Actigraphy
Encyclopedia
Actigraphy is a non-invasive method of monitoring human rest/activity cycles. A small actigraph unit, also called an actimetry sensor, is worn by a patient to measure gross motor activity. Motor activity often under test is that of the wrist, measured by an actigraph in a wrist-watch-like package. The unit continually records the movements it undergoes. The data can be later read to a computer and analysed offline. In some applications, such as the Fitbit
or the WakeMate
, the data is transmitted and analysed on the fly.
arm. They are useful for determining sleep patterns and circadian rhythm
s and may be worn for several weeks at a time. Contrary to polysomnography
, the patient remains movable and does not necessarily need to be located in a laboratory while the required data is being recorded. This permits the patient to stay in his or her natural sleep environment which may render the measured data more generally applicable. Sleep actigraphs are also more affordable than performing a polysomnography and can therefore be advantageous as well, particularly when conducting large field tests.
Actigraphy is useful for assessing daytime sleepiness in situations where a laboratory sleep latency test is not appropriate. It is used to clinically evaluate insomnia
, circadian rhythm sleep disorder
s, excessive sleepiness and restless legs syndrome
. It is also used in assessing the effectiveness of pharmacologic, behavioural, phototherapeutic or chronotherapeutic treatments for such disorders.
Actigraphy has been actively used in sleep-related studies since the early 1990s.. However, it has not traditionally been used in routine diagnosis of sleep disorders but is increasingly being employed in sleep clinics to replace full polysomnography. The main reason for this development is the fact that, while retaining mobility, actigraphy offers reliable results with an accuracy that is close to those of polysomnography (above 90%) The technique is more extensively used in academic research and is being increasingly employed in new drug clinical trials where sleep quality is seen as a good indicator of quality of life.
: around the waist, near the hip. They are useful for determining the amount of activity and possibly the number of calories burned by the wearer. They are worn for a number of days.
For some uses, the following are examples of additional features:
s use an actigraph to identify periods of lighter sleep, when the sleeper should wake more easily.
, Sleep Cycle alarm clock, generates graphs of body movement during sleep and has a similar alarm clock function.
Fitbit
Fitbit Inc. is a company headquartered in San Francisco, California, United States. Led by James Park and Eric Friedman, the company is known for its product of the same name, the Fitbit Tracker, a wireless-enabled wearable device that measures data such as the number of steps walked, quality of...
or the WakeMate
WakeMate
The WakeMate is an electronic device with sensors to monitor the sleep state of the user using actigraphy. It connects to the user's mobile phone via Bluetooth to record sleep data and to signal the phone to wake them in the lightest phase of sleep within the 20-minute window prior the desired...
, the data is transmitted and analysed on the fly.
Sleep
Sleep actigraphs are generally watch-shaped and worn on the wrist of the non-dominantHandedness
Handedness is a human attribute defined by unequal distribution of fine motor skills between the left and right hands. An individual who is more dexterous with the right hand is called right-handed and one who is more skilled with the left is said to be left-handed...
arm. They are useful for determining sleep patterns and circadian rhythm
Circadian rhythm
A circadian rhythm, popularly referred to as body clock, is an endogenously driven , roughly 24-hour cycle in biochemical, physiological, or behavioural processes. Circadian rhythms have been widely observed in plants, animals, fungi and cyanobacteria...
s and may be worn for several weeks at a time. Contrary to polysomnography
Polysomnography
Polysomnography , also known as a sleep study, is a multi-parametric test used in the study of sleep and as a diagnostic tool in sleep medicine. The test result is called a polysomnogram, also abbreviated PSG...
, the patient remains movable and does not necessarily need to be located in a laboratory while the required data is being recorded. This permits the patient to stay in his or her natural sleep environment which may render the measured data more generally applicable. Sleep actigraphs are also more affordable than performing a polysomnography and can therefore be advantageous as well, particularly when conducting large field tests.
Actigraphy is useful for assessing daytime sleepiness in situations where a laboratory sleep latency test is not appropriate. It is used to clinically evaluate insomnia
Insomnia
Insomnia is most often defined by an individual's report of sleeping difficulties. While the term is sometimes used in sleep literature to describe a disorder demonstrated by polysomnographic evidence of disturbed sleep, insomnia is often defined as a positive response to either of two questions:...
, circadian rhythm sleep disorder
Circadian rhythm sleep disorder
Circadian rhythm sleep disorders are a family of sleep disorders affecting, among other things, the timing of sleep. People with circadian rhythm sleep disorders are unable to sleep and wake at the times required for normal work, school, and social needs. They are generally able to get enough sleep...
s, excessive sleepiness and restless legs syndrome
Restless legs syndrome
Restless legs syndrome or Willis-Ekbom disease is a neurological disorder characterized by an irresistible urge to move one's body to stop uncomfortable or odd sensations. It most commonly affects the legs, but can affect the arms, torso, and even phantom limbs...
. It is also used in assessing the effectiveness of pharmacologic, behavioural, phototherapeutic or chronotherapeutic treatments for such disorders.
