EFFECTS OF INHALED NEBULIZED MORPHINE ON VENTILATION AND BREATHLESSNESS DURING EXERCISE IN HEALTHY MAN

1. Nebulized inhaled morphine has been reported to increase exercise e ndurance in patients with chronic lung disease and to relieve dyspnoea in patients with malignant disease. Potential mechanisms include a ce ntral effect occurring after systemic drug absorption or a local actio n mediated by receptors in the lung. 2. The ventilatory effects of neb ulized morphine (10 and 25 mg) were therefore compared with those of i ntravenous morphine (1.0 and 2.5 mg) and placebo in a double-blind stu dy involving 12 young healthy males. Submaximal cycle ergometry with r espiratory gas analysis was performed 15 min after drug administration and breathlessness assessed using a linear visual analogue scale. 3. Neither dose of inhaled morphine had statistically significant effects on spirometry, heart rate, ventilation, respiratory gases or breathle ssness at any level of exercise. The slopes and intercepts of the line s relating ventilation to breathlessness were also unaffected. 4. Intr avenous morphine 2.5 mg reduced breathlessness slightly at the highest equivalent workload [mean (least significant range) 33 mm (26-40 mm)] compared with placebo [41 mm (34-48 mm), P<0.05] but had no other sig nificant effects.5. These results do not support the hypothesis that i ntrapulmonary opiate receptors modulate the sensation of breathlessnes s in healthy man. The possibility that inhaled morphine may affect bre athlessness caused by other factors, such as disease, has not been exc luded.