Preeminent role of the cardiorenal axis in the antihypertensive response to an arteriovenous fistula: an in silico analysis

Predicting chronic responses to calcium channel blockade with a virtual population of African Americans with hypertensive chronic kidney disease

Chronic kidney disease (CKD) is associated with the progressive loss of functional nephrons and hypertension (HTN). Clinical studies demonstrate calcium channel blocker (CCB) therapy mitigates the decline in renal function in humans with essential HTN. However, there are few long-term clinical studies that determine the impact of CCBs in patients with hypertensive CKD. African Americans (AA) have a higher prevalence of CKD and a faster progression to total kidney failure as compared to the white population but the mechanisms are poorly understood. Both clinical evidence (the African American Study of Kidney Disease and Hypertension, or AASK trial) and experimental studies have demonstrated that CCB may expose glomerular capillaries to high systemic pressures and exacerbate CKD progression. Therefore, using a large physiological model, we set out to replicate the AASK trial findings, predict renal hemodynamic responses and the role of the renin-angiotensin system during CCB antihypertensive therapy in a virtual population, and hypothesize mechanisms underlying those findings. Our current mathematical model, HumMod, is comprised of integrated systems that play an integral role in long-term blood pressure (BP) control such as neural, endocrine, circulatory, and renal systems. Parameters (n=341) that control these systems were randomly varied and resulted in 1400 unique models that we define as a virtual population. We calibrated these models to individual patient level data from the AASK trial: BP and glomerular filtration rate (GFR) before and after 3 years of amlodipine (10 mg/day). After calibration, the new virtual population (n=165) was associated with statistically similar BP and GFR before and after CCB. Baseline factors such as elevated single nephron GFR and low tubuloglomerular feedback were correlated with greater declines in renal function and increased glomerulosclerosis after 3 years of CCB. Blocking the renin-angiotensin system (RAS) in the virtual population decreased glomerular pressure, limited glomerular damage, and further decreased BP (-14 ± 8 mmHg) as compared to CCB alone (-11 ± 9 mmHg). Our simulations echo the potential risk of CCB monotherapy in AA CKD patients and support blockade of the renin angiotensin system as a valuable tool in renal disease treatment when combined with CCB therapy.

Modeling the physiological roles of the heart and kidney in heart failure with preserved ejection fraction during baroreflex activation therapy

Heart failure (HF) is a leading cause of death and is increasing in prevalence. Unfortunately, therapies that have been efficacious in patients with HF with reduced ejection fraction (HFrEF) have not convincingly shown a reduction in cardiovascular mortality in patients with HF with preserved ejection fraction (HFpEF). It is thought that high sympathetic nerve activity (SNA) in the heart plays a role in HF progression. Clinical trials demonstrate that baroreflex activation therapy reduces left ventricular (LV) mass and blood pressure (BP) in patients with HFpEF and hypertension; however, the mechanisms are unclear. In the present study, we used HumMod, a large physiology model to simulate HFpEF and predict the time-dependent changes in systemic and cardiac hemodynamics, SNA, and cardiac stresses during baroreflex activation. The baseline HFpEF model was associated with elevations in systolic BP, diastolic dysfunction, and LV hypertrophy and stiffness similar to clinical HFpEF. Simulating 12 mo of baroreflex activation resulted in reduced systolic BP (-25 mmHg) and LV mass (-15%) similar to clinical evidence. Baroreflex activation also resulted in sustained decreases in cardiac and renal SNA (-22%) and improvement in LV β1-adrenergic function. However, the baroreflex-induced reductions in BP and improvements in cardiac stresses, mass, and function were mostly attenuated when renal SNA was clamped at baseline levels. These simulations suggest that the suppression of renal SNA could be a primary determinant of the cardioprotective effects from baroreflex activation in HFpEF.NEW & NOTEWORTHY Treatments that are efficacious in patients with HFrEF have not shown a significant impact on cardiovascular mortality in patients with HFpEF. We believe these simulations offer novel insight into the important roles of the cardiac and renal nerves in HFpEF and the potential mechanisms of how baroreflex activation alleviates HFpEF disease progression.

Device Therapy of Hypertension

In the past decade, efforts to improve blood pressure control have looked beyond conventional approaches of lifestyle modification and drug therapy to embrace interventional therapies. Based upon animal and human studies clearly demonstrating a key role for the sympathetic nervous system in the etiology of hypertension, the newer technologies that have emerged are predominantly aimed at neuromodulation of peripheral nervous system targets. These include renal denervation, baroreflex activation therapy, endovascular baroreflex amplification therapy, carotid body ablation, and pacemaker-mediated programmable hypertension control. Of these, renal denervation is the most mature, and with a recent series of proof-of-concept trials demonstrating the safety and efficacy of radiofrequency and more recently ultrasound-based renal denervation, this technology is poised to become available as a viable treatment option for hypertension in the foreseeable future. With regard to baroreflex activation therapy, endovascular baroreflex amplification, carotid body ablation, and programmable hypertension control, these are developing technologies for which more human data are required. Importantly, central nervous system control of the circulation remains a poorly understood yet vital component of the hypertension pathway and mandates further investigation. Technology to improve blood pressure control through deep brain stimulation of key cardiovascular control territories is, therefore, of interest. Furthermore, alternative nonsympathomodulatory intervention targeting the hemodynamics of the circulation may also be worth exploring for patients in whom sympathetic drive is less relevant to hypertension perpetuation. Herein, we review the aforementioned technologies with an emphasis on the preclinical data that underpin their rationale and the human evidence that supports their use.