Dissection flap fenestration can reduce re-apposition force of the false lumen in type-B aortic dissection: a computational and bench study

Thoracic endovascular aortic repair (TEVAR) has been widely adopted as a standard for treating complicated acute and high-risk uncomplicated Stanford Type-B aortic dissections. The treatment redirects the blood flow towards the true lumen by covering the proximal dissection tear which promotes sealing of the false lumen. Despite advances in TEVAR, over 30% of Type-B dissection patients require additional interventions. This is primarily due to the presence of a persistent patent false lumen post-TEVAR that could potentially enlarge over time. We propose a novel technique, called slit fenestration pattern creation, which reduces the forces for re-apposition of the dissection flap (i.e., increase the compliance of the flap). We compute the optimal slit fenestration design using a virtual design of experiment (DOE) and demonstrate its effectiveness in reducing the re-apposition forces through computational simulations and benchtop experiments using porcine aortas. The findings suggest this potential therapy can drastically reduce the radial loading required to re-appose a dissected flap against the aortic wall to ensure reconstitution of the aortic wall (remodeling).

Novel patch biomaterial treatment for colon diverticulosis in swine model

Current leading managements for diverticular disease cannot prevent the recurrence of diverticulitis, bleeding and/or other complications. There is an immediate need for developing new minimal invasive therapeutic strategies to prevent and treat this disease. Through a biomechanical analysis of porcine colon with diverticular lesions, we proposed a novel adhesive patch concept aiming at mechanical reconstruction of the diseased colon wall. This study aims to evaluate the surgical feasibility (safety and efficacy) of pulmonary visceral pleura (PVP) patch therapy using a pig model of diverticulosis. Six female Yucatan miniature pigs underwent collagenase injection (CI) for the development of diverticular lesions. The lesions in each animal either received patch implantation (treated group, n = 40 for 6 pigs) or left intact (untreated group, n = 44 for 6 pigs). The normal colonic wall in each animal received patch implantation at two spots to serve as control (n = 12 for 6 pigs). After 3 months of observation, the performance and safety of the patch treatment were evaluated through macroscopic and histological examination. We found that 95% of pouch-like herniation of the mucosa was prevented from the colon wall with the treatment. The pouch diameter was significantly reduced in the treated group as compared to the untreated group (p < 0.001). The patch application caused a significant increase in the levels of collagen of the colon tissue as compared to the untreated and control groups (p < 0.001). No difference was found in the lymphocyte and macrophage inflammatory infiltrate between the groups. Our results suggest that patch treatment efficiently inhibits the diverticular pouch deformation and promotes the healing of the colon wall with a normal inflammatory response, which may minimize the risk of diverticulosis reoccurrence and complications over time.

Distinct hemodynamic responses to (pyr)apelin-13 in large animal models

This study tested the hypothesis that (pyr)apelin-13 dose-dependently augments myocardial contractility and coronary blood flow, irrespective of changes in systemic hemodynamics. Acute effects of intravenous (pyr)apelin-13 administration (10 to 1,000 nM) on blood pressure, heart rate, left ventricular pressure and volume, and coronary parameters were measured in dogs and pigs. Administration of (pyr)apelin-13 did not influence blood pressure (P = 0.59), dP/dt_max (P = 0.26), or dP/dt_min (P = 0.85) in dogs. However, heart rate dose-dependently increased > 70% (P < 0.01), which was accompanied by a significant increase in coronary blood flow (P < 0.05) and reductions in left ventricular end-diastolic volume and stroke volume (P < 0.001). In contrast, (pyr)apelin-13 did not significantly affect hemodynamics, coronary blood flow, or indexes of contractile function in pigs. Furthermore, swine studies found no effect of intracoronary (pyr)apelin-13 administration on coronary blood flow (P = 0.83) or vasorelaxation in isolated, endothelium-intact (P = 0.89) or denuded (P = 0.38) coronary artery rings. Examination of all data across (pyr)apelin-13 concentrations revealed an exponential increase in cardiac output as peripheral resistance decreased across pigs and dogs (P < 0.001; R² = 0.78). Assessment of the Frank-Starling relationship demonstrated a significant linear relationship between left ventricular end-diastolic volume and stroke volume across species (P < 0.001; R² = 0.70). Taken together, these findings demonstrate that (pyr)apelin-13 does not directly influence myocardial contractility or coronary blood flow in either dogs or pigs.NEW & NOTEWORTHY Our findings provide much needed insight regarding the pharmacological cardiac and coronary effects of (pyr)apelin-13 in larger animal preparations. In particular, data highlight distinct hemodynamic responses of apelin across species, which are independent of any direct effect on myocardial contractility or perfusion.

