Baroreflex effectiveness index: an additional measure of baroreflex control of heart rate in daily life

2001 ◽  
Vol 280 (3) ◽  
pp. R744-R751 ◽  
Author(s):  
Marco Di Rienzo ◽  
Gianfranco Parati ◽  
Paolo Castiglioni ◽  
Roberto Tordi ◽  
Giuseppe Mancia ◽  
...  
Keyword(s):  
Baroreflex Sensitivity ◽  
Time Window ◽  
Sinus Node ◽  
Normal Subjects ◽  
Pulse Interval ◽  
Arterial Baroreflex ◽  
Additional Measure ◽  
Baroreflex Control ◽  
Healthy Humans ◽  
Effectiveness Index

In healthy subjects, progressive beat-to-beat increases or decreases in systolic blood pressure (SBP) ramps are not always accompanied by baroreflex-driven lengthening or shortening in pulse interval (PI) ramps, respectively. This phenomenon has been quantified by a new index, the baroreflex effectiveness index (BEI), defined as the ratio between the number of SBP ramps followed by the respective reflex PI ramps and the total number of SBP ramps observed in a given time window. Specificity of BEI was shown in eight cats by a −89% reduction of BEI after sinoaortic denervation. In 14 healthy humans, the 24-h average BEI value was 0.21, with a marked day-night modulation (≈0.25 day, ≈0.15 night) in counterphase with modulation of baroreflex sensitivity (BRS). Our analysis indicates that 1) in normal subjects, arterial baroreflex can induce beat-by-beat PI changes in response to only 21% of all SBP ramps, possibly because of central inhibitory influences or of interferences at sinus node level by nonbaroreflex mechanisms and 2) BEI provides information on the baroreflex function that is complementary to BRS.

scholarly journals Baroreflex sensitivity, blood pressure buffering, and resonance: what are the links? Computer simulation of healthy subjects and heart failure patients

2007 ◽  
Vol 102 (4) ◽  
pp. 1348-1356 ◽  
Author(s):  
Hedde van de Vooren ◽  
Maaike G. J. Gademan ◽  
Cees A. Swenne ◽  
Ben J. TenVoorde ◽  
Martin J. Schalij ◽  
...  
Keyword(s):  
Heart Failure ◽  
Blood Pressure ◽  
Baroreflex Sensitivity ◽  
Sinus Node ◽  
Peripheral Resistance ◽  
Normal Subjects ◽  
Baroreflex Control ◽  
Loop Control ◽  
Heart Failure Patients ◽  
Vasomotor Function

The arterial baroreflex buffers slow (<0.05 Hz) blood pressure (BP) fluctuations, mainly by controlling peripheral resistance. Baroreflex sensitivity (BRS), an important characteristic of baroreflex control, is often noninvasively assessed by relating heart rate (HR) fluctuations to BP fluctuations; more specifically, spectral BRS assessment techniques focus on the BP-to-HR transfer function around 0.1 Hz. Skepticism about the relevance of BRS to characterize baroreflex-mediated BP buffering is based on two considerations: 1) baroreflex-modulated peripheral vasomotor function is not necessarily related to baroreflex-HR transfer; and 2) although BP fluctuations around 0.1 Hz (Mayer waves) might be related to baroreflex BP buffering, they are merely a not-intended side effect of a closed-loop control system. To further investigate the relationship between BRS and baroreflex-mediated BP buffering, we set up a computer model of baroreflex BP control to simulate normal subjects and heart failure patients. Output variables for various randomly chosen combinations of feedback gains in the baroreflex arms were BP resonance, BP-buffering capacity, and BRS. Our results show that BP buffering and BP resonance are related expressions of baroreflex BP control and depend strongly on the sympathetic gain to the peripheral resistance. BRS is almost uniquely determined by the vagal baroreflex gain to the sinus node. In conclusion, BP buffering and BRS are unrelated unless coupled gains in all baroreflex limbs are assumed. Hence, the clinical benefit of a high BRS is most likely to be attributed to vagal effects on the heart instead of to effective BP buffering.

