Renal Innervation in Resistant Hypertension: A Review of Pathophysiology and Renal Denervation as Potential Treatment

Hypertension, blood-brain barrier disruption and changes in intracranial pressure

Intracranial pressure (ICP) is pressure within the cranium, between 5 and 15 mmHg in a normal brain, and is influenced by the dynamic balance between brain tissue, cerebrospinal fluid (CSF) and cerebral blood volume. ICP is vital for cerebral health, impacting outcomes in various neurological conditions. Disruptions, such as cerebral haemorrhage, hydrocephalus and malignant hypertension, can lead to elevated ICP, a dangerous condition known as intracranial hypertension (IH). Systemic hypertension significantly impacts cerebral health by causing microvascular damage, dysfunction of the blood-brain barrier (BBB) and impairment of intracranial compliance (ICC). This increases the risk of IH), cerebral ischaemia, neuroinflammation and lacunar infarction, further worsening neurological dysfunction. This review describes the complex relationship between hypertension and ICP regulation, focusing on the mechanisms underlying ICP and ICC adjustments in hypertensive conditions and emphasizing the role of BBB integrity and cerebral blood flow (CBF) dynamics. It discusses how the sympathetic output might change the regulation of CBF and the maintenance of ICP, highlighting how hypertensive conditions can impair this mechanism, increasing the risk of cerebral ischaemia. The neurovascular unit, including astrocytes and microglia, plays a significant role in this process, contributing to IH in hypertensive patients. Understanding the effects of hypertension on ICP and ICC could lead to therapies aimed at preserving BBB integrity, reducing inflammation and improving cerebral compliance, potentially preventing brain dysfunction and reducing stroke risk in hypertensive patients. This review underscores the need for early detection and intervention to mitigate the severe consequences of uncontrolled hypertension on cerebral health.

A comprehensive review on cardiovascular disorders development due to salt intake: an emphasis on policy implementation

Excessive salt consumption has been linked with the emergence of hypertension, which further leads to cardiovascular disease development among other medical conditions. This has resulted in leading world institutions such as the WHO coming up with relevant plans to minimize its use. Lower-middle-income countries (LMICs) have greatest burden of noncommunicable diseases (NCDs), with hypertension being a common condition. Reduction of salt intake is a great control measure in minimizing the rise in prevalence of hypertension or cardiovascular diseases. Many countries have agreed and even formulated their salt reduction policies as recommended by the WHO, however, the challenge is widely noted in implementation. Thus, few countries have been able to achieve the global WHO recommended standards of daily salt intake. Salt is the main source of sodium in our diets, which is an essential component responsible for the balance of the extracellular fluid volume but may lead to salt-induced hypertension when used excessively. The achievement of salt reduction is predicated on multiple factors such as knowledge, attitude and practice of the public. Therefore, localizing interventions with strategies such as public media campaigns, reformulation of processed foods (mandatory and voluntary) and front-of-packaging labelling awareness. Some of the reasons for failure in implementation include economic challenges, lack of visionary leadership, stakeholder struggles and poor planning and execution of strategies. This review aims to elaborate on the development of cardiovascular diseases or hypertension due to salt usage and the recent advancement regarding salt reduction policies. Further, we assess the need for proper implementation with the United Kingdom as a case study. In conclusion, most governments have made the right decisions in developing or recommending salt reduction strategies to the food industry. However, more focus is needed to ensure effective implementation of the plans.

The road to renal denervation for hypertension and beyond (HF): two decades of failed, succeeded, and to be determined

Activation of the sympathetic nervous system has been attributed to the development of hypertension. Two established approaches for treating hypertension are pharmacotherapy and lifestyle changes. With an improved understanding of renal nerve anatomy and physiology, renal denervation has been proposed as an alternative treatment for hypertension. Specifically, it has been shown that the interruption of sympathetic nerves connecting the kidney and the sympathetic nervous system can reduce blood pressure. Here, we present a review on how renal denervation can help hypertension patients, specifically focusing on our novel understanding of renal nerve anatomy, denervation technique, and subsequent clinical trials, and how it may be used to treat other cardiovascular diseases like heart failure.