Novel swine model of colonic diverticulosis

The pathophysiology of colonic diverticulosis has not been completely understood. The development of appropriate animal models is essential to study diverticular disease. To date, no large animal models are available for this disease condition. The objective of this study was to develop a swine model by damaging the colon wall, combined with or without a low-fiber diet to mimic the pathogenesis of diverticulosis. To create a weakness on the colon wall, collagenase was applied in vivo to degrade the collagen in the colon wall. Three groups of Yucatan minipigs were included. Group 1 (n = 12) underwent collagenase injection (CI) with a low-fiber diet for 6 mo, group 2 (n = 8) underwent CI alone with a standard swine diet for 6 mo, and group 3 (n = 12) received a low-fiber diet alone for 6 mo. We found that diverticulosis occurred in 91.7% (11 of 12) of pigs in the CI + diet group and 100% (8 of 8) in CI-alone group. Moreover, around 30-75% of colon CI spots for each pig developed diverticular lesions. Diet alone for 6 mo did not induce diverticulosis. The endoscopic and histological examinations revealed the formation of multiple wide-mouthed diverticular lesions along the descending colon. Our results provide convincing evidence of the high efficacy of the reduced colon wall strength caused by CI in the development of a swine model of diverticulosis. Low-fiber diet consumption for 6 mo had no influence on the generation time or incidence rate of diverticulosis. In this model, digestion of the collagen in the colonic wall is sufficient to cause diverticulosis. NEW & NOTEWORTHY Effective large animal models of diverticulosis are currently lacking for the study of diverticular disease. This study marks the first time that a swine model of diverticulosis was developed by damaging colon wall structure, combined with or without a low-fiber diet. We found that a defect of colon wall could result in colon diverticular lesions within 6 mo in swine. This animal model mimicking the pathological process of diverticulosis is of great clinical value.

Biomechanical Material Characterization of Stanford Type-B Dissected Porcine Aortas

Aortic dissection (AD) involves tearing of the medial layer, creating a blood-filled channel called false lumen (FL). To treat dissections, clinicians are using endovascular therapy using stent grafts to seal the FL. This procedure has been successful in reducing mortality but has failed in completely re-attaching the torn intimal layer. The use of computational analysis can predict the radial forces needed to devise stents that can treat ADs. To quantify the hyperelastic material behavior for therapy development, we harvested FL wall, true lumen (TL) wall, and intimal flap from the middle and distal part of five dissected aortas. Planar biaxial testing using multiple stretch protocols were conducted on tissue samples to quantify their deformation behavior. A novel non-linear regression model was used to fit data against Holzapfel–Gasser–Ogden hyperelastic strain energy function. The fitting analysis correlated the behavior of the FL and TL walls and the intimal flap to the stiffness observed during tensile loading. It was hypothesized that there is a variability in the stresses generated during loading among tissue specimens derived from different regions of the dissected aorta and hence, one should use region-specific material models when simulating type-B AD. From the data on material behavior analysis, the variability in the tissue specimens harvested from pigs was tabulated using stress and coefficient of variation (CV). The material response curves also compared the changes in compliance observed in the FL wall, TL wall, and intimal flap for middle and distal regions of the dissection. It was observed that for small stretch ratios, all the tissue specimens behaved isotropically with overlapping stress–stretch curves in both circumferential and axial directions. As the stretch ratios increased, we observed that most tissue specimens displayed different structural behaviors in axial and circumferential directions. This observation was very apparent in tissue specimens from mid FL region, less apparent in mid TL, distal FL, and distal flap tissues and least noticeable in tissue specimens harvested from mid flap. Lastly, using mixed model ANOVAS, it was concluded that there were significant differences between mid and distal regions along axial direction which were absent in the circumferential direction.

