Acute effect of clonidine on left ventricular pressure-volume relation in hypertensive patients with diastolic heart dysfunction

Mathematical modeling of antihypertensive therapy

Hypertension is a multifactorial disease arising from complex pathophysiological pathways. Individual characteristics of patients result in different responses to various classes of antihypertensive medications. Therefore, evaluating the efficacy of therapy based on in silico predictions is an important task. This study is a continuation of research on the modular agent-based model of the cardiovascular and renal systems (presented in the previously published article). In the current work, we included in the model equations simulating the response to antihypertensive therapies with different mechanisms of action. For this, we used the pharmacodynamic effects of the angiotensin II receptor blocker losartan, the calcium channel blocker amlodipine, the angiotensin-converting enzyme inhibitor enalapril, the direct renin inhibitor aliskiren, the thiazide diuretic hydrochlorothiazide, and the β-blocker bisoprolol. We fitted therapy parameters based on known clinical trials for all considered medications, and then tested the model's ability to show reasonable dynamics (expected by clinical observations) after treatment with individual drugs and their dual combinations in a group of virtual patients with hypertension. The extended model paves the way for the next step in personalized medicine that is adapting the model parameters to a real patient and predicting his response to antihypertensive therapy. The model is implemented in the BioUML software and is available at https://gitlab.sirius-web.org/virtual-patient/antihypertensive-treatment-modeling.

Is the Sympathetic System Detrimental in the Setting of Septic Shock, with Antihypertensive Agents as a Counterintuitive Approach? A Clinical Proposition

Mortality in the setting of septic shock varies between 20% and 100%. Refractory septic shock leads to early circulatory failure and carries the worst prognosis. The pathophysiology is poorly understood despite studies of the microcirculatory defects and the immuno-paralysis. The acute circulatory distress is treated with volume expansion, administration of vasopressors (usually noradrenaline: NA), and inotropes. Ventilation and anti-infectious strategy shall not be discussed here. When circulation is considered, the literature is segregated between interventions directed to the systemic circulation vs. interventions directed to the micro-circulation. Our thesis is that, after stabilization of the acute cardioventilatory distress, the prolonged sympathetic hyperactivity is detrimental in the setting of septic shock. Our hypothesis is that the sympathetic hyperactivity observed in septic shock being normalized towards baseline activity will improve the microcirculation by recoupling the capillaries and the systemic circulation. Therefore, counterintuitively, antihypertensive agents such as beta-blockers or alpha-2 adrenergic agonists (clonidine, dexmedetomidine) are useful. They would reduce the noradrenaline requirements. Adjuncts (vitamins, steroids, NO donors/inhibitors, etc.) proposed to normalize the sepsis-evoked vasodilation are not reviewed. This itemized approach (systemic vs. microcirculation) requires physiological and epidemiological studies to look for reduced mortality.

Drawing Inspiration from Developmental Biology for Cardiac Tissue Engineers

A sound understanding of developmental biology is part of the foundation of effective stem cell-derived tissue engineering. Here, the key concepts of cardiac development that are successfully applied in a bioinspired approach to growing engineered cardiac tissues, are reviewed. The native cardiac milieu is studied extensively from embryonic to adult phenotypes, as it provides a resource of factors, mechanisms, and protocols to consider when working toward establishing living tissues in vitro. It begins with the various cell types that constitute the cardiac tissue. It is discussed how myocytes interact with other cell types and their microenvironment and how they change over time from the embryonic to the adult states, with a view on how such changes affect the tissue function and may be used in engineered tissue models. Key embryonic signaling pathways that have been leveraged in the design of culture media and differentiation protocols are presented. The cellular microenvironment, from extracellular matrix chemical and physical properties, to the dynamic mechanical and electrical forces that are exerted on tissues is explored. It is shown that how such microenvironmental factors can inform the design of biomaterials, scaffolds, stimulation bioreactors, and maturation readouts, and suggest considerations for ongoing biomimetic advancement of engineered cardiac tissues and regeneration strategies for the future.

Clinical Practice: Should we Radically Alter our Sedation of Critical Care Patients, Especially Given the COVID-19 Pandemics?

