Submitted on October 11, 2007
Accepted on January 5, 2008
Spontaneous Baroreflex Control of Heart Rate vs. Cardiac Output: Altered Coupling in Heart Failure
Javier A. Sala-Mercado1, Masashi Ichinose2, Robert L Hammond1, Matthew Coutsos1, Tomoko K Ichinose3, Marco Pallante4, Ferdinando Iellamo4, and Donal S O'Leary1*
1 Department of Physiology, Wayne State University, Detroit, Michigan, United States
2 Faculty of Human development, Kobe University, Kobe, Hyogo, Japan; Department of Physiology, Wayne State University, Detroit, Michigan, United States
3 Laboratory for Human performance Research, Osaka International University, Moriguchi, Osaka, Japan; Department of Physiology, Wayne State University, Detroit, Michigan, United States
4 Internal Medicine, University of Rome, Rome, Italy
* To whom correspondence should be addressed. E-mail: doleary{at}med.wayne.edu.
Dynamic cardiac baroreflex responses are frequently investigated by analyzing the spontaneous reciprocal changes in arterial pressure and heart rate (HR). However, whether the spontaneous baroreflex-induced changes in HR translate into changes in cardiac output (CO) is unknown. In addition, this linkage between changes in HR and changes in CO may be different in subjects with heart failure (HF). We examined these questions using conscious dogs before and after pacing-induced HF. Spontaneous baroreflex sensitivity in the control of HR and CO were evaluated as the slopes of the linear relationships between HR or CO and left ventricular systolic pressure (LVSP) during spontaneous sequences of 
3 consecutive beats when HR or CO changed inversely vs. pressure. Furthermore, the translation of baroreflex HR responses into CO responses (HR-CO translation) was examined by computing the overlap between HR and CO sequences. In normal resting conditions, 44.0 ± 4.4 % of HR sequences overlapped with CO sequences suggesting that only around half of the baroreflex HR responses cause CO responses. In HF, HR-LVSP, CO-LVSP, and the HR-CO translation significantly decreased when compared to the normal condition (-2.29 ± 0.5 vs. -5.78 ± 0.7 beats min-1 mmHg-1; -70.95 ± 11.8 vs. -229.89 ± 29.6 ml min-1 mmHg-1; 19.66 ± 4.9 vs. 44.0 ± 4.4 % respectively). We conclude that spontaneous baroreflex HR responses do not always cause changes in CO. In addition, HF significantly decreases HR-LVSP, CO-LVSP and HR-CO translation.
