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How to measure baroreflex sensitivity
TL;DR: The use of vasoactive drugs and the analysis of spontaneously occurring changes in blood pressure and heart rate are described.
Abstract: In normal subjects arterial baroreflexes play a key role in short-term blood pressure adjustments to a variety of environmental stresses, thereby maintaining circulatory homeostasis. These responses are mediated by the sympathetic and parasympathetic nervous systems through their effects on heart rate, venous return, contractility and peripheral resistance. The evaluation of baroreflex sensitivity (BRS) has recently found unexpected exploitations as alterations in the baroreflex control of heart rate have been associated with an increased propensity for cardiac mortality and sudden cardiac death [1]. Among several quantitative approaches developed for evaluating BRS including the analysis of reflex responses to pharmacological or mechanical manipulations of baroreceptors, this article describes the use of vasoactive drugs and the analysis of spontaneously occurring changes in blood pressure and heart rate.
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TL;DR: In CHF patients in sinus rhythm, TF-BRS conveys relevant clinical and prognostic information, but its measurability is markedly affected by ectopic activity, and a new prognostic index can be computed in almost all patients.
83 citations
TL;DR: The data indicate that different baroreflex components and mechanisms may be impaired in patients with depression and may contribute to their increased cardiac risk.
Abstract: BACKGROUND: Recent studies have shown that depressive disorder is associated with impaired baroreceptor or baroreflex sensitivity, which is proposed to be a predisposing factor for sudden death in patients with manifest cardiac disease. These studies have not evaluated the afferent and efferent components of the cardiac baroreflex loop or other baroreflex mechanisms that regulate target processes (cardiac metabolism and blood pressure variability) related to the impairment. The objective of this study was to gain more insight into autonomic functioning in depressive disorder to more fully examine the potential basis for increased cardiac mortality. METHODS: The subjects were 28 women and men with unipolar major depression who were taking antidepressant medications and who were in partial remission and free of cardiovascular or other serious disease, and 28 healthy control subjects matched for sex, age, and ethnicity. The two samples were compared for negative affective dispositions (anger expression, hostility, defensiveness, anxiety), spontaneous (closed-loop) baroreflex activity, heart rate, heart rate variability, systolic blood pressure, and heart rate-systolic blood pressure double product under resting conditions. RESULTS: Depressed patients showed a general disposition to anger suppression coupled with higher hostility and anxiety, and lower defensiveness. The patients showed higher general sympathetic activity (high levels of blood pressure, low-frequency heart rate variability) and lower parasympathetic-related activity (high heart rate and reduced high frequency heart rate variability) with affected cardiac metabolism estimated by the double product. Depressed patients had lower baroreflex sensitivity related to a higher gain of the afferent component of the baroreflex without respective gain adjustment of its efferent component (reflex gain 'de-afferentation'). It was coupled with a compensatory higher number of effective baroreflex reactions (reflex gating 're-afferentation'). Antidepressant agents and depressed mood had additional independent effects on baroreflex sensitivity through the efferent component of the cardiac baroreflex loop. CONCLUSIONS: The data indicate that different baroreflex components and mechanisms may be impaired in patients with depression and may contribute to their increased cardiac risk.
79 citations
TL;DR: The data show that renal transplantation improves blood pressure and HRV and restores baroreflex function to near normal range on the long-term follow-up and these effects may contribute to the improvement of blood pressure control and survival after successful transplantation.
Abstract: Background. Renal transplantation improves the uraemic autonomic dysfunction and heart rate variability (HRV). The effects of successful transplantation on blood pressure variability (BPV) and baroreflex function are not well defined. Methods. BPV, HRV and baroreceptor indices were determined in (1) 52 non-diabetic chronic haemodialysis patients, (2) 44 transplanted patients, 24 in the first year after renal transplantation (≤I year) and 20 at least 1 year (>1 year) after renal transplantation, and (3) 41 control individuals with normal renal function, age-matched to (1) and (2). Power spectrum analysis of interbeat intervals (IBI) and systolic blood pressure (SBP) was performed in the low-frequency (LF 0.04-0.15 Hz) and the high-frequency (HF 0.15-0.40 Hz) bands. Spontaneous baroreceptor sensitivity (BRS) was determined by the sequence (slope) and spectral (a coefficient) techniques. Results. In haemodialysis patients, BPV was increased, while HRV, BRS slope and LF a and HF a coefficients were markedly decreased as compared to control individuals. Renal transplantation was associated with normalization of BPV at short term (≤1 year) and long term and with improvement of HRV at a long-term (> 1 year) follow-up. In patients with long-standing functioning grafts (>1 year), baroreceptor indices were significantly increased and returned to values similar to those of the control subjects. Conclusions. Our data show that renal transplantation improves blood pressure and HRV and restores baroreflex function to near normal range on the long-term follow-up. These effects may contribute to the improvement of blood pressure control and survival after successful transplantation.