The high number of patients infected with the SARS-CoV-2 virus requiring care for ARDS puts sedation in the critical care unit (CCU) to the edge. Depth of sedation has evolved over the last 40 years (no-sedation, deep sedation, daily emergence, minimal sedation, etc.). Most guidelines now recommend determining the depth of sedation and minimizing the use of benzodiazepines and opioids. The broader use of alpha-2 adrenergic agonists ('alpha-2 agonists') led to sedation regimens beginning at admission to the CCU that contrast with hypnotics+opioids ("conventional" sedation), with major consequences for cognition, ventilation and circulatory performance. The same doses of alpha-2 agonists used for 'cooperative' sedation (ataraxia, analgognosia) elicit no respiratory depression but modify the autonomic nervous system (cardiac parasympathetic activation, attenuation of excessive cardiac and vasomotor sympathetic activity). Alpha-2 agonists should be selected only in patients who benefit from their effects ('personalized' indications, as opposed to a 'one size fits all' approach). Then, titration to effect is required, especially in the setting of systemic hypotension and/or hypovolemia. Since no general guidelines exist for the use of alpha-2 agonists for CCU sedation, our clinical experience is summarized for the benefit of physicians in clinical situations in which a recommendation might never exist (refractory delirium tremens; unstable, hypovolemic, hypotensive patients, etc.). Because the physiology of alpha-2 receptors and the pharmacology of alpha-2 agonists lead to personalized indications, some details are offered. Since interactions between conventional sedatives and alpha-2 agonists have received little attention, these interactions are addressed. Within the existing guidelines for CCU sedation, this article could facilitate the use of alpha-2 agonists as effective and safe sedation while awaiting large, multicentre trials and more evidence-based medicine.

Hypothesis: Fever control, a niche for alpha-2 agonists in the setting of septic shock and severe acute respiratory distress syndrome?

During severe septic shock and/or severe acute respiratory distress syndrome (ARDS) patients present with a limited cardio-ventilatory reserve (low cardiac output and blood pressure, low mixed venous saturation, increased lactate, low PaO2/FiO2 ratio, etc.), especially when elderly patients or co-morbidities are considered. Rescue therapies (low dose steroids, adding vasopressin to noradrenaline, proning, almitrine, NO, extracorporeal membrane oxygenation, etc.) are complex. Fever, above 38.5-39.5°C, increases both the ventilatory (high respiratory drive: large tidal volume, high respiratory rate) and the metabolic (increased O2 consumption) demands, further limiting the cardio-ventilatory reserve. Some data (case reports, uncontrolled trial, small randomized prospective trials) suggest that control of elevated body temperature ("fever control") leading to normothermia (35.5-37°C) will lower both the ventilatory and metabolic demands: fever control should simplify critical care management when limited cardio-ventilatory reserve is at stake. Usually fever control is generated by a combination of general anesthesia ("analgo-sedation", light total intravenous anesthesia), antipyretics and cooling. However general anesthesia suppresses spontaneous ventilation, making the management more complex. At variance, alpha-2 agonists (clonidine, dexmedetomidine) administered immediately following tracheal intubation and controlled mandatory ventilation, with prior optimization of volemia and atrio-ventricular conduction, will reduce metabolic demand and facilitate normothermia. Furthermore, after a rigorous control of systemic acidosis, alpha-2 agonists will allow for accelerated emergence without delirium, early spontaneous ventilation, improved cardiac output and micro-circulation, lowered vasopressor requirements and inflammation. Rigorous prospective randomized trials are needed in subsets of patients with a high fever and spiraling toward refractory septic shock and/or presenting with severe ARDS.

