Continuous Positive Airway Pressure in Severe Obstructive Sleep Apnea Reduces Pain Sensitivity

Study Objective: To evaluate effects of CPAP on pain sensitivity in severe OSA patients. Design: Within-subject treatment study. Setting: Hospital-based sleep disorders center. Patients: Twelve severe OSA patients (7 men, 5 women), 50.2 +/- 12.5 years, with no pain. Interventions: The morning after a diagnostic nocturnal polysomnogram (NPSG), patients underwent a training session of finger withdrawal latency (FWL) testing to a radiant heat stimulus, a validated human behavioral model of thermal nociception. Baseline FWL in seconds was obtained after the training session. CPAP pressure was titrated on a second night in the laboratory. Two nights after titration, patients returned to sleep in the laboratory on CPAP. FWL was tested in the morning after awakening, after 6-8 wks of CPAP use, and finally (within 6-8 weeks) after 2 nights of discontinuation of CPAP. Mean FWL in seconds (sec) was compared using MANOVAs with nights as the within subject variable. Results: Apnea-hypopnea index (AHI) decreased from 50.9 +/- 14.5 to 1.4 +/- 1.0 with CPAP, and sleep continuity improved. In parallel, FWL increased significantly from a mean baseline of 9.8 +/- 1.3 sec to 13.7 +/- 5.1 sec (P = 0.01) and with continued CPAP use (5.1 +/- 2.3 h nightly) for 6-8 weeks FWL remained elevated (21.1 +/- 16.2 sec). After the 2-night CPAP discontinuation, apnea/hypopneas returned and sleep was fragmented (AHI = 32.6 +/- 19.8). FWL decreased to 11.6 +/- 5.9 sec relative to intermediate-term CPAP use (P = 0.03). Conclusion: CPAP treatment reduces pain sensitivity in OSA patients. Future studies will focus on patients with OSA and chronic pain and identify mediating mechanisms.