LF HRV power as an index of sympathetic inhibition
Authors: Shekh Vera Evgenievna 
Published: June 2021

Although the spectral power of HF HRV oscillations is widely accepted as a measure of the cardiovagal activity, the interpretation of LF HRV power is more controversial. It was suggested that LF HRV power provides information about the sympathetic or/and parasympathetic outflow, baroreflex modulation of cardiac autonomic outflows, vasomotor tone modulation, and mechanisms of central autonomic outflow. As follows from these contradictory hypotheses, till now there is no widely accepted interpretation of LF power. We hypothesize that LF HRV power is an index of sympathetic inhibition.The participants, 150 men, and 149 women were enrolled from V.N. Karazin Kharkiv National University student population. The ECG recording, HRV analysis, and blood pressure (BP) measurements were performed four times with an hour interval. The average values were included in the analysis. The stepwise multiple linear regression analysis with centered variables was performed to evaluate a contribution of LnLF and LnHF power in heart rate (HR), systolic and diastolic BP (SBP and DBP), adjusted also for sex, BMI, height, two‐way, three‐way, four‐way interactions, and in addition, for presence of hypertension. Statistical analysis was performed with the SPSS statistical program, version 22.The multiple linear regression analysis revealed that resting HR was negatively associated with LnHF at high significant level (P<0.001) and with LnLF at lower significant level (P=0.021) (Table 1). The negative association between HR and LnHF power was expected, as it is widely accepted that HF power represents a cardiovagal outflow which predominates at rest. As it follows from the positive association between HR and LnHF by LnLF interaction (LnHF*LnLF) (Table 1), the LnHF and LnLF work in a reciprocal manner: either LnLF or LnHF can reduce HR at a higher degree with a predominance of LnHF in apparently healthy individuals. There are at least three variants of interpretation of the negative association between HR and LnLF power such as the LF power represents: 1) both sympathetic and parasympathetic activities with predominance of the cardiovagal outflow; 2) inhibitory influences of a variety of peripheral reflexes on the medullary presympathetic neurons; 3) the central hyporeactive immobility and sympathoinhibition.The SBP and DBP were positively associated with gender (men) and BMI and negatively with LnLF power in men with high values of BMI (Table 1) indicating the negative feedback control of blood pressure. Since there are no parasympathetic nerves directly influencing blood pressure, the second possibility was accepted in congruence with idea that LF power is an index of the baroreflex modulation of cardiac autonomic outflows specifically of the sympathetic limb of this negative feedback controlling mechanism.The introduction of one more variable and number of interactions increases the complexity of the linear regression model but may give more information. The model including also presence of prehypertension (51 independent centered variables and interactions) indicates that SBP was negatively associated with LnLF in normotensive participants only (not shown), demonstrating according to our hypothesis lack of sympathoinhibition in prehypertensives.In conclusion, from HRV and stepwise multiple regression analysis with centered independent variables and interactions, it is suggested that LnLF power represent sympathoinhibitory negative feedback controlling mechanisms.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.