A centrally acting antihypertensive, clonidine, combined to a venous dilator, nitroglycerin, to handle severe pulmonary edema

A patient, with known left ventricular failure presented with severe pulmonary edema, an ejection fraction of 10% to 15%, knee mottling, and lactates of 7 mM L⁻¹. He was treated with unusually high-dose nitroglycerin (NTG) intravenously (IV; NTG ≈ 70 mg for 1 hour). To suppress dyspnea, systolic blood pressure had to be lowered from ≈ 150-160 to ≈ 100-120 mm Hg. To lower NTG requirement, an α-2 agonist, clonidine, was administered (300 μg IV for 2 hours). Dyspnea, tachypnea, and tachycardia subsided for 1 to 2 hours, allowing to reduce NTG infusion to 2 to 4 mg h⁻¹. State-of the-art treatment was superimposed: sitting position with leg down, noninvasive ventilation, positive end-expiratory pressure, bolus of furosemide 250 mg, and administration of 1000 mL of crystalloid for 1 hour under echocardiographic guidance. We ascribed the resistance to NTG to the activation of the sympathetic, vasopressin, and renin-angiotensin systems ("neurohormonal activation"). α-2 agonists reduce the sympathetic activation observed during severe left ventricular failure and overall oxygen consumption, evoke systemic and pulmonary arterial dilation, increase diastolic time, and improve diastolic function and diuresis. Because the α-2 agonist, dexmedetomidine, is available as an IV drug on the North American market, a niche may exist in the setting of emergency medicine/coronary care. This awaits evidence-based documentation.

Acute iterative bronchospasm and "do not re-intubate" orders: sedation by an alpha-2 agonist combined with noninvasive ventilation

A male patient presented with bronchospasm and acute respiratory distress. The patient had presented 2 previous episodes of severe bronchospasm following abdominal surgery, leading twice to intubation, mechanical ventilation, and conventional sedation. As the patient positively rejected a third episode of intubation + mechanical ventilation, noninvasive ventilation (pressure support = 8 cm H₂O, positive end-expiratory pressure = 10 cm H₂O), inhaled therapy, and clonidine orally (≈ 4 μg/kg) were combined. Over 1 to 2 hours, the acute respiratory distress disappeared. Noninvasive ventilation was discontinued on the next morning (day 2). The patient was discharged from the critical care unit on day 3 on good condition but died at a later interval from iterative bronchospasm. Evidence-based documentation of the effects of alpha-2 agonists in the setting of acute bronchospasm in the emergency department or status asthmaticus in the critical care unit is awaited.

Is there a place for pressure-support ventilation and high positive end-expiratory pressure combined to alpha-2 agonists early in severe diffuse acute respiratory distress syndrome?

Acute respiratory distress syndrome (ARDS) is associated with a high mortality linked primarily to co-morbidities (sepsis, cardiac failure, multiple organ failure, etc.). When the lung is the single failing organ, quick resolution of ARDS should skip some complications arising from a prolonged stay in the critical care unit. In severe ARDS (PaO2/FIO2=P/F<100 with positive end-expiratory pressure (PEEP) ≥ 5 cm H2O), current recommendations are to intubate the trachea of the patient and use mechanical ventilation, low tidal volume, high PEEP, prone positioning and possibly neuromuscular blockade in association with intravenous sedation. Another strategy is possible. Firstly, spontaneous ventilation (SV) coupled with pressure support (PS) ventilation and high PEEP is possible from tracheal intubation onwards, with the possible exception of the short period following immediately tracheal intubation. Secondly, using alpha-2 adrenergic agonists (e.g. clonidine, dexmedetomidine) can provide first-line sedation from the beginning of mechanical ventilation, as they preserve respiratory drive, lower oxygen consumption and pulmonary hypertension and increase diuresis. Alpha-2 agonists are to be supplemented, if appropriate, by drugs devoid of effect on respiratory drive (neuroleptics, etc.). The expected benefits would be to prevent acquired diaphragmatic weakness, accumulation of sedation, cognitive dysfunction, and presumably improved outcome. This hypothesis should be tested in a double blind randomized controlled trial.

[Dexmedetomidine and clonidine: a review of their pharmacodynamy to define their role for sedation in intensive care patients]

Alpha-2 adrenergic agonists ("alpha-2 agonists") present multiple pharmacodynamic effects: rousable sedation, decreased incidence of delirium in the setting of critical care, preservation of respiratory drive, decreased whole body oxygen consumption, decreased systemic and pulmonary arterial impedance, improved left ventricular systolic and diastolic function, preserved vascular reactivity to exogenous catecholamines, preserved vasomotor baroreflex with lowered set point, preserved kidney function, decreased protein catabolism. These pharmacodynamic effects explain the interest for these drugs in the critical care setting. However, their exact role for sedation in critically ill-patients remains open for further studies. Given the few double-blind randomized multicentric trials available, the present non exhaustive analysis of the literature aims at presenting the utilization of alpha-2 agonists as potential first-line sedative agents, in the critical care setting. Suggestions regarding the use of alpha-2 agonists as sedatives are detailed.

