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[Figure: see text]. [ABSTRACT FROM AUTHOR]

Maintenance of adequate cerebral perfusion during normal physiological challenges requires integration between cerebral blood flow (CBF) and systemic blood pressure control mechanisms. Previous studies have shown that cardiac baroreflex sensitivity (BRS) is inversely related to some measures of cerebral autoregulation. However, interactions between the sympathetic arterial baroreflex and cerebral perfusion control mechanisms have not been explored. To determine the nature and magnitude of these interactions we measured R–R interval, blood pressure, CBF velocity, and muscle sympathetic nerve activity (MSNA) in 11 healthy young males. Sympathetic BRS was estimated using modified Oxford method as the relationship between beat-to-beat diastolic blood pressure (DBP) and MSNA. Integrated control of CBF was quantified using transfer function analysis (TFA) metrics derived during rest and Tieck's autoregulatory index following bilateral thigh cuff deflation. Sympathetic BRS during modified Oxford trials was significantly related to autoregulatory index (r = 0.64, p = 0.03). Sympathetic BRS during spontaneous baseline was significantly related to transfer function gain (r = −0.74, p = 0.01). A more negative value for sympathetic BRS indicates more effective arterial baroreflex regulation, and a lower transfer function gain reflects greater cerebral autoregulation. Therefore, these findings indicate that males with attenuated CBF regulation have greater sympathetic BRS (and vice versa), consistent with compensatory interactions between blood pressure and cerebral perfusion control mechanisms.

Maintenance of adequate cerebral perfusion during normal physiological challenges requires integration between cerebral blood flow (CBF) and systemic blood pressure control mechanisms. Previous studies have shown that cardiac baroreflex sensitivity (BRS) is inversely related to some measures of cerebral autoregulation. However, interactions between the sympathetic arterial baroreflex and cerebral perfusion control mechanisms have not been explored. To determine the nature and magnitude of these interactions we measured R-R interval, blood pressure, CBF velocity, and muscle sympathetic nerve activity (MSNA) in 11 healthy young males. Sympathetic BRS was estimated using modified Oxford method as the relationship between beat-to-beat diastolic blood pressure (DBP) andMSNA. Integrated control of CBF was quantified using transfer function analysis (TFA) metrics derived during rest and Tieck's autoregulatory index following bilateral thigh cuff deflation. Sympathetic BRS during modified Oxford trials was significantly related to autoregulatory index (r = 0.64, p = 0.03). Sympathetic BRS during spontaneous baseline was significantly related to transfer function gain (r = -0.74, p = 0.01). A more negative value for sympathetic BRS indicates more effective arterial baroreflex regulation, and a lower transfer function gain reflects greater cerebral autoregulation. Therefore, these findings indicate that males with attenuated CBF regulation have greater sympathetic BRS (and vice versa), consistent with compensatory interactions between blood pressure and cerebral perfusion control mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: In humans, assessment of the sympathetic component of the arterial baroreceptor reflex (sBRS) is usually based on microneurographic recordings of muscle sympathetic nerve activity (MSNA), while inducing reflex changes with intravenous administration of vasoactive drugs (modified Oxford method). This method has several limitations, among which its poor temporal resolution. Some studies have proposed alternative methods by using spontaneous changes in arterial pressure (AP) and MSNA, usually collected under baroreflex closed-loop conditions (AP alters MSNA while MSNA alters AP), which makes the results difficult to interpret. In rats, a method has been developed and validated (Kanbar et al., 2007 ), which uses oscillations of renal SNA at the frequency of the heart beat. At this frequency, the baroreflex operates under open-loop conditions because of the low-pass filter properties of the resistance vasculature. The goal of the present study was to examine whether this method is applicable in humans. Data were previously collected by Gujic et al. (2007) . Briefly, MSNA and AP were recorded in 16 young healthy subjects during a 5-minute baseline resting period then during a modified Oxford test (sodium nitroprusside and phenylephrine administrations). Using the 5-minute baseline recordings, spontaneous sBRS was assessed through empirical mode decomposition over consecutive 20-second periods. Spontaneous sBRS was significantly related to pharmacological sBRS (R=0.67, n =16, P =0.004). During the 5-minute period, spontaneous sBRS exhibited variations (CV=21.7±1.7%) that were negatively correlated with AP in five subjects (R=−0.61±0.03, P <0.05) and positively correlated with MSNA in ten subjects (R=0.73±0.03, P <0.05). The new method is able to correctly estimate sBRS, and reveals the existence of previously unrecognized fast fluctuations of sBRS. [Copyright &y& Elsevier]

The sensitivity of baroreflex control of sympathetic nerve activity (SNA) represents the responsiveness of SNA to changes in blood pressure. In a slightly different analysis, the baroreflex threshold measures the probability of whether a sympathetic burst will occur at a given diastolic blood pressure. We hypothesized that baroreflex threshold analysis could be used to estimate the sensitivity of the sympathetic baroreflex measured by the pharmacological modified Oxford test. We compared four measures of sympathetic baroreflex sensitivity in 25 young healthy participants: the "gold standard" modified Oxford analysis (nitroprusside and phenylephrine), nonbinned spontaneous baroreflex analysis, binned spontaneous baroreflex analysis, and threshold analysis. The latter three were performed during a quiet baseline period before pharmacological intervention. The modified Oxford baroreflex sensitivity was significantly related to the threshold slope (r = 0.71, P < 0.05) but not to the binned (1 mmHg bins) and the nonbinned spontaneous baroreflex sensitivity (r = 0.22 and 0.36, respectively, P > 0.05), which included burst area. The threshold analysis was also performed during the modified Oxford manipulation. Interestingly, we found that the threshold analysis results were not altered by the vasoactive drugs infused for the modified Oxford. We conclude that the noninvasive threshold analysis technique can be used as an indicator of muscle SNA baroreflex sensitivity as assessed by the modified Oxford technique. Furthermore, the modified Oxford method does not appear to alter the properties of the baroreflex. [ABSTRACT FROM AUTHOR]

Background: Volatile anesthetics have been shown to decrease baroreflex. In humans, cardiovagal baroreflex curve is best described to be sigmoidal and analysis of sigmoid model can provide more information, such as threshold (THR), saturation (SAT), maximal gain (Gmax), operating range (OR, difference between THR and SAT), operational point (OP, relative position of resting set point within the OR) in addition to the linear gain. We compared the changes in the sigmoid model of the systolic blood pressure (SBP)-RR interval relation between awake state and general anesthesia., Methods: Sigmoid curve was obtained using the 'modified Oxford technique' (bolus sodium nitroprusside followed by bolus phenylephrine) to perturb SBP in awake group and 2 vol% sevoflurane anesthesia group. Radial arterial beat-by-beat SBP and raw RR interval data points were plotted and then binned in 2 mmHg SBP increments. Curve fittings were performed using symmetric four-parameter sigmoid model and asymmetric five-parameter sigmoid model. Gmax was calculated from the first derivative of the logistic function., Results: Compared with awake control, general anesthesia caused decreases of linear gain, Gmax and OR. RR interval THR and SBP THR were unaffected, whereas SBP SAT increased and RR interval SAT decreased, resulting from reduced linear gain and curvature parameter. Resting set point fell and OP shifted significantly to THR region., Conclusions: Sigmoidal baroreflex curve revealed diminished gains, OR and OP during general anesthesia. Moreover, our results demonstrate that the analysis of sigmoid baroreflex arc across the entire baroreflex range provide more unique information beyond that of linear gain.