Background: In COPD, a decreased inspiratory capacity to total lung capacity ratio (IC/TLC) is associated with dynamic hyperinflation and poor exercise capacity. The association with upper-extremity force measured by handgrip strength (HGS) and 6-min walk distance (6MWD) has not been previously described. We hypothesized that IC/TLC affects muscle strength in the upper and lower extremities, affecting HGS and 6MWD.
Methods: We prospectively measured lung function, HGS, and 6MWD in 27 patients with COPD and 12 healthy nonsmokers twice, 1 year apart. The patients were classified according to level of hyperinflation: IC/TLC > 25% or IC/TLC ≤ 25%.
Results: Patients with COPD had reduced lung function, static hyperinflation, and reduced HGS and 6MWD compared with the control subjects on both evaluations (P < .01). There was a statistically significant deterioration in HGS, IC/TLC, and 6MWD after 1-year follow-up in the COPD compared with the control group (P < .001). More hyperinflation (IC/TLC < 0.25) was associated with lower HGS and 6MWD (P < .001). Changes in IC/TLC correlated with changes in HGS (r = 0.429, P < .05). Multivariate analysis determined that IC/TLC is an independent factor associated with HSG and 6MWD.
Conclusions: HGS and 6MWD are reduced in patients with COPD, particularly in those with hyperinflation and evidence of longitudinal deterioration not seen in control subjects. This finding suggests that resting hyperinflation may exert a detrimental effect on cardiac function and plays a role in reduced exercise performance in patients with COPD.