Clinical practice
“The highly heterogeneous nature of the enrolled patient population reflects clinical practice,” the authors point out. For example, cluster 1 included patients with the best lung function, compared with those in clusters 2, 3, and 4 – which may be due, at least in part, to the aggravation in disease severity with age given that patients in cluster 1 were the youngest overall.
The fact that those in cluster 4 had the worst performance may also have been because of age and disease severity, the authors note, as those in cluster 4 had the highest proportion of patients on long-term oxygen therapy, again suggestive of disease severity. “Of note, these patients show the most impaired 6MWT responses despite the use of oxygen supplementation during walking,” the researchers added.
The authors also suggest that patients such as those in cluster 4 may require specific PR modalities in order to optimize their functional benefits. In contrast, those in cluster 1 had a significantly higher body mass index, compared with those in the other 3 clusters, which, interestingly enough, was not associated with more severe functional exercise impairment. The fact that older age participants, such as those in cluster 3 as well as those with high BMI in cluster 1, were both able to improve their 6MWD post-PR to the same extent as younger patients without obesity suggests that most older or overweight/obese patients can still show clinically significant improvement in 6MWD post PR, as the authors suggest.
Notably, the 6MWT was the only test available both pre-and post PR, making this an important limitation of the study, because only one aspect of the effect of PR was evaluated, omitting other physical and psychosocial benefits of PR, investigators suggest.
Adds to the literature
Asked to comment on the findings, Sachin Gupta, MD, attending physician, pulmonary & critical care medicine, Alameda Health System, Highland Hospital, Oakland, Calif., felt that these data add to the literature in defining COPD patient profiles, helping to categorize those in whom to expect greater walk distance improvements with PR versus those who will respond less well.
“Because 6MWD is a surrogate marker for quality of life (QOL) and mortality, further analysis in the form of a randomized controlled trial to determine long-term outcomes among the four clusters with adjustment for baseline characteristics would help determine the extent to which certain patient clusters may respond to PR,” Dr. Gupta told this news organization in an email.
At the same time, he suggested that while patients may not experience much net benefit in their 6MWD, their QOL or mortality risk may still improve with PR. “I cannot recall a patient ever describing their experience with PR as anything other than positive,” Dr. Gupta stressed.
“And as the authors [themselves] note, because PR serves to benefit patients beyond the 6MWD, I would not recommend limiting PR referrals based on the patient clusters identified,” he said.
The authors had no conflicts of interest to declare. Dr. Gupta declared that he is an employee and shareholder at Genentech.