34 citations
TL;DR: Findings indicate the sit-to-stand method is a statistically reliable BRS assessment tool and suitable for the examination of baroreflex hysteresis.
Abstract: Baroreflex assessment has diagnostic and prognostic utility in the clinical and research environments, and there is a need for a reliable, simple, noninvasive method of assessment. The repeated sit...
17 citations
Cites methods from "How to measure baroreflex sensitivi..."
...Directional BRS for all three methods were calculated using the same approach, also described by others (24, 41)....
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TL;DR: The authors focus on the mechanisms of resistance to antihypertensive therapy (particularly for monotherapy with either angiotensin-converting enzyme inhibitors or angiotENSin II antagonists) in the treatment of diabetic hypertension.
Abstract: Resistance to antihypertensive drugs is common in hypertensive patients with type 2 diabetes. This is unfortunate because hypertension is one of the most important risk factors for development of cardiovascular events, and the goal blood pressure level is set lower in diabetic subjects than in nondiabetic subjects. Previous outcome trials in diabetic subjects have mainly focused on end points such as microalbuminuria or the incidence of cardiovascular events rather than on reduction of blood pressure; some reports, however, have suggested mechanisms for the drug resistance. These include several clinical conditions known to be associated with difficulty in reducing blood pressure specifically in diabetes mellitus: change in the renin-angiotensin system and chymase, volume overload, central sympathetic hyperactivity, sleep apnea, secondary hypertension, pseudoresistance (white coat hypertension), and poor compliance related to subclinical depression. In this review, the authors focus on the mechanisms of resistance to antihypertensive therapy (particularly for monotherapy with either angiotensin-converting enzyme inhibitors or angiotensin II antagonists) in the treatment of diabetic hypertension.
16 citations
References
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TL;DR: These observations provide the first description in humans of the baroreceptor-heart rate reflex in daily life, characterized by marked within-subject variations hi sensitivity due in part to hemodynamic, temporal, and behavioral factors.
Abstract: The baroreceptor control of the sinus node was evaluated in 10 normotensive and 10 age-matched essential hypertensive subjects in whom ambulatory blood pressure was recorded intra-arterially for 24 hours and scanned by a computer to identify the sequences of three or more consecutive beats in which systolic blood pressure (SBP) and pulse interval (PI) progressively rose (+PI/+SBP) or fell (-PI/-SBP) in a linear fashion, according to a method validated in cats. In normotensive subjects, several hundred +PI/+SBP and -PI/-SBP sequences of 3 beats were found whereas the number of sequences of 4, 5, and more than 5 beats showed a progressive drastic reduction. The mean slopes of +PI/+SBP (7.6 +/- 2.0 msec/mm Hg) and -PI/-SBP (6.4 +/- 1.5 msec/mm Hg) sequences were similar, but in both instances there was a large scattering of the values around the mean (variation coefficients: 64.2 +/- 4.7 and 62.6 +/- 2.4%). The slopes decreased as a function of the sequence length and baseline heart rate and increased to a marked extent during the night as compared with daytime values. All sequences were more rare (-33.2% for +PI/+SBP and -31.7% for -PI/-SBP) and less steep in hypertensive subjects (-40.3 and -36.2%, respectively), who failed to show the marked nighttime increase in slope observed in normotensive subjects. To our knowledge, these observations provide the first description in humans of the baroreceptor-heart rate reflex in daily life. This reflex is characterized by marked within-subject variations in sensitivity due in part to hemodynamic, temporal, and behavioral factors.(ABSTRACT TRUNCATED AT 250 WORDS)
602 citations
"How to measure baroreflex sensitivi..." refers background in this paper
...[18], is based on the identification of three or more consecutive beats in which progressive increases in systolic blood pressure are followed by progressive lengthening in RR interval or, progressive decreases in systolic blood pressure are followed by a progressive shortening in RR interval....
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TL;DR: Reduced sensitivity of the baroreflexes in hypertension, with respect to control of heart rate is demonstrated, and a distinction is made between this change in sensitivity and simple resetting of the reflex.
