Sleep News

The science of consumer sleep technology: A peek under the hood

under-the-hood

“Boy under a car, man looking under the hood.” Kentucky 1972, William Gidney Photographs and Writings, Duke University, David M. Rubenstein Rare Book & Manuscript Library

There are so many different kinds of consumer sleep technology (CST) devices available today… How do they work?

It depends on what they are: how they are used (Are they worn? Embedded? Interactive) and what they seek to measure (Sleep metrics? Respiratory information?).

While the manufacturers of these gadgets offer what may appear to be new ways to measure sleep, what they are actually doing is building new digital applications that borrow from old-school methods used in clinical sleep medicine research and diagnostics for decades.

Let’s take a look under the hood.

What is polysomnography?

Polysomnography is the technical term for what takes place during a sleep study. In these studies, many (‘poly‘) different biological measures of sleep (‘-somno‘) are collected through a number of sensors (‘-graphy‘) in a combined effort to capture a comprehensive and objective picture of the subject’s sleep health.

Polysomnography is considered the gold standard in clinical sleep technology because of its comprehensive value. It gives the observing clinician a broad snapshot of what happens during a patient’s sleep period on any given night.

Human beings (ideally) sleep a third of the day. That provides a clinician a good opportunity to acquire data about a subject’s sleep “biology.”

After all, sleep is a whole-body process which affects multiple systems and which has influence over the brain and body—right down to the level of the cells.

Tests done over the course of a sleep period are very effective in identifying the underlying problems (and, ideally, the root causes) behind a patient’s sleep complaints.

These sleep tests are considered “objective.” This means they provide measurable data that reflects factual information about biological processes that occur during sleep, which are not reflected by opinion or speculation.

For instance, a patient may explain that they are told they snore, but that they don’t believe they do. That is a “subjective” matter which can then be made provable by a trip to the lab, where a snore sensor applied during a sleep study can clearly verify or deny the snoring claim.

Consumer sleep technology: borrowing from the gold standard

The following technologies are found in various applications of CST. Here, SHC explains their value when used in polysomnography, then their uses in CST are described.

gears-iconActigraphy

Polysomnography

In an overnight sleep lab, actigraphy refers to technological methods for measuring and recording physical movement.

Patients who complain of tossing and turning are often given an actigraphy device to take home with them. It’s usually worn on the arm and records their night-to-night movements to confirm restlessness.

In a lab environment, sleep technologists use a different approach. A patient wears sensors on their legs—and sometimes their arms—to trace muscle movements, from fine to large. This is called electromyelography (EMG).

EMG sensors are also applied to the face to measure movements in the jaw which help confirm REM stage sleep.

EMG is far more useful for tracing movement patterns in sleep because its data can be compared against other collected biological data to confirm that sleep is actually taking place at the time of movement.

Consumer sleep technology

With actigraphy alone—perhaps the most common technology built into wearable and embedded devices—there’s not usually any way to confirm that the movement being recorded is taking place during sleep.

At best, actigraphy can prove that movement takes place at night, but it can neither confirm nor deny that sleep has happened or not happened.

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Heart rate monitoring

Polysomnography

You’ve all heard of EKG (electrocardiography; alternately, ECG). This is how we can measure and record heart rate as well as cardiac rhythms.

In a sleep lab environment, EKG patches are applied to the chest to track heart rhythms and pulse; this data is taken into account along with all of the other vital signs collected during a sleep study. This includes audio and video recording, blood oxygen levels, respiratory patterns, movements, and other data gathered in real time.

Consumer sleep technology

Many wearables are equipped with pulse-reading technology that is probably more useful to users for their fitness interests.

Sudden changes in pulse rate during the night, while one is asleep, are usually indicative of movement—getting up to use the bathroom, or turning over in bed, for instance.

However, without some other way to monitor that activity (such as a video), it’s hard to know whether a sudden quickening in pulse measured by a wearable device might be indicative of some underlying cardiac rhythm issue, or simply the result of a stretch of REM sleep, or a sign of some other movement disorder of sleep.

