Not snoring but you could still be at risk: What to know about ‘silent sleep apnoea'

You’ll know that your bed partner has obstructive sleep apnoea (OSA) because they sound like they’re fending off a Brazilian jiujitsu opponent’s chokehold during sleep – a mixed track of snoring and repeated gasping – caused by the sleeper’s throat muscles relaxing and partially blocking the airway.

OSA sufferers also tend to wake frequently at night to urinate. The oxygen and sleep deprivation can increase levels of hormones that promote sodium and water excretion as well as lower the kidneys’ ability to conserve water. With so much going on at night, it is no wonder that patients are also plagued by excessive sleepiness and morning headaches in the day. 

But what if you don’t hear any snoring at all? You could still have OSA or other forms of sleep apnoea such as central sleep apnoea, where the brain fails to signal your muscles to breathe. These silent forms of sleep apnoea can just as well lead to daytime sleepiness, morning headaches and frequent nightly trips to the bathroom the way OSA does.

“The term ’silent sleep apnoea’ has been bandied about colloquially to describe a condition that does not manifest with the typical symptoms, with loud disruptive snoring being the most obvious and disruptive,” said Dr Crystal Cheong, a senior consultant with National University Hospital’s Department of Otolaryngology – Head & Neck Surgery (ENT). 

Dr Shaun Loh, an ENT surgeon from Gleneagles Hospital, agreed that there is no formal medical diagnosis as “silent sleep apnoea” but highlighted that a significant number of patients do not snore, feel that they sleep fairly well, and function reasonably well in the day. 

“Yet, they have moderate to severe sleep apnoea,” he said. “These patients, who do not fit the typical profile, are often missed and therefore termed as ‘silent sleep apnoeics’.” 

WHY SHOULD YOU WATCH FOR IT? 

While you may have a quieter night’s sleep, your sleep buddy may literally be fighting for their lives. 

The silent form is characterised by intervals of zero airflow, whereas in OSA, there are still periods of partial airflow, explained Singapore General Hospital’s associate consultant Dr Adele Ng from Department of Otorhinolaryngology – Head & Neck Surgery. “There is no snoring as there is a complete cessation of airflow due to the complete collapse of the upper airway,” she said. “In a way, this makes the silent form more serious.”

As a result, there are repeated drops in blood oxygen levels during sleep, which increase “the risk of developing diabetes, hypertension, high cholesterol, obesity, glaucoma, stroke, ischaemic heart disease (and heart attacks), abnormal heart rhythm, dementia and cancer”, added Dr Ng.

The inability to maintain deep, stable sleep also affects the brain, said Dr Loh. “Deep sleep plays an important role in metabolic recovery and in clearing waste products from the brain. When this process is repeatedly interrupted, it contributes to impaired concentration, cognitive decline and potentially, a higher risk of dementia over the long term, which has been reported in multiple research studies.”

WHEN SHOULD YOU SUSPECT SOMETHING IS OFF?

"The first presentation is often not a sleep complaint but rather, a cardiovascular or metabolic issue that prompts further evaluation,” said Dr Loh. For instance, said Dr Cheong, developing hypertension at an unexpectedly relatively young age, without other obvious causes. 

Have your sleep assessed if your hypertension is difficult to treat, or if you have arrhythmias (heart rhythm abnormalities) that are difficult to control, excessive red blood cells in the bloodstream, unexplainable fatigue or frequent urination at night, she said.

Women, especially, should pay close attention to other signs such as insomnia, mood changes and excessive weight gain as they tend to display fewer classical symptoms such as snoring loudly, continued Dr Cheong. “Sometimes, a patient’s anatomy may not produce major vibrations of the upper airway tissue, despite inadequate airflow.”

As mentioned earlier, look out too for OSA's other symptoms such as excessive daytime sleepiness or unrefreshed sleep. “Some people may have morning headaches or frequent urination at night. Your bed partner may witness breathing pauses during sleep," said Dr Ng.

CAN YOU COUNT ON WEARABLES TO DETECT SLEEP APNOEA – SILENT OR OTHERWISE?

Yes and no, said the doctors. “A formal sleep study assesses brain activity to determine sleep stages, and measures breathing flow, oxygen levels, heart rate, respiratory effort and other physiological parameters,” explained Dr Loh. 

“Wearables, on the other hand, rely mainly on heart rate, body movement and sometimes, oxygen trends to estimate sleep. The way these signals are interpreted depends on each brand’s proprietary algorithm, so accuracy can vary,” he said.

Dr Cheong added that “mild sleep apnoea may not be detected with wearables, and patients with more complicated health conditions may not be suitable for these simplified tests”.

But there can still be a purpose for wearables – as initial screening tools, said Dr Ng. “If your device alerts breathing disruptions or low oxygen levels during sleep, it is highly recommended to consult a sleep doctor. You can also use these devices as informal monitoring tools after treatment to monitor improvement in sleep parameters or oxygen saturation during sleep.”

Another plus: “The benefits of wearables include comfort and convenience as you can sleep in your own home instead of the hospital sleep laboratory, allowing for analysis of a ‘normal’ night’s rest,” explained Dr Cheong. Moreover, “some devices allow for repeated tracking over weeks, providing a more long-term trend instead of just one night of data”.

WHAT IF YOU CAN’T FALL ASLEEP AT THE HOSPITAL TO ASSESS SLEEP APNOEA?

The inability to fall asleep in an unfamiliar environment is common and even has a name: the first-night effect. That and being covered with sensors can also affect your natural sleep behaviour and cause anxiety, acknowledged Dr Cheong.

“However, a sleep study in the sleep laboratory (aka attended polysomnography) is considered the gold-standard test because it captures a lot of details of a patient’s sleep, which can be pieced together for a more holistic and accurate picture of one’s sleep state and breathing issues,” she explained. 

The good news is, the doctors need just four hours of measured sleep, said Dr Cheong, so don’t worry excessively about not being able to fall asleep as quickly as you normally do, or waking up during the test. 

There are home tests that can be done as well such as using the clinically validated WatchPAT (peripheral arterial tonometry) device, said Dr Ng. It measures peripheral arterial tone, heart rate, oximetry and body position to diagnose sleep-related breathing disorders via a wrist device with a finger probe and chest sensor. Its limitation: WatchPAT estimates sleep stages using sensors but does not measure brain waves directly like a lab study.

HOW IS SLEEP APNOEA TREATED?

Pretty much the same way OSA is treated, said Dr Cheong. “Continuous positive airway pressure (CPAP) therapy is the first-line treatment as it is extremely efficacious at ensuring smooth airflow and stabilising the upper airway muscles. Oral appliances worn during sleep and surgery on the upper airway are alternatives for patients who cannot tolerate CPAP.”

Dr Loh noted that “a big part of the consultation is helping patients understand that, even in the absence of obvious symptoms, untreated sleep apnoea can still have important long-term consequences for the heart, brain and overall health”.