Effect of Closed-Loop Vibration Stimulation on Heart Rhythm during Naps

Figures

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  Figure 1. (a) Developed system consisting of ECG recording, HR detection, and stimulus actuation. These processes are repeated in a closed-loop manner. (b) Closed-loop vibration system diagram and devices used in the experiment. ECG—electrocardiogram; HR—heart rate.

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  Figure 2. Block diagram of the closed-loop processes. BPM—beats per minute.

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  Figure 3. Example of a heart rate density distribution from subject 1 under the −3% stimulation condition at an n of 2.0. The stimulus BPM was computed on the basis of the mean HR calculated over the previous 5 min. Orange line: position of the stimulus BPM. Shaded green: area of the densities between stimulus BPM ± n BPM, n = 0.5, 1.0, and 2.0 BPM.

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  Figure 4. Phase synchronization and synchrogram method. Each R-peak location of the ECG (red dots) is placed at the corresponding location of the instantaneous phase on the stimulus (blue line). A synchronization epoch was determined for the segment where the variation in the points was maintained within δ = 2π/(nΔ) and prolonged for T seconds. n, Δ and T were set to 1, 5 and 30, respectively. ECG—electrocardiogram.

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  Figure 5. HRV parameters under each experimental condition: (a) time and (b) frequency-domain HRV results. * p < 0.03 and ** p < 0.01 between the baseline and stimulation conditions (Wilcoxon rank-sum test). HRV—heart rate variability.

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  Figure 6. HR densities in stimulus BPM ± 0.5 BPM for each experimental condition. * p < 0.01 between the baseline and stimulation conditions (Wilcoxon rank-sum test). HR, heart rate.

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  Figure 7. Results of the HRV extracted every 15 min under the baseline and −3% stimulation conditions: (a) nHF and (b) LF/HF parameter results. HRV—heart rate variability; nHF—normalized high-frequency band power; LF/HF—ratio of the low-frequency power to the high-frequency power.