Actigraphy, Polysomnography, and Circadian Rhythm Disorders
Consideration of Methods to Clinically Evaluate Sleep Patterns
One of the perks of sleep testing is that we have established objective and validated measures to measure many variables of interest. Polysomnography (PSG) is the gold-standard in neurological sleep research. This measure uses electrodes in order to assess eye movement (electrooculography — EOG), muscle movement (electromyography — EMG), and brain activity (electroencephalography — EEG). While PSG is necessary in order to pursue some types of seep research, and vital to the identification of many sleep-related neurological disorders, it is a moderately invasive method that can affect sleep latency (how long it takes to fall asleep). It also requires a polysomnographic technologist in order to ensure standardized electrode placement and recording. Because of this, it is not typically cost-effective or feasible for identifying sleep patterns.
Actigraphy, which has been validated against PSG, is a measure of body movement by accelerometers in order to examine sleep-wake patterns. These watch-like devices are worn on the wrist of an individual’s non-dominant hand and can be worn at home for consecutive days and weeks to reveal an individual’s sleep patterns. Because we become atonic during sleep (most notably during rapid eye-movement sleep), actigraphs can detect sleep onset and awakenings. We have software that can use this information in order to determine sleep efficiency and quality, among other useful and interesting sleep variables.
Some sleep disorders, including both delayed and advanced sleep phase disorder, as well as other circadian rhythm disorders, such as free running circadian rhythm disorder, are difficult to detect without actigraphy. Delayed sleep phase disorder is a circadian rhythm disorder where the individual’s melatonin production is delayed (it is more complex than this, but this disorder is often treated by taking melatonin in the evening, along with early light exposure). These individuals are often unable to sleep until early in the morning, which can result in considerable challenges in meeting social and occupational demands.
If one were using PSG for one or two nights, this clinician may see normal sleep and miss a pattern of consistently delayed sleep and short sleep time. It is not uncommon for a person with this disorder to struggle to meet social, occupational, and academic obligations — as a result, they may have inconsistent patterns, sometimes sacrificing sleep for these obligations, other times sleeping early in the morning and waking in the afternoon. Two nights of PSG will probably not reveal the patterns, and then the clinician may rule out sleep disorders of this nature.
Not unlike delayed sleep phase disorder, free running circadian rhythm disorder is a disorder where the individual does not have a circadian rhythm that aligns with our 24 hour day-night cycle — it instead gradually shifts, using the slightly longer internal clock to determine sleep-wake patterns. Actigraphy is especially useful in detecting this disorder, as the changes in sleep onset can only be seen after several days of observation. PSG is not useful here because it is not feasible for more than a few days at a time, and would miss the gradually shifting sleep schedule specific to this rare disorder.
These are just a few examples of the practicality of actigraphy in a clinical context (in these examples, detecting diagnostically meaningful sleep patterns). Hopefully I’ve provoked a little insight for, and interest in, the fascinating world of measurement that is objective sleep testing. Subjective sleep measurement is a bit less straightforward, but I intend to use it to inspire a future post.
