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    • Spearman rank order correlations between PSG

    2018-10-26

    Spearman rank-order correlations between PSG and actigraphy measures are presented in Table 3. Positive correlations were noted between PSG and both wrist actigraphy sleep summary measures (original: r=0.24–0.53, all p<0.05 and spline-modified: r=0.29–0.56, all p<0.05). In general, the correlations with PSG measures were improved or comparable when using spline-modified data except for WASO and number of awakenings. Across all epochs, the minute-by-minute agreement between PSG sleep scores and those obtained using the original wrist actigraphy data was 81% (± standard deviation: 10%). The spine-modified wrist actigraphy data produced a similar agreement with PSG (81%±9%). For the hip actigraphy data, spline-modified hip actigraphy recordings produced higher agreement (78%±12%) than the original data (74%±14%). Bland–Altman plots of PSG sleep relative to original and spline-modified wrist actigraphy are presented in Fig. 2 along with the corresponding ICCs. Similarities between PSG and the sleep scores are observed if there are small differences between means that Epigenetics Compound Library cluster near the horizontal line, indicating small differences, and by moderate to strong ICCs. Dissimilar results produce larger differences that are typically outside the 95% limit of agreement. Relative to the original wrist actigraphy data, the spline-modified wrist data generated sleep efficiencies that were closer to those obtained using PSG. The original wrist data (Fig. 2 top panel) tended to have a less symmetric distribution around zero with more positive differences, whereas the spline-modified wrist actigraphy measures tended to have a more symmetric distribution around zero (Fig. 2 bottom panel). The ICC for sleep efficiency between PSG and the predicted wrist data (0.47) also was higher than the corresponding ICC between PSG and the original wrist data (0.29). Bland–Altman plots for both the original (Fig. S2 top panel) and spline-modified hip actigraphy (Fig. S2 bottom panel) data had positive differences and similar averages, indicating that both measures had estimated sleep efficiencies greater than PSG and that they were missing assignment of wakefulness epochs captured by PSG. Hip actigraphy from the original data had a distinct negative linear relationship, indicating that differences between PSG and original hip data decreased as mean sleep efficiency increased. Sleep efficiencies from both the original and spline-modified hip actigraphy data had low ICCs in relation to PSG (0.01 and 0.09, respectively).
    Discussion Characterization of sleep via wrist actigraphy has gained popularity in clinical and research settings, and has helped advance the understanding of how sleep disruption can affect the incidence or mortality of various diseases including depression, obesity, hypertension, cardiovascular disease and cancer [6–13]. Actigraphy is more cost-efficient and can be used to collect data over many consecutive nights while also being less disruptive to natural sleep than is PSG. Actigraphy has been used in some cases to help establish diagnoses of insomnia [25] or circadian rhythm sleep disorders [26]; however, clinical consensus is that a full-night PSG exam is required for establishing a sleep disorder diagnosis. In this study, the original wrist actigraphy data for this previously non-validated monitor had only modest correspondence with PSG, and the correspondence of hip actigraphy data with PSG was unsatisfactory. Several of the average sleep measures were statistically different between PSG and actigraphy; correlations between these data were low; and minute-by-minute agreement was modest. These correspondences were lower than other published comparisons. For example, minute-to-minute agreement between wrist actigraphy and PSG was 86–95% in studies of other actigraphy devices [24,27,28], whereas ribosomal subunits was 80% in the present study. For most sleep summary measure comparisons, the spline-modified sleep measures obtained using wrist-mounted actigraphs produced better agreement with PSG-defined sleep than the data summarized using the standard method for the original wrist-mounted data.