Assessment of autonomous nerve system through non-linear heart rate variability outcomes in sedentary healthy adults

BACKGROUND: Heart rate variability (HRV) is a psycho-physiological phenomenon with broad health implications. Different data analysis methods have been used to assess the autonomic nervous system activity, but the validation of new indexes that accurately describe its balance through non-invasive methods (i.e., HRV analysis) is of clinical interest. This study aimed: (i) to evaluate the association of the Stress Score (SS) and the Sympathetic/Parasympathetic Ratio (S/PS) with time domain and frequency domain analysis of HRV, and (ii) to set reference values of SS and S/PS in sedentary healthy adults. METHODS: A total of 156 sedentary healthy adults (38.4 ± 15.57 years old, 81 women), aged were involved in this study. HRV was measured for 15 min in a supine position at rest. SS and S/PS were calculated from the non-linear HRV analyses based on Poincare Plot. RESULTS: Stress Score showed a non-linear negative power-law relationship with SDNN (β = −0.969; R(2) = 0.963; P < 0.001), RMSSD (β = −0.867; R(2) = 0.722; P < 0.001), high frequency (β = −0.834; R(2) = 0.752; P =< 0.001), low frequency (β = −0.627; R(2) = 0.330; P < 0.001), SD1 (β = −0.867; R(2) = 0.722; P < 0.001) and SD2 (β = −1.000; R(2) > 0.999; P < 0.001). There was observed a negative cubic relationship between SS with PNN50 (β = −1.972; R(2) = 0.644; P < 0.001). A linear regression model was conducted between SS with Ratio Low/High Frequency (β = 0.026; R(2) < 0.001; P = 0.750). Non-linear power-law regression models were built between S/PS and SDNN (β = −0.990; R(2) = 0.981; P < 0.001), RMSSD (β = −0.973; R(2) = 0.939; P < 0.001), high frequency (β = −0.928; R(2) = 0.970; P < 0.001), low frequency (β = −2.344; R(2) = 0.557; P < 0.001), SD1 (β = −0.973; R(2) = 0.939; P < 0.001) and SD2 (β = −0.611; R(2) = 0.908; P < 0.001). A non-linear negative regression model was built between S/PS and PNN50 (β = −3.412; R(2) = 0.868; P < 0.001). A linear regression model was conducted between S/PS and SD2/SD1 (β = 0.075; R(2) = 0.006; P < 0.001). CONCLUSION: Our results support the use of SS as a sympathetic activity marker, and S/PS as an indicator of the sympathetic and parasympathetic activity of the autonomic nervous system in sedentary healthy adults.