Study objectives: To measure route of breathing in chronic asthmatic patients during and after an acute severe exacerbation.
Patients or participants: Thirteen asthmatic patients were studied during hospital admission for acute asthma and, in 9 patients, again when asymptomatic. Nine healthy subjects were also studied.
Interventions: Spontaneous route of breathing was qualitatively assessed using oral and nasal thermistor probes, and was then quantified using a dual compartment face mask with attached pneumotachographs.
Measurements and results: All asthmatic patients had severe bronchoconstriction initially (FEV(1), 46 +/- 3% of predicted) that had resolved at follow-up (FEV(1), 91 +/- 6% of predicted). No healthy subject had evidence of bronchoconstriction (FEV(1), 102 +/- 5% of predicted). During acute asthma, 11 asthmatics were spontaneously breathing oronasally, as assessed using thermistor probes, while all 13 breathed oronasally via face mask. When assessed using thermistor probes, seven of nine asymptomatic asthmatic patients studied were breathing exclusively via the nose; however, all breathed oronasally via face mask. In contrast, while eight of nine healthy subjects were also breathing exclusively via the nose when assessed using thermistor probes, all breathed nasally only via face mask.
Conclusions: Thus, when asymptomatic and at rest, asthmatic patients breathe exclusively via the nose. However, during acute exacerbations of asthma, these patients switch to oronasal breathing. Unlike healthy subjects, chronic asthmatic patients also switch to oronasal breathing when wearing a face mask, irrespective of the degree of bronchoconstriction. We speculate that asthmatics may have an increased tendency to switch to oral breathing, a factor that may contribute to the pathogenesis of their asthma.