Applications and benefits of activity-based monitoring.
Activity-based monitoring has proven useful in a variety of clinical investigations of sleep and sleep-related disorders such as insomnia, narcolepsy, parasomnias, circadian rhythm sleep disorders, periodic limb movement disorder, restless legs syndrome, and sleep-related breathing disorders such as obstructive sleep apnea. In most instances activity-based monitoring devices (actigraphs) are worn on the wrist, ankle, or trunk to record movement with an accelerometer. A large electronic memory, also built into the device, allows the study’s subject to record both movement and nonmovement data for up to 1 to 2 weeks depending on the device used. Because activity-based monitoring devices are small, they are convenient and can be worn during both sleep and wakefulness without adversely affecting the wearer’s routine activities.1,2
Some activity-based monitors are programmable and allow the selection of specific modes of operation (ie, they allow variation in sensitivity level or epoch interval); others have a single fixed mode.3 Data from an actigraph are downloaded into a computer through an interface unit or directly via a USB port. Typically, a direct connection allows for faster transfer of data. Computer algorithms are then used to automatically score actigraph records. Most manufacturers of activity-based monitors also provide computer programs to analyze the data collected by the actigraph.
According to practice guidelines developed by the American Academy of Sleep Medicine (AASM),4 activity-based monitoring is a useful adjunct to history, physical examination, and subjective sleep diaries for the diagnosis and treatment of sleep disorders. Activity-based monitoring can detect daytime sleepiness in situations in which more standard techniques, such as the multiple sleep latency test (MSLT), may be impractical. In addition, activity-based monitoring is effective in demonstrating multiday rest-activity patterns, and can be used to estimate sleep-wake patterns in clinical situations in which sleep diaries, direct observations, or other methods cannot provide similar information.
Activity-based monitoring is a practical and useful means of monitoring the effectiveness of interventions designed to alter sleep.5 It is not indicated for the routine diagnosis, assessment of severity, or management of sleep disorders; however, as detailed in the AASM guidelines, it can provide clinically meaningful information in the following situations4:
• When demonstration of multiday rest-activity patterns is necessary to diagnose a disorder, document severity, and guide proper treatment.
• When more objective information regarding the day-to-day timing, amount, or patterns of sleep is needed to guide clinical decision-making.
• When a reported sleep disturbance appears inconsistent with clinical impressions or laboratory findings.
• To clarify the effects of, and possibly evaluate compliance with, treatment.
• In patients who are symptomatic and cannot give an accurate history, or in whom polysomnography has already been conducted.
• To characterize and monitor circadian-rhythm patterns or disturbances in special populations, including: the elderly; newborns, infants, children, and adolescents; hypertensive patients; and patients with depression or other psychiatric morbidity.
• To determine the rest-activity pattern during portable sleep apnea testing. (The use of activity-based monitoring alone in the detection of obstructive sleep apnea is not currently established.)
Activity-based monitoring may also be useful as an outcome measure in clinical trials performed in patients with sleep disorders, as well as outcome studies conducted in healthy adults.4
There are several advantages to using activity-based monitoring for sleep assessment. Because it can take place outside of the sleep laboratory and without direct supervision by a sleep medicine specialist, subjects can be evaluated while sleeping in their own beds and over many nights. In addition, activity-based monitoring can be used reliably in infants,6 children,7 elderly patients,8 and the critically ill8—groups that usually pose special testing challenges. Finally, studies have shown that activity-based monitoring provides reliable results that correlate well with polysomnographic results.9,10
The accuracy, simplicity of use, and low intrusiveness of activity-based monitoring make it ideal for determining sleep-wake states in highly sensitive patients such as infants. In one study,11 an accelerometer was used for a dual purpose: to determine an infant’s position in the crib and to identify sleep-wake states. The accuracy of predicted sleep-wake states was established in comparison to the sleep-wake states recorded by technicians in a polysomnographic study. Both statistical and neural predictors of this study provided an accuracy of up to 92%. The results support the use of body motion as a reliable method for determining sleep-wake states in infants. The investigators determined that use of the accelerometer for the dual purpose allowed them to minimize intrusiveness.
Although the wrist is a commonly used site for actigraph placement (eg, actigraph watches), the superiority of actigraph placement on any one part of the body has not been established. Either wrist may be used. Assessments of placement differences have shown little variation in scoring whether the actigraph is placed on the nondominant or dominant wrist.3,12 In general, the decision of anatomic site is based on the equipment at hand, convenience, and patient preference.
It is recommended that patients complete a sleep log during the period of activity-based monitoring. Concomitant completion of a sleep log provides important supplemental data for the purpose of artifact rejection and for marking bedtime and lights on, which in turn, allows the accurate determination of sleep parameters by activity-based monitoring.4
Increased wakefulness during the night generally decreases the accuracy of activity-based monitoring,13 and this decreased accuracy has been most well documented in patients with insomnia.3 To obtain the most accurate results, activity-based monitoring should be conducted for a minimum of three consecutive 24-hour periods.4
Activity-based monitoring provides an objective and quantifiable measure of physical activity and, with some devices, energy (caloric) expenditure. Contemporary activity-based monitoring devices provide a convenient and reliable means of studying sleep/wake patterns, and are becoming well established in the assessment and monitoring of patients with a wide variety of sleep disorders. However, activity-based monitoring results alone are unlikely to provide the practitioner with sufficient information to diagnose sleep disorders.
John D. Zoidis, MD, is a contributing writer for Sleep Review.
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