Applicability of recent methods used to estimate spontaneous baroreflex sensitivity to resting mice

2008 ◽  
Vol 294 (1) ◽  
pp. R142-R150 ◽  
Author(s):  
Dominique Laude ◽  
Véronique Baudrie ◽  
Jean-Luc Elghozi
Keyword(s):  
Baroreflex Sensitivity ◽  
Low Frequency ◽  
Pulse Interval ◽  
Arterial Baroreflex ◽  
Baroreflex Control ◽  
Spectral Estimates ◽  
Sequence Method ◽  
Highly Correlated ◽  
Spontaneous Baroreflex ◽  
Sequence Techniques

Short-term blood pressure (BP) variability is limited by the arterial baroreflex. Methods for measuring the spontaneous baroreflex sensitivity (BRS) aim to quantify the gain of the transfer function between BP and pulse interval (PI) or the slope of the linear relationship between parallel BP and PI changes. These frequency-domain (spectral) and time-domain (sequence) techniques were tested in conscious mice equipped with telemetric devices. The autonomic relevance of these indexes was evaluated using pharmacological blockades. The significant changes of the spectral bandwidths resulting from the autonomic blockades were used to identify the low-frequency (LF) and high-frequency (HF) zones of interest. The LF gain was 1.45 ± 0.14 ms/mmHg, with a PI delay of 0.5 s. For the HF gain, the average values were 2.0 ± 0.19 ms/mmHg, with a null phase. LF and HF bands were markedly affected by atropine. On the same 51.2-s segments used for cross-spectral analysis, an average number of 26.4 ± 2.2 slopes were detected, and the average slope in resting mice was 4.4 ± 0.5 ms/mmHg. Atropine significantly reduced the slopes of the sequence method. BRS measurements obtained using the sequence technique were highly correlated to the spectral estimates. This study demonstrates the applicability of the recent methods used to estimate spontaneous BRS in mice. There was a vagal predominance in the baroreflex control of heart rate in conscious mice in the present conditions.

Hyperventilation alters arterial baroreflex control of heart rate and muscle sympathetic nerve activity

2000 ◽  
Vol 279 (2) ◽  
pp. H536-H541 ◽  
Author(s):  
Philippe Van de Borne ◽  
Silvia Mezzetti ◽  
Nicola Montano ◽  
Krzysztof Narkiewicz ◽  
Jean Paul Degaute ◽  
...  
Keyword(s):  
Heart Rate ◽  
Sympathetic Nerve ◽  
Baroreflex Sensitivity ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Normal Subjects ◽  
Arterial Baroreflex ◽  
Baroreceptor Sensitivity ◽  
Nerve Activity ◽  
Baroreflex Control

Interactions between mechanisms governing ventilation and blood pressure (BP) are not well understood. We studied in 11 resting normal subjects the effects of sustained isocapnic hyperventilation on arterial baroreceptor sensitivity, determined as the α index between oscillations in systolic BP (SBP) generated by respiration and oscillations present in R-R intervals (RR) and in peripheral sympathetic nerve traffic [muscle sympathetic nerve activity (MSNA)]. Tidal volume increased from 478 ± 24 to 1,499 ± 84 ml and raised SBP from 118 ± 2 to 125 ± 3 mmHg, whereas RR decreased from 947 ± 18 to 855 ± 11 ms (all P < 0.0001); MSNA did not change. Hyperventilation reduced arterial baroreflex sensitivity to oscillations in SBP at both cardiac (from 13 ± 1 to 9 ± 1 ms/mmHg, P < 0.001) and MSNA levels (by −37 ± 5%, P < 0.0001). Thus increased BP during hyperventilation does not elicit any reduction in either heart rate or MSNA. Baroreflex modulation of RR and MSNA in response to hyperventilation-induced BP oscillations is attenuated. Blunted baroreflex gain during hyperventilation may be a mechanism that facilitates simultaneous increases in BP, heart rate, and sympathetic activity during dynamic exercise and chemoreceptor activation.

Comparison of phenylephrine bolus and infusion methods in baroreflex measurements

1990 ◽  
Vol 69 (3) ◽  
pp. 962-967 ◽  
Author(s):  
J. T. Sullebarger ◽  
C. S. Liang ◽  
P. D. Woolf ◽  
A. E. Willick ◽  
J. F. Richeson
Keyword(s):  
Heart Rate ◽  
Arterial Pressure ◽  
Baroreflex Sensitivity ◽  
Heart Rate Response ◽  
Pressor Response ◽  
Plasma Catecholamines ◽  
Systolic Arterial Pressure ◽  
Normal Subjects ◽  
Vagus Nerves ◽  
Baroreflex Control

Phenylephrine (PE) bolus and infusion methods have both been used to measure baroreflex sensitivity in humans. To determine whether the two methods produce the same values of baroreceptor sensitivity, we administered intravenous PE by both bolus injection and graded infusion methods to 17 normal subjects. Baroreflex sensitivity was determined from the slope of the linear relationship between the cardiac cycle length (R-R interval) and systolic arterial pressure. Both methods produced similar peak increases in arterial pressure and reproducible results of baroreflex sensitivity in the same subjects, but baroreflex slopes measured by the infusion method (9.9 +/- 0.7 ms/mmHg) were significantly lower than those measured by the bolus method (22.5 +/- 1.8 ms/mmHg, P less than 0.0001). Pretreatment with atropine abolished the heart rate response to PE given by both methods, whereas plasma catecholamines were affected by neither method of PE administration. Naloxone pretreatment exaggerated the pressor response to PE and increased plasma beta-endorphin response to PE infusion but had no effect on baroreflex sensitivity. Thus our results indicate that 1) activation of the baroreflex by the PE bolus and infusion methods, although reproducible, is not equivalent, 2) baroreflex-induced heart rate response to a gradual increase in pressure is less than that seen with a rapid rise, 3) in both methods, heart rate response is mediated by the vagus nerves, and 4) neither the sympathetic nervous system nor the endogenous opiate system has a significant role in mediating the baroreflex control of heart rate to a hypertensive stimulus in normal subjects.

