Mathematical model-based markers of autonomic nervous activity during the Valsalva Maneuver and comparison to heart rate variability

This work exhibits limitations of some time–frequency markers of heart rate variability (SDNN: standard deviation of normal-to-normal intervals, RMSSD: root mean square successive difference of normal-to-normal intervals, LF: power of low frequency components 0.015–0.15 Hz, HF: power of high frequency components 0.15–0.4 Hz) as tool for assessing autonomic nervous activity on the cardiovascular system during the Valsalva Maneuver (VM) and proposes a new approach based on a physiologically based mathematical model.Our mathematical model fits measured heart rate and galvanic skin response during intra-thoracic and intra-abdominal pressure elevation, simulates the baroreflex and estimates parameters that should quantify mean autonomic tone of parasympathetic activity (MATpar), maximal autonomic tone of parasympathetic activity (MATpar, total autonomic tone of sympathetic activity (TATsym) and autonomic tone balance (ATB) on 5 healthy subjects.An extended statistical analysis including multivariable linear regression analysis and correlation analysis was performed in order to study patterns of variation of our model-based estimates and possible relationships with time–frequency markers of heart rate variability during the tachycardia phase 2 and bradycardia phase 4 of the VM. It was found that, MATpar significantly decreased by 32 ± 8% (p < 0.001) from 0.87 ± 0.02 n.u. (normalized unit) in phase 1 to 0.58 ± 0.05 n.u. in phase 2 and was found to be significantly correlated to HF (R = 0.87, p < 0.05) that decreased from 0.5 ± 0.21 n.u. to 0.1 ± 0.01 n.u. Meanwhile TATsym increased by 2135 ± 711% (p < 0.001) from 0.14 ± 0.05 n.u. to 2.89 ± 0.7 n.u. and was significantly correlated to LF (R = 0.95, p < 0.05) that increased from 0.49 ± 0.21 n.u. to 0.89 ± 0.01. MATpar significantly increased by 87 ± 63% (p < 0.001) from 0.53 ± 0.18 n.u. in phase 3 to 0.89 ± 0.02 n.u. in phase 4 and was found to be significantly correlated to RMSSD (R = 0.91, p < 0.05) that increased from 18.61 ± 5.23 ms to 36.31 ± 7.02 ms. Meanwhile TATsym significantly decreased by 82 ± 13% (p < 0.01) from 1.46 ± 1.4 n.u. to 0.14 ± 0.05 n.u. and was significantly correlated to SDNN (R = 0.91, p < 0.05) that decreased from 28.79 ± 8.17 ms to 22.62 ± 9.63 ms.An additional Wilcoxon sign test suggested the following markers that might provide the most significant assessment of autonomic nervous activity in a given phase of VM: SDNN in phases 0 & 5, TATsym in phases 1 & 2 and ATB in phases 3 & 4 for sympathetic activity assessment; RMSSD in phases 0 & 5, MATpar in phases 1 & 2, MATpar in phases 3 & 4 for parasympathetic activity assessment.Results suggest that statistical quantities derived from mathematical models of cardiovascular control provide useful information for assessing the distinct contribution of sympathetic and parasympathetic branches on heart rate variability during the Valsalva Maneuver.