The current study has limitations. First, the study lacks an appropriate control group. We examined patients who did not receive LVRS but returned for follow-up pulmonary function tests at 1 year and found less weight gain. However, these patients were, by definition, a different group because they did not meet criteria for LVRS. Thus, the comparison is not as useful. The group of patients selected for LVRS could have had unique metabolic requirements or respiratory muscle recruitment that led to differences in resting energy expenditure. Thus, without an appropriate control group, we must be cautious about attributing the weight gain to LVRS. Second, the sample size was small. It is conceivable that we did not find any relationship between increased weight at 1 year and improvement in lung mechanics because we did not have enough patients to see the difference. Third, we did not have complete follow-up on all patients. Because of this, there is the potential for bias in the data, especially if the patients who did not undergo follow-up assessment had all lost weight. Here
This does not appear to be the case. The data at 1 year represent 88% of the patients eligible for follow-up. Of the five patients who did not return within 60 days of their 1-year anniversary of LVRS, three had gained weight in a visit either preceding or following this cut-off. Thus, the incomplete follow-up does not appear to represent a bias in data collection that favors patients who gained weight. Third, this study only measured total body weight. It would be important to whether the gains in total body weight were lean body mass or fat. Several studies of nutritional supplementation in malnourished patients with COPD have shown that it is possible to increase body weight, although these gains are predominantly in body fat and not lean body mass. In addition to understanding the type of changes in body composition in these patients, it would be of interest to know whether there were changes in total caloric intake or in diet composition. Finally, all patients were encouraged to return to pulmonary rehabilitation postoperatively. We did not track which patients returned to formal exercise or home-based exercise programs. Differences in physical activity could have played a role in the weight gain in these individuals. The answer to all these questions will require additional studies. The upcoming multicenter National Emphysema Treatment Trial will provide an opportunity to examine these questions with a larger patient population matched in every respect except for LVRS.
In summary, this study shows that patients with severe emphysema gain weight after LVRS. This intriguing finding may lead to insights into the reasons that emphysema patients are prone to malnutrition and help researchers to design therapies to help all malnourished patients with COPD. Further examination of this issue in the context of the upcoming clinical trial of LVRS may provide further insight into the mechanism of this effect.