Previous studies have shown that opiates increase the maximal external work performed at exhaustion in patients with chronic obstructive pulmonary disease (COPD). The mechanism responsible for this improvement in exercise tolerance is unknown. The purpose of this study was to determine the effects of an oral morphine solution (0.8 mg/kg) on the exercise tolerance, perception of dyspnea, and arterial blood gases of patients with COPD. Thirteen eucapnic patients with stable COPD (FEV1 = 0.99 +/- 0.48) underwent duplicate incremental cycle ergometer tests to exhaustion (Emax) after the ingestion of placebo and after the ingestion of morphine. After the ingestion of morphine, the maximal workload increased by 18% (p less than 0.001) and the VO2 increased by 19.3% (p less than 0.001). Ten of the 13 patients had a higher ventilation at Emax after morphine ingestion. Despite the higher ventilation at Emax after morphine, the mean Borg score was not significantly higher. At Emax after morphine ingestion, the PaO2 (65.8 +/- 11.6 mm Hg) was significantly lower and the PaCO2 (43.5 +/- 8.3 mm Hg) was significantly higher than at Emax after placebo (71.9 +/- 15.5 and 38.3 +/- 8.5, respectively). When data at the highest equivalent workload were analyzed, the ventilation and the Borg scores were significantly lower, whereas the VO2 and VCO2 were comparable. From this study, we conclude that the administration of opiates can substantially increase the exercise capacity of patients with COPD. The improved exercise tolerance appears to be related to both a higher PaCO2 resulting in lowered ventilation requirements for a given workload and also to a reduced perception of breathlessness for a given level of ventilation.

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A recent study showed that indomethacin reduces the perception of dyspnea during submaximal exercise in normal subjects (1). The purpose of this study was to determine whether indomethacin alters the perception of dyspnea in patients with chronic airflow obstruction during exercise. In a randomized double-blind crossover fashion, 11 subjects (FEV1 = 0.97 +/- 0.58 L) performed an incremental (15 W/min) cycle ergometer exercise test to exhaustion on 2 study days. Testing was performed 3 to 4 h after placebo or 50 mg of indomethacin. Perception of dyspnea was measured using the modified Borg scale. Minute ventilation, workload, and Borg scale measurements at exhaustion and during moderate exercise were determined. The data demonstrated no statistically significant differences between values obtained for minute ventilation, workload, or Borg scale measurements on placebo and indomethacin study days. Contrary to the previous findings in normal subjects, indomethacin failed to significantly alter perceived dyspnea during exercise in patients with chronic airflow limitation. This suggests that prostanoids do not play a major role in the perception of dyspnea in these patients during exercise.