BACKGROUND: It is well documented that the perception of dyspnea (POD), subjectively reported by patients, is related to the activity and strength of the inspiratory muscles, and influences the use of 'as needed' beta₂-agonists.
STUDY OBJECTIVE: To investigate the relationship among the increase in inspiratory muscle strength after specific inspiratory muscle training, beta₂-agonist consumption and the POD in patients with persistent, mild to moderate asthma.
METHODS: Inspiratory muscle strength, daily beta₂-agonist consumption and the POD were measured in 30 patients with mild to moderate asthma. Patients were then randomly assigned to two groups: one group received specific inspiratory muscle training until an increase of more than 20 cm H₂O was reached, and one group was a control group and received sham training. Inspiratory muscle strength, the POD and daily beta₂-agonist consumption were assessed during and after the training period.
RESULTS: There was no good correlation between the baseline maximal inspiratory pressure and the POD, or between the baseline maximal inspiratory pressure and the mean daily beta₂-agonist consumption. However, there was a significant correlation between the POD and the mean daily beta₂-agonist consumption. The increase in inspiratory muscle strength after the inspiratory muscle training was closely correlated with the decrease in the POD (P<0.001) and the decrease in beta₂-agonist consumption (P<0.001).
CONCLUSIONS: The present study shows that, in patients with mild to moderate, persistent asthma, there is a correlation between the POD and the mean daily beta₂-agonist consumption. When the inspiratory muscles are strengthened, there is a significant decrease in the POD and in beta₂-agonist consumption.