Walking Uphill Aggravates Dyspnea and Dynamic Hyperinflation at Equivalent Oxygen Uptake in COPD Patients.

Background/

Objectives

COPD patients often complain of severe dyspnea when walking uphill, even up a mild incline. This study aimed to determine whether the dyspnea experienced during uphill walking is disproportionate to the increased mechanical work required to overcome gravity.

Methods

Fourteen COPD patients (FEV1 49 ± 11% predicted) and nine healthy participants performed three symptom-limited exercise tests on a treadmill, each at a fixed grade: 1%, 2.5%, and 4% for COPD patients; and 1%, 3%, and 5% for healthy participants. Treadmill speed was increased stepwise (3 min/stage). Inspiratory capacity (IC) maneuvers were performed during the last minute of each stage. Borg dyspnea scores (0-10) at the different inclines were compared at a uniform level of oxygen uptake (iso-V˙O2).

Results

Borg dyspnea scores by COPD patients at the highest iso-V˙O2 attained were significantly higher at 4% treadmill grade compared to 2.5% and compared to 1% grade (7 ± 2 vs. 5 ± 2 vs. 5 ± 2, respectively; p < 0.001 for 4% vs. 1% grade, p < 0.005 for 4% vs. 2.5%). Dynamic hyperinflation worsened with grade, as reflected by decrease in inspiratory reserve volume (IRV) at the highest common iso-V˙O2 attained: 798 ± 336 mL at 1% grade vs. 698 ± 325 mL at 2.5% (p < 0.004) vs. 564 ± 350 mL at 4% (p < 0.002 for 4% vs. 1%; p < 0.004 for 4% vs. 2.5%). In contrast, healthy participants showed no significant grade-dependent differences in dyspnea or IRV at iso-V˙O2.

Conclusions

Walking uphill in itself increases breathlessness of COPD subjects at iso-V˙O2, suggesting that the increased dyspnea cannot be explained simply by the increased work. This phenomenon may be related to dynamic hyperinflation, which is worse at steeper inclines.