Researchers discover link between sedentary lifestyle and the common sleep disorder

Toronto (Jan. 29, 2009) - Novel findings from a study published in the February 1st issue of the American Journal of Respiratory and Critical Care Medicine may lead to new methods of preventing or treating obstructive sleep apnea.

The study, "Relationship between Overnight Rostral Fluid Shift and Obstructive Sleep Apnea in Nonobese Men", led by Dr. Douglas Bradley, Director of the Sleep Research Laboratory at Toronto Rehabilitation Institute (Toronto Rehab), discovered fluid that accumulates in the legs throughout the day may shift to the neck during sleep. This causes compression of the upper airway, a key characteristic of obstructive sleep apnea. The findings also demonstrated a correlation between the volume of leg fluid and the amount of time spent sitting the previous day. In other words, people who are largely inactive may be predisposed to obstructive sleep apnea.

Obstructive sleep apnea, a common disorder that affects approximately nine per cent of men and four per cent of women, causes people to stop breathing for brief periods of time while asleep. The disorder has been linked to an increased risk of sleepiness, which affects people's ability to drive, work and perform everyday tasks. Obstructive sleep apnea has also been connected to other serious conditions, such as high blood pressure, heart attack and stroke. Researchers do not know what causes sleep apnea. While there is a correlation between obstructive sleep apnea and obesity, studies have shown that 60 per cent of people with obstructive sleep apnea are not obese. This prompted Dr. Bradley and his team to hone in on other causes, such as fluid displacement, in non–obese men.

"I was puzzled by the high incidence of sleep apnea I was seeing in many patients with congestive heart failure," says Bradley. "I also noticed that patients with kidney failure have a high incidence of sleep apnea. The majority of the patients were not obese, so another factor had to be at work. The one thing these groups have in common is fluid retention."

The study results have major implications for people with desk jobs. "Gravity forces fluid down to the bottom of the body when you are sitting and your legs are inactive," says Bradley. "Standing and walking cause the calf muscles to contract, pumping fluid from the legs up through the veins toward the heart. The message is: try to be active throughout the day — get up and walk around periodically."

Currently, the most effective treatment for sleep apnea is the use of a continuous positive airway pressure (CPAP) machine during sleep. The device supplies pressurized air into the throat keeping the airway open. This treatment method is effective but also intrusive. These new findings suggest that obstructive sleep apnea may be prevented, or made far less severe, by adopting a more active lifestyle to prevent fluid accumulation in the legs, and by raising the head of the bed to prevent displacement of fluids into the neck throughout the night.

"The idea that fluid movement is responsible for sleep apnea is, in some ways, revolutionary," says Bradley, who leads Toronto Rehab's Sleep and Cardiopulmonary Research Team. "It opens up a whole new field of research. I think researchers, including myself, will be looking into the implications of this for some time to come."

About the study
Dr. Bradley's team conducted a series of experiments with 23 healthy, non–obese men. They found the average nighttime increase in neck circumference in the general population was less than half a centimetre, compared to people with sleep apnea, whose neck circumferences increased by an average of one and a half centimetres. The larger neck circumference resulted in obstructive sleep apnea due to the increased narrowing of the airway. It was determined that the increased neck circumference was caused by fluid moving from the legs to the upper body during sleep. It is unknown if the results are applicable to women and people who are overweight.

About Toronto Rehab

Toronto Rehab is at the forefront of one of the most important and emerging frontiers in health care today, rehabilitation sciences. As a fully affiliated teaching and research hospital of the University of Toronto, Toronto Rehab is Canada's largest academic provider of adult rehabilitation services, complex continuing care and long–term care. Toronto Rehab is advancing rehabilitation knowledge and practice through research and education.

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