Baroreflex control of sinus node during dynamic exercise in humans: effects of central command and muscle reflexes

1997 ◽  
Vol 272 (3) ◽  
pp. H1157-H1164 ◽  
Author(s):  
F. Iellamo ◽  
J. M. Legramante ◽  
G. Raimondi ◽  
G. Peruzzi
Keyword(s):  
Arterial Pressure ◽  
Sinus Node ◽  
Knee Extension ◽  
Dynamic Exercise ◽  
Free Flow ◽  
Cardiac Response ◽  
Central Command ◽  
Arterial Baroreflex ◽  
Flow Conditions ◽  
Baroreflex Control

This study evaluated the influence of central command and muscle afferent stimulation (mechanical and chemical) on the integrated arterial baroreflex control of the sinus node during dynamic exercise. Twenty-two healthy men performed voluntary knee extension and electrically induced dynamic knee extension under free-flow and arrested-flow (n = 18) conditions. Systolic arterial pressure (SAP) and pulse interval (PI) were measured continuously and noninvasively. The arterial baroreflex was evaluated by analyzing the slopes of sequences of three or more consecutive beats characterized by the SAP and PI of the following beat; both increased or decreased in a linear fashion. Compared with rest, both voluntary exercise and electrically induced exercise under arrested-flow conditions resulted in a maintained baroreflex sensitivity (BRS; 11.7 +/- 1.2 vs. 9.6 +/- 0.7 and 11.3 +/- 1.4 vs. 9.8 +/- 1.5 ms/mmHg, respectively; not significant), with an apparent rightward shift in the regression line relating SAP to PI. Electrically induced exercise under free-flow conditions resulted in a significant decrease in BRS (12.1 +/- 1.4 vs. 8.8 +/- 0.8 ms/mmHg; P < 0.05). These data suggest that the central command and muscle chemoreflex act to preserve the BRS, possibly "resetting" the baroreceptor-cardiac response relationship, whereas stimulation of mechanosensitive receptors appears capable of modifying the integrated baroreflex control of sinus node function in humans. The first two mechanisms seem, however, to overwhelm the latter to maintain BRS, thus permitting a concomitant increase in arterial pressure and heart rate.

Effects of aging on 24-h dynamic baroreceptor control of heart rate in ambulant subjects

1995 ◽  
Vol 268 (4) ◽  
pp. H1606-H1612 ◽  
Author(s):  
G. Parati ◽  
A. Frattola ◽  
M. Di Rienzo ◽  
P. Castiglioni ◽  
A. Pedotti ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Systolic Blood Pressure ◽  
Baroreflex Sensitivity ◽  
Regression Line ◽  
Domain Analysis ◽  
Pulse Interval ◽  
Alpha Coefficient ◽  
Baroreflex Control ◽  
Effects Of Aging

The effects of aging on the dynamic modulation of baroreflex sensitivity over 24 h was assessed in eight elderly (mean age +/- SD, 63.9 +/- 3.2 yr) and in eight young (23.9 +/- 6.1 yr) mild or moderate essential hypertensive patients, who were subject to a 24-h intra-arterial (Oxford technique) blood pressure recording in ambulatory conditions. The sensitivity of baroreflex control of the heart rate was dynamically assessed by quantifying 1) the slope of the regression line between pulse interval (the reciprocal of heart rate) and systolic blood pressure changes over spontaneously occurring hypertension-bradycardia or hypotension-tachycardia sequences (time domain analysis) and 2) the ratio between spectral-powers of pulse interval and systolic blood pressure around 0.1 Hz (alpha-coefficient: frequency domain analysis). The 24-h average sequence slope was lower in old than in young individuals (4.4 +/- 0.5 vs. 9.9 +/- 1.3 and 4.8 +/- 0.7 vs. 8.4 +/- 1.4 ms/mmHg for hypertension-bradycardia and hypotension-tachycardia sequences, respectively; P < 0.05 for both). Similar results were obtained by using the alpha-coefficient approach. The marked nighttime increase in baroreflex sensitivity observed in young individuals was much less evident in the elderly. Thus 24-h baroreflex sensitivity is markedly impaired by aging. The impairment becomes manifest also as an inability to increase baroreflex sensitivity at night.

