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Sleep Medicine Update: June 2012 (Review)
Want to keep up with sleep, without falling asleep? We'll try to make it easy for you: Here are some of the latest and most notable articles in sleep medicine. (This summary will be updated and re-posted as new research is published. Please suggest articles for inclusion in the comments or by email.)
Obstructive Sleep Apnea (OSA) and Cardiovascular Risk
Obstructive sleep apnea (OSA) is associated with increased cardiovascular risk, based on the results of non-randomized, observational trials [1, 2, 3]. Treatment of moderate and severe OSA with continuous positive airway pressure (CPAP) is associated with a reduction in cardiovascular risk; this association also derives from observational, non-randomized trials [4, 5]. OSA's contribution to cardiovascular risk, independent of the comorbidities common to OSA (obesity, metabolic syndrome, etc.), cannot be determined with confidence; this is because randomizing symptomatic OSA patients to no treatment is unethical given treatment's certain benefits on cognitive function, accident & injury risk, etc.
CPAP may improve the parameters of the metabolic syndrome (obesity, dyslipidemia, and insulin resistance). Among 90 patients with severe, symptomatic OSA (AHI ~48 and daytime somnolence) randomized to CPAP or sham CPAP for 3 months, then crossed-over, those receiving "real" CPAP had statistically significant declines in body mass index (BMI), body fat, total cholesterol, LDL and triglycerides, and hemoglobin A1C levels [NEJM 2011].
Whether someone with obstructive sleep apnea feels sleepy during the day might influence their cardiovascular risk. Among 723 patients in Spain with moderate OSA but without daytime sleepiness (apnea-hypopnea index or AHI > 19; Epworth Sleepiness Scale < 11), who were randomized to receive either CPAP therapy or no intervention, there was no statistically significant difference in the rate of new onset (incidence) of hypertension or cardiovascular events (including acute coronary syndrome, stroke, TIA, or heart failure) after ~4 years of follow-up. However, there were numerically more cases of hypertension and cardiovascular events in the control group, including more serious events (e.g., 8 vs. 2 nonfatal myocardial infarctions) and the study may have been underpowered to detect an important difference. [Barbe, JAMA 2012]
Obstructive Sleep Apnea (OSA) and Hypertension
An impressive body of observational evidence suggests that untreated obstructive sleep apnea causes or worsens hypertension, but OSA's effect on blood pressure overall is quite low. A recent paper showed that people with OSA who were intolerant or noncompliant with CPAP were about 1.5 to 2 times more likely to develop hypertension over 12 years of follow-up, compared to controls without OSA. People with OSA who used CPAP developed hypertension less often during the study than controls without OSA (hazard ratio = 0.71). [Marin, JAMA 2012]
Due to the research limitations described above, it has so far been impossible to prove OSA causes hypertension. People who are noncompliant or intolerant of CPAP may be different in unmeasured ways (and therefore more likely to develop high blood pressure) than people who use CPAP.
In the above-mentioned JAMA trial, most people with OSA (almost 2/3) did not develop hypertension over 12 years. Treatment of obstructive sleep apnea with CPAP results only in very small reductions in blood pressure -- about 2-4 mm Hg in systolic and diastolic blood pressure, on average. [Barbe, AJRCCM 2010; Sharma, NEJM 2011]
Exercise Can Improve Obstructive Sleep Apnea (OSA)
Most patients with OSA are obese and sedentary, and many will not exercise. However, those that do may experience a significant improvement in their obstructive sleep apnea severity and symptoms, even without significant weight loss. Among 43 patients randomized to 2.5 hours of exercise per week or placebo (stretching) for 12 weeks, the exercisers experienced a decline in AHI from ~32 to ~25/hr, without losing weight; the "stretchers" had no change in AHI. [Sleep 2011] REFERENCES (more are in the above text's hyperlinks): Barbe F et al. Effect of Continuous Positive Airway Pressure on the Incidence of Hypertension and Cardiovascular Events in Nonsleepy Patients With Obstructive Sleep Apnea: A Randomized Controlled Trial. JAMA 2012;307:2161-2168. Sharma SK et al. CPAP for the metabolic syndrome in patients with obstructive sleep apnea. NEJM 2011 Dec 15;365(24):2277-86. Kline CE et al. The effect of exercise training on obstructive sleep apnea and sleep quality: a randomized controlled trial. Sleep 2011;Dec 1;34(12):1631-40.