Recruitment was made near impossible due to circumstances surrounding the epidemic

This project will assess patients with diagnosed obstructive sleep apnea, to investigate the impact of poor sleep on central pain mechanisms. Furthermore, the project will explore if restoring good sleep hygiene can improve the central pain mechanisms that may be associated with the risk of chronic pain.

Chronic pain affects approx. 20% of the world's population and greatly affects the quality of life of the patients. Recent studies have found that multiple chronic pain patients are characterized by central sensitization and other studies have even found that the degree of central sensitization might be important for pain relieving effects to, e.g., surgery or pharmaceutical treatment. These studies highlight the importance of assessing central sensitization but also indicate that central sensitization can be influenced by multiple factors and it is deemed important to assess such factors in experimental and clinical settings to improve our understanding of the field.

Sleep impairment and the effects on central pain pathways One common complaint among chronic pain patients is that their sleep is affected. It is estimated that at least 50% of chronic pain patients also suffer from sleep disturbances. This is alarming since sleep is well-known to provide neural maturation, facilitate learning, memory, cognition, and general productivity and a lack of sleep impact all of these important processes. Furthermore, earlier studies have shown that partial and total sleep deprivation affect even healthy participants and impair both peripheral and central pain pathways and may indicate that regular sleep is important to maintain a proper healthy response to pain. This notion is supported by evidence showing an association between sleep impairment (e.g. partial or total sleep deprivation) and impaired conditioned pain modulation (CPM), which is the human surrogate model for diffuse noxious inhibitory control. It is also well-established that CPM is impaired in chronic pain patients suffering from back pain, fibromyalgia, or severe knee osteoarthritis (OA). Davies et al. demonstrated that restoring sleep could predict resolution of chronic widespread pain. However, the underlying mechanisms linking impaired sleep and a reduction in pain inhibition are still unclear. Certain neurotransmitters such as serotonin and brain areas such as the periaqueductal gray matter are known to modulate both sleep stages and nociception, and may partly explain the association between impaired sleep and reduction in pain inhibition.

Nonetheless, little is known about the effect of sleep impairment on central pain mechanisms in clinical cohorts. This is important since it is still unclear if restoring a good quality of sleep can modulate the central pain pathway changes known to occur when having impaired sleep and/or chronic pain.

One approach to this question is to assess patients known to suffer from sleep impairment. In this respect, obstructive sleep apnea (OSA) patients are known to present with worsened sleep due to the collapse of the pharyngeal musculature throughout the night. This leads to excessive daytime sleepiness and a decrease in quality of life. Furthermore, pain tolerance has been shown to be decreased in elderly who are diagnosed with OSA. However, little is known about OSA patients and pain sensitivity, and if the sleep impairment also affects the central pain pathways. If so, this may provide an important first step in understanding the possible benefit of restoring restoring normal regular sleep, as routinely achieved through gold standard treatment, and if this can modulate central changes known to occur in chronic pain patients.

Therefore, this project will focus on obstructive sleep apnea (OSA) patients to investigate if central pain mechanisms are affected by poor sleep and if golden standard sleep therapy through continuous positive airway pressure (CPAP) improves central pain mechanisms.

Inclusion Criteria:

• Men and women presenting with an apnea-hypopnea (AHI) index > 15 (moderate-to-severe sleep apnea) measured by cardiorespiratory monitoring (CRM) and scheduled for treatment at Søvncenter Nord
• Age 18-80

Exclusion Criteria:

• Pregnancy
• Intake of drugs labelled with the red warning triangle and misuse of cannabis and opioids
• No previous or current neurologic or mental illnesses
• Lack of ability to cooperate
• Non-fluent in Danish (reading, speaking, and comprehension)

Men and women presenting with an apnea-hypopnea (AHI) index > 15 (moderate-to-severe sleep apnea) measured by cardiorespiratory monitoring (CRM) [10] and scheduled for treatment at Søvncenter Nord