Doctors already know that weight loss can be an effective treatment for improving sleep apnoea, although the reasons for this have remained unclear. Now, new research has uncovered that a reduction in tongue fat is the key to why fat loss helps in instances of Obstructive Sleep Apnoea (OSA).
MRI reveals how a reduction in tongue fat lessens the severity of OSA
A team of researchers from the Perelman School of Medicine at the University of Pennsylvania carried out a study where they measured the impact of weight loss on the upper airway, using magnetic resonance imaging (MRI), collecting data from obese patients. Their findings, which were published in the American Journal of Respiratory and Critical Care Medicine last week, revealed that the reduction in tongue fat that accompanies overall weight loss is the primary factor reducing symptom severity in OSA.
While 22 million Americans have sleep apnoea, effective treatment options are limited
Roughly 22 million Americans suffer from sleep apnoea, which causes people’s breathing to stop and start while they are sleeping, resulting in sufferers repeatedly waking throughout the night, detrimentally affecting their sleep and overall health due to continued sleep disturbances. Symptoms of the disorder include loud snoring, waking with a sore or dry throat, waking with choking or gasping sensations, morning headaches, and sleepiness during the rest of the day. It is also linked with an increased risk of suffering from high blood pressure and stroke.
Obesity has long been determined as the primary risk factor for developing sleep apnoea, although other factors such as having enlarged tonsils, or a recessed jaw are known to play a role also. Current treatments focus mainly on the use of continuous positive airway pressure (CPAP) machines, although they have only been found to be useful in around three-quarters of cases, with 1 in 4 struggling to tolerate the machine. Other than using the machine, doctors can offer upper airway surgery in some cases, however, as with all surgery, this carries risks. Therefore, the development of alternative, effective methods of treatment is desperately needed.
In 2014, researchers found that obese patients, suffering from sleep apnoea, also had significantly larger tongues. For the first time, the underlying reason why weight loss has proven to be an effective treatment for OSA was hinted at. The increase in tongue fat that is associated with obesity was a likely factor in sleep apnoea.
The new study conducted by US scientists aimed to gather evidence to determine whether this was, in fact, the case. 67 patients with mild to severe obstructive sleep apnoea as well as a body mass index greater than 30 were recruited for the six-month study that compared the volumes of the pharynx and abdomen before and after diet or weight loss surgery to reduce patients’ body weights by 10%. MRI scans alongside statistical analysis were able to determine the reductions in tongue volume, showing that a reduction in tongue fat volume was the primary factor linking weight loss with improvements in sleep apnea.
Also, data from the study revealed that reduced volumes in the pterygoid (a jaw muscle that controls chewing) and pharyngeal lateral wall (muscles on the sides of the airway) were also associated with overall weight loss, linking to improvements in sleep apnoea, but to a lesser degree than reductions in the volume of tongue fat.
What the team discovered with their new study is likely to open new avenues, exploring new, more effective treatments. The researcher's highlight that more studies will likely follow, aimed at figuring out how diets can be amended to help target a reduction in tongue fat, also looking into whether cold therapies, similar to those that are effective at reducing stomach fat, could be effective in targeting a reduction in tongue fat.
Compliance with CPAP therapy may help prevent cardiovascular complications
Results show that there was a significant reduction in systolic and diastolic blood pressures among sleep apnoea patients who were compliant with CPAP therapy for three months. Successful treatment of sleep apnoea also was associated with decreased vascular tone and arterial stiffness. Following one week of treatment withdrawal, these improvements disappeared and reverted to baseline values.
"We were surprised by the very rapid improvements in arterial tone, seen as early as four weeks into treatment, and how quickly they reversed after only a few days of treatment withdrawal," said principal investigator Claudia Korcarz, DVM, RDCS, manager and senior scientist at the University of Wisconsin Atherosclerosis Imaging Research Program (UW AIRP) in Madison. "We noticed these improvements in young, normotensive subjects. These findings demonstrate that the vascular effects of sleep apnea are reversible if treated early in the disease process, suggesting that we might be able to mitigate the long-term risk of chronic exposure to OSA."
The research abstract was published recently in an online supplement of the journal Sleep and will be presented Wednesday, June 4, in Minneapolis, Minnesota, at SLEEP 2014, the 28th annual meeting of the Associated Professional Sleep Societies LLC.
The study group comprised 47 adults with a mean age of about 41 years who had been recently diagnosed with OSA. They were evaluated before and after three months of CPAP therapy, as well as one week after treatment withdrawal. Carotid to radial artery pulse wave velocity and central aortic blood pressures were obtained by applanation tonometry. Brachial artery size and flow-mediated dilation were measured with B-mode ultrasound.
Subjects were considered to be compliant with treatment if they used CPAP therapy for at least four hours per night. Thirty-seven of the 47 participants met this criteria, using CPAP therapy for an average of 6.1 hours per night.
Korcarz noted that these findings reinforce that the effective treatment of OSA can have positive implications for cardiovascular health.
"The early diagnosis and treatment with well-monitored, continuous use of CPAP therapy in otherwise healthy young adults with moderate to severe obstructive sleep apnoea might prevent the future development of hypertension and reduce the risk of cardiovascular complications associated with the disease," said Korcarz.
The AASM reports that obstructive sleep apnoea is a common sleep illness affecting up to seven percent of men and five percent of women. It involves repetitive episodes of complete or partial upper airway obstruction occurring during sleep despite an ongoing effort to breathe. The most effective treatment option for OSA is CPAP therapy, which helps keep the airway open by providing a stream of air through a mask that is worn during sleep.
The research was performed under the supervision of Dr. Ruth Benca and Dr. James Stein in the University of Wisconsin School of Medicine and Public Health.