Long-Term, Patient-Level Analysis of Radiofrequency Renal Denervation in the SYMPLICITY Clinical Trial Program

BACKGROUND

Renal denervation (RDN) lowers blood pressure (BP) in patients with uncontrolled hypertension. Current guidelines recommend RDN for patients with uncontrolled BP despite the use of antihypertensive (AH) medications. Durability of BP reductions and assessment of which patient baseline characteristics correlate with subsequent BP reductions are scarce.

OBJECTIVES

The authors leveraged patient data from the entire SYMPLICITY Clinical program to model long-term BP reductions and assess patient characteristics associated with future BP reductions.

METHODS

Repeated BP measurements from each patient were analyzed using linear mixed models. Models were fitted with office systolic BP (SBP), 24-h ambulatory SBP, office diastolic BP (DBP), and 24-h ambulatory DBP as outcome variables. Baseline BP, baseline number of AH medications, AH medications over time, and other variables were included as fixed effects.

RESULTS

The mixed model included data from 4,155 patients treated with the Symplicity RDN system. The mean age was 60 ± 12 years, 40.4% of whom were female. Estimated, longitudinal office and 24-h ambulatory SBP changes through 36 months, after adjusting for AH medication effects, were biphasic, with a steep reduction after RDN through the first 6 months followed by continuous and steady reductions in office and 24-h SBP and DBP afterward through 36 months. Higher baseline office systolic or 24-h ambulatory SBP were correlated with greater reductions through follow-up in office and 24-h SBP, respectively. Patient characteristics consistent with high sympathetic nerve activity, such as atrial fibrillation and type 2 diabetes, emerged as statistically significant covariates associated with greater office systolic and office and 24-h diastolic BP reductions, respectively.

CONCLUSIONS

Modeling suggested patients have durable BP reductions following RDN, with a steep immediate reduction followed by a steady reduction through 3 years.

Possible organ-protective effects of renal denervation: insights from basic studies

Inappropriate sympathetic nervous activation is the body's response to biological stress and is thought to be involved in the development of various lifestyle-related diseases through an elevation in blood pressure. Experimental studies have shown that surgical renal denervation decreases blood pressure in hypertensive animals. Recently, minimally invasive catheter-based renal denervation has been clinically developed, which results in a reduction in blood pressure in patients with resistant hypertension. Accumulating evidence in basic studies has shown that renal denervation exerts beneficial effects on cardiovascular disease and chronic kidney disease. Interestingly, recent studies have also indicated that renal denervation improves glucose tolerance and inflammatory changes. In this review article, we summarize the evidence from animal studies to provide comprehensive insight into the organ-protective effects of renal denervation beyond changes in blood pressure.

Clinical Effect of Renal Arterial Sympathetic Radiofrequency Ablation on Secondary Hypertension

Sympathetic hyperactivity is one of the main mechanisms of secondary hypertension. Reducing renal sympathetic activity through surgery can effectively reduce blood pressure. Many cases have shown that renal denervation (RDN) can selectively block renal artery sympathetic nerve activity to control refractory hypertension. This surgery is a minimally invasive surgery, and the risk of surgery-related adverse events is significantly reduced compared with surgery. Therefore, the purpose of this study is to explore the efficacy of radiofrequency ablation of renal artery sympathetic nerve in the treatment of secondary hypertension. Eight patients with secondary hypertension diagnosed by the cardiovascular department of our hospital and treated with RDN were followed up for 3-18 months, of which 5 cases were followed up for more than 12 months and 8 cases were followed up for more than 3 months. Eight patients were treated with radiofrequency ablation of renal artery catheter. The parameters such as preoperative blood pressure, antihypertensive drugs, organ function, intraoperative ablation resistance, power, time, and temperature were determined. The related changes of blood pressure, antihypertensive drugs, and visceral function and the occurrence of side effects at 1 week and 1, 3, 6, and 12 months after operation were related to the operation. In conclusion, RDN has a significant clinical effect in the treatment of refractory hypertension, with stable postoperative blood pressure drop, reduced drug dosage, and less side effects.