Actigraphy Improves Measurement of Sleep Functioning
ISTSS eNewsletter, Traumatic StressPoints, March 2008
Ihori Kobayashi, M.S.
Department of Psychology, Kent State University
Brian J. Hall, M.A.
Department of Psychology, Kent State University
Patrick A. Palmieri, Ph.D.
Summa-Kent State Center for the Treatment and Study of Traumatic Stress, Department of Psychiatry, Summa Health System, Department of Psychology, Kent State University
Sleep-related difficulty is an important diagnostic indicator of posttraumatic stress disorder (PTSD); two sleep-related symptoms are included in the PTSD diagnostic criteria. The re-experiencing symptom cluster contains experiencing nightmares or distressing dreams related to traumatic events, and the hyperarousal symptom cluster includes insomnia defined as difficulty in falling or staying asleep. Many studies have demonstrated a consistent relationship between nightmares, insomnia, and PTSD and these sleep symptoms are quite common; up to 90% of patients diagnosed with PTSD report these difficulties (Germain, Shear, Hall, & Buysse, 2007; Neylan et al., 1998).
Sleep disturbance exacerbates daytime PTSD symptoms (Germain et al., 2007), attenuates overall treatment gains, and relates to negative health outcomes (Clum, Nishith, & Resick, 2001). Although decreasing overall sleep disturbance is important in PTSD treatment, it is a sometimes overlooked and difficult treatment target. Because of the significant impact sleep has on the course of this disorder and treatment outcomes, it is important for researchers and clinicians to measure sleep among traumatized patients. In this article, we first review conventional sleep assessment methods, and then we discuss the utility of actigraphy, a relatively new sleep measure that is beginning to receive more attention in studies of PTSD.
Conventional methods for measuring sleep include daily sleep diaries/logs, sleep questionnaires, and polysomnography (PSG). A sleep diary is a self-report measure designed to gather information relevant to respondents’ sleep (e.g., time they went to bed, fell asleep, and finally woke up; nightmares) and daytime behaviors which may affect their nighttime sleep (e.g., caffeine consumption, naps). Respondents are instructed to complete a sleep diary daily, typically for at least one week. A sleep questionnaire is also a self-report measure, one that is designed to assess habitual sleep patterns. Respondents are asked to answer questions based on their overall sleep experience, usually in the past week or past month. Sleep diaries and questionnaires are inexpensive and easy to administer; however, they suffer from limitations inherent in any self-report measures such as subjectivity and dependence on respondents’ memory as well as ability and willingness to follow instructions.
PSG is a procedure of monitoring physiological activities (e.g., electrical brain activity, eye movements, respiration) during sleep, and it typically takes place in a sleep lab. PSG yields various objective sleep parameters such as total sleep time, sleep efficiency (% of total time in bed that is actually spent asleep), and the duration of different sleep stages including rapid eye movement, or REM, sleep. Although PSG is considered to be the gold standard for sleep measurement, it has several disadvantages. PSG is costly in terms of equipment, the need for trained technicians, and patient expense. Lab-based PSG requires participants/patients to sleep in unfamiliar environments with many sensors attached to their bodies, an artificial situation that generates data with suspect ecological validity. Observing sleep in patients’ regular sleep settings is particularly important because sleep is influenced by nighttime routines and environmental factors. In addition, it is impractical to conduct long-term monitoring of sleep patterns with lab-based PSG because of cost and the burden placed on patients/participants.
Actigraphy is a relatively new method of measuring sleep functioning that provides objective information and addresses some limitations of conventional measures. It utilizes an actigraph, a small electronic instrument generally worn on the wrist like a watch but that also can be placed on the waist and ankle. Actigraphs contain an accelerometer that measures multi-directional movement several times per second, resulting in activity counts that are averaged over a brief period (usually 30 seconds or 1 minute) and stored in the actigraph for up to several weeks. Patients/participants usually wear an actigraph continuously for at least 3 days but can wear them for several weeks at a time. At the end of the monitoring period the stored data are downloaded to a computer for analysis. Typical scoring programs are able to draw histograms (see Figure 1 for an example) indicating activity levels for specified time periods and determine when an individual was asleep or awake based on a threshold of activity set by the user or a computer algorithm. This sleep-wake analysis allows for the derivation of sleep parameters such as total sleep time, sleep onset latency (the length of time between going to bed and falling asleep), and sleep efficiency.