Baroreflex gain and vasomotor sympathetic modulation in resistant hypertension

Noninvasive Assessment of Temporal Dynamics in Sympathetic and Parasympathetic Baroreflex Responses

Background

The baroreflex system is crucial for cardiovascular regulation and autonomic homeostasis. A comprehensive assessment requires understanding the simultaneous temporal dynamics of its multiple functional branches, which traditional methods often overlook.

Objective

To develop and validate a noninvasive method for simultaneously assessing the temporal dynamics of sympathetic and parasympathetic baroreflexes using pulse contour analysis and the sequence method.

Methods

Beat-to-beat blood pressure and ECG recordings were analyzed from 55 preoperative cardiothoracic surgery patients in the supine position and 21 subjects from the EUROBAVAR dataset in both supine and standing positions. Systolic arterial pressure (SAP), interbeat interval (IBI), cardiac output (CO), myocardial contraction (dP/dtmax), and systemic vascular resistance (SVR) were estimated using pulse contour analysis. Baroreflex sensitivity (BRS) was calculated via the sequence method and correlated with hemodynamic and heart rate variability (HRV) parameters.

Results

Parasympathetic BRS for IBI was correlated with the root mean square of successive differences of ECG RR intervals (RMSSD-HRV) at 0-beat delay. Sympathetic BRS for SVR strongly correlated with SVR, CO, and RMSSD-HRV, particularly at 3-beat delay, and was uniquely associated with SAP at 1-beat delay. Sympathetic BRS for dP/dtmax correlated with dP/dtmax at 1-beat delay. In contrast, BRS for CO correlated with CO and SVR at 0- and 3-beat delays. Postural changes mainly affected parasympathetically-mediated BRS for IBI and, to a lesser extent, the sympathetic vascular and myocardial branches.

Conclusions

This method effectively captures multiple baroreflex responses and their temporal dynamics, revealing distinct autonomic mechanisms and the impact of postural changes. Further validation is warranted.

Baroreflex activation therapy for heart failure with reduced ejection fraction: A comprehensive systematic review and meta-analysis

Background

In recent years, baroreflex activation therapy (BAT) has been utilized to treat heart failure with reduced ejection fraction (HFrEF). However, the supporting literature on its efficacy and safety is still limited. This investigation elucidates the effects of BAT in HFrEF patients to provide a reference for future clinical applications.

Methods

This investigation follows Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) 2020 guidelines. Relevant investigations on the use of BAT in HFrEF patients were searched and selected from 5 databases, including Web of Science, MEDLINE, PubMed, Embase, and Cochrane Library, from inception to December 2022. The methodological quality of eligible articles was assessed via the Cochrane risk of bias tool, and for meta-analysis, RevMan (5.3) was used.

Results

Randomized controlled trials comprising 343 participants were selected for the meta-analysis, which revealed that in HFrEF patients, BAT enhanced the levels of LVEF (MD: 2.97, 95 % CI: 0.53 to 5.41), MLHFQ (MD: -14.81, 95 % CI: -19.57 to -10.06) and 6MWT (MD: 68.18, 95 % CI: 51.62 to 84.74), whereas reduced the levels of LVEDV (MD: -15.79, 95 % CI: -32.96 to 1.37) and DBP (MD: -2.43, 95 % CI: -4.18 to -0.68).

Conclusion

It was concluded that BAT is an efficient treatment option for HFrEF patients. However, to validate this investigation, further randomized clinical trials with multiple centers and large sample sizes are needed.

Sympathetic Neural Mechanisms in Hypertension: Recent Insights

PURPOSE OF REVIEW

To examine published and unpublished data documenting the role of sympathetic neural factors in the pathogenesis of different hypertensive phenotypes. These phenotypes relate to attended or unattended blood pressure measurements, to nighttime blood pressure profile alterations, and to resistant, pseudoresistant, and refractory hypertension. Results of original clinical studies as well as of recent meta-analyses based on the behavior of different sympathetic biomarkers in various hypertensive forms will be also discussed.

RECENT FINDINGS

Studies performed in the past decade have shown that office blood pressure measurements, including in recent years those characterizing unattended or attended blood pressure assessment, are associated with profound changes in the behavior of different sympathetic biomarkers. This is the case for the clinical hypertensive phenotypes characterized by alterations in the nocturnal blood pressure profile and by sleep duration abnormalities. This is also the case for the clinical conditions defined as resistant, refractory, and pseudoresistant hypertension. Data reviewed in the present paper highlight the relevance of sympathetic neural factors in the development and progression of different clinical hypertensive phenotypes. This suggests that a common hallmark of the majority of the essential hypertensive states detectable in current clinical practice is represented by the alteration in the sympathetic blood pressure control.

The Sympathetic Nervous System in Hypertension: Roadmap Update of a Long Journey

The present paper will provide an update on the role of sympathetic neural factors in the development and progression of essential hypertension by reviewing data collected in the past 10 years. This will be done by discussing the results of the published studies in which sympathetic neural function in essential hypertension and related disease has been investigated via sophisticated and highly sensitive techniques, such as microneurographic recording of sympathetic nerve traffic and regional norepinephrine spillover. First, the relevance of the pathophysiological background of the neurogenic alterations will be discussed. It will be then examined the behavior of the sympathetic neural function in specific clinical phenotypes, such as resistant hypertension, pseudoresistant hypertension, and hypertensive states displaying elevated resting heart values. This will be followed by a discussion of the main results of the meta-analytic studies examining the behavior of sympathetic nerve traffic in essential hypertension, obesity, metabolic syndrome, and chronic renal failure. The sympathetic effects of renal denervation and carotid baroreceptor stimulation as well as the possible involvement of sympathetic neural factors in the determination of the so-called "residual risk" of the treated hypertensive patients will be finally discussed.

