Continuous assessment of hemodynamic control by complex demodulation of cardiovascular variability

TLDR

CDM provides continuous, time‑dependent amplitude changes of specific frequency components in cardiovascular signals. The study evaluated CDM’s usefulness for assessing cardiovascular variability and applied it to track low‑ and high‑frequency heart‑rate and blood‑pressure amplitudes during postural tilt. CDM was used to determine the time‑dependent responses of LF and HF amplitudes of heart rate and blood pressure during head‑up and head‑down tilt. Simulations confirmed CDM’s <15‑s resolution and robustness, while in 23 healthy subjects it revealed rapid HF heart‑rate decay and overshoot with tilt, rhythmic 48–100‑s LF blood‑pressure fluctuations synchronized with heart‑rate LF, demonstrating CDM’s ability to continuously monitor autonomic cardiovascular control and its phasic modulation during upright posture.

Abstract

Usefulness of complex demodulation (CDM) in assessing the frequency components of cardiovascular variability was assessed and, subsequently, this technique was utilized to determine the time-dependent responses of the low-frequency (LF) and high-frequency (HF) amplitudes of heart rate and blood pressure variabilities during postural tilt. CDM provides the time-dependent changes in amplitude of a particular frequency component on a continuous basis. Analysis of simulated data showed that CDM has sufficient frequency resolution to separately measure LF and HF amplitudes with a time resolution &lt; 15 s and that CDM is robust to alterations in the frequency of the components. Analysis of actual data during postural tilt test in 23 young healthy subjects demonstrated that the HF amplitude of heart rate, an index of cardiac parasympathetic tone, rapidly decayed with head-up tilt (P &lt; 0.01) and increased quickly showing an overshoot with tilt back to the supine position (P &lt; 0.01). The LF amplitude of blood pressure, an index of vasomotor sympathetic activity, showed marked rhythmic fluctuation at an interval of 48-100 s during head-up tilt (P &lt; 0.01), synchronizing with similar fluctuation in the LF amplitude of heart rate (P &lt; 0.01). These results suggest that CDM can be used to provide a continuous assessment of cardiovascular variability components and that the dynamic responses of autonomic circulatory control to upright posture result in a phasic modulation of LF amplitude.