Introduction
Sleep is a key component of health and the accurate measure of sleep and wake states has been the subject of many scientific studies. There are many ways to measure sleep, including subjective and objective tests. Currently, polysomnography is the objective standard by which all other sleep studies are judged against. In recent years, the use of actigraphy 1 has been validated as a reliable and convenient option that can be used to assess sleep. While conventional actigraphy continues to be studied in various uses, there has been a flood of commercial devices available using similar accelerometer technology. These are made available directly to consumers at an affordable cost. These devices purport to be able to assess sleep duration and quality. In the face of emerging and disruptive technology, do subjective sleep assessments like sleep diaries have a role? In this essay, we will try to compare the use of actigraphy to other measures of sleep, namely polysomnography, commercial devices and sleep diaries.
Actigraphy
In 1995, the American Sleep Disorders Association supported the use actigraphy as a research tool but declared that there was little evidence to use it in clinical medicine 2. In 2007, the American Academy of Sleep Medicine supported the clinical use of actigraphy in circadian rhythm disorders, insomnia, hypersomnia, and obstructive sleep apnea 3. This change was the result of better technology and larger datasets. As actigraphy devices continue to improve and more data becomes available, it is being used in a wider clinical setting.
The modern day actigraphy device is usually an actiwatch, a small wristwatch device that monitors and records movement data. This data is then stored and scored, using computer algorithms, to determine sleep or wakes states. There are several commercially available actigraphy devices, each with a preset algorithm for determining sleep wake states. It is an objective test and can provide information across an extended time period. The data is collected in the patient’s home and does not require a change in the natural habits and environment of the patient. As an objective test, it does not require any subjective inputs from the patient. It does requires a device and the cost of the study will be higher than that of a conventional sleep diary but lower than that of polysomnography.
There are limitations to actigraphy. Insana et al 4 performed a study that compared sleep wake scorings on actigraphy and polysomnograms in infants. They found that while actigraphy was sensitive in scoring sleep, it was not specific, with poor wake identification. This has been consistent with similar studies in the past 5. The failure of wake-time detection could be explained by the awake patient lying still in bed. Actigraphy has been found to overestimate total sleep time (TST) as a result 6. As such, actigraphy may not be suitable for detecting sleep in patients who have frequent arousals and reduced TST, or patients who are immobile or bed bound. Actigraphy is also unable to measure sleep stages unlike a conventional PSG.
Comparison
When deciding which sleep study is most suitable for the required application, the factors that must be considered include the likely clinical diagnosis, the burden to the patient: cost, comfort and inconvenience, the importance of assessing sleep in the natural environment, and the value of understanding sleep stages and architecture. Different tests have different strengths and weaknesses and one may be more appropriate than the other in specific situations. It is also common to utilise more than 1 simultaneously.
Sleep diary
A sleep diary data is valuable as it provides documentation of the variability of the patient’s daily sleep and wake schedule. It is also less costly to maintain than a device that measures sleep. However, it requires active input for the diary entries. There will be recall bias and entries may be influenced by the patient’s expectations of sleep and wake patterns. In 2004, Carney et al 7 showed that his subjects reported their sleep onset to be one hour before the time recorded in the actigraphy data.
A sleep diary in combination with actigraphy will enhance the quality of the information obtained. The diary can offer information on sleep and awake times to differentiate periods of inactivity from actual sleep. It can also explain daily variabilties in the information collected by the actigraph that might not easily be accounted for such as naps, specific events that alter a routine behaviour.
In circadian rhythm sleep disturbances, sleep diaries and actigraphy are useful as they can be used to collect information for an extended period of time to establish a pattern and consistency to come to a diagnosis. This would not be possible with a PSG.
Polysomnography
This remains the gold standard in determination of sleep wake states. It is able to independently measure multiple variables used to determine and diagnose sleep disorders. However it is costly, requires the patient to be tested in an unfamiliar environment. The test itself may alter and affect the quality of the data obtained. Data cannot be obtained over an extended period of time and there is no correlation while the patient’s normal routine or sleeping habits.
In the diagnosis of insomnia, the use of a PSG would accurately assess total sleep time. However, the test itself might create a “first night effect” and lead to worsening of insomnia with reduction in sleep efficiency and total sleep time 8. With actigraphy, it is possible to evade the first night effect as shown in a study done by Sanchez et al 9, with parameters such as total sleep time, sleep efficiency and wake after sleep onset validated with PSG findings 10.
In the diagnosis of sleep disordered breathing, a PSG remains the gold standard. However, in-lab PSG testing remains costly. Therefore majority of patients will likely undergo home sleep testing. The use of an actigraph in place of electroencephalogram leads will enable a cost effective measure of total sleep time instead of total recording time as a denominator for eventual apnea hypopnea index scoring 11.
Commercial Devices
There are a large number of devices available, with little or no validation studies done. However, they are inexpensive and widely available and have a reach of millions of uses with a potential database that may allow large-scale analysis of sleep patterns and disorders. Most devices, however, come with disclaimers to state that they were not designed to diagnose, treat, cure or prevent disease. Example of a device that was validated is the Up by Jawbone against actigraphy 12 and PSG 13. There was good correlation of TST, WASO in both studies with PSG data. This finding should not be surprising as the technology in most these devices are largely based on accelerometers and actigraphy. However, the study by Toon et al 12 showed that a smarphone based application MotionX 24/7 did not accurately reflect sleep or wake states. Therefore, it would be prudent to validate individual devices as they become available.
Conclusion
While polysomnography remains the gold standard of sleep testing in eyes of many, actigraphy continues to be a useful test for the right application. It can yield valuable information over an long period of assessment, provide objective data without subjective inputs and has been validated in measures such as total sleep time, sleep efficiency and wake after sleep onset. It is valuable in disorders such as circadian rhythm disorders, insomnia and sleep disordered breathing. It is complementary and may be used in combination with other tests. In comparison with other tools for sleep tests, it has practical value as well as limitations. Understanding these aspects would help maximize the value of actigraphy.
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