American Journal of Respiratory and Critical Care Medicine

The adverse effect of long-term steroid treatment on respiratory muscle function remains controversial. We evaluated inspiratory muscle strength and endurance in steroid-dependent asthmatics in comparison with other asthmatics or with patients with chronic obstructive pulmonary disease exhibiting a comparable level of lung hyperinflation. Inspiratory muscle function was assessed by maximal inspiratory pressure (Pimax) and by an incremental inspiratory threshold loading test in 19 patients who had had steroid-dependent asthma (SDA) requiring a mean daily dose of 20.7 +/- 0.8 mg prednisone for 5 +/- 1.4 yr. They were compared with 16 healthy control subjects, 30 patients with COPD, and 16 patients with non-steroid-dependent asthma (NSDA). Pimax as percentage of predicted values (%Pimax) was not significantly different in patients with SDA (77 +/- 5%) or NSDA (83 +/- 6%) than in control subjects (93 +/- 4%). In contrast, %Pimax was lower in patients with COPD (59 +/- 4.4%) than in those with SDA or NSDA (p < 0.05) or the control subjects (p < 0.0001). A significant correlation was found between %Pimax and hyperinflation assessed by the FRC/TLC ratio (r = 0.42; p < 0.001). Inspiratory endurance, defined as the ratio of maximal peak inspiratory pressure sustained for 2 min to individual Pimax (Plim2/Pimax), was significantly lower in the SDA (43 +/- 3%; p < 0.0001), NSDA (65 +/- 4%; p = 0.01), and COPD (55 +/- 3%; p < 0.0001) groups than in the control group (76 +/- 2%). Plim2/Pimax was also lower in patients with SDA than in those with COPD (p = 0.0073) or NSDA (p < 0.0001). Hyperinflation plays a major role in inspiratory muscle dysfunction associated with obstructive lung disorders, but the finding of a significantly decreased endurance in patients with SDA when compared with patients with COPD, despite a lower level of hyperinflation in the former group, points to a deleterious effect of long-term corticosteroid treatment on inspiratory muscle function in asthmatics.


No related items
American Journal of Respiratory and Critical Care Medicine

Click to see any corrections or updates and to confirm this is the authentic version of record