Daytime stress, shoulder/neck-pain, and the relation to nocturnal heart rate variability
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Stress and musculoskeletal pain (MSP) may affect the regulation of the autonomic nervous system. Earlier studies have revealed that subjects with MSP show reduced heart rate variability (HRV) during sleep indicating an increased sympathetic drive at rest. However, it is unclear whether daytime exposures, such as work stress, stress in leisure, and daytime MSP, affect nocturnal HRV. The aim of this study was therefore to investigate the possible association between daytime stress, shoulder/neck pain (SNP), and nocturnal HRV. Twenty-five female subjects working in health care service participated in the study. Subjective scores of stress and pain were obtained on an hourly basis throughout the workday and subsequent evening. An index for long-term pain was also calculated. Electrocardiography (ECG) was monitored at the end of the workday and until 1 hour after awakening the morning after. Both time and frequency HRV parameters were extracted for further analyses. High stress in leisure time was associated with higher nocturnal HRV (p< .05). In contrast, long-term pain tended to be associated with reduced HRV. Pain or stress during the workday had no effect on nocturnal HRV. The differences between groups were all found for the time domain variable pNN50. No difference was present for the frequency domain parameter. The results of this study both agree with, and are in contrast to earlier studies of MSP and the association with nocturnal HRV. The contrasting results make it difficult to draw a conclusive remark and further studies are needed to elucidate the association between stress, shoulder/neck pain, and nocturnal HRV.