Antihypertensive effect of 3,3,5,5-tetramethyl-4-piperidone, a new compound extracted from Marasmius androsaceus

AIM OF THE STUDY

To evaluate the antihypertensive effect of 3,3,5,5-tetramethyl-4-piperidone (TMP), a new compound extracted from Marasmius androsaceus. Besides, the hemodynamic profiles and pertinent mechanism of the compound were explored.

MATERIALS AND METHODS

Acute and chronic antihypertensive effects of TMP were examined in spontaneous hypertensive rats (SHRs) and reno-hypertensive rats (two kidneys one clip model, 2K1C). Anesthetized dogs were used to evaluate the hemodynamic effects of TMP. Moreover, the cat nictitating membrane response was used to test the ganglionic blocking property of TMP.

RESULTS

TMP (2.5, 5 and 10mg/kg, p.o.) notably reduced the blood pressure of SHR in 30 min. Two-week administration of TMP (2.5, 5 and 10mg/kg, p.o.) also decreased the blood pressure of 2K1C rats. TMP (30 mg/kg, i.v.) abolished the response of the nictitating membrane induced by preganglionic stimulation. The results of hemodynamic study in anesthetized dogs showed that, except for the reduction in blood pressure and left ventricular work, no other changes were detected. The results of heart rate variability analysis indicated an intact sympathetic-vagal balance after TMP treatment.

CONCLUSIONS

TMP is a new antihypertensive compound, and the effect is partially related to ganglionic blocking.

Improvement of cardiac diastolic function by long-term centrally mediated sympathetic inhibition in one-kidney, one-clip hypertensive rabbits

BACKGROUND

Hypertension is associated with left ventricular hypertrophy (LVH) and diastolic dysfunction. The sympathetic nervous system (SNS) is strongly implicated in these alterations. The possible beneficial effect of a centrally mediated sympathetic inhibition on the diastolic function in severe hypertension has never been studied. We have evaluated the cardiac effects (remodeling, diastolic and systolic functions) of a long-term treatment with a centrally acting drug, rilmenidine, in a model of severe renovascular hypertension.

METHODS

One-kidney, one-clip (1K,1C) Goldblatt hypertensive rabbits were randomized in two groups, one receiving rilmenidine (5 mg/kg/day) for 6 weeks and the other treated with vehicle only. Hemodynamic effects and left ventricular (LV) remodeling were evaluated by serial tail cuff pressure measurements, and echocardiography every 15 days. These measurements were followed up with invasive hemodynamic measurements and histological analysis.

RESULTS

Rilmenidine induced a decrease of 8% in blood pressure, a significant bradycardia (19% at 6 weeks after treatment) and an 18% reduction in LV mass, without reduction of ejection fraction (EF). These effects were accompanied by an improvement of the diastolic function, as shown by isovolumic relaxation time and decrease in Tau index, an E/A ratio reversion, and an Ea velocity increase. Moreover, reduction in the atrial (A) and atrial reverse (Ar) velocities, without any effect on LV filling pressures, was observed.

CONCLUSIONS

In 1K,1C Goldblatt rabbits, which mimic most of the characteristics of human hypertensive cardiopathy, we have shown, for the first time, that a central inhibition of the SNS rapidly reverses cardiac hypertrophy and problems associated with primary LV relaxation, without negative inotropic action.

