Week: 610.6

Guest: Prof. Thomas Bixler, Penn State University Hershey Med. School

Topic: Sleep Apnea

Host/Producer: Steve Girard

NEMA: Sleep apnea...do you know what it is, or what it does? Many of us don’t, but this condition can affect your cardiovascular health. Today, our guest is Professor Edward Bixler of the Penn State Hershey Medical School...who’s brought out some new aspects of the disorder in a recent study...

BIXLER: Sleep apnea is a problem where people stop breathing when they are asleep. There are basically two kinds of sleep apnea. One is where you continue to try to breathe...this is called ‘obstructive’, and the soft palate or the back of the throat collapses when you try to take a breath in. And the only way that you can get a breath in is to wake up. So, not only does it stop you from breathing, but it also wakes you up...so it’s causing very severe stress on your cardiovascular system, as well as very seriously disturbing your sleep. The other type of sleep apnea is called ‘central’, and this is where you just stop breathing, and you then start eventually and this doesn’t seem to have as strong an impact on your sleep as does ‘obstructive’, and it’s relatively infrequent.

NEMA: You found some things that are pretty surprising in your study...please tell us more about it....

BIXLER: What we did here was basically to look at the age distributions of individuals who have sleep apnea. Now, what’s in the literature, and what was common belief was that sleep apnea...the prevalence of sleep apnea increased with age. That is, it’s the elderly that are at most risk for sleep apnea. But when you look at a clinical sample, this is where patients come into the sleep laboratory to be treated, you seldom see an elderly person with sleep apnea. In other words, you don’t see a 75 or 80 year old...you typically see somebody around age 55. So, the basic question was very simplistic: Which distribution is correct? And we approached this with an epidemiologic study, where we first of all did a phone interview of men in the local area, and reviewed the symptoms related to sleep apnea, and these are things like: do they snore? ...are they overweight?...do they have hypertension?...do they have daytime sleepiness? From that sample, we brought into the lab a sample of 741. The reason that we brought them into the lab was that is that’s the only way that you can really diagnose sleep apnea. But we were able to over sample those that were at much higher risk, that is, those that had all of the symptoms of sleep apnea, we felt would be more likely to have sleep apnea, and in fact, that’s the way it worked out. Once we had the lab evaluations completed, we then looked at the age distribution of sleep apnea...well, first of all, we evaluated the presence of sleep apnea in two ways. First was just simply counting events, which is the way that most of the research studies are done. And this is to count the number of obstructive or central apneas, to count the number of hypotnias...

NEMA: Dr. Bixler, what is a hypotnia?

BIXLER: A hypotnia is where there is a partial restriction of airflow. It isn’t a complete cessation, but it’s a partial restriction. And all of these must last at least ten seconds. And with the hypotnia, there must also be a decrease in the blood level, the oxygen levels in the blood. An index is calculated called the apnea / hypotnia index, and this is based on the number of events divided by the number of hours the person is asleep. We then looked at the distribution by age of the apnea hypotnia index, and when we looked simply at the apnea/hypotnia index, we evaluated sleep apnea in a second way. One was based on a clinical definition, and this is where you have an apnea/hypotnia index that is greater than or equal to ten...that is you have at least ten events per hour of sleep...but the patient also had to have other symptoms, such as daytime sleepiness, various cardiovascular problems...for example, hypertension, had a stroke or these kinds of problems. In other words, the clinician was looking at the whole picture, not just simply counting events.

NEMA: What did you find when you looked into the levels of sleep apnea according to age?

