Cardiovagal Baroreflex Hysteresis Using Ellipses in Response to Postural Changes

Figures

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  FIGURE 1. Identification of the spontaneous CBC in the course of respiration for elliptic processing. (A) Electrocardiogram signal ECG with rising RR values for the marked intervals #1 to #3 (expiration) and falling RR for the intervals ♢1 to ♢3 (inspiration). (B) The blood pressure P with the associated rising and falling systolic pressure PS values. (C) Vertices with filled dots correspond to rising PS and RR, and empty dots correspond to falling PS and RR. The shown ellipse represents the overall ellipse of the image-based procedure.

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  FIGURE 2. Beat-to-beat analysis of up sequences composed out of ith points, i.e., from #1 to #3, and down sequences out of ♢1 to ♢3 points; both sequences compose the spontaneous CBC for supine and standing. (A) The differences between the consecutive (i+1) and i values within the sequence of the systolic blood pressure PS. (B) Normalized differences of (A). (C) The differences between the consecutive (i+1) and i values within the sequence of RR values. (D) Normalized differences of (C). (E) The associated values of the baroreflex sensitivity BRS for all differences.

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  FIGURE 3. The effect of postural changes on the estimated ellipses of the spontaneous CBC in the course of respiration. (A) Supine versus standing is illustrated; the shaded regions mark interquartile ranges, and bold lines mark median values. Inner and outer ellipses represent, respectively, the 25th to 75th interquartile, and the middle ellipse is the median ellipse. The supine position displays more elongated and steeper hysteresis (with respect to the axis of the systolic pressure PS) than the standing position. The inset to the left shows the schematic behavior of the whole hysteresis, including both postural positions. The frequency distributions of (B) PS and (C) RR-values RR for supine and standing with p as the probability.

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  FIGURE 4. Derived courses of PS and RR out of the estimated median and IQR ellipses for the spontaneous CBC. The shaded regions represent the 25th and 75th interquartile ranges. (A) Supine. (B) Standing. The respective maxima and delays are marked between median-related courses of PS and RR.

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  FIGURE 5. Distribution of (A) the area AO of the estimated ellipses of the spontaneous CBC and (B) the ratio of minor to major axis length (=lO_MINOR/lO_MAJOR) for supine and standing with p as the probability of the distribution.

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  FIGURE 6. Radar plot of PS, PD, RR, AO, BRS, and the ratio lO_MINOR/lO_MAJOR of the spontaneous CBC for supine and standing. Whereas medians of RR and BRS are elevated, PD and the ratio lO_MINOR/lO_MAJOR are declined for supine than standing. The values AO and PS do not significantly change for postural change.

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  FIGURE 7. The magnitude of hysteresis loop (Figure 1C) in terms of changes (A) ΔPS of PS as a function of RR and (B) ΔRR of RR as a function of PS of the estimated ellipses of the spontaneous CBC for supine and standing (Figure 3A). The magnitude along PS is increased and along RR is reduced for standing as compared with supine.

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  FIGURE 8. The probability p for the overlap of up and down sequences within the hysteresis of the estimated ellipses of the spontaneous CBC for supine and standing. The ratio a/(b/2)—for the definition, see the inset figure to the right—goes to zero the broader the width of the hysteresis (=b) and the more linear is the down sequence or, in analogy, the up sequence (linearity is inversely proportional to a). For a/(b/2) ≤ 1, the up and down sequences do not overlap; otherwise, sequences overlap with their strong fluctuations. Intersected sequences forming the hysteresis are less frequent (17.4% of all cases) than nonintersected sequences.

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  FIGURE 9. Absolute number of used up and down sequences and sequences forming CBCs in all subjects of EuroBaVar data set.