Real‐Time Analysis of the Heart Rate Variability During Incremental Exercise for the Detection of the Ventilatory Threshold

Figures

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  Figure 1. Quantitative imaging of the power spectrum of heart rate variability during incremental exercise. A, C, D, and E, Representative graphs of the high‐frequency component (HF; red), coefficient of component variance ratio of the low‐frequency component to the HF (CCV L/H; blue) and heart rate (HR; green) with an RAMP (15 W/min) protocol ergometer are shown in the healthy volunteer (A) and patients with myocardial infarctions ([C]; a normal value of the HF, [D] a very low value of the HF, [E] a vacillated pattern of the HF). A power spectral analysis of RR intervals measured at 1000 Hz, quantified the power spectral densities of the HF and LF using the maximum entropy method. With updating the data every heartbeat, the HF and LF were visualized as these graphs without a delay during the CPX. B, The power spectrum density (PSD) in a healthy volunteer at every particular point during exercise: rest, warm‐up, warm‐up—ventilator threshold (VT), VT, VT—peak, recovery. The vertical and horizontal lines show the power spectrum density and frequency, respectively. CCV indicates coefficient of component variance; CPX, cardiopulmonary test; HF, high‐frequency component; L/H, the ratio of the…

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  Figure 2. Changes in the power spectrum of the heart rate variability during incremental exercise. Individual patient data during the cardiopulmonary test for (A) the high‐frequency component (HF), (B) low‐frequency component (LF), (C) ratio of the LF and HF (L/H), and (D) coefficient of variation of the RR intervals (CVRR). VT indicates ventilatory threshold.

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  Figure 3. Validity testing of the oxygen uptake (VO 2) at the HRVT, LT, and VT in healthy subjects (n=30). The graphs in the left panel show the relationship between each VO 2 at the heart rate variability threshold (HRVT), ventilator threshold (VT), and lactate threshold (LT) (A, C, and E). The graphs in the right panel show the Bland‐Altman plots (B, D, and F), which indicate the respective differences between each VO 2 at the HRVT, LT, and VT (y‐axis) for each individual against the mean of the VO 2 at the HRVT, LT, and VT (x‐axis). The dark lines in each Bland‐Altman plot represent a ±1.96 SD.

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  Figure 4. Validity testing of the VO 2 at the HRVT and VT; HF 0.15 to 1.0 Hz (n=30). The graphs in the left panel show the relationship between each VO 2 at the heart rate variability threshold (HRVT) and ventilator threshold (VT) when the HF was defined as 0.15 to 0.4 Hz (A). The graphs in the right panel show the Bland‐Altman plots (B), which indicate the respective differences between each VO 2 at the HRVT and VT (y‐axis) for each individual against the mean of the VO 2 at the HRVT and VT (x‐axis). The dark lines in each Bland‐Altman plot represent a ±1.96 SD. AT indicates ; HF, high‐frequency component; VO 2, oxygen uptake.

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  Figure 5. Validity testing of the VO 2 at the HRVT, LT, and VT in patients with MI (n=32). The graphs in the left panel show the relationship between each VO 2 at the heart rate variability threshold (HRVT) and ventilator threshold (VT) (A). The graphs in the right panel show the Bland‐Altman plots (B), which indicate the respective differences between each VO 2 at the HRVT and VT (y‐axis) for each individual against the mean of the VO 2 at the HRVT and VT (x‐axis). The dark lines in each Bland‐Altman plot represent a ±1.96 SD. LT indicates lactate threshold; MI, myocardial infarction; VO 2, oxygen uptake.