The effects of a single mild dose of morphine on chemoreflexes and breathing in obstructive sleep apnea

The effect of morphine on breathing and ventilatory chemoreflexes in obstructive sleep apnea (OSA) is unknown. It has been assumed that acute morphine use may induce deeper respiratory depression in OSA but this has not been investigated. We evaluated awake ventilatory chemoreflexes and overnight polysomnography on 10 mild-moderate OSA patients before and after giving 30 mg oral controlled-release morphine. Morphine plasma concentrations were analysed. We found a 30-fold range of morphine plasma concentrations with the fixed dose of morphine, and a higher plasma morphine concentration was associated with a higher CO(2) recruitment threshold (VRT) (r=0.86, p=0.006) and an improvement in sleep time with Sp(O(2)) (T90) (r=-0.87, p=0.005) compared to the baseline. The improvement in T90 also significantly correlated with the increase of VRT (r=-0.79, r=0.02). In conclusion, in mild-to-moderate OSA patients, a single common dose of oral morphine may paradoxically improve OSA through modulating chemoreflexes. There is a large inter-individual variability in the responses, which may relate to individual morphine metabolism.