Prolonged job strain exposure and HRV analysis, as a marker of autonomic deregulation in a sample of North Italian nurses

Introduction
The analysis of Heart Rate Variability (HRV) has been suggested as a marker of cardiovascular autonomic regulation, and part of the pathway linking job stress and cardiovascular diseases. The aim of this study is to evaluate the association between prolonged job strain and autonomic deregulation, pursued through the HRV analysis

Methods
295 healthy nurses were investigated twice one year apart, through the administration of the Karasek’s JCQ and Siegrist’s ERI questionnaires. Of them, 36 healthy nurses, who gave the consent and reported in both occasions high level of strain (n.10), intermediate level of strain at the first screening and high levels one year latter (n. 7) and low level of strain in both occasions (n. 19), two 24-h ECG recordings were obtained for a working and a resting day. Both time and frequency domain measures of HRV were calculated. A regression model was applied to assess trends in HRV parameters across stress categories (α=0.05, two side).

Results
During the working time, from low to high strain categories, decrements were observed for SDNN (172.0, 148.8 and 133.9; p = 0,007), SDNN Index (72,3, 60,1 and 57,4; p = 0,0213), and SDANN (150.4, 137.7 and 122.2; p = 0,0344) in the time domain, and for the HF (p = 0,0348) and LF (p = 0,0274) in the frequency domain. Only LF alterations persisted in the resting time of the working day (p = 0,049), while in the resting day no differences among job strain categories were observed in both domains.

Discussion
In our study, HRV analysis confirms part of previous findings sustaining an autonomic deregulation on cardiac control in high job stress workers, during work time, and support the theory of a depressive modulation of the vagal tone, in persistent job stress conditions.