Dynamic Cardiac Output Regulation during Exercise, Muscle Metaboreflex Activation and Heart Failure

We tested whether moderate dynamic exercise (EX) and muscle metaboreflex activation (MMA) affects dynamic baroreflex control of heart rate (HR), cardiac output (CO), and the influence of stroke volume (SV) fluctuations on CO regulation in normal (N) and pacing‐induced heart failure (HF) dogs by employing transfer function analyses of the relationships between spontaneous changes in left ventricular systolic pressure (LVSP) and HR, LVSP and CO, HR and CO, and SV and CO at low and high frequencies (Lo‐F, 0–0.25 Hz; Hi‐F 0.25‐0.6 Hz). In N dogs, EX significantly decreased transfer function gains for LVSP‐HR and LVSP‐CO in Hi‐F and reduced the LVSP‐CO gain in Lo‐F. MMA further reduced LVSP‐HR gain in Lo‐F. Coherence for HR‐CO in Hi‐F was decreased by EX and MMA, whereas that in Lo‐F was sustained at high levels (> 0.8) in all the settings. HF significantly reduced LVSP‐HR gain in Hi‐F. LVSP‐CO gain was decreased in both Lo‐F and Hi‐F. EX and MMA caused similar effects as observed in N conditions. In HF, the coherence for HR‐CO in Lo‐F decreased significantly in all settings, the coherence for SV‐CO in Lo‐F was significantly higher. We conclude that EX and MMA reduces dynamic baroreflex control of HR and CO and those are substantially diminished in HF. In N conditions HR modulation plays a major role in CO regulation. In HF, influence of HR modulation wanes and fluctuations of SV dominates in CO variations. NIH HL 55473