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Refractory Hypertension in African-Americans: Sleep Apnea May Double Risk (CME/CE)


Action Points

  • Untreated moderate or severe obstructive sleep apnea may contribute to resistant hypertension in African-Americans.
  • Study results lend further support to guidelines encouraging OSA screening in patients with hypertension.

CME Author: Zeena Nackerdien

Study Authors: Dayna A. Johnson, S. Justin Thomas et al.

Target Audience and Goal Statement

Sleep specialists, pulmonologists, and internists

To comprehend the association of sleep apnea with uncontrolled blood pressure (BP) and resistant hypertension in African-Americans.

Questions Addressed

Aberrant sleep patterns (e.g., short and excessive sleep duration and poor sleep quality) and sleep disorders are associated with a range of chronic conditions (high blood pressure, obesity, cardiovascular diseases [CVD], diabetes mellitus, and stroke) and all-cause mortality. Ongoing studies underscore concerns regarding safety that was first raised when major industrial disasters such as the Exxon Valdez oil spill was first associated with inadequate sleep; however, according to Alex Krist, MD, vice-chair of the US Preventive Services Task Force: “We don’t know as much about the benefits of treating sleep apnea as we should.”

Obstructive sleep apnea (OSA) is a common sleep breathing disorder marked by partial (hypopnea) or complete (apnea) blockage of airflow during sleep. The result is heavy snoring, choking, and gasping for air. Several studies have shown that continuous positive airway pressure (CPAP) therapy, the standard of care for OSA, is associated with (1) a CVD risk reduction of 64% ; (2) reduced brain injury and cognitive dysfunctions ; (3) increased workplace productivity; (4) improved hemodynamic functions and metabolic diseases; and (5) reduced OSA morbidity and early mortality.

Lead author of the current study, Dayna A. Johnson, PhD, MPH, MS, MSW, a postdoctoral research fellow at Brigham and Women’s Hospital and Harvard Medical School, made the following comments in a separate release preceding this analysis: “African Americans experience a disproportionate burden of numerous health problems, including obesity, diabetes, hypertension, and CVD, all of which have been shown to be associated with sleep. It seems plausible that sleep apnea and insomnia are important risk factors contributing to these health disparities.”

While a prior investigation assessed the link between OSA and uncontrolled BP among a population of African-Americans, the outcomes were based on questionnaires. There is therefore a need to examine objectively measured sleep apnea (based on the respiratory event index) and a key physiological stress of OSA, nocturnal hypoxemia, in relation to uncontrolled BP and resistant hypertension among blacks with hypertension. The study aim was to test whether OSA and its related hypoxemia burden would be linked with more severe forms of hypertension.

Study Synopsis and Perspective

The Jackson Heart Study involved more than 5,300 African-American residents of Jackson, Miss. It was the largest single-site prospective investigation of CVD undertaken in African-Americans. During 2012 and 2016, Jackson Heart Sleep Study participants (n=913) underwent an in-home Type 3 sleep apnea study, clinic blood pressure measurements, and anthropometry. Home-based sleep testing was done using a validated device (Embletta-Gold device, Embla, Broomfield, CO) to objectively identify OSA.

The apnea-hypopnea index (AHI) was used to define sleep apnea. Mild, moderate, and severe sleep apnea were associated with AHI indices of >5, >15, and >30, respectively.

Nocturnal hypoxemia was quantified as percent sleep time with <90% oxyhemoglobin saturation. This study sample was restricted to participants with hypertension (high BP, use of antihypertensive medication, or self-reported diagnosis).

Prevalent hypertension was defined as either a systolic BP ≥130mmHg or diastolic BP >80mmHg, use of antihypertensive medication, or self-report of a diagnosis of hypertension. Uncontrolled blood pressure was defined as systolic BP ≥130 mmHg or diastolic BP ≥80 mmHg with use of one or more classes of antihypertensive medication. Resistant BP was defined as systolic BP ≥130 mm Hg or diastolic BP ≥80 mm Hg with the use of three or more classes of antihypertensive medication (including a diuretic), or use of four or more classes of antihypertensive medication regardless of BP level.

