Spontaneous baroreflex control of cardiac output during dynamic exercise, muscle metaboreflex activation, and heart failure.
We have previously shown that spontaneous baroreflex-induced changes in heart rate (HR) do not always translate into changes in cardiac output (CO) at rest. We have also shown that heart failure (HF) decreases this linkage between changes in HR and CO. Whether dynamic exercise and muscle metaboreflex activation (via imposed reductions in hindlimb blood flow) further alter this translation in normal and HF conditions is unknown. We examined these questions using conscious, chronically instrumented dogs before and after pacing-induced HF during mild and moderate dynamic exercise with and without muscle metaboreflex activation. We measured left ventricular systolic pressure (LVSP), CO, and HR and analyzed the spontaneous HR-LVSP and CO-LVSP relationships. In normal animals, mild exercise significantly decreased HR-LVSP (-3.08 +/- 0.5 vs. -5.14 +/- 0.6 beats.min(-1).mmHg(-1); P < 0.05) and CO-LVSP (-134.74 +/- 24.5 vs. -208.6 +/- 22.2 ml.min(-1).mmHg(-1); P < 0.05). Moderate exercise further decreased both and, in addition, significantly reduced HR-CO translation (25.9 +/- 2.8% vs. 52.3 +/- 4.2%; P < 0.05). Muscle metaboreflex activation at both workloads decreased HR-LVSP, whereas it had no significant effect on CO-LVSP and the HR-CO translation. HF significantly decreased HR-LVSP, CO-LVSP, and the HR-CO translation in all situations. We conclude that spontaneous baroreflex HR responses do not always cause changes in CO during exercise. Moreover, muscle metaboreflex activation during mild and moderate dynamic exercise reduces this coupling. In addition, in HF the HR-CO translation also significantly decreases during both workloads and decreases even further with muscle metaboreflex activation.
Ichinose
Masashi
M
Department of Physiology, Wayne State University School of Medicine, Detroit, MI 48201, USA.
Sala-Mercado
Javier A
JA
O'Leary
Donal S
DS
Hammond
Robert L
RL
Coutsos
Matthew
M
Ichinose
Tomoko
T
Pallante
Marco
M
Iellamo
Ferdinando
F
D000818:Animals; D017704:Baroreflex / Q000502:physiology*; D002302:Cardiac Output / Q000502:physiology*; D003627:Data Interpretation, Statistical; D004285:Dogs; D005260:Female; D006333:Heart Failure / Q000378:metabolism* / Q000503:physiopathology*; D006339:Heart Rate / Q000502:physiology; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D010805:Physical Conditioning, Animal / Q000502:physiology*; D012018:Reflex / Q000502:physiology*; D013318:Stroke Volume / Q000502:physiology; D016277:Ventricular Function, Left / Q000502:physiology