect of bronchial challenge on breathing patterns and arterial oxygenation in stable asthma

The effect of histamine or methacholine inhalational challenge on breathing patterns and oxygen saturation was investigated in ten stable asthmatic patients. We used the respiratory inductive plethysmograph to record respiratory timing and minute ventilation along with an ear oximeter to measure oxygen saturation (SaO2). As FEV1 fell during the challenge procedure, SaO2 also fell (average 3 percent). Furthermore, with histamine challenge, expiratory time (Te), inspiratory time (Ti), and breath period (Ttot) all increased; minute ventilation probably also fell. These changes in breathing pattern and SaO2 were reversed by inhalation of a beta 2-agonist. However, no such changes in breathing patterns were observed with methacholine challenge despite a similar fall in FEV1. Bronchial challenge produces hypoxia in stable asthmatic patients, which might result from a combination of hypoventilation with alteration in alveolar ventilation/perfusion relationships.