Actigraphy has been actively used in sleep-related studies since the early 1990s.. However, it has not traditionally been used in routine diagnosis of sleep disorders but is increasingly being employed in sleep clinics to replace full polysomnography. The main reason for this development is the fact that, while retaining mobility, actigraphy offers reliable results with an accuracy that is close to those of polysomnography (above 90%) The technique is more extensively used in academic research and is being increasingly employed in new drug clinical trials where sleep quality is seen as a good indicator of quality of life.
Activity
Activity actigraphs are worn and used similar to a pedometerPedometer
A pedometer is a device, usually portable and electronic or electromechanical, that counts each step a person takes by detecting the motion of the person's hips...
: around the waist, near the hip. They are useful for determining the amount of activity and possibly the number of calories burned by the wearer. They are worn for a number of days.
Movement
Movement actigraphs are generally larger and worn on the shoulder of the dominant arm. They contain a 3D actigraph as opposed to a single dimension one, and have a high sample rate and a large memory. They are used for only a few hours, and can be used to determine problems with gait and other physical impairments.The actigraph unit
The unit itself is an electronic device which generally consists of:- a piezoelectric accelerometerAccelerometerAn accelerometer is a device that measures proper acceleration, also called the four-acceleration. This is not necessarily the same as the coordinate acceleration , but is rather the type of acceleration associated with the phenomenon of weight experienced by a test mass that resides in the frame...
, - a low-pass filterLow-pass filterA low-pass filter is an electronic filter that passes low-frequency signals but attenuates signals with frequencies higher than the cutoff frequency. The actual amount of attenuation for each frequency varies from filter to filter. It is sometimes called a high-cut filter, or treble cut filter...
which filters out everything except the 2–3 Hz band, thereby ensuring external vibrations are ignored, - a timer to start/stop the actigraph at specific times, and to accumulate values for a specific time frame,
- a memory to store the resulting values, and
- an interface, usually USB, serial, or low-power wireless, to program the timer and download the data from memory.
Measurements
Actigraphs have a number of different ways of accumulating the values from the accelerometer in memory. ZCM (zero crossing mode) counts the number of times the accelerometer waveform crosses 0 for each time period. PIM (proportional integral mode) measures the area under the curve, and adds that size for each time period. TAT (time above threshold) uses a certain threshold, and measures the length of time that the wave is above a certain threshold. Literature shows that PIM provides most accurate measurements for both sleep and activity, though the difference with ZCM is marginal.Features
Actigraph units vary widely in size and features and can be expanded to include additional measurements. However, there are a number of limiting factors:- Fastest sample rate: 1-minute intervals provide adequate detail to measure sleep, but could be too slow for measuring other parameters.
- Amount of memory: Together with sample rate, the amount of memory determines how long measurements can be taken.
- Battery usage: Some actigraphs have a short battery life.
- Weight: the heavier the actigraph, the more disruptive its use.
- Water resistance: for proper measurements it is often desirable that the actigraph be worn in the shower, bathtub, or even while swimming/diving.
For some uses, the following are examples of additional features:
- Watch functionality: making the device more attractive to the user.
- User input: most actigraphs now include a button so the user can indicate a specific event that occurs, for example lights out at bedtime.
- Subjective user input: for example a query function to allow surveys at specific times.
- Sensors which monitor:
- temperature
- ambient light
- sound levels
- parkinsonian tremor
- skin resistance
- a full EEG data stream
Actigraph
- Fitbit Wireless Activity Tracker
- Jawbone UP fitness tracking wristband and iOS app
- Precision Control Design: wrist-worn actigraphs
- WakeMate
Alarm clocks and watch
Some modern alarm clockAlarm clock
An alarm clock is a clock that is designed to make a loud sound at a specific time. The primary use of these clocks is to awaken people from their night's sleep or short naps; they are sometimes used for other reminders as well. To stop the sound, a button or handle on the clock is pressed; but...
s use an actigraph to identify periods of lighter sleep, when the sleeper should wake more easily.
Smartphone applications
An application for Apple's iPhoneIPhone
The iPhone is a line of Internet and multimedia-enabled smartphones marketed by Apple Inc. The first iPhone was unveiled by Steve Jobs, then CEO of Apple, on January 9, 2007, and released on June 29, 2007...
, Sleep Cycle alarm clock, generates graphs of body movement during sleep and has a similar alarm clock function.
External links
- American Academy of Sleep Medicine – Practice parameters for the role of actigraphy in the study of sleep and circadian rhythms: An update for 2002
- http://www.acsm-msse.org/pt/re/msse/abstract.00005768-200409000-00026.htm;jsessionid=EGV2oXf1VwE3h24pSzos7mnaSrNuqJu7tco1AuGHNjH4WGODCzwO!987057721!-949856145!9001!-1?index=1&results=1&count=10&searchid=1&nav=search%20Reliability of Accelerometry-Based Activity Monitors: A Generalizability Study. Gregory J. Welk, Jodee A. Schaben, and James R. Morrow, Jr. Medicine & Science In Sports & Exercise, Vol. 36, No. 9, pp. 1637–1645, 2004.] – Medicine & Science in Sports & Medicine, the official Journal of the American College of Sports Medicine