Preliminary clinical study of real-time three-dimensional echocardiographic volume-time curve in evaluating left ventricular diastolic function

The volume-time curve change in patients with normal left ventricular (LV) diastolic function and diastolic dysfunction was evaluated by real-time three-dimensional echocardiography (RT3DE). LV diastolic dysfunction was defined by E'<A' in pulse-wave tissue Doppler for inter-ventricular septal (IVS) of mitral annulus. In 24 patients with LV diastolic dysfunction, including 12 patients with delayed relaxation (delayed relaxation group) and 12 patients with pseudo-normal function (pseudo-normal group) and 24 normal volunteers (control group), data of full-volume image were acquired by real-time three-dimensional echocardiography and subjected to volume-time curve analysis. EDV (end-diastolic volume), ESV (end-systolic volume), LVEF (left ventricular ejection fraction), PER (peak ejection rate), PFR (peak filling rate) from RT3DE were examined in the three groups. Compared to the control group, PFR (diastolic filling index of RT3DE) was significantly reduced in the delayed relaxation group and pseudo-normal group (P<0.05). There were no significant differences in EDV, ESV, LVEF, PER (P>0.05). It is concluded that PFR, as a diastolic filling index of RT3DE, can reflect the early diastolic function and serve as a new non-invasive, quick and accurate tool for clinical assessment of LV diastolic function.

Baseline hemodynamic and echocardiographic indices in anesthetized calves

The experimental calf model is used to assess mechanical circulatory support devices and prosthetic heart valves. Baseline indices of cardiac function have been established for the normal awake calf but not for the anesthetized calf. Therefore, we gathered hemodynamic and echocardiographic data from 16 healthy anesthetized calves (mean age, 189.0 +/- 87.0 days; mean body weight, 106.9 +/- 32.3 kg) by cardiac catheterization and noninvasive echocardiography, respectively. Baseline hemodynamic data included heart rate (65 +/- 12 beats per minute), mean aortic pressure (113.5 +/- 17.4 mm Hg), left ventricular end-diastolic pressure (16.3 +/- 38.9 mm Hg), and mean pulmonary artery pressure (21.7 +/- 8.3 mm Hg). Baseline two-dimensional echocardiographic data included left ventricular systolic dimension (3.5 +/- 0.7 cm), left ventricular diastolic dimension (5.6 +/- 0.8 cm), end-systolic intraventricular septal thickness (1.7 +/- 0.2 cm), end-diastolic intraventricular septal thickness (1.2 +/- 0.2 cm), ejection fraction (63 +/- 10%), and fractional shortening (37 +/- 10%). Doppler echocardiography revealed a maximum aortic valve velocity of 0.9 +/- 0.5 m/s and a cardiac index of 3.7 +/- 1.1 L/minute/m2. The collected baseline data will be useful in assessing prosthetic heart valves, cardiac assist pumps, new cannulation techniques, and robotics applications in the anesthetized calf model and in developing calf models of various cardiovascular diseases.

Targeted inhibition of Ca2+/calmodulin-dependent protein kinase II in cardiac longitudinal sarcoplasmic reticulum results in decreased phospholamban phosphorylation at threonine 17

To investigate the role of Ca2+/calmodulin-dependent kinase II in cardiac sarcoplasmic reticulum function, transgenic mice were designed and generated to target the expression of a Ca2+/calmodulin-dependent kinase II inhibitory peptide in cardiac longitudinal sarcoplasmic reticulum using a truncated phospholamban transmembrane domain. The expressed inhibitory peptide was highly concentrated in cardiac sarcoplasmic reticulum. This resulted in a 59.7 and 73.6% decrease in phospholamban phosphorylation at threonine 17 under basal and beta-adrenergic stimulated conditions without changing phospholamban phosphorylation at serine 16. Sarcoplasmic reticulum Ca2+ uptake assays showed that the Vmax was decreased by approximately 30% although the apparent affinity for Ca2+ was unchanged in heterozygous hearts. The in vivo measurement of cardiac function showed no significant reductions in positive and negative dP/dt, but a moderate 18% decrease in dP/dt40, indicative of isovolumic contractility, and a 26.1% increase in the time constant of relaxation (tau) under basal conditions. The changes in these parameters indicate a moderate cardiac dysfunction in transgenic mice. Although the 3 and 4-month-old transgenic mice displayed no overt signs of cardiac disease, when stressed by gestation and parturition, the 7-month-old female mice develop dilated heart failure, suggesting the important role of Ca2+/calmodulin-dependent kinase II pathway in the development of cardiac disease.