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Sleep apnea linked to impaired exercise capacity

Date: Nov-25-2014
A new study shows that compared to people who do not have the disorder, those

who suffer from sleep apnea may not be capable of burning sufficiently high levels of

oxygen during strenuous aerobic exercise.

Researchers found that people who suffer from obstructive sleep apnea - a condition where breathing stops and starts during sleep - are also likely to have a lower peak oxygen uptake during aerobic activity.

This was the conclusion of a study led by the University of California San Diego

(UCSD) and published in the Journal of Clinical Sleep Medicine.

Obstructive sleep apnea - or more commonly just sleep apnea - is a condition where

breathing starts and stops during sleep. A common feature is gasping or snorting

noises during sleep - these are the moments when sleep is interrupted.

People who suffer from sleep apnea may also feel sleepy during the day because due

to frequent interruption, night-time sleep is not sufficiently restorative.

Sleep apnea is linked to increased risk of a number of cardiovascular diseases,

including high blood pressure, stroke, heart disease and irregular heart beat.

Researchers believe that an early marker of higher risk for stroke and heart

attack is a measure of exercise capacity known as VO2 max or peak VO2 - the maximum

oxygen a person burns during strenuous exercise.

VO2 max is commonly measured during cardiopulmonary exercise testing (CPET)

where a patient's heart and lung function is assessed during aerobic activity such as

riding a bicycle.

The authors note that there is increasing interest in using CPET as a way to

categorize sleep apnea patients in terms of heart risk.

However, lead author Jeremy Beitler, assistant clinical professor in pulmonary and

critical care medicine at UCSD, and colleagues suspect that using CPET and VO2 max in

this way with sleep apnea patients may not be as straightforward as it might

seem.

The relationship between sleep apnea and exercise capacity is not clear, they note

in their study background. So they set out to test the idea that sleep apnea itself

might be linked to impaired exercise capacity.

Obesity is not a reason apnea is linked to impaired exercise capacity

And what they found confirmed their suspicions; people with moderate to severe

obstructive sleep apnea appear to have a lower peak oxygen uptake during aerobic

activity compared to people who do not suffer from the sleep disorder.

One explanation might be that apnea sufferers are also more likely to be obese,

and would be expected to be less fit anyway. But the team found patients with sleep

apnea had reduced aerobic fitness even when compared with people of similar body mass

index.

Prof. Beitler says that encouraging patients with sleep apnea to exercise more

might be part of the answer, but it is not the whole answer:

"We believe the sleep apnea itself causes structural changes in muscle that

contributes to their difficulty exercising."

In their investigation, the team evaluated men and women with a range of apnea

symptoms. They assessed the severity of each patient's condition and also screened

them for other sleep disorders that might interfere with the study findings.

Eventually, 15 men and women with moderate to severe apnea and 19 with mild or no

apnea (the controls) took part in the CPET aerobic fitness assessment. After

undergoing resting state assessments, the participants were asked to pedal an

exercise bike, gradually increasing resistance until reaching the point of

exhaustion.

Moderate to severe sleep apnea linked to 14% lower VO2 max

After adjusting for baseline differences, the results showed that the participants

with moderate to severe apnea had on average 14% lower VO2 max than the controls.

Using the data from the sleep evaluation together with the CPET results, the

researchers also found a link between the severity of apnea - as measured by the

number of times breathing stops for 10 seconds or more per hour of sleep - and

reduced peak VO2.

The team also found that this measure of apnea severity - known as Apnea Hypopnea

Index - could predict 16% of the variability seen in the group's peak VO2, a

result that Prof. Beitler sees as "a big discrepancy."

The researchers conclude that sleep apnea is linked to impaired exercise capacity

and say further research is needed to evaluate whether CPET can contribute usefully

to the prognosis of patients with sleep apnea.

In September 2014, Medical News Today reported a study that showed the

reason sleep apnea causes brain damage is because of weaker blood flow in the brain.

Written by Catharine Paddock PhD

Not to be reproduced without permission.

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Courtesy: Medical News Today
Note: Any medical information available in this news section is not intended as a substitute for informed medical advice and you should not take any action before consulting with a health care professional.