Data and analysis scripts: sleep fragmentation hypersensitize healthy young women to deep and superficial experimental pain

This repository contains the analytical data, analysis scripts, and the markdown document and figure outputs produced by those scripts.

There are three analysis sections:

1. Demographics, which provides summaries of basic demographic information for the participants, and information on participant menstrual cycles, sleep quality, and general health.
   
2. Regression, which describes the regression modelling of the effect of sleep fragmentation on the intensity of ischaemic pain over a ten-minute period on the morning after each nights sleep.
   
3. Other, which describes the analysis of the effect sleep fragmentation had on mood, sleep quality, morning vigilance, and somatosensory thersholds to noxious (pin-prick) and innocuous (von Frey hairs) punctate mechanical stimuli.

Each of the sections has its own README which describes the content in more detail.

In addition, the scripts (and the output from those scripts) that were used to process the data for publication (i.e., publication-ready figures and tables) can be found in: Manuscript.

Overview of the study

Background

Patients experiencing chronic pain frequently complain of night-time awakenings. This fragmentation of their sleep is a consequence of their pain, but the relationship between pain and sleep is bidirectional, such that sleep disruption may also contribute directly to the maintenance and/or exacerbation of pain.

Objectives

To establish whether sleep fragmentation (rather then deprivation) affects pain perception, we investigated whether two nights of sleep fragmentation alters the sensitivity of healthy, pain-free, women to experimentally-induced deep muscle ischaemic pain. As a secondary outcome, we also assessed whether sleep fragmentation altered somatosensory threshold to punctate mechanical stimuli (von Frey hairs and pin-prick).

Methods

Eleven healthy females were studied over 1 baseline night (control night), and two successive nights of sleep fragmentation (experimental nights). The order of the baseline night and fragmentation nights were randomized. Sleep fragmentation involved 8 forced awakenings (1/hour of sleep) of variable duration. On the morning after each intervention (control and experimental nights 1 and 2) the sub-maximal effort tourniquet test was used to induce forearm ischaemia. Participants rated the intensity of the ischaemic pain on a 100mm visual analogue scale (VAS, anchored at: 0 = no pain, 100 = worst pain ever experienced) at 1-minute intervals over a 10-minute period starting immediately after the sub-maximal exercise. The tourniquet remained in place until the end of the 10-minute measurement period.

Participants also completed assessments of mechanical thresholds for innocuous (von Frey hairs) and noxious (pin-prick) stimuli, mood (profile of mood states), sleep quality (VAS) and morning vigilance (VAS).

Results

After 1 night of sleep fragmentation, ischaemic pain perception increased compared to the control night, despite no changes being observed in thresholds for noxious and innocuous mechanical stimuli. Sleep fragmentation was also associated with lower mood, sleep quality, and morning vigilance.

A second successive night of sleep fragmentation was also associated with increased ischaemic pain perception compared to the control night (but not worse than the first night of sleep fragmentation). Moreover, the second night of sleep disruption was associated with reduced pin-prick thresholds. A second successive night of sleep fragmentation was associated with worsening of the already lower mood, sleep quality, and morning vigilance seen after the first night.

Conclusion

Our data support a role for sleep fragmentation in increased pain perception.