Actigraphy

Actigraphy is a non-invasive method of monitoring human rest/activity cycles. A small actigraph unit, also called an actimetry sensor, is worn for a week or more to measure gross motor activity. The unit is usually in a wrist-watch-like package worn on the wrist. The movements the actigraph unit undergoes are continually recorded and some units also measure light exposure. The data can be later read to a computer and analysed offline; in some brands of sensors the data are transmitted and analysed in real time. Actigraphy is a non-invasive method of monitoring human rest/activity cycles. A small actigraph unit, also called an actimetry sensor, is worn for a week or more to measure gross motor activity. The unit is usually in a wrist-watch-like package worn on the wrist. The movements the actigraph unit undergoes are continually recorded and some units also measure light exposure. The data can be later read to a computer and analysed offline; in some brands of sensors the data are transmitted and analysed in real time. Sleep actigraphs are generally watch-shaped and worn on the wrist of the non-dominant arm for adults and usually on the ankle for children. They are useful for determining sleep patterns and circadian rhythms and may be worn for several weeks at a time. In the medical setting, traditional polysomnography has long been cited as 'the 'gold standard' for sleep assessment.' Since the 1990s, however, actigraphy has increasingly been used to assess sleep/wake behavior. Studies have found actigraphy to be helpful for sleep research because it tends to be less expensive and cumbersome than polysomnography. Unlike polysomnography, actigraphy allows the patient to be movable and to continue her or his normal routines while the required data are being recorded in his or her natural sleep environment; this may render the measured data more generally applicable. As sleep actigraphs are more affordable than polysomnographs, their use has advantages, particularly in the case of large field studies. However, actigraphy cannot be considered as a substitute to polysomnography. A full night sleep measured with polysomnography may be required for some sleep disorders. Indeed, actigraphy may be efficient in measuring sleep parameters and sleep quality, however it is not provided with measures for brain activity (EEG), eye movements (EOG), muscle activity (EMG) or heart rhythm (ECG). Actigraphy is useful for assessing daytime sleepiness in place of a laboratory sleep latency test. It is used to clinically evaluate insomnia, circadian rhythm sleep disorders, excessive sleepiness. It is not recommended for the diagnosis of restless legs syndrome. It is also used in assessing the effectiveness of pharmacologic, behavioural, phototherapeutic or chronotherapeutic treatments for such disorders. The data, recorded over time, is in some cases more relevant than the result of polysomnography, particularly in assessing circadian rhythms and disorders thereof as well as insomnia. With the actigraphy it is also possible to determine some general information related to the sleep and the sleep quality of the subject, such as his/her chronotype, the sleep onset latency, the total sleep duration, the sleep consolidation (sleep efficiency), the time spent in bed, mouvements, and the sleep cycle. Research showed that both sleep and wake are not equally assessed by actigraphy devices. When compared, data collected through polysomnographs and actigraphs defines sensitivity; which is the proportion of sleep correctly detected by both methods. Actigraphy reveals itself to be more likely to detect sleep than wake phases. Actigraphy has been actively used in sleep-related studies since the early 1990s. It has not traditionally been used in routine diagnosis of sleep disorders, but technological advances in actiograph hardware and software, as well as studies verifying data validity, have made its use increasingly common. 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% for estimating total sleep time but dropping to 55% for a 4 - way sleep stage estimation problem). The technique is increasingly employed in new drug clinical trials where sleep quality is seen as a good indicator of quality of life. The technique has also been used in studies with individuals in both health and disease, e.g., Alzheimer's and fibromyalgia, conditions. Activity actigraphs are worn and used similarly to a pedometer: around the waist, near the hip. They are useful for determining the amount of wake-time activity, and possibly estimating the number of calories burned, by the wearer. They are worn for a number of days to collect enough data for valid analysis. 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.