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Blood oxygen monitoring

Polysomnography

Most people have encountered a pulse oximeter at least once in their life: this is the fingertip probe that glows an eerie red. It tracks your pulse like EKG does, but it also includes a unique sensor that uses infrared light to determine how oxygen rich your blood is.

If your blood has an appropriate amount of oxygen in it, then you will maintain a pulse oximeter reading of at least 90 percent blood oxygen saturation on your pulse oximeter.

Sleep studies use overnight pulse oximetry to track blood oxygen levels and pulse rate for the entirety of the study, and home sleep apnea tests typically include these devices as well. Any drops in oxygen saturation are recorded for the doctor to review afterward, with drops below 90 percent a reason for concern.

However, unlike with CST records and analytics, patients don’t have direct access to that information.

Consumer sleep technology

Some athletes use wearable pulse oximeters as part of their training; these typically don’t have the means to report and/or record blood oxygen levels for more than a short period of time and aren’t useful for overnight sleep tracking.

However, some wearables have incorporated them into their designs.

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Respiratory pattern recording

Polysomnography

The best way to identify problems with breathing while asleep is through a combination of sensors which include respiratory pattern recorders.

At a sleep clinic, and as part of a home sleep apnea test (HSAT), respiratory effort belts are placed on the patient’s body so that they encircle the waist and the chest.

These belts are built with specialized sensors embedded inside the elastic belt material; they measure the rise and fall of the diaphragm and the chest during breathing while asleep.

These respiratory patterns should present as even, smooth, wave forms that resemble gentle sloping peaks and valleys.

However, someone with a sleep breathing disorder will present with different wave patterns which indicate a problem requiring further attention.

Consumer sleep technology

A handful of wearable tracking devices come equipped with these belts, which plug into either a smartphone or a nightstand device for the purposes of respiratory effort recording.

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Electroencephalography

Polysomnography

Electroencephalography (also referred to as EEG) is what allows physicians and technicians to identify the presence of actual sleep.

The brain emits different wave patterns depending upon whether you are awake (W), drowsy (N1), asleep (N2), deeply asleep (N3), or in dream sleep (REM). These patterns have specific markers to identify them, and they can be traced and measured by means of EEG.

Naturally, sleep labs incorporate this technology into their patient preparation. In fact, it’s these sensors, glued to the scalp, which most patients find the most difficult to adjust to for the purposes of a sleep study.

The positioning of the sensors is critical, as certain areas in the brain create these specific kinds of wave forms. This is why sleep technologists use a tape measure to locate these precise spots, because accuracy of these signals is critical to an accurate study.

Consumer sleep technology

EEG is not commonly included in most CST devices, though some new technologies are starting to find ways, however limited, to do so.

Keep in mind: a sleep lab will require a patient to wear 10 or more sensors on the scalp, whereas a sleep tracking device may only use up to three (with one of them serving as a “ground”).

Since different wave forms from different parts of the brain are how we know to recognize different stages of sleep, it’s unclear how accurate CST can actually be in identifying and differentiating sleep stages using such limited means.

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Air flow measurement

Polysomnography

In-lab and home sleep testing includes air flow measurement to identify breathing patterns and potential obstructions in breathing (apneas and hypopneas).

It’s important to track air flow in the event you are looking to differentiate between kinds of sleep apnea.

This is very important, as obstructive sleep apnea (OSA) is different from central sleep apnea (CA). OSA is a mechanical issue with a mechanical fix, and CA is a neurological problem which requires a different approach because the airway, itself, isn’t obstructed.

Consumer sleep technology

There aren’t any consumer sleep technology devices (that SHC is aware of) that offer an air flow sensor to collect this data.

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Body position tracking

Polysomnography

Sleep labs employ the use of body position technology during overnight sleep studies. The reasons are typically related to sleep breathing concerns.

People with OSA may only have problems with obstructions while sleeping on their backs. Often, sleeping on either the right or left side will offer relief for those with mild OSA.