Validated Computational Model to Compute Re-apposition Pressures for Treating Type-B Aortic Dissections

The use of endovascular treatment in the thoracic aorta has revolutionized the clinical approach for treating Stanford type B aortic dissection. The endograft procedure is a minimally invasive alternative to traditional surgery for the management of complicated type-B patients. The endograft is first deployed to exclude the proximal entry tear to redirect blood flow toward the true lumen and then a stent graft is used to push the intimal flap against the false lumen (FL) wall such that the aorta is reconstituted by sealing the FL. Although endovascular treatment has reduced the mortality rate in patients compared to those undergoing surgical repair, more than 30% of patients who were initially successfully treated require a new endovascular or surgical intervention in the aortic segments distal to the endograft. One reason for failure of the repair is persistent FL perfusion from distal entry tears. This creates a patent FL channel which can be associated with FL growth. Thus, it is necessary to develop stents that can promote full re-apposition of the flap leading to complete closure of the FL. In the current study, we determine the radial pressures required to re-appose the mid and distal ends of a dissected porcine thoracic aorta using a balloon catheter under static inflation pressure. The same analysis is simulated using finite element analysis (FEA) models by incorporating the hyperelastic properties of porcine aortic tissues. It is shown that the FEA models capture the change in the radial pressures required to re-appose the intimal flap as a function of pressure. The predictions from the simulation models match closely the results from the bench experiments. The use of validated computational models can support development of better stents by calculating the proper radial pressures required for complete re-apposition of the intimal flap.

Regulation of myocardial oxygen delivery in response to graded reductions in hematocrit: role of K+ channels

This study was designed to identify mechanisms responsible for coronary vasodilation in response to progressive decreases in hematocrit. Isovolemic hemodilution was produced in open-chest, anesthetized swine via concurrent removal of 500 ml of arterial blood and the addition of 500 ml of 37 °C saline or synthetic plasma expander (Hespan, 6% hetastarch in 0.9% sodium chloride). Progressive hemodilution with Hespan resulted in an increase in coronary flow from 0.39 ± 0.05 to 1.63 ± 0.16 ml/min/g (P < 0.001) as hematocrit was reduced from 32 ± 1 to 10 ± 1% (P < 0.001). Overall, coronary flow corresponded with the level of myocardial oxygen consumption, was dependent on arterial pressures ≥ ~ 60 mmHg, and occurred with little/no change in coronary venous PO₂. Anemic coronary vasodilation was unaffected by the inhibition of nitric oxide synthase (L-NAME: 25 mg/kg iv; P = 0.92) or voltage-dependent K⁺ (K _V) channels (4-aminopyridine: 0.3 mg/kg iv; P = 0.52). However, administration of the K _ATP channel antagonist (glibenclamide: 3.6 mg/kg iv) resulted in an ~ 40% decrease in coronary blood flow (P < 0.001) as hematocrit was reduced to ~ 10%. These reductions in coronary blood flow corresponded with significant reductions in myocardial oxygen delivery at baseline and throughout isovolemic anemia (P < 0.001). These data indicate that vasodilator factors produced in response to isovolemic hemodilution converge on vascular smooth muscle glibenclamide-sensitive (K _ATP) channels to maintain myocardial oxygen delivery and that this response is not dependent on endothelial-derived nitric oxide production or pathways that mediate dilation via K _V channels.

