Analysis of Respiratory Sinus Arrhythmia and Directed Information Flow between Brain and Body Indicate Different Management Strategies of fMRI-Related Anxiety

Figures

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  Figure 1. Cardio-respiratory phase-relations: upper curves show heart rate (HR, solid line) and cardiac beat-to-beat interval (RRI, dotted line), lower curves show respiration. Slow cardiac and respiratory waves are presented in both panels for reasons of comparability. The left panel depicts positive (classical) RSA with inspiration coinciding with increasing HR (decreasing RRI) and expiration coinciding with decreasing HR (increasing RRI). This phase-relation typically occurs in a resting and relaxed state. The right panel depicts negative (inverse) RSA with inspiration coinciding with decreasing HR (increasing RRI) and expiration coinciding with increasing HR (decreasing RRI). This phase-relation occurs rarely. In awake subjects, it has predominantly been observed in situations of elevated anxiety and during slow breathing.

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  Figure 2. Examples of ~10 averaged BOLD (A–C), respiration (D) and RRI (E)-peak-triggered waves (mean ± SEM) of the subjects of group 1 (#11, #18, #3). Time intervals are shown from 6 s before to 6 s after the trigger. Numbers indicate the time shift in seconds between the peak and trigger. The red ellipse marks respiratory motion artefacts of the BOLD signal. The time shifts between breathing (line D) and respiratory BOLD artefacts (ROIs 96, 100; line C) are indicated by blue stippled lines, and the time shifts between respiratory BOLD artefacts and associated neural BOLD waves (ROI 103, 105; line B) are indicated by red stippled lines (only in the first two columns). The coherent breathing and RRI waves (lines D and E) in the first two subjects (#11, #18) indicate negative RSA (nRSA) while the out-of-phase behavior of breathing and RRI waves in the third column (subject #3) is characteristic for classical (positive) RSA (modified from [70]).

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  Figure 3. Example from subject #11. (A) Records of respiratory (upper trace) and RRI waves (lower trace); abscissa: time [s]. Some respiratory and RRI periods with PD transitions are marked in red. Note that transitions in the RRI rhythm precede changes in the respiratory rhythm by one period. (B) RRI peak (longest RR interval)-triggered respiratory (resp), RRI and BOLD waves from the PCG, pons and amygdala (blue and gray lines: mean ± SEM). The red and green circles have been automatically inserted by the computer program and mark local maxima on the negative and positive time scale, respectively. The coherence of respiratory and RRI waves indicates nRSA (upper line, left and middle panels). The vascular BOLD artefact in the right pons (lower line, left panel) slightly precedes respiration (red stippled line). The red horizontal arrow indicates the neural-BOLD coupling time (NBC) between the vessel motion artefact and the neural BOLD component. Note the non-sinusoidal oscillation in the amygdala (lower line, middle panel). (C) Information flow between RRI and respiration, blue lines indicate flow from respiration to RRI, red lines indicate flow from RRI to respiration. The numbers 1–8 on…

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  Figure 4. Example from subject #18. (A) Records of respiratory (upper trace) and RRI waves (lower trace); abscissa: time [s]. Some respiratory and RRI periods with PD transitions are marked in red. Note that transitions in the RRI rhythm precede the changes in the respiratory rhythm. (B) RRI peak (longest RR interval)-triggered respiratory (resp), RRI and slow BOLD waves (mean ± SEM; more details see text). Note the fast oscillation in the amygdala (lower line, middle panel). (C) Information flow is predominant from RRI to respiration; for further explanations, see Figure 3.

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  Figure 5. Example from subject #14 with dominant fast respiration in the 0.2–0.4 Hz band. (A) Records of respiratory and RRI waves. Some RRI periods with 1:3 coupling are marked with red semi-circles, indicating superposition of fast wavelets at ~0.3 Hz originating from the respiratory rhythm on slow RRI waves at ~0.1 Hz. (B) RRI peak (longest RR interval)-triggered respiratory (resp), RRI and slow BOLD waves (mean ± SEM; more details, see text). (C) The information flow diagram indicates a predominant flow from RRI to respiration. For further explanations, see Figure 3.

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  Figure 6. Example from subject #6 with dominant fast respiration in the 0.2–0.4 Hz band (for more detailed explanation, please see Figure 3). The RRI peak-triggered vascular BOLD waves were derived from MFG as depicted in the upper middle and right panels. The blue stippled vertical line indicates the maxima of slow BOLD waves about ~2 s before the RRI peak (longest RR interval), this means, a negative time delay indicating the vascular origin of the BOLD waves. Note the ~0.32 Hz oscillations in the amygdala (lower middle panel).

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  Figure 7. Directed coupling strengths for group 2 (n = 6) with high anxiety and predominant respiration in the 0.2–0.4 Hz frequency band. Each box shows the strength of coupling on the vertical scale. The width of bars is proportional to the mean error. The blue color shows the flow from the signal marked below the given column to the signal marked on the left, and the red color shows the flow from the signal marked on the left to the signal marked below. Violet areas mark an overlap of the two flow directions. Significant differences between couplings of inflow and outflow are marked by asterisks (p < 0.05). Red stippled ellipses mark the dominant downward flow (on the left) and the information flow from RRI to respiratory signal (on the right). The insert in the right upper corner indicates a diagram with the most important downward flows. Less pronounced flows, especially upward flows, are not shown.

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  Figure 8. AS values obtained from all 10 subjects in sessions R1 and R4. In the interest of greater clarity, the subjects of group 1 are presented in the left panel and the subjects of groups 2 and 3 in the right panel. Subject #6 (group 3) is marked as ☐- - -☐.