Clusters of Insomnia Disorder - an exploratory cluster analysis of objective sleep parameters reveals differences in neurocognitive functioning, quantitative EEG and heart rate variability
Study Objectives: To empirically derive and evaluate potential clusters of Insomnia Disorder through cluster analysis from polysomnography (PSG). We hypothesized that clusters would differ on neurocognitive performance, sleep-onset measures of quantitative (q)-EEG and heart rate variability (HRV). Methods: Research volunteers with Insomnia Disorder (DSM-V) completed a neurocognitive assessment and overnight PSG measures of Total Sleep Time (TST), Wake-time After Sleep Onset (WASO) and Sleep Onset Latency (SOL) were used to determine clusters. Results: From 96 volunteers with insomnia disorder, cluster analysis derived at least two clusters from objective sleep parameters: Insomnia with normal objective sleep duration (I-NSD: n=53) and Insomnia with short sleep duration (I-SSD: n=43). At sleep-onset, differences in HRV between I-NSD and I-SSD clusters suggest attenuated parasympathetic activity in I-SSD (p <.05). Preliminary work suggested three clusters by retaining the I-NSD and splitting the I-SSD cluster into two: I-SSD A (n=29): defined by high WASO and I-SSD B (n=14): a second I-SSD cluster with high SOL and medium WASO. The I-SSD B cluster performed worse than I-SSD A and I-NSD for sustained attention (p ≤.05). In an exploratory analysis, q-EEG revealed reduced spectral power also in I-SSD B before (Delta, Alpha, Beta-1) and after sleep-onset (Beta-2) compared to I-SSD A and I-NSD (p ≤.05). Conclusions: Two insomnia clusters derived from cluster analysis differ in sleep onset HRV. Preliminary data suggest evidence for three clusters in insomnia with differences for sustained attention and sleep-onset q-EEG.