Multinomial logistic regression modelling was used to determine the association between OSA severity and uncontrolled BP or resistant hypertension after adjustment.

The analysis had data on 664 sleep study participants who were predominantly female (69.1%), obese (58.6%), and college educated (51.3%). A little over a quarter (25.7%) had OSA that was untreated (94%). About half (48%) had uncontrolled hypertension and 14% had resistant hypertension.

The authors reported that OSA and <90% oxyhemoglobin saturation were not associated with uncontrolled BP. However, severe OSA was associated with a 3.5-fold increase in risk for resistant hypertension in the unadjusted analysis.

After adjustment for relevant confounders, participants with moderate or severe OSA were twice as likely to have resistant hypertension (OR 2.04, 95%, 1.14-3.67), reported Dayna Johnson, PhD, of Emory University in Atlanta, and colleagues.

Each standard deviation higher than <90% oxyhemoglobin saturation was associated with an adjusted odds ratio for resistant hypertension of 1.25 (95% CI 1.01-1.55), they wrote in Circulation.

The findings suggest that untreated OSA may be an important contributor to resistant hypertension in a high-risk African-American population, Johnson told MedPage Today.

“This study identifies a risk factor for hard-to-control hypertension that until now has gone under-recognized in African-Americans,” she noted, adding that the findings are particularly important given the disproportionately high rate of uncontrolled high blood pressure (BP) among blacks.

African-Americans have the highest prevalence of hypertension of any racial or ethnic group in the U.S., and they have a 90% higher odds of having uncontrolled high blood pressure than non-Hispanic whites. Johnson said and stated that the reasons for this disparity are not well understood.

“We know that African-Americans tend to have higher rates of severe sleep apnea, so it made sense to look at poor sleep as a possible contributing factor to resistant hypertension,” she explained.

Study strengths include the large, African-American, community-based sample size, and use of home sleep testing to objectively assess OSA. Johnson said the lack of geographical diversity among the African-American participants limits generalizability.

Source Reference: Circulation, Dec. 10, 2018, DOI: 10.1161/CIRCULATIONAHA.118.036675

Study Highlights: Explanation of Findings

Estimates of resistant hypertension in the U.S. range from 9% of all adults to 19%; the latter percentage pertains specifically to African-Americans. Moderate to severe OSA was very common in study participants with hypertension, with a prevalence of 26% and was mostly undiagnosed (6% of participants with OSA reported a prior diagnosis). The proportion of individuals with hypertension was 15%. After adjusting for confounders, the investigators noted that moderate or severe OSA were associated with resistant hypertension.

“We looked at African-Americans in Jackson, Mississippi and the people in our cohort were not all that representative of African-American’s overall in the U.S.,” Johnson said. “Most were women and their ages were similar (mean age 64.9 ± 10.6), and about half had college degrees.”

She said studies in more diverse populations of African-Americans and other races are needed to determine if the findings are generalizable.

“I suspect that undiagnosed or untreated sleep apnea contributes to resistant hypertension in everyone, but African-Americans may be more sensitive to this,” Johnson said. “This could partially explain resistant hypertension in this population.”

The researchers did not examine the potential mechanisms to explain how uncontrolled OSA may affect BP, but earlier research suggested that it caused BP spikes during the night while BP remained higher during the day.

“The findings add to the understanding of how poor sleep and sleep disorders influence cardiovascular risk,” said Michael Twery, PhD, of the National Heart, Lung, and Blood Institute (NHLBI) National Center on Sleep Disorders Research in Bethesda, Maryland, in a press statement. “This report underscores the need for studies to determine whether screening groups at high risk for sleep apnea, such as African-Americans, would facilitate early medical intervention and reduce the risk or severity of heart disease.”

Finally, the investigators suggest that “future studies should test whether diagnosis and treatment of OSA may be interventions for improving BP control and decreasing the burden of resistant hypertension among blacks.”

Salynn Boyles wrote the original story for MedPage Today.

  • Reviewed by
    Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner
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