Abstract: Sudden intravenous injections of small amounts of angiotensin or phenylephrine were given to 30 subjects to produce modest, brief increases in directly measured systemic arterial pressure. A plot of each systolic pressure against the second succeeding cardiac cycle length produced a linear distribution, the slope of which was expressed as the millisecond increase in cycle length per mm Hg rise in systolic pressure. The slope is an index of baroreflex sensitivity and was found to have an average value of 12.8 in 18 subjects without hypertension and 2.8 in 12 others with hypertension. When all results were pooled, there was an inverse relationship between the resting mean arterial pressure and slope of the baroreflex regression lines. The findings demonstrate reduced sensitivity of the baroreflexes in hypertension, with respect to control of heart rate. A distinction is made between this change in sensitivity and simple resetting of the reflex.
579 citations
TL;DR: The two most important techniques used to study the autonomic nervous system--heart rate variability and baroreflex sensitivity--are reviewed, and the clinical and experimental data suggesting that these techniques are powerful predictors of future arrhythmic events are discussed in depth.
463 citations
"How to measure baroreflex sensitivi..." refers background in this paper
...The evaluation of baroreflex sensitivity (BRS) has recently found unexpected exploitations as alterations in the baroreflex control of heart rate have been associated with an increased propensity for cardiac mortality and sudden cardiac death [1]....
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TL;DR: In moderate to severe CHF, a depressed sensitivity of vagal reflexes parallels the deterioration of clinical and hemodynamic status and is significantly associated with poor survival.
Abstract: Background In chronic heart failure (CHF), arterial baroreflex regulation of cardiac function is impaired, leading to a reduction in the tonic restraining influence on the sympathetic nervous system. Because baroreflex sensitivity (BRS), as assessed by the phenylephrine technique, significantly contributes to postinfarction risk stratification, the aim of the present study was to evaluate whether in CHF patients a depressed BRS is associated with a worse clinical hemodynamic status and unfavorable outcome. Methods and Results BRS was assessed in 282 CHF patients in sinus rhythm receiving stable medical therapy (age, 52±9 years; New York Heart Association [NYHA] class, 2.4±0.6; left ventricular ejection fraction [LVEF], 23±6%). The BRS of the entire population averaged 3.9±4.0 ms/mm Hg (mean±SD) and was significantly related to LVEF and hemodynamic parameters (LVEF, P<.005; cardiac index and pulmonary wedge pressure, P<.001 by regression analysis). Patients in NYHA classes III or IV and those with severe m...
459 citations
"How to measure baroreflex sensitivi..." refers background or methods in this paper
...In patients with congestive heart failure [9] even higher doses (up to 10 mcg/kg) have been used to elicit baroreceptor responses....
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...0 ms/mm Hg (SD) in two large series of patients with a previous myocardial infarction [14] and with congestive heart failure [9] respectively....
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...At variance, in patients with heart failure in stable clinical condition it may be necessary to increase the rate of infusion of the drug as these patients show slower blood pressure changes [9]....
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TL;DR: The electrical activity of single afferent cardiac fibres isolated from the third and fourth left thoracic sympathetic rami communicantes of anaesthetized cats recorded in Fig. 1.1.
Abstract: 1. We recorded the electrical activity of single afferent cardiac fibres isolated from the third and fourth left thoracic sympathetic rami communicantes of anaesthetized cats. Their conduction velocities ranged from 12 to 32 m/sec.2. The endings of each fibre were localized to one cardiac chamber by mechanical probing of the opened heart performed at the end of the experiment.3. The impulse activity was spontaneous and, in fibres with atrial or ventricular endings, it was in phase with a particular atrial or ventricular event.4. This nervous activity increased during increases in pressure occurring in the chamber where the endings were located. Conversely, decreases in pressure were accompanied by decreased nervous discharge.5. In some experiments the left coronary artery was perfused at different flows and pressures. Brief decreases or increases in coronary flow and pressure decreased or increased, respectively, the discharge of fibres with atrial or ventricular endings. Fibres were excited by intracoronary injections of veratridine.6. Cessation of coronary pump flow increased the discharge of fibres with atrial or ventricular endings only when myocardial ischaemia was accompanied by signs of heart failure.7. These afferent cardiac sympathetic fibres which provide the spinal cord with continuous specific information on cardiac events are likely to contribute to the neural control of circulation.
283 citations
"How to measure baroreflex sensitivi..." refers background in this paper
...The presence of a necrotic and noncontracting segment may indeed alter the geometry of the beating heart and increase beyond normal the firing of sympathetic and vagal afferent fibers by mechanical distortion of their sensory endings [13]....
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