In obstructive sleep apnea (OSA), the short-latency inhibitory reflex (IR) of inspiratory muscles to airway occlusion is prolonged in proportion to the severity of the OSA. The mechanism underlying the prolongation may relate to chronic inspiratory muscle loading due to upper airway obstruction or sensory changes due to chronic OSA-mediated inflammation. Continuous positive airway pressure (CPAP) therapy prevents upper airway obstruction and reverses inflammation. We therefore tested whether CPAP therapy normalized the IR abnormality in OSA. The IR responses of scalene muscles to brief airway occlusion were measured in thirty-seven adult participants with untreated, mostly severe, OSA, of whom 13 were re-studied after the initiation of CPAP therapy (usage >4 hours/night). Participants received CPAP treatment as standard clinical care and the mean CPAP usage between initial and subsequent studies was 6.5 hours/night (range 4.1-8.8 hours/night) for a mean of 19 months (range 4-41 months). The duration of the IR in scalene muscles in response to brief (250 ms) inspiratory loading was confirmed to be prolonged in the participants with OSA. The IR was assessed before and after CPAP therapy. CPAP treatment did not normalize the prolonged duration of the IR (60 ± 21 ms pre-treatment vs 59 ± 18 ms post-treatment, mean ± SD) to airway occlusion observed in participants with severe OSA. This suggests that the prolongation of IR reflects alterations in the reflex pathway that may be irreversible, or a specific disease trait.
- obstructive sleep apnea
- scalene muscle
- reflex inhibition
- Copyright © 2015, Journal of Applied Physiology