Bupivacaine Inhibits Baroreflex Control of Heart Rate in Conscious Rats

2000 ◽  
Vol 92 (1) ◽  
pp. 197-197 ◽  
Author(s):  
Kyoung S. K. Chang ◽  
Don R. Morrow ◽  
Kazuyo Kuzume ◽  
Michael C. Andresen
Keyword(s):  
Heart Rate ◽  
Baroreflex Sensitivity ◽  
Cardiovascular Reflexes ◽  
Pulse Interval ◽  
Dependent Manner ◽  
Baroreflex Control ◽  
Conscious Rats ◽  
Reflex Bradycardia ◽  
Adrenergic Antagonist ◽  
Dose Dependent

Background Because exposure to intravenously administered bupivacaine may alter cardiovascular reflexes, the authors examined bupivacaine actions on baroreflex control of heart rate in conscious rats. Methods Baroreflex sensitivity (pulse interval vs. systolic blood pressure in ms/mmHg) was determined before, and 1.5 and 15.0 min after rapid intravenous administration of bupivacaine (0.5, 1.0, and 2.0 mg/kg) using heart rate changes evoked by intravenously administered phenylephrine or nitroprusside. The actions on the sympathetic and parasympathetic autonomic divisions of the baroreflex were tested in the presence of a muscarinic antagonist methyl atropine and a beta-adrenergic antagonist atenolol. Results Within seconds of injection of bupivacaine, mean arterial pressure increased and heart rate decreased in a dose-dependent manner. Baroreflex sensitivity was unaltered after administration of 0.5 mg/kg bupivacaine. In addition, 1 mg/kg bupivacaine at 1.5 min depressed phenylephrine-evoked reflex bradycardia (0.776 +/- 0.325 vs. 0.543 +/- 0.282 ms/mmHg, P &lt; 0.05) but had no effect on nitroprusside-induced tachycardia. Bupivacaine (2 mg/kg), however, depressed reflex bradycardia and tachycardia (phenylephrine, 0.751 +/- 0.318 vs. 0.451 +/- 0.265; nitroprusside, 0.839 +/- 0.256 vs. 0.564 +/- 0.19 ms/mmHg, P &lt; 0.05). Baroreflex sensitivity returned to prebupivacaine levels by 15 min. Bupivacaine (2 mg/kg), in the presence of atenolol, depressed baroreflex sensitivity (phenylephrine, 0.633 +/- 0.204 vs. 0.277 +/- 0.282; nitroprusside, 0.653 +/- 0.142 vs. 0.320 +/- 0.299 ms/mmHg, P &lt; 0.05). In contrast, bupivacaine did not alter baroreflex sensitivity in the presence of methyl atropine. Conclusions Bupivacaine, in clinically relevant concentrations, inhibits baroreflex control of heart rate in conscious rats. This inhibition appears to involve primarily vagal components of the baroreflex-heart rate pathways.

Post-Adrenalectomy Hypotension in Rats; Absence of Baroreflex Resetting or Effect of Naloxone

1983 ◽  
Vol 64 (4) ◽  
pp. 371-376 ◽  
Author(s):  
S. M. Gardiner ◽  
T. Bennett
Keyword(s):  
Blood Pressure ◽  
Arterial Blood Pressure ◽  
Tap Water ◽  
Sinus Node ◽  
Pulse Interval ◽  
Baroreflex Control ◽  
Systemic Arterial Blood Pressure ◽  
Arterial Blood ◽  
Blood Pressures ◽  
Adrenalectomized Rats

1. Male Wistar rats were either bilaterally adrenalectomized or sham-operated, and given 1% sodium chloride solution instead of tap water to drink. Seven days later, arterial blood pressures were recorded directly from conscious freely moving rats. 2. Systolic and diastolic blood pressures were significantly lower in the adrenalectomized rats, whereas heart rates were significantly higher than in sham-operated animals. The tachycardia was due to a combination of sympathetic hyperactivity and reduced vagal tone, which may have been reflex responses to a reduction in effective blood volume. 3. Baroreflex control of the sinus node was assessed from the pulse interval responses to rises (induced by methoxamine) or falls (induced by glyceryl trinitrate or sodium nitroprusside) in systemic arterial blood pressure. The relation between pulse interval and systolic blood pressure was described by the same curve in sham-operated and adrenalectomized rats, indicating that, in the latter, there was no change in baroreflex setting or sensitivity. 4. Intravenous administration of naloxone (2mg/kg) had no effect on systemic arterial blood pressure in adrenalectomized rats, suggesting that endogenous opiates were not contributing to the hypotension.

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