Effects of inspiratory muscle thixotropy on the 6-min walk distance in COPD

Thixotropy conditioning of inspiratory muscles at lower lung volumes decreases functional residual capacity (FRC) of following breath cycles with increases in inspiratory capacity. It remains uncertain whether this conditioning would improve exercise tolerance in chronic obstructive pulmonary disease (COPD). Sixteen male stable COPD patients with mild to severe airway obstruction participated. Before the study, all patients completed the 6-min walk test at least twice. The 6-min walk distance (6MWD) was measured after single inspiratory muscle training (IMT) maneuver or without intervention (control) in a randomized cross-over fashion. The 6MWD was also measured after thixotropy conditioning of inspiratory muscles at the maximal expiratory position or without intervention (control). There were no significant differences in the 6MWD after the IMT maneuver (493.2+/-83.7m, P>0.05) versus without intervention (495.7+/-85.9m). The 6MWD after thixotropy conditioning (526.2+/-96.3m, P=0.030) was significantly higher than the 6MWD without intervention (504.3+/-94.1m). The 95% confidence interval of the difference was from 2.6 to 41.2m. Percentage predicted FRC correlated positively with differences in the 6MWD between control and after the thixotropy conditioning maneuver (r=0.78, P=0.007), whereas percentage predicted forced expiratory volume in 1s or the BODE index did not correlate with differences in the 6MWD (P>0.05). Thixotropy conditioning increases self-paced walking distance in patients with COPD. Patients with higher resting FRC benefited more from the conditioning with greater walking distance.