Ask the Doctors November 2011 Issue

Ask The Doctors: November 2011

I recently saw a news item about how people who don’t spend a lot of time in the deeper stages of sleep are at a greater risk of developing high blood pressure. I have slightly elevated blood pressure, but I do wake up a few times a night. Will poor sleep make it harder to manage my blood pressure?

You are correct. A recent study demonstrated a connection between difficult-to-control hypertension and two factors: less total sleep, and less time spent in rapid eye movement (REM) sleep. It has been known for a long time that sleep disorders such as obstructive sleep apnea (OSA) can predispose people to high blood pressure. This is probably because people with OSA experience multiple nocturnal episodes of low oxygen, or “hypoxia,” in their bloodstream.

Hypoxia leads to the release of adrenaline-like substances in the blood, which over the long term can lead to higher blood pressure.  Also, it does not help that most people with OSA are overweight, and being overweight is an independent risk factor for hypertension.

For patients suffering from OSA, the most useful plan is to make serious efforts at weight loss, and to utilize continuous positive airway pressure (CPAP) or bilevel positive airway pressure (BiPAP) to treat the sleep apnea. As you suggest, milder sleep disturbances such as decreased REM sleep could worsen your blood pressure control.
 But this is not an issue that requires major academic focus. The best way to avoid such sleep problems is, quite simply, to tire yourself out enough during the day.  If you engage in daily, vigorous exercise, and avoid napping, your quality of sleep at night should be much better. And then you should not require pharmacologic sleep aids, either. If possible, try to exercise in the morning, as that has been shown to improve your body’s sleep rhythms. Exercise late at night may raise your body temperature, making it more difficult to fall asleep.

I have been prescribed beta-blockers to help treat my recently diagnosed atrial fibrillation.  But I’ve known people who have taken beta-blockers for migraines and others who take them to calm nerves during panic attacks.  How can one medication treat so many different problems?  How do these drugs really work?

Have you ever seen an angry cat—back arched, hissing with muscles all aquiver, pupils dilated, hair on end, claws extended, and ready to attack or beat a hasty retreat at any minute? To me, that animal is the ultimate living example of what physicians refer to as the Sympathetic Nervous System (SNS), also known as the “fight or flight” response. In the human body, the effects of the SNS are to increase heart rate, blood pressure (BP), blood flow to vital organs, muscle tension, and reaction time. Just as for the feline, these effects can often spell the difference between survival and death.  However, if the SNS is overactive at other times, the results can be detrimental.

High BP can be due, in part, to an overactive SNS. Signals from both the bloodstream and from nerves overstimulate “beta-adrenergic receptors,” tiny molecules on the surfaces of cells that transmit signals to the inside. This leads to higher heart rate, higher force of cardiac contraction, and higher BP. Beta-blockers can help reduce BP by blocking these signals before they can reach the inside of cells.  You mentioned that you take beta-blockers to treat atrial fibrillation—in this case, the drug yields benefit by reducing the heart rate. Migraine headaches can be prevented by beta-blockade, probably by preventing spasm of blood vessels. Beta-blockers can also reduce tremors (remember the trembling cat?), thus helping people with panic attacks and performance anxiety. Although beta-blockers sometimes exert adverse effects such as fatigue and sexual dysfunction, when prescribed appropriately they can certainly play an important role in the treatment of human disease.