Obstructive sleep apnea is a common and underdiagnosed sleep disorder characterized by respiratory disturbance and reduced oxygen saturation of hemoglobin in red blood cells during sleep. Although sleep-disordered breathing is associated with increased pain sensitivity in individuals without chronic pain, preliminary evidence from our group and others suggests that sleep disordered breathing may be associated with reduced pain sensitivity in patients with temporomandibular disorder pain and those with chronic headache. The present study investigated the association of overnight oxygen saturation and pain sensitivity in a sample of patients with knee osteoarthritis who were free of chronic head and jaw pain. Older men (N = 44) and women (N = 93) with knee osteoarthritis underwent one night of ambulatory polysomnography (PSG), including pulse oximetry to measure oxygen saturation. Following PSG, participants engaged in multimodal quantitative sensory testing to evaluate pain sensitivity. Regression models controlling for age, race, sex, body mass index, systolic blood pressure, insomnia severity, and apnea-hypopnea index revealed that lower oxygen saturation predicted significantly lower clinical pain (p < .01), higher thermal pain threshold at the forearm (p < .01) and patella (p < .05), marginally higher pressure pain threshold at the trapezius (p = .08), and lower suprathreshold thermal pain sensitivity (p < .05). In contrast, lower oxygen saturation predicted greater mechanical temporal summation at the patella and finger (ps < .05). Oxygen saturation was not associated with conditioned pain modulation. The results partially support limited previous evidence for respiratory disturbance-induced hypoalgesia in chronic pain, which may result from altered baroreceptor activity. But opposing effects on mechanical temporal summation suggest that sleep disordered breathing may differentially alter the activity of C versus Aδ fibers. Future studies of chronic musculoskeletal pain should employ a multimodal assessment of sleep disordered breathing to help understand individual differences in pain sensitivity.
© 2013 Published by Elsevier Inc.