Abstract-This study examined the effect of continuous positive airway pressure (CPAP) treatment on blood pressure in patients with obstructive sleep apnea. Thirty-nine patients with sleep apnea were studied. Ambulatory blood pressure monitoring was obtained before and after patients were randomized to receive either 1 week of CPAP or placebo CPAP (CPAP administered at ineffective pressure). Blood pressure was examined over daytime hours (6 AM to 10 PM) and during nighttime hours (10 PM to 6 AM). Daytime mean arterial blood pressure decreased significantly but equally in both the active treatment group and the placebo treatment group (Pϭ0.001). Nighttime mean arterial pressure levels decreased to a much greater extent over time in the patients who received active CPAP treatment (Pϭ0.032). CPAP does appear to decrease nighttime blood pressure. However, the decrease in daytime blood pressure may reflect a nonspecific response (ie, placebo), since both the active treatment group and the placebo treatment group developed comparable decreases in blood pressure. Treatments for OSA are multiple, but, after weight loss, the most commonly used treatment is nocturnal continuous positive airway pressure (CPAP). The great majority of OSA patients can have their apnea successfully treated with this methodology. 5 Because of the comorbidity of hypertension and OSA, many investigators have examined how CPAP affects BP levels. 6 -19 Table 1 summarizes these endeavors. As the table suggests, many of the studies report a beneficial effect of CPAP on BP. The studies suggest that CPAP acutely decreases nighttime BP in hypertensive OSA patients but not in normotensive patients and that longer-term use of CPAP decreases both nocturnal and diurnal BP. However, certain design aspects are striking. The studies generally have a small sample size (average of 14 patients per study), and most of them use neither randomization nor a control group. Most studies combined normotensives and hypertensives, and many hypertensives were studied while they were receiving antihypertensive treatment. Few studies examined patients in the absence of antihypertensive medication. Most studies did not describe how they dealt with data from patients who were noncompliant with the CPAP treatment.Only half of the studies used ambulatory blood pressure monitoring (ABPM). ABPM techniques acquire a more complete and representative sample of BP readings than would be obtained by casual BP measurement in the physician's office. In addition, ABPM allows examination of BP patterns in awake and in sleeping patients.Most notably, only 1 study used a placebo control (an oral placebo) for CPAP, and that study found no effect of CPAP on 24-hour ambulatory BP. 8 BP is notoriously influenced by nonspecific effects. The CPAP apparatus itself could be a very powerful stimulus for placebo responses. For this reason, we performed a double-blind placebo trial of CPAP versus placebo CPAP on BP as gauged by ABPM. MethodsPatients were located by public advertisements and word-of-m...

Abstract-Investigators have reported variable findings regarding the role of race in diurnal blood pressure patterns. We performed a review and meta-analysis of this literature to identify the overall effect of race on circadian blood pressure patterns. Eighteen studies involving 2852 participants were reviewed. Meta-analyses were conducted using effect sizes calculated from the data provided directly in the study reports. Separate meta-analyses were conducted on effect sizes for differences between blacks and whites in daytime and nighttime systolic and diastolic blood pressure and nocturnal dip in systolic and diastolic blood pressure. To evaluate discrepancies in findings from studies involving American versus non-American blacks, overall meta-analyses as well as within-subset meta-analyses of black/white differences were conducted for comparisons involving American and non-American blacks. Results of overall meta-analyses indicate that blacks experience higher levels of systolic and diastolic blood pressure, both at night and during the day. These differences were significantly greater at night than during the day (PϽ0.05). Results of within-subset analyses involving American blacks mirrored those for all black/white comparisons, except that the effect of race on nocturnal dip, ie, that American blacks experienced less of a dip in both systolic and diastolic blood pressure at night, was significant (PϽ0.05). In contrast, the effect of race on nocturnal dip was not significant for comparisons involving non-American blacks. These results suggest a consistent difference in the chronobiology of blood pressure, particularly in American blacks. (Hypertension. 1999;33:1099-1104.)

The possibility of ethnic differences in sleep architecture was initially examined in conjunction with studies of sleep apnea (study 1). This possibility was then examined in another cohort of patients to determine whether the results might generalize (study 2). Polysomnography was obtained in both cohorts as part of larger protocols investigating sympathetic nervous system activity, blood pressure, and sleep. Sleep monitoring took place in an inpatient clinical research center of a university hospital. Study 1 focused on sleep apnea physiology and involved volunteers with sleep apnea who were otherwise healthy. Study 2 focused on differences in stress reactivity between American Black and White subjects and involved hypertensive and normotensive volunteers who were otherwise healthy. Analyses include 61 participants from study 1 and 35 participants from study 2. Ethnicity in both cohorts was determined by self-report. Participants in both studies were monitored during sleep with traditional polysomnography including electroencephalography (EEG), electromyography (EMG), electrooculography (EOG), and oximetry. In Study 1, Blacks had longer TST (P < 0.01), more REM sleep (P < 0.05), and less WASO (P < 0.05) than Whites. After controlling for RDI, Blacks had longer TST and spent a smaller percentage of time in deep sleep (P < 0.05). In study 2, Blacks had longer TST and REM sleep, lower percent deep sleep, and lower percent deep sleep controlling for RDI (P < 0.05). In two separate studies, Blacks had longer TST, more minutes of REM, and lower percentage deep sleep. These findings suggest possible ethnic differences in sleep architecture.