The use of accelerometry as a tool to measure disturbed nocturnal sleep in Parkinson’s disease

Immobility during sleep in a normal and a PD subject and a comparison with sleep stages. Figures 1a, b are frequency histograms of BKS (>80) obtained from 6 days of recording. The X axis is the value of the BKS unit and the Y axis the number of BKS units with that value. The grey shaded region shows BKS？>？110. a These are two histograms obtained from a non-PD subject. The black bars show the frequency of BKS of different values from the night period (23:00–06:00) and the red bars are the BKS from the day period in the same individual. It shows a marked peak in BKS at approximately 120 in the night period which is not present in the day period. b A histogram from a PWP. The BKS？>？80 are from the night period (23:00–06:00). Note that inactive BKS are reduced but the most obvious feature is the loss of the peak of BKS with scores >110. c This represents the findings of 10 individuals whose PSG was reported as normal. Each 2？min required for a BKS score is associated with four PSG scores of sleep state. The PSG sleep scores were given an ordinal value (awake？=？0 and REM？=？4) and the median 'PSG value' of the four associated with each BKS was estimated. For each individual, the median PSG value for all BKS in each of the four BKS categories was calculated (each dot represents an individual). The heavy horizontal red lines indicate the median of all 'PSG values' (i.e., each score from each individual pooled) of each BKS state (the lighter lines are the interquartile ranges). Thus, the median PSG value for BKS？<？40 was 'awake'; for BKS 40–80 was between awake and N1; for BKS 80–110 was between N1 and N2; and for BKS？>？110 was N