PURPOSE: To determine, by means of a randomized, double-blind, placebo controlled study, whether intravenous dopamine, a carotid body inhibitor, depresses exercise ventilation and improves exercise endurance –in a manner similar to supplemental oxygen.
METHODS: Seventeen COPD patients (7 men) with forced expiratory volume in one second of 41±12% predicted who did not demonstrate severe exercise desaturation (SPO2>85%) were enrolled. Each performed 4 constant work rate tests at 85% of the peak value achieved in ramp testing (62±23 watts). Breath-holding time (BHT) was assessed before each test. In randomized order, patients received: intravenous saline infusion+air breathing (saline-air), intravenous dopamine infusion(5μg/kg/min)+air (dopamine-air), saline+50% oxygen (saline-oxygen), or dopamine+50% oxygen (dopamine-oxygen). Ventilation (VE) and heart rate (HR) at the time of the shortest of these tests (isotime (Iso)) and time constant of phase II VE kinetics (τVE) were determined. As results were not normally distributed, median values are reported.
RESULTS: Compared to saline-air, oxygen (with or without dopamine) prolonged BHT and τVE, reduced isotime VE and increased exercise endurance, but did not alter isotime HR. Compared to saline-air, dopamine also prolonged BHT and reduced isotime VE, but did not alter τVE or exercise endurance; isotime HR was increased. (see Table).
CONCLUSION: In COPD patients, the carotid body inhibitor dopamine was similar to supplemental oxygen in that it prolonged breath holding time and diminished the ventilatory response to exercise. However, we failed to demonstrate that dopamine increased exercise tolerance. We speculate that this may be related to dopamine’s cardio-stimulatory effects.
CLINICAL IMPLICATIONS: Carotid body inhibitors without such cardio-excitatory effects might prove more beneficial in improving exercise tolerance in COPD patients.
DISCLOSURE: Michelle Cao, None.