Consumer sleep technology

Sensors to identify body position can be part of some forms of wearable sleep tracking technology, but this data is only of limited use to the consumer if they aren’t also measuring breathing and brainwave patterns.

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Eye movement recording

Polysomnography

EOG stands for electrooculography, which is a technology for measuring and recording eye movement.

For the purposes of sleep testing in a clinical or laboratory environment, EOG sensors placed near the eyes are used to track two states during sleep: wake and REM, or rapid-eye movement sleep.

Rapid eye movement sleep occurs during the dreaming phase of sleep and is a vastly different stage when compared to the other stages, which is why it is given its own designation.

In some ways, the brain is more active during REM than when it is awake and alert.

REM sleep brings a flurry of biological changes with it, including paralysis in the body below chin level, and increased or erratic respiration, heart rate, and blood pressure.

Consumer sleep technology

Some sleep tracking devices claim that by monitoring pulse, breathing patterns, body temperature, and skin responses, they can distinguish between REM and other stages of sleep without the use of EOG.

This might be true, but it would require sophisticated metrics to yield accurate statistics, which may or may not be the case with CST devices that aren’t used in combination with a sleep program overseen by a medical professional.

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Ambient light sensors

Polysomnography

Generally speaking, sleep labs do not use ambient light sensors because sleep studies are conducted in extremely dark environments, so there’s no need to do so.

Consumer sleep technology

Some forms of CST employ sensors that capture light level status in a sleeping space. Usually this is because these devices are built to align with light for the purposes of waking up people through simulated dawn technology or soft alarms that incorporate light as part of their functionality.

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Snore sound recording or measurement

Polysomnography

Snore sensors are small vibration-sensitive microphones used in the sleep lab setting to measure the presence of, as well as the severity and frequency, of snoring.

They can also capture other sounds that point to sleep apnea, sleep talking, and other noise-producing behaviors while asleep.

Consumer sleep technology

Some products in the CST category include snore analysis to record, measure, and track snoring, usually through a microphone inside the device.

These could be useful records to obtain before a visit to the sleep physician, as this information can give them an indication of the nature of the snoring complaint.

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Skin temperature sensors

Polysomnography

One’s skin and core body temperatures change during the night while asleep. These changes occur as part of the processes of the circadian system and are considered normal.

In a sleep lab environment, skin temperature sensors aren’t typically used because of the more-than-adequate collection of other types of equipment to monitor biological signs during sleep.

One exception involves the less common use of transcutaneous monitoring of skin temperature for tracing oxygen-carbon dioxide imbalances in the blood stream which help to identify sleep-breathing disorders like obesity-related hypoventilation.

Consumer sleep technology

Consumer sleep technology can sometimes measure temperature, especially in the case of fitness tracking devices which serve to identify temperature increases to provide useful cautions about overheating.

However, this helpful use of galvanic skin response technology in CST may not be as relevant or applicable for measuring other metrics, like REM sleep.

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Consumer sleep technologies: a work in progress

The key takeaway when reviewing these technologies is this: while the in-lab diagnostic sleep study is considered comprehensive, there is no single gadget on the market that can accomplish the same level of data recording that polysomnography can.

So, while a wearable device, sleep tracking app, embedded gadget, or other sleep device may employ some of these technologies, they are mostly of limited use, only able to provide very basic information.

Still, simple tasks like capturing snoring, periods of restlessness, or body positions can be useful to record and analyze. Even the act of tracking one’s sleep in order to understand it better is a good reason to use some kinds of CST.

This is not to say that these devices won’t eventually be able to do a more comprehensive job. In fact, a lot of research is going into making them more accurate and relevant to people with sleep disorders.

As with any other kind of new technology, one has to start somewhere. CST is a product category that’s currently a work in progress, and some of its new technological applications are interesting and exciting to consider.

In addition, programs that incorporate apps or wearables with physician-attended therapeutics (line, online, or via telemedicine) offer promising new ways to use CST more proactively to identify and treat some of the more difficult sleep problems we encounter, such as sleep apnea and insomnia.

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  1. #ICYMI : Personal sleep technology – SleepyHead CENTRAL

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