Reinstating respiratory heart rate variability improves hemodynamic responses during exercise in heart failure with reduced ejection fraction

Fig. 1. Experimental set-up. A, Timeline of experimental protocol. B, Schematic of the experimental set-up and representative simultaneous recordings in awake sheep during RespHRV pacing. Blue ovals on the heart schematic indicate the placement positions of implanted flow probes. BP; blood pressure, CO; cardiac output, CoBF; coronary artery blood flow, dEMG; diaphragmatic electromyography (edited to remove ECG contamination for visual presentation), HR; heart rate

Fig. 2. Conscious 24-h data for 3-week protocol. A, Two weeks of RespHRV pacing (blue: n = 6) significantly increased cardiac output compared to monotonic pacing (red: n = 8) (A, RespHRV: * P = 4.82 × 10–6. One-way ANOVA, effect of time. # P = 0.0065. Two-way ANOVA, interaction effect). B, Both RespHRV and mono groups were paced to an equivalent heart rate (RespHRV: * P = 0.027, n = 6, Mono: * P = 2.68 × 10–6, n = 8 One-way ANOVA, effect of time). No change in C, mean arterial pressure (RespHRV: n = 5, Mono: n = 6), D, systemic vascular resistance (RespHRV: n = 5, Mono: n = 6), E, coronary artery blood flow (both groups, n = 5), or F. coronary artery vascular resistance (RespHRV: n = 5, Mono: n = 4) between 2 weeks RespHRV or monotonic pacing. A–F, Each data point is a 24-h average

Fig. 3. Hemodynamic responses to exercise in RespHRV-paced heart failure sheep. A Raw data trace of the hemodynamic exercise responses. B, A timeline of the graded exercise protocol. Change compared to baseline C, heart rate (baseline: *P = 4.1 × 10–4; post 2-week RespHRV -pacing: **P = 1.7 × 10–3. One-way ANOVA, effect of exercise, n = 6). D, cardiac output (baseline: *P = 2.6 × 10–5; post 2-week RespHRV pacing: **P = 1.6 × 10–3. One-way ANOVA, effect of exercise. # P = 3.7 × 10–4. Two-way ANOVA, Group effect, n = 6). E, cardiac power (baseline: *P = 2.4 × 10–4; Post 2-weeks RespHRV pacing: *P = 0.022. One-way ANOVA, effect of exercise. # P = 1.6 × 10–4. Two-way ANOVA, group effect, n = 5). F, coronary artery blood flow (baseline: *P = 4.1 × 10–3; post 2-weeks RespHRV pacing: * P = 6.6 × 10–5. One-way ANOVA, effect of exercise. # P = 1.7 × 10–3. Two-way ANOVA, group effect. † P = 0.078. Mixed-effects analysis, interaction effect, n = 5). G, Mean arterial pressure, (baseline only: *P = 0.019. One-way ANOVA, effect of exercise, n = 5) during exercise before (light blue) or after (dark blue) 2 weeks of RespHRV pacing. H, Heart rate recovery post-exercise (n = 6. # P = 0.046, paired t…

Fig. 4. Hemodynamic responses to exercise in monotonically paced heart failure sheep. In stark contrast to RespHRV-paced sheep (see Fig. 3) A–F, no difference in any hemodynamic parameters during exercise before (red) or after 2 weeks of monotonic pacing (dark red) were observed. A, Heart rate (baseline: *P = 6.3 × 10–7; post 2-week mono-pacing: *P = 1.5 × 10–9. One-way ANOVA, effect of exercise, n = 8). B, Cardiac output (baseline: *P = 1.8 × 10–5; post 2-week Mono-pacing: *P = 7.4 × 10–8. One-way ANOVA, effect of exercise, n = 8). C, Cardiac power (baseline: *P = 7.9 × 10–4; post 2-week mono-pacing: *P = 1.0 × 10–6. One-way ANOVA, effect of exercise, n = 6). D, Coronary artery blood flow (baseline: *P = 0.014; post 2-week mono-pacing: **P = 3.5 × 10–2. One-way ANOVA, effect of exercise, n = 5). E, Mean arterial pressure (baseline: *P = 0.020; post 2-week mono-pacing: *P = 0.030. One-way ANOVA, effect of exercise, n = 6). F, Heart rate recovery, presented fitted with first-order exponential decay (n = 8)

Fig. 5. Single beat hemodynamics, normalized to heart period, during exercise. A Representative schematics of single-beat hemodynamics. Yellow highlighted area indicates area under the curve: cardiac output (CO) = stroke volume, coronary artery blood flow (CoBF) = total coronary blood flow per beat. Red asterisk indicates peak flow per beat. All data are normalized to heart period. B – M, Data points represent the change in a given parameter from baseline (stood on treadmill) to max exercise. Lighter circles represent the pre-pacing exercise test, with connecting lines to darker circles showing post-pace exercise test. B Change in stroke volume, normalized to heart period increases after RespHRV pacing (P = 0.025, paired t test), with no change in peak aortic flow C. D + E, No change in stroke volume of peak aortic flow after monotonic pacing. F + G, Total coronary artery blood flow, and peak coronary artery blood flow per beat increase more during exercise after RespHRV pacing (F: P = 0.017, G: P = 0.014, paired t test). H + I, With no change in coronary hemodynamics during exercise after monotonic pacing. J–M, Neither RespHRV nor monotonic pacing resulted in a change in the increase in…

Fig. 6. Experimental set-up and 5-week drugs with RespHRV protocol. A, A modified timeline from Fig. 1A showing experimental protocol in drug animals. B, Two weeks of RespHRV pacing on the background of drugs (n = 6) significantly increased cardiac output (*P = 7.5 × 10–14, one-way ANOVA, effect of time), D, heart rate over time (*P = 3.9 × 10–28, one-way ANOVA, effect of time, drugs for 4 weeks, drugs + paced for 2 weeks), E, systemic vascular resistance (*P = 3.7 × 10–9, one-way ANOVA, effect of time). No change in C, mean arterial pressure (n = 6), F, coronary artery blood flow (n = 6), or G. coronary artery vascular resistance (n = 6). B-G, Each data point is a 24-h average