Baroreceptor Modulation of the Cardiovascular System, Pain, Consciousness, and Cognition

Baroreceptors are mechanosensitive elements of the peripheral nervous system that maintain cardiovascular homeostasis by coordinating the responses to external and internal environmental stressors. While it is well known that carotid and cardiopulmonary baroreceptors modulate sympathetic vasomotor and parasympathetic cardiac neural autonomic drive, to avoid excessive fluctuations in vascular tone and maintain intravascular volume, there is increasing recognition that baroreceptors also modulate a wide range of non-cardiovascular physiological responses via projections from the nucleus of the solitary tract to regions of the central nervous system, including the spinal cord. These projections regulate pain perception, sleep, consciousness, and cognition. In this article, we summarize the physiology of baroreceptor pathways and responses to baroreceptor activation with an emphasis on the mechanisms influencing cardiovascular function, pain perception, consciousness, and cognition. Understanding baroreceptor-mediated effects on cardiac and extra-cardiac autonomic activities will further our understanding of the pathophysiology of multiple common clinical conditions, such as chronic pain, disorders of consciousness (e.g., abnormalities in sleep-wake), and cognitive impairment, which may result in the identification and implementation of novel treatment modalities. © 2021 American Physiological Society. Compr Physiol 11:1373-1423, 2021.

Sympathetic Nerve Traffic and Arterial Baroreflex Function in Apparent Drug-Resistant Hypertension

True drug-resistant hypertension (RHT) is characterized by a marked neuroadrenergic activation and reflex alterations compared with the nonresistant hypertensive state. It is unknown however, whether this behavior is specific for the RHT state or is also shared by apparent RHT (ARHT). In 38 middle-age patients with RHT, 44 treated essential controlled hypertensives (HT) and 32 ARHT; we evaluated sphygmomanometric, beat-to-beat (Finapres) and 24-hour (Spacelabs) blood pressure, heart rate and muscle sympathetic nerve traffic (microneurography). Measurements included plasma aldosterone, plasma norepinephrine, homeostasis model assessment index, and spontaneous baroreflex-muscle sympathetic nerve traffic sensitivity. All the various above-mentioned blood pressure values were significantly greater in both RHT and ARHT as compared with HT, while 24-hour blood pressure was significantly lower in ARHT as compared with RHT. In ARHT, muscle sympathetic nerve traffic was significantly lower than RHT (74.8±5.2 versus 89.2±4.8 bursts/100 hb, P<0.01) and similar to HT (69.7±4.8 bursts/100 hb, P=NS). RHT showed, at variance from the other 2 groups, greater plasma aldosterone and homeostasis model assessment index values and an impaired baroreflex function. In RHT, but not in ARHT and HT, muscle sympathetic nerve traffic was significantly and inversely related to baroreflex function (r=-0.40, P<0.02) and directly to plasma aldosterone and homeostasis model assessment index values (r=0.34-0.36, P<0.05). Plasma norepinephrine and heart rate values were not significantly different in the 3 groups. These data provide evidence that the marked sympathetic activation and baroreflex dysfunction detected in RHT is not present in ARHT, which displays a sympathetic and baroreflex profile superimposable to that seen in HT. These differences in the neurogenic function may have important clinical and therapeutic implications.

Autonomic and Vascular Control in Prehypertensive Subjects with a Family History of Arterial Hypertension

BACKGROUND

Individuals with a family history of systemic arterial hypertension (FHSAH) and / or prehypertension have a higher risk of developing this pathology.

OBJECTIVE

To evaluate the autonomic and vascular functions of prehypertensive patients with FHSAH.

METHODS

Twenty-five young volunteers with FHSAH, 14 normotensive and 11 prehypertensive subjects were submitted to vascular function evaluation by forearm vascular conductance(VC) during resting and reactive hyperemia (Hokanson®) and cardiac and peripheral autonomic modulation, quantified, respectively, by spectral analysis of heart rate (ECG) and systolic blood pressure (SBP) (FinometerPRO®). The transfer function analysis was used to measure the gain and response time of baroreflex. The statistical significance adopted was p ≤ 0.05.

RESULTS

Pre-hypertensive individuals, in relation to normotensive individuals, have higher VC both at rest (3.48 ± 1.26 vs. 2.67 ± 0.72 units, p = 0.05) and peak reactive hyperemia (25, 02 ± 8.18 vs. 18.66 ± 6.07 units, p = 0.04). The indices of cardiac autonomic modulation were similar between the groups. However, in the peripheral autonomic modulation, greater variability was observed in prehypertensive patients compared to normotensive individuals (9.4 [4.9-12.7] vs. 18.3 [14.8-26.7] mmHg2; p < 0.01) and higher spectral components of very low (6.9 [2.0-11.1] vs. 13.5 [10.7-22.4] mmHg2, p = 0.01) and low frequencies (1.7 [1.0-3.0] vs. 3.0 [2.0-4.0] mmHg2, p = 0.04) of SBP. Additionally, we observed a lower gain of baroreflex control in prehypertensive patients compared to normotensive patients (12.16 ± 4.18 vs. 18.23 ± 7.11 ms/mmHg, p = 0.03), but similar delay time (-1.55 ± 0.66 vs. -1.58 ± 0.72 s, p = 0.90).

CONCLUSION

Prehypertensive patients with FHSAH have autonomic dysfunction and increased vascular conductance when compared to normotensive patients with the same risk factor.