Pulmonary adaptations to 12 wk of supervised high intensity interval training in COPD: a nonrandomized controlled pilot study

This study investigates the change in diffusing capacity from rest to submaximal exercise in patients with mild to severe chronic obstructive pulmonary disease (COPD) compared with a healthy, age- and sex matched control group, and investigates if the diffusing capacity can be altered by high-intensity interval training (HIIT). Thirty-five patients with COPD and 15 healthy age- and sex matched controls were included. Pulmonary diffusing capacity was measured using the combined single-breath method using carbon monoxide and nitric oxide (D_L,CO,NO), which were measured at rest and during 60% of peak workload (W_Lpeak) to estimate the alveolar-capillary reserve (change from rest to exercise). A subgroup of 12 patients with COPD and 12 control participants completed a 12-wk supervised HIIT intervention with measurements of D_L,CO,NO, computed tomography-based lung tissue mass, and single-photon emission computed tomography to assess the pulmonary perfusion distribution pre and post the HIIT intervention. The alveolar-capillary reserve was reduced in patients with COPD in a severity-dependent manner compared with the healthy control group and this was unaltered following the HIIT intervention, despite an increase in exercise capacity. HIIT did not increase lung tissue mass, nor did it improve the pulmonary perfusion distribution during exercise in either group. Alveolar-capillary reserve is reduced in a severity-dependent manner in COPD, and a 12-wk supervised HIIT intervention did not induce any changes in either the alveolar-capillary reserve or lung tissue mass, suggesting that the concomitant increase in exercise capacity is likely due to extrapulmonary adaptations. (Clinical Trial Registration IDs: NCT05552833 and NCT05583396)<b>NEW & NOTEWORTHY</b> Using the combined measurement of the diffusing capacity for carbon monoxide and nitric oxide, we found that the increase in diffusing capacity during submaximal exercise, that is, the alveolar-capillary reserve, was reduced in patients with COPD in a severity-dependent manner. A 12-wk supervised high-intensity training intervention increased exercise capacity but without any changes in alveolar-capillary reserve or lung tissue mass, supporting that the increase in exercise capacity is not caused by pulmonary adaptations.