Glucagon-Like Peptide 1 Receptor Activation Augments Cardiac Output and Improves Cardiac Efficiency in Obese Swine After Myocardial Infarction

This study tested the hypothesis that glucagon-like peptide 1 (GLP-1) therapies improve cardiac contractile function at rest and in response to adrenergic stimulation in obese swine after myocardial infarction. Obese Ossabaw swine were subjected to gradually developing regional coronary occlusion using an ameroid occluder placed around the left anterior descending coronary artery. Animals received subcutaneous injections of saline or liraglutide (0.005-0.015 mg/kg/day) for 30 days after ameroid placement. Cardiac performance was assessed at rest and in response to sympathomimetic challenge (dobutamine 0.3-10 μg/kg/min) using a left ventricular pressure/volume catheter. Liraglutide increased diastolic relaxation (dP/dt; Tau ¹/₂; Tau ¹/_e) during dobutamine stimulation (P < 0.01) despite having no influence on the magnitude of myocardial infarction. The slope of the end-systolic pressure volume relationship (i.e., contractility) increased with dobutamine after liraglutide (P < 0.001) but not saline administration (P = 0.63). Liraglutide enhanced the slope of the relationship between cardiac power and pressure volume area (i.e., cardiac efficiency) with dobutamine (P = 0.017). Hearts from animals treated with liraglutide demonstrated decreased β1-adrenoreceptor expression. These data support that GLP-1 agonism augments cardiac efficiency via attenuation of maladaptive sympathetic signaling in the setting of obesity and myocardial infarction.

Obesity alters molecular and functional cardiac responses to ischemia/reperfusion and glucagon-like peptide-1 receptor agonism

This study tested the hypothesis that obesity alters the cardiac response to ischemia/reperfusion and/or glucagon like peptide-1 (GLP-1) receptor activation, and that these differences are associated with alterations in the obese cardiac proteome and microRNA (miRNA) transcriptome. Ossabaw swine were fed normal chow or obesogenic diet for 6 months. Cardiac function was assessed at baseline, during a 30-minutes coronary occlusion, and during 2 hours of reperfusion in anesthetized swine treated with saline or exendin-4 for 24 hours. Cardiac biopsies were obtained from normal and ischemia/reperfusion territories. Fat-fed animals were heavier, and exhibited hyperinsulinemia, hyperglycemia, and hypertriglyceridemia. Plasma troponin-I concentration (index of myocardial injury) was increased following ischemia/reperfusion and decreased by exendin-4 treatment in both groups. Ischemia/reperfusion produced reductions in systolic pressure and stroke volume in lean swine. These indices were higher in obese hearts at baseline and relatively maintained throughout ischemia/reperfusion. Exendin-4 administration increased systolic pressure in lean swine but did not affect the blood pressure in obese swine. End-diastolic volume was reduced by exendin-4 following ischemia/reperfusion in obese swine. These divergent physiologic responses were associated with obesity-related differences in proteins related to myocardial structure/function (e.g. titin) and calcium handling (e.g. SERCA2a, histidine-rich Ca(2+) binding protein). Alterations in expression of cardiac miRs in obese hearts included miR-15, miR-27, miR-130, miR-181, and let-7. Taken together, these observations validate this discovery approach and reveal novel associations that suggest previously undiscovered mechanisms contributing to the effects of obesity on the heart and contributing to the actions of GLP-1 following ischemia/reperfusion.

KV7 channels contribute to paracrine, but not metabolic or ischemic, regulation of coronary vascular reactivity in swine

Hydrogen peroxide (H2O2) and voltage-dependent K(+) (KV) channels play key roles in regulating coronary blood flow in response to metabolic, ischemic, and paracrine stimuli. The KV channels responsible have not been identified, but KV7 channels are possible candidates. Existing data regarding KV7 channel function in the coronary circulation (limited to ex vivo assessments) are mixed. Thus we examined the hypothesis that KV7 channels are present in cells of the coronary vascular wall and regulate vasodilation in swine. We performed a variety of molecular, biochemical, and functional (in vivo and ex vivo) studies. Coronary arteries expressed KCNQ genes (quantitative PCR) and KV7.4 protein (Western blot). Immunostaining demonstrated KV7.4 expression in conduit and resistance vessels, perhaps most prominently in the endothelial and adventitial layers. Flupirtine, a KV7 opener, relaxed coronary artery rings, and this was attenuated by linopirdine, a KV7 blocker. Endothelial denudation inhibited the flupirtine-induced and linopirdine-sensitive relaxation of coronary artery rings. Moreover, linopirdine diminished bradykinin-induced endothelial-dependent relaxation of coronary artery rings. There was no effect of intracoronary flupirtine or linopirdine on coronary blood flow at the resting heart rate in vivo. Linopirdine had no effect on coronary vasodilation in vivo elicited by ischemia, H2O2, or tachycardia. However, bradykinin increased coronary blood flow in vivo, and this was attenuated by linopirdine. These data indicate that KV7 channels are expressed in some coronary cell type(s) and influence endothelial function. Other physiological functions of coronary vascular KV7 channels remain unclear, but they do appear to contribute to endothelium-dependent responses to paracrine stimuli.

