Sleep Apnea Raises Blood Pressure
MADISON - When you stop breathing during sleep, it doesn’t just raise your frightened bed partner’s blood pressure.
Expert commentary in journal calls sleepers with apnea "ticking time bombs" for heart disease.
A new study by researchers from the University of Wisconsin School of Medicine and Public Health (SMPH), in the June issue of the journal Sleep, found that sleepers who had periods of interrupted breathing during sleep were more likely to lose the expected drop in nighttime blood pressure. What physicians call "non-dipping" of their nighttime blood pressure is a cause for concern.
"Blood pressure normally varies from daytime to nighttime,’’ explains lead researcher Dr. Mae Hla, professor of medicine at UW SMPH. "Normally, when a person goes to sleep, blood pressure should drop by 10 to 20 percent of the daytime pressure."
This nighttime drop may help protect the body against bad cardiovascular events. And blood pressure that fails to drop at night is associated with hypertension, heart attacks and stroke.
People with obstructive sleep apnea are "ticking time bombs" for developing cardiovascular disease, notes a commentary in Sleep that highlights the new research findings from Wisconsin.
"We know that sleep apnea is related to bad cardiovascular outcomes such as hypertension, heart failure and strokes," Hla said. "Nocturnal non-dipping may be a biological marker for the development of cardiovascular problems in people with sleep apnea."
Hla and her colleagues looked at data from patients in the long-running Wisconsin Sleep Cohort, a study which has been measuring the sleep patterns of healthy volunteers since 1989. Using data from 328 members of the sleep cohort group, the authors showed that people who had sleep apnea or hypopnea – periods when they stopped breathing or when air flow was greatly reduced, causing blood oxygen levels to drop – often went on to develop "non-dipping" of nighttime systolic blood pressure when researchers tested them again an average of 7.2 years later.
In fact, the research showed that sleep apnea caused "non-dipping" to occur. Sleepers who had between five and 15 apnea or hypopnea events per hour of sleep were three times more likely to have "non-dipping" compared to those without sleep apnea when they were retested years later. Sleepers with more than 15 apnea events per hour were more than four times as likely to develop the condition compared to those without the sleep breathing disorder.
While apnea and cardiovascular problems have been linked before, this is the first study that shows people with apnea who start out with normal nighttime blood pressure had developed the "non-dipping" blood pressure when rechecked several years later. Hla said the long-running nature of the Wisconsin Sleep Cohort study makes such work possible.
"This data set is rich with information and it is important to be able to ask the right questions,’’ she said. "The next step will be to determine if the non-dippers in the cohort develop cardiovascular diseases at a rate higher than those who have normal dipping."
Hla’s co-authors on the study are the Wisconsin Sleep Cohort Study director Terry Young, professor; Paul Peppard, assistant professor; Mariana Szklo-Coxe, scientist; and Maryan Stubbs, researcher, all of the population health sciences department at Wisconsin.
Date Published: 06/13/2008