Association between slow wave sleep and blood pressure in insomnia.

Study objectives: The majority of patients with insomnia exhibit abnormal sleep in objective testing (e.g., decreased sleep duration, decreased slow wave sleep (SWS). Previous studies have suggested that some of these objective measures of poor sleep, such as decreased sleep duration, are associated with a higher risk of hypertension in insomnia. We examined the relationship between SWS and morning and evening blood pressure (BP) levels in patients with clinically diagnosed insomnia.

Methods: A total of 229 normal sleepers and 1378 insomnia patients were included in this study. Insomnia was defined based on standard diagnostic criteria with symptoms lasting ≥6 months. All subjects underwent in-laboratory polysomnography. Patients were classified into quartiles of percent SWS. Evening and morning hypertension were defined using BP measurements taken in the evening before and in the morning after polysomnography, respectively. Multivariable logistic regression models were used to assess the relationship between insomnia, SWS and hypertension.

Results: Insomniacs with <3.5% SWS (OR 3.27, 95% CI 1.31-7.66) and those with 3.5-10.2% SWS (OR 2.38, 95% CI 1.28-5.91) had significantly greater odds of morning hypertension compared to normal sleepers. No associations were seen in insomnia with 10.2-15.8% SWS and with >15.8% SWS. Significant effect modifications by sex (p=0.043) were found, as decreased SWS was associated with morning hypertension only in men. Odds of evening hypertension were not significantly associated with SWS.

Conclusion: Decreased SWS is associated with morning hypertension in a dose-dependent manner in insomnia, especially in men.