Lean and Obese Coronary Perivascular Adipose Tissue Impairs Vasodilation via Differential Inhibition of Vascular Smooth Muscle K+ Channels

OBJECTIVE

The effects of coronary perivascular adipose tissue (PVAT) on vasomotor tone are influenced by an obese phenotype and are distinct from other adipose tissue depots. The purpose of this investigation was to examine the effects of lean and obese coronary PVAT on end-effector mechanisms of coronary vasodilation and to identify potential factors involved.

APPROACH AND RESULTS

Hematoxylin and eosin staining revealed similarities in coronary perivascular adipocyte size between lean and obese Ossabaw swine. Isometric tension studies of isolated coronary arteries from Ossabaw swine revealed that factors derived from lean and obese coronary PVAT attenuated vasodilation to adenosine. Lean coronary PVAT inhibited K(Ca) and KV7, but not KATP channel-mediated dilation in lean arteries. In the absence of PVAT, vasodilation to K(Ca) and KV7 channel activation was impaired in obese arteries relative to lean arteries. Obese PVAT had no effect on K(Ca) or KV7 channel-mediated dilation in obese arteries. In contrast, obese PVAT inhibited KATP channel-mediated dilation in both lean and obese arteries. The differential effects of obese versus lean PVAT were not associated with changes in either coronary KV7 or K(ATP) channel expression. Incubation with calpastatin attenuated coronary vasodilation to adenosine in lean but not in obese arteries.

CONCLUSIONS

These findings indicate that lean and obese coronary PVAT attenuates vasodilation via inhibitory effects on vascular smooth muscle K(+) channels and that alterations in specific factors such as calpastatin are capable of contributing to the initiation or progression of smooth muscle dysfunction in obesity.

Cardiovascular and hemodynamic effects of glucagon-like peptide-1

Glucagon-like peptide-1 (GLP-1) is an incretin hormone that has been shown to have hemodynamic and cardioprotective capacity in addition to its better characterized glucoregulatory actions. Because of this, emerging research has focused on the ability of GLP-1 based therapies to drive myocardial substrate selection, enhance cardiac performance and regulate heart rate, blood pressure and vascular tone. These studies have produced consistent and reproducible results amongst numerous laboratories. However, there are obvious disparities in findings obtained in small animal models versus those of higher mammals. This species dependent discrepancy calls to question, the translational value of individual findings. Moreover, few studies of GLP-1 mediated cardiovascular action have been performed in the presence of a pre-existing comorbidities (e.g. obesity/diabetes) which limits interpretation of the effectiveness of incretin-based therapies in the setting of disease. This review addresses cardiovascular and hemodynamic potential of GLP-1 based therapies with attention to species specific effects as well as the interaction between therapies and disease.

Perivascular adipose tissue and coronary vascular disease

Coronary perivascular adipose tissue is a naturally occurring adipose tissue depot that normally surrounds the major coronary arteries on the surface of the heart. Although originally thought to promote vascular health and integrity, there is a growing body of evidence to support that coronary perivascular adipose tissue displays a distinct phenotype relative to other adipose depots and is capable of producing local factors with the potential to augment coronary vascular tone, inflammation, and the initiation and progression of coronary artery disease. The purpose of the present review is to outline previous findings about the cardiovascular effects of coronary perivascular adipose tissue and the potential mechanisms by which adipose-derived factors may influence coronary vascular function and the progression of atherogenesis.