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. 2019 Jan 23;13:17. doi: 10.3389/fnins.2019.00017

FIGURE 1.

FIGURE 1

The effect of respiration on the sequence method. In both excerpts of systolic arterial pressure (SAP, A) and pulse interval (PI, B) time series, obtained from a healthy rat, it is noticeable the influence of respiration, increasing and decreasing beat-by-beat SAP and PI with a period of three to four beats. Three up ramps were found in the SAP series, as shown in red (first ramp), blue (second ramp) and green (third ramp). The first up PI ramp found after each up SAP ramp was highlighted using the same color. Nevertheless, the sequence method may associate several PI ramps to a given SAP ramp, depending on the delay adopted (horizontal lines). For instance, the first up SAP ramp (red) can be associated with the PI ramps found in delays 0, 3, 7, and 11. Similarly, the second SAP ramp (blue) can be associated with the PI ramps found after 3 and 7 beats of delay. The same behavior occurs with the third SAP ramp. Therefore, BEI is expected to be higher for delays 0, 3, 7, and 11. In other words, BEI will oscillate with a period of three to four beats, due to the repetitive nature of the ramps imposed by the respiration.