Kristal Wong ’22, Neurological Sciences, 4/12/20

A man with obstructive sleep apnea (OSA) sleeping with a continuous positive airway pressure (CPAP) Machine. Source: Wikimedia Commons.

Imagine the poster child of an obstructive sleep apnea (OSA) patient, someone who frequently has periods of apnea – the cessation of breathing – during sleep due to the obstruction of upper airways. Chances are that you would think of an older, rather obese male. While experts cite that sleep apnea occurs three to five times more in men than in women, current data from Brigham and Woman’s Hospital warn us that these statistics may be a misrepresentation of the true sleep apnea distribution.2An American team led by Dr. Christine Won, director of the Women’s Sleep Health Program at the Yale University Medical Center’s Department of Sleep Medicine, suggests that differences in sleep patterns of female OSA patients may cause variability in the diagnosis, leaving less females to be diagnosed with OSA.1

OSA is defined by AHI4P, apnea-hypoxemia index of 4% desaturation hypopnea criterion. An AHI4P frequency greater than or equal to 15 times per hour during sleep is the threshold for OSA diagnosis.2 Typically, a diagnosis of OSA from a sleep pulmonologist requires a sleep study to track the instances and duration of apnea and levels of oxygen, a measurement of good breathing, in a patient during sleep. If diagnosed with OSA, a patient is typically instructed to sleep with a continuous positive airway pressure (CPAP) machine. A CPAP machine helps the body to breathe by creating a pressurized vacuum to help release carbon dioxide from the body. These machines are needed for patients with OSA as obstructions in their upper airways prevents the body from removing CO2 from the body. In this study, Won and her team also included data from polysomnography (PSG), a tool that also tracks sleep stages but is not typically used by professionals in OSA diagnosis, to track the oxygen levels and apnea instances of her atherosclerotic patients with OSA or OSA-like symptoms.2

In the study with 2,057 men and women, they found that a 57% diagnosis rate for both groups when considering an AHI3P (3% desaturation vs. 4% desaturation with AHI4P) OSA diagnosis criteria for her cohort, but only during REM sleep, an important stage of sleep characterized by rapid eye movements.2 This finding suggests the contrary to established data: women were just as likely to be diagnosed with OSA as men. Won and her team studied the REM phase because they believe that the REM period holds two significances towards general health. First, they suggest that OSA symptoms of apnea and desaturations during REM sleep pose the greatest cardiovascular risk during this stage of sleep.1Second, they allude to the fact that women tend to wake up more frequently during the night due to a lower arousal threshold during non-REM sleep, but not during REM sleep.2 For OSA patients, this seemingly natural evolutionary pressure could cause females to wake up before incidences of apnea and desaturation occur, resulting in less OSA episodes than meets current OSA criteria. Since women are less likely to have interruptions during REM sleep, they are more likely to have uninterrupted episodes of apnea. Thus, criteria based solely on REM sleep phases would more accurately record episodes of apnea for women.2

Furthermore, by including instances of OSA episodes during REM and non-REM sleep stages, current testing is not taking into account the variability of female OSA phenotypes. The lack of OSA diagnosis could risk millions of women from receiving proper treatment. Additionally, these women may not be aware of their heightened risk for cardiovascular disease. Therefore, proper diagnoses of OSA with revised criterion that account for the gendered difference, such as hormones changes and sleep-arousal thresholds, should be implemented in OSA testing.2 This gender inequality inherent in the healthcare system is something that we must recognize and mitigate as evinced by the need for proper diagnosis of possible life-threatening conditions such as OSA that does not solely rely on the mechanics of one type of body.

 

References:

  1. Wallace, C. (2020, April). Sleep Apnea is DIfferent for Women. Scientific American, 355(4), 25.https://www.scientificamerican.com/article/sleep-apnea-is-different-for-women/
  2. Won, C. H. J., Reid, M., Sofer, T., Azarbarzin, A., Purcell, S., White, D., Wellman, A., Sands, S., & Redline, S. (2019). Sex differences in obstructive sleep apnea phenotypes, the multi-ethnic study of atherosclerosis. SLEEPJ, XX, 1–8. https://doi.org/10.1093/sleep/zsz274