Cardiovagal baroreflex sensitivity is not correlated to sympathetic baroreceptor sensitivity within healthy, young individuals

The purpose of this study was to evaluate the relationship between the cardiac and sympathetic baroreflex sensitivities within healthy, young individuals. The gains in cardiac (as measured by changes in R‐R interval, RRI, and heart rate, HR) and sympathetic (as measured by changes in muscle sympathetic nerve activity, MSNA) baroreflex during rapid changes in arterial blood pressure were compared in 27 normotensive individuals (18 men and 9 women; age 24 yrs ±1.24; body mass index 24 ±0.51 cm/kg 2 , mean ±SEM). Heart rate, arterial blood pressure (brachial artery catheter), and peroneal MSNA were recorded under resting conditions (HR 58 ±1.6 bpm; SBP 124 ±2.7 mmHg; DBP 71 ±1.7 mmHg; MAP 87 ±1.7 mmHg; MSNA BF 17 ±1.6 bursts/min) as well as during rapid changes in arterial blood pressure induced by sequential boluses of nitroprusside and phenylephrine (Modified Oxford technique). Integrated baroreflex sensitivities for MSNA and HR were analyzed using the slopes of the linear portions of the MSNA‐diastolic blood pressure and RRI‐systolic blood pressure relationships, respectively. When individual cardiac baroreflex sensitivity was compared to sympathetic baroreflex sensitivity, no correlation (R 2 =0.0003) was found. These results indicate that although both cardiac and sympathetic efferents function in baroreflex control of the autonomic system, there does not appear to be a direct correlation in their function within healthy normotensive individuals. Research Support: NIH HL083947 and Swedish Medical Council grant 12170