People with sleep-disordered breathing were less likely to experience a normal nighttime decrease in systolic blood pressure and were at increased risk of adverse cardiac and other outcomes, according to a new prospective study.
Data from a previous study showed that most people experience a 10%–20% dip in blood pressure at nighttime (Hypertension 1995;26:60-9). Other data have shown an association between sleep apnea syndrome and a failure to experience the beneficial nighttime decrease in blood pressure, but the evidence is limited to cross-sectional studies (Am. J. Hypertens. 2001;14:887-92; Chest 2002;122:1148-55).
The current study's findings are important because “nocturnal nondipping” associated with sleep-disordered breathing (SDB) has been linked in earlier studies to target organ damage and a poor cardiovascular prognosis (Can. J. Cardiol. 2007;23:132-8; JAMA 1999;282:539-46).
Dr. Khin Mae Hla and her associates of the departments of medicine and population health sciences at the University of Wisconsin, Madison, assessed 328 adults in the ongoing Wisconsin Sleep Cohort Study. Mean patient age was 49 years, 63% were men, and the mean body mass index was 29 kg/m
The chances of developing systolic non-dipping were significantly correlated with baseline SDBseverity in a dose-response fashion. Patients scoring less than 5 on the Apnea-Hypopnea Index (no or minimal SDB) were used as a reference group. Those with mild SDB (score of 5 to 15) were three times as likely to develop systolic nondipping (adjusted odds ratio, 3.1), and those with moderate to severe SDB (score of 15 or greater) were more than four times as likely to develop systolic nondipping (OR, 4.4). The researchers controlled for possible confounders, including age, gender, body mass index, smoking, and alcohol use. Use of continuous positive airway pressure (CPAP) by 11 patients, antihypertensive medication use (42 patients), and inclusion of 8 patients with a history of cardiovascular disease did not significantly alter the findings, though inclusion of the CPAP patients was a possible limitation of the study, said the researchers. Grants from the National Institutes of Health helped fund the study.