Circadian Rhythm Analysis
Advanced Actigraphy Software Tools
Actigraphy has long been regarded as valued method for examining the temporal aspects of sleep behaviour. Due to it’s inherent unobtrusiveness, the MotionWatch 8 can be worn continuously for up to 90 days hence capturing long-term activity-rest patterns.
Many sleep disorders present with a disturbed cirdadian rhythm and it is usually possible to determine from the Actigraphy data the likely diagnosis and also to continue to monitor for improvement post-intervention.
Light exposure is the primary zeitgieber that entrains the 24 hour activity-rest pattern. The MotionWatch 8 incorporates a light sensor with a range up to 64,000lux to allow monitoring of exposure to bright light. The MotionWatch 8 has been applied in many chronobiology studies by leading researchers from around the world.
The double plotted Actogram below shows an example of data over a one month period for a patient with a total loss of 24 hour entrainment. This is an extreme case, but illustrates the value of Actigraphy when examining sleep disorders.
The specific characteristics of circadian rhythms may be of interest to researchers and clinicians, and thus need to be quantified. Many circadian rhythms resemble a cosine wave, and indeed there is a long tradition in circadian rhythm research to fit a cosine curve to the data, and to use the mesor (mean), amplitude and phase of the fitted curve as variables of interest; this method is known as Cosinor-analysis.
Activity data, however, seldom resemble a cosine wave, and it is consequently not appropriate to apply Cosinor-analysis in order to obtain valid parameters describing the rhythms. Therefore, a number of alternative quantification methods have been developed. These Non Parametric methods do not suppose the rhythm to have a cosine-like shape.
It has been shown that the nonparametric variables are valuable in research, i.e. they are sensitive to rhythm disturbances in disease processes and aging, as well as to their amelioration by several treatments.
The MotionWare software provides the function of Non-Parametric Circadian Rhythm Analysis (NPCRA) which is included in the package as standard. The NPCRA analysis is based upon the work of Dr. Eus Van Someren at the Netherlands Institute for Brain Research.
The NPCRA window provides a table of resulting Non-Parametric variables with the following meanings:
- IS (Interdaily Stability): quantifies the degree of regularity in the Activity-Rest pattern with a range of 0 to 1 where a value of 0 indicates a total lack of rhythm and a value of 1 indicates a perfectly stable rhythm.
- IV (Intra-Daily Variability): quantifies the degree of fragmentation of activity-rest periods. Typical healthy subjects will show a single prolonged activity period and a single prolonged rest period per 24 hour cycle. Certain physiological conditions may lead to multiple short-length periods of activity-rest within any 24 hour period. The variable has a theoretical range of 0 to 2 with higher values indicating higher fragmentation. Typical values for healthy subjects will be below 1.
- L5 (Least 5) Average: all days of data are overlaid and averaged in 24-hour periods. The L5 average provides the average activity level for the sequence of the least five active hours. This value provides an indication of how restful (inactive) and regular the sleep periods are.
- L5 Start Hour: Indicates the onset of the L5 sequence and provides an indication of the phase of the most restful hours.
- M10 (Most 10) Average: all days of data are overlaid and averaged in 24-hour periods. The M10 average provides the average activity level for the sequence of the highest (most) ten active hours. This value provides an indication of how active and regular the wake periods are.
- M10 Start Hour: Indicates the onset of the M10 sequence and provides an indication of the phase of the most active hours.
- RA (Relative Amplitude): First we calculate the Amplitude (AMP) which is the difference between the average activity level in the M10 and that in the L5 periods. To remove sensitivity to overall activity level, we then calculate the RA by dividing the AMP by the sum of the L5 and M10. The variable has a theoretical range of 0 to 1 with higher values indicating a rhythm with higher amplitude.
The NPCRA analysis is based upon the work of Dr. Eus Van Someren at the Netherlands Institute for Brain Research. The publications below provide details of this research.
Click or tap here to view the reference papers in our Research Library