1. Effects of Baroreflex on Heart Rate Variability Evgeny G
Effects of Baroreflex on Heart Rate Variability Evgeny G. Vaschillo, Bronya Vaschillo, Jennifer F. Buckman, Tam Nguyen, Vladimir Fonoberov, Igor Mezic, and Marsha E. Bates Center of Alcohol Studies. Rutgers, The State University of New Jersey
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INTRODUCTION
It is known that HRV structure depends on the activity of sympathetic and parasympathetic system, however the origin of the HR oscillation has not been studied sufficiently. The phenomenon of respiratory sinus arrhythmia cannot cover all varieties of oscillations in HR frequency spectrum. The arterial baroreflex system (BRS) is an important generator of oscillations in the HR.
BRS includes at least three interrelated branches that link blood pressure (BP) to heart rate (HR), vascular tone (VT), and stroke volume (SV). Each branch is a closed-loop control system which has its own resonance frequency (RF). As a multi-resonance system, the baroreflex can produce heart rate (HR) oscillations at resonance frequencies in response to cardiovascular perturbations caused, for example, by breathing, cognitive processes, emotions, or physical load. In response to rhythmical stimulation, a closed-loop resonance system produces not only resonance oscillations, but also harmonics multiple to RF and beats oscillations, i.e., amplitude-modulated oscillation caused by interference between two slightly different frequencies.
RESULTS
All 0.1 Hz stimulation procedures elicited high amplitude HR oscillations at frequency of 0.1 Hz. In most cases, RRI spectra demonstrated peaks not only at 0.1 Hz, but also at frequencies multiple to 0.1 Hz, i.e., at 0.2, 0.3, and 0.4 Hz. In some cases, RRI spectra had double peaks at ~ 0.1 Hz which served as evidence for beats. A B
Figure 2. A - Averaged across all participants, frequency spectra of beat to beat intervals (RRI) for 4 different tasks. B - Power spectral density of RRI in 232 participants for 4 different tasks.
In most participants, 0.2, 0.3, and 0.4 Hz harmonics in RRI spectra appeared in response to rhythmical stimulation of the cardiovascular system at a rate of 0.1 Hz. When stimulated by 0.1 Hz paced breathing, 0.3 and 0.4 Hz harmonics in RRI spectra were less expressed than by rhythmical emotionally valenced cue presentation, whereas 0.1 Hz spectral component was significantly higher.
Figure 3. Examples of HRV beats in stimulation tasks and beat fragments.
DISCUSSION
Multiple harmonics most likely arise via baroreflex non-linearity, whereas beats are likely to appear due to the difference between the resonance frequency of the baroreflex closed-loop and the stimulation frequency.
When BP oscillation lies in non-linear areas of the baroreflex characteristics (Fig. 4), i.e., mean BP is high or low, then there are conditions for the harmonics to occur. Thus, valenced picture cue stimulation at 0.1 Hz increases mean BP, moving BP oscillation to the non-linear area. Paced breathing at 0.1 Hz slightly changes mean BP, but considerably increases BP oscillation which remains in the linear area, although can somewhat reach the non-linear area.
Beat frequencies in RRI most likely arise when fading resonance oscillation, caused by internal or external perturbations, superposes RRI oscillation, caused by rhythmical stimulation at a frequency slightly different to RF.
GOAL OF THE STUDY
The goal was to show that the baroreflex is affecting HRV by adding resonance oscillations, multiple harmonics, and beats oscillations.
Figure 5. Representation of how beat frequencies work. The two slightly different frequency waves (f1 and f2) combine to produce the third graph by superposition.
With two different frequencies (f1 and f2), the rate with which the amplitude of the wave pulsates is the beat frequency and is the difference between the two frequencies, expressed with the simple equation:
f pulsating = f1 – f2
One manifestation of the beat frequency is a pulsating amplitude.
Linear
Area
Non –
Linear
Area
Figure 4. Sigmoid characteristics for quantification of RRI baroreflex response to blood pressure oscillation. (Eckberg and Sleight, 1992).
METHOD
HRV responses to 5-minute rhythmical 0.1 Hz stimulation produced by paced breathing (6P) and emotionally valenced (Negative – Ng and Alcohol – AL) picture cue presentation (5 s picture on – 5 s off) in 232 young participants were assessed.
We examined whether the baroreflex:
Generates the RF harmonics,
Produces beats oscillation when the system is rhythmically stimulated at a frequency close to, but not exactly, the RF.
Non –
Linear
Area
CONCLUSION
These findings suggest that the baroreflex can affect HRV producing RF oscillations, beats oscillations, and multiple to RF harmonics. They also present a strong support for the conceptualization of the baroreflex system as a classical closed-loop control system.
This research was supported by grants and contracts from the National Institutes of Health (R01 AA015248, K02 AA00325, K01 AA017473, P20 DA017552, and HHSN C).
Presented at the ISARP annual meeting, October Athens, Greece.