BIXLER: When we looked at the age specific prevalence, based just on counting events...in other words just looking at the apnea/hypotnia index, we saw an increase with age in roughly a linear fashion. So, what other research studies found, we also found. When we looked at the clinically defined sleep apnea, in other words looking at the total clinical picture, rather than just counting events...we found an age distribution that peaked around age 55 and then began to decline. So, we began to look a little more carefully at what we were seeing here, to see if we could understand the data a little bit better, and when we eliminated the ‘central’ events from our index...in other words we looked at just the ‘obstructive’ apnea plus hypotnia and calculated an index based on that...we found that the age specific prevalence peaked around age 55 and then leveled off. Somewhat similar to the clinically defined sleep apnea. When we looked at the ‘central’ index, included ‘central’ apneas by the number of hours of sleep... this begins in middle age and increases with age. Now, we took this one step further, something that nobody has ever done before, and that is to look at severity. We measured severity of apnea in two ways, one is that there is usually a decrease in the oxygenation of the blood in response to an apnea. That is, when you stop breathing, the oxygen level in the blood drops. So, we looked at that as a measure of severity. We also looked at the number of events, or the apnea/hypotnia index, as a measure of severity. Now when we looked at those individuals that don’t have any apnea at all, we found that the oxygenation, or the saturation of oxygen in the blood, decreases slightly with age, which is kind of what you would expect. When you get older, you don’t function quite as well. When we began to look at various thresholds of the apnea/hypotnia index as a function of age, we found something very different. We found that severity decreased with age. That is, the most severe cases were in the young.

NEMA: So, what were the conclusions of these findings?

BIXLER: First of all, there appears to be two types of sleep apnea. One is basically age related, and this is perhaps being reflected by what we’re seeing in terms of ‘central’ apnea. Because this only begins in middle age and increases in the elderly. And the other type is more disease related. And this occurs more severely in the young, and if you think about this, there is an indication that sleep apnea does occur in families...suggesting perhaps genetic predisposition. So, what this may be suggesting is that the role of the genetic contribution has been underestimated, and the idea here is that those with a stronger genetic predisposition are going to express the disease younger and more severely. And those with the mildest predisposition are going to express it much later, and be extremely mild. The reason that we see this sort of peaking distribution in the clinical population can probably be explained by the fact that those who have the most severe disease, which occurs in the young, don’t survive. They’re dying of heart attacks due to hypertension or some other cardiovascular problem, and so those that we see that are elderly are more robust in some of these breathing problems, and are less vulnerable. So, the bottom line from this is that if someone has the symptoms of sleep apnea, and they’re young, this should be treated much more aggressively than in the older population. That’s not to say you shouldn’t treat the older population, it’s just that you should be more aggressive with the young.

NEMA: A lot of people may not make the connection between having interrupted breathing or sleep patterns at night...and cardiovascular health....

BIXLER: And this is a problem. The presence of snoring....especially in the young, not so much in the older population, but especially in the young is a strong indicator of a possible contribution to hypertension. This is something that needs to be followed up very carefully with...a physician. If there’s any indication of breath cessation or daytime sleepiness then the person should clearly be evaluated at a sleep laboratory to make sure they don’t have sleep apnea. But even if they just have snoring, their blood pressure at a minimum should be monitored regularly. And physicians should be asking questions about people who snore, especially in the young.

NEMA: What can be done to help the younger sufferer of sleep apnea?

BIXLER: Usually what’s associated with sleep apnea is overweight, so one of the first-line treatments of sleep apnea is weight loss...and this is very effective. Unfortunately, it’s very difficult for some people to lose weight...and it’s difficult for many individuals to keep the weight off once they’ve lost it. The other treatment is called CPAP, or Continuous Positive Airway Pressure..where an individual who, when they go to bed, will place a mask over their face which keeps the lungs inflated and won’t allow them to collapse or obstruct. And this is extremely effective, but the problem with it is compliance, because people, once they start feeling better, they don’t want to put the mask on at night when they go to sleep.

NEMA: So losing weight is the biggest key to halting the sleep apnea condition?

BIXLER: If you lose weight, you will improve your...or you can eliminate the sleep apnea, and/or snoring...just by simply losing weight. So, weight is a factor for sleep apnea. Weight is also a direct factor for hypertension. Sleep apnea and overweight in combination is a stronger...you have a stronger risk for hypertension than just either one alone.

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about the National Emergency Medicine Association. I’m Steve Girard at The Heart of the Matter.