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| Subscribe to Clinical Compass™ | VOLUME 2, ISSUE 5 - FEBRUARY 27, 2007 | |||||||||||||||||||||||||||
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FROM THE CLINICAL KNOWLEDGE CENTER Gender Influences on Sleep and Respiration in Patients with Obstructive Sleep Apnea Syndrome by Michelle Ostrander, PhD Next week (March 5th-11th) has been designated National Sleep Awareness Week by the National Sleep Foundation (NSF). The purpose of this event is to recognize the overriding importance and impact of sleep in our lives. A key focus of this year's National Sleep Awareness Week is gender differences and sleep. Clinical and epidemiologic research has revealed profound gender differences in both normal sleep and the risk of certain sleep disorders. Women exhibit better sleep quality than men with longer sleep times, shorter sleep-onset latency and higher sleep efficiency, yet women have more sleep-wake complaints than men. Insomnia and restless leg syndrome are more predominant in women, whereas obstructive sleep apnea syndrome (OSAS) is more prevalent in men, although this gap narrows in older patients. A recent retrospective study of Greek men and women diagnosed with OSAS sheds further light on the influence of gender on sleep quality and respiratory events in OSAS. Researchers at the Sleep Disorder Center at the University of Athens in Greece utilized polysomnographic data collected during the past 3 years to assess sleep architecture and respiratory events in OSAS patients referred to the center. A total of 1010 OSAS patients were included in the study with a male-to-female ratio of 5:1 (844 men and 166 women). Body mass index (BMI) did not differ between men and women (BMI=31.6±5.5 kg/m² in men versus BMI=32.5±8.1 kg/m² in women), but women were significantly older than men (56.9±10.6 vs. 50.6±11.7 years, P<.001). Of note is that 35% of male OSAS patients were less than 40 years of age, whereas only 13% of female OSAS patients fell within this age group. Several indices of sleep quality and architecture were calculated including total sleep time, sleep latency, sleep efficiency index (total sleep time divided by time spent in bed), rapid-eye movement (REM) onset latency, and wake after sleep onset (WASO, time spent awake during sleep period time). Apnea and hypopnea respiratory events per hour of sleep were determined. Hypopnea was defined as a decrease in the amplitude of respiratory effort to 10%-50% of baseline during sleep with a duration > 10 s that resulted in 4% reduction of hemoglobin saturation or an arousal. The apnea-hypopnea index (AHI) was calculated by dividing the number of apnea and hypopnea events by number of hours of sleep. AHI was determined during total sleep time, non-REM (NREM) sleep, and REM sleep. REM difference was determined by taking the difference between AHI in REM sleep less the AHI in NREM sleep. The researchers found that sleep quality in female OSAS patients was significantly worse as determined by several measures. In women, sleep efficiency was lower (79.4% vs. 85.1%, P=.001), sleep latency was prolonged (27.7±27.7 vs. 17.9±18.1 min, P=.0001), REM sleep latency was prolonged (161.5±76.2 vs. 145.7±71.4 min, P=0.018), and WASO was greater (42.6±46.5 vs. 30.7±34.9 min, P=.0003). Other measures of sleep quality did not vary by gender. Gender differences were also found in measures of respiratory events during sleep. Women exhibited shorter mean duration of respiratory events than men for total sleep time (18.6±3.9 vs. 21.4±5.6 s, P=.0001), for REM sleep (18.2±3.4 vs. 20.5±5.2, P=.001) and for NREM sleep (21.4±6.1 vs. 24.8±8.4, P=.001). Women exhibited a lower AHI during total sleep time than men (33.2±27.2 vs. 42.4±28.2, P=.001), as well as a lower AHI during NREM sleep than men (32.6±28.7 vs. 42.9±28.9, P=.001), although there were no gender differences in AHI-REM. For subjects that had REM sleep (651 men and 133 women), the "REM difference" was calculated. A positive REM difference was observed in a larger percentage of women than men (60.9% vs. 41.8%, respectively) and the REM difference was greater in women than in men (19.76±13.43 vs. 14.21±11.18, P=.0001). Overall, findings from this study demonstrate substantial gender differences in sleep quality and respiratory events in OSAS patients. One important finding that has emerged from this study is that obesity is not the only risk factor for developing OSAS. Weight did not differ between male and female OSAS patients, but female patients were older than male patients. This raises the intriguing possibility that increased age and female hormonal status are modifying factors for OSAS in women, perhaps via hormonal effects on upper airway muscle activity. One limitation of this study is that data for menopausal status of female patients were not available from the medical records, which limits the interpretation of the influence of hormonal status on these polysomnographic findings. Another drawback of this study is the lack of data on the prevalence of insomnia in these patients, which could limit interpretation of greater WASO time in women given that insomnia is generally more prevalent in women than men. The researchers note that data from this retrospective study differ markedly in certain respects from the findings of Spanish and North American studies on gender differences in OSAS, and they thus recommend future prospective general population-based studies to better define the nature of clinical features of OSAS. Do you have feedback for the author? Click here to send us an email. References
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