The study of the effects of noninvasive positive pressure ventilation to reduce chronic compensated CO2 retention in COPD patients1ignores the possible adaptive advantage of “resetting” the Pco2 to a higher level than normal. As experts in the mechanics of COPD have argued in the past, chronic compensated CO2 retention will allow for CO2 homeostasis at a lower level of alveolar, and thus minute, ventilation. This may result in decreased dyspnea during exercise.3 Some time ago, we reported on a group of patients with very advanced COPD and quite high Pco2 levels, ranging from 75 to 110 mm Hg (mean, 90 mm Hg) with partial bicarbonate compensation: mean HCO3- of 45 mEq/L and pH 7.32. Of course, these patients also received long-term nasal oxygen. All were functional to a remarkable degree in view of severe airflow obstruction: mean FEV1, 0.41 L (range, 0.31 to 0.67 L). One patient worked daily as a road inspector! Mean survival was 17 months.4 I have also had many patients gain remarkable relief from dyspnea while receiving oxygen and exercise during pulmonary rehabilitation. It is as if their brain adjusts to the work of breathing by “living” at a high but compensated Pco2. Thus, in my view, we should not focus on just one physiologic manifestation of COPD, and we must sometimes be reminded about the wisdom of nature.