Inspiratory muscle strength in acute asthma

Study objectives: The aim of this study was to measure inspiratory pressure -generating capacity in patients presenting with acute asthma, as it has be en suggested that inspiratory muscle fatigue may contribute to breathlessne ss and acute respiratory failure. Design: Descriptive study. Setting: Emergency departments of two inner-city hospitals. Patients: Fifty-one patients with acute asthma, and 45 patients without res piratory disease who served as control subjects. Measurements and results: Maximum inspiratory pressure-generating capacity was measured soon after presentation by the sniff nasal inspiratory pressur e (SNIP) method. The mean (SD) SNIP was 110 cm H2O (23 cm H2O) in men with asthma (mean for control subjects, 126 cm H2O [25 cm H2O]; p < 0.05) and 80 cm H2O [24 cm H2O] in women with asthma (mean for control subjects, 105 cm H2O (26 cm H2O); p < 0.01). In a second study of simultaneous SNIP and int rathoracic pressure measurements in a group of patients with acute asthma ( n = 10) and control subjects (n = 11), the effect of airways obstruction on SNIP was assessed. The measurement of sniff esophageal pressure was more n egative than SNIP by approximately 16% in asthmatic patients and by 4% in c ontrol subjects. Taking account of the likely effect of airways obstruction on SNIP, the reduction in inspiratory pressure-generating capacity that wa s observed in these patients with moderately severe acute asthma was minor and was consistent with the modest hyperinflation observed. Conclusions: This study did not fmd evidence of inspiratory muscle weakness or fatigue in patients with moderately severe acute asthma presenting to t he emergency department.