ARTICLES

Cardiovascular consequences of Sleep Apnea

Related research into sleep apnea has long noted that patients with Obstructive Sleep Apnea (OSA) also tend to present with hypertension (high blood pressure).

The reasons for this link have been explored by a number of different studies in an attempt to determine whether one condition inexorably leads to the other, or whether they simply have related causal factors.

A recent study by Bradley and Floras from the Sleep Research Laboratory at the Toronto Rehabilitation Institute, Canada, has tracked the consequences of blood oxygen desaturation caused by frequent nocturnal apneas.

They found that OSA exposes the cardiovascular system to cycles of hypoxia, exaggerated negative intrathoracic pressure, and arousals.

These noxious stimuli can, in turn, depress myocardial contractility, activate the sympathetic nervous system, raise blood pressure, heart rate, and myocardial wall stress, depress parasympathetic activity, provoke oxidative stress and systemic inflammation, activate platelets, and impair vascular endothelial function.

Epidemiological studies have shown significant independent associations between OSA and hypertension, coronary artery disease, arrhythmias, heart failure, and stroke.

In randomised trials, treating OSA with continuous positive airway pressure lowered blood pressure, attenuated signs of early atherosclerosis, and, in patients with heart failure, improved cardiac function.

Current data therefore suggest that OSA increases the risk of developing cardiovascular diseases, and that its treatment has the potential to diminish such risk.

Clearly the cycles of oxygen desaturation which result from sleep apnea have consequences on the heart and circulatory system. Further research is required to determine the consequences of this on other major organ systems and on cognitive function which are also know to be impacted by blood oxygen desaturation.

The study appears in The Lancet, 2009

Sleep Apnea and Driving

Sleepiness is a key symptom of obstructive sleep apnea and is often the reason that a sufferer first seeks medical help. We know from research that sleepiness behind the wheel increases the chance of traffic accidents. Once the link between alcohol and road accidents was demonstrated, new tighter laws were introduced (and enforced) to deter drink-driving. Is sleepy-driving next?

It is already a requirement of many Australian states that all medical conditions which are likely to impact upon driving ability must be reported to licensing authorities. But, recent moves to identify sleep apnea in professional drivers in the US are being closely monitored and may be followed by road traffic authorities in Australia.

Truck drivers and other professional drivers in the US may soon be required to participate in a sleep study to screen for obstructive sleep apnea before they receive their certification.

Maggi Gunnels, director of medical programs for the US Federal Motor Carrier Safety Administration, recently confirmed that the Administration’s medical review board is expected to recommend that a sleep study be required for professional drivers who are of a predetermined level of obesity. Those who test positive for OSA would be required to treat the condition with surgery or CPAP before being certified.

Professional drivers associations are expected to oppose this recommendation based on weight, unless a “direct causal relationship” between a truck driver’s obesity and OSA is clear.

But further research just published in the Journal of Occupational and Environmental Medicine reiterates the findings and demonstrates a link between obesity in truck drivers, untreated OSA and an increased incidence of accidents. There is also a strong body of research which directly links obesity to OSA, with an estimated 80% likelihood.

This whole issue must seem like a Pandora’s box to traffic authorities. If professional drivers are screened to make sure OSA is treated, would the police or traffic authorities then have to monitor CPAP compliance? How would this be done? Would there be random tests of some type, CPAP machine data reviews at the road-side or some form of on-line monitoring?

As so often happens, professional drivers are in the spotlight not because they are the biggest cause of problems, but because they are relatively easy to reach. They need a special license for their job and their livelihoods depend upon complying with the terms of the license. But professional drivers account for only a small percentage of road accidents.

What about the vast majority of road users who are not professional drivers? They are as likely to be obese, as likely to have sleep apnea and may be more likely to drive while sleepy How would they be policed?

The issue will probably filter down through tightening laws and through the denial of insurance claims – when someone is shown not to have exercised their duty of care to others by recklessly ignoring a medical condition that results in an accident, they will foot the bill.

The fact is that if you have OSA, or if you are sleepy during the day or if you drift off or fall asleep while driving, you must find a way to treat it. Surgery can work. And CPAP, with a comfortable and effective mask, is a simple and life-sustaining option.

What is clear is that sleepiness, whether caused by a medical condition or simply by not being alert, is a major and preventable cause of road accidents. While the authorities are increasingly aware of this as a potential means of addressing the road toll, it is individual responsibility that is the key to solving the problem, just as it was with drink-driving. A drink-driving charge is not cool, funny or socially acceptable in any sense.

Falling asleep behind the wheel should not evoke sadness or sympathy. Any driver, whether professional or not, who puts themselves, their passengers and other road users in danger is quite simply the same as a drink-driver. Do it and you’re “a bloody idiot”.

Expanding Waist Worsens Kids’ Sleep Apnea

For children who have trouble breathing during sleep, gaining weight around the middle may make things worse, new research shows.

Approximately 2 percent of children have Obstructive Sleep Apnea (OSA), which is frequently treated by removing the tonsils and adenoids.

Gaining weight is known to worsen OSA in adults, but this relationship has not been demonstrated before in children.

It’s not clear what factors increase the likelihood that a child with mild OSA will experience worsening of their symptoms, Dr. A. M. Li and colleagues point out in a report in the medical journal Thorax.

To investigate, a team from The Chinese University of Hong Kong followed 56 children with mild OSA for two years. At the end of the study, they re-assessed 45 of the subjects and found that in 13 cases, the OSA had become worse.

The 13 children whose sleep apnea had worsened showed a greater increase, on average, in their waist size than the children whose condition hadn’t worsened.

In addition, more of the children who experienced a worsening of OSA had large tonsils at the study’s outset and at follow-up.

The study authors say children with mild OSA apnea and large tonsils, especially boys, should be followed closely so that any worsening of the condition can be detected early.

And, obviously, weight control is an important aspect of managing mild OSA in children.

The study appears in Thorax, 2010.

Study Describes Inverse Relationship Between OSA and Diabetes

We have known for some time that Obstructive Sleep Apnea (OSA) and diabetes have common causal factors. A number of studies have demonstrated that both OSA and Type II Diabetes occur together as part of metabolic syndrome.

Researchers at the University of Chicago recently demonstrated “for the first time that there is a clear, graded, inverse relationship between OSA severity and glucose control in patients with Type II Diabetes.”

That is, the more severe the OSA the more variable the level of glucose in the system.

Study author Renee S. Aronsohn, MD also concluded that undiagnosed OSA is common among patients with Type II Diabetes.

The researchers found 77% of subjects had OSA, with just 5 having previously had a sleep study. None were undergoing treatment. This finding points to a lack of understanding of the links between OSA and other common disorders, such as Type II diabetes.

After polysomnography, 38% of the study participants were classified as having mild OSA, 25% had moderate OSA, and 13% had severe OSA.

Relative to patients without OSA, the presence of mild, moderate, or severe OSA significantly increased mean adjusted HbA1c values (the main glycaemic control marker in diabetes) by 1.49%, 1.93%, and 3.69%, respectively.

According to the study authors, these effect sizes are comparable to those of widely used diabetes medications, meaning that having OSA may negate or reduce the beneficial effects of some hypoglycaemic drugs.

“Our findings have important clinical implications as they support the hypothesis that reducing the severity of OSA may improve glycaemic control,” said Aronsohn. “Thus effective treatment of OSA may represent a novel and non-pharmacologic intervention in the management of Type II Diabetes.”

The study appears in the American Journal of Respiratory and Critical Care Medicine.