321 research outputs found
Electrical Conductance Device for Stent Sizing
The minimum stent area (MSA) has been clinically established as a significant predictor of restenosis, thrombosis, and ischemia using intra-vascular ultrasound (IVUS). Unfortunately, IVUS measurements are far from routine because of significant cost of IVUS, the training required, the subjectivity of image interpretation and the time added to the procedure. The objective of this study is to verify the accuracy of a conductance catheter for stent sizing. Here, we introduce an easy and entirely objective device and method for real time determination of MSA. A 10 kHz, 35 μA rms current is passed through the external electrodes of an intravascular catheter while the conductance is measured across a separate set of electrodes. Both phantom and ex vivo validations of metal stent sizing in five porcine carotid arteries were confirmed. The accuracy of the measurements were found to be excellent in phantoms (root mean square, rms, of 3.4% of actual value) and in ex-vivo vessels (rms = 3.2% of measured value). An offset of conductance occurs when a conductive metal stent (e.g., bare metal stent) is deployed in the vessel, while the slope remains the same. This offset is absent in the case of drug eluting stent where the metal is coated (i.e., insulated) or non-metal bioresorbable stent. The present device makes easy, accurate and reproducible measurements of the size of stented blood vessels within 3.2% rms error. This device provides an alternative method to sizing of stent (i.e., MSA) in real-time without subjective interpretation and with less cost than IVUS
A rate-insensitive linear viscoelastic model for soft tissues
It is well known that many biological soft tissues behave as viscoelastic materials with hysteresis curves being nearly independent of strain rate when loading frequency is varied over a large range. In this work, the rate-insensitive feature of biological materials is taken into account by a generalized Maxwell model. To minimize the number of model parameters, it is assumed that the characteristic frequencies of Maxwell elements form a geometric series. As a result, the model is characterized by five material constants: micro(0), tau, m, rho and beta, where micro(0) is the relaxed elastic modulus, tau the characteristic relaxation time, m the number of Maxwell elements, rho the gap between characteristic frequencies, and beta=micro(1)/micro(0) with micro(1) being the elastic modulus of the Maxwell body that has relaxation time tau. The physical basis of the model is motivated by the microstructural architecture of typical soft tissues. The novel model shows excellent fit of relaxation data on the canine aorta and captures the salient features of vascular viscoelasticity with significantly fewer model parameters
Endothelial barrier dysfunction in diabetic conduit arteries: a novel method to quantify filtration
The endothelial barrier plays an important role in atherosclerosis, hyperglycemia, and hypercholesterolemia. In the present study, an accurate, reproducible, and user-friendly method was used to further understand endothelial barrier function of conduit arteries. An isovolumic method was used to measure the hydraulic conductivity (Lp) of the intact vessel wall and medial-adventitial layer. Normal arterial segments with diameters from 0.2 to 5.5 mm were used to validate the method, and femoral arteries of diabetic rats were studied as an example of pathological specimens. Various arterial segments confirmed that the volume flux of water per unit surface area was linearly related to intraluminal pressure, as confirmed in microvessels. Lp of the intact wall varied from 3.5 to 22.1 × 10−7 cm·s−1·cmH2O−1 over the pressure range of 7–180 mmHg. Over the same pressure range, Lp of the endothelial barrier changed from 4.4 to 25.1 × 10−7 cm·s−1·cmH2O−1. During perfusion with albumin-free solution, Lp of rat femoral arteries increased from 6.1 to 13.2 × 10−7 cm·s−1·cmH2O−1 over the pressure range of 10–180 mmHg. Hyperglycemia increased Lp of the femoral artery in diabetic rats from 2.9 to 5.5 × 10−7 cm·s−1·cmH2O−1 over the pressure range of 20–135 mmHg. In conclusion, the Lp of a conduit artery can be accurately and reproducibly measured using a novel isovolumic method, which in diabetic rats is hyperpermeable. This is likely due to disruption of the endothelial glycocalyx
Influence of Peri-duodenal Non-constrictive Cuff on the Body Weight of Rats
Background
Weight loss has been found to improve or re-
solve cardiovascular comorbidities. There is a significant need
for reversible device approaches to weight loss.
Methods
Non-constrictive cuff (NCC) is made of implantable
silicone rubber with an internal diameter greater than the
duodenum. Ten or 11 NCC were individually mounted along
the duodenum from the pyloric sphincter toward the distal
duodenum to cover ~22 mm in the length. Twelve Wistar rats
were implanted with NCC, and six served as sham, and both
groups were observed over 4 months. Six rats with implant
had their NCC removed and were observed for additional
4weeks.
Results
The food intake decreased from 40.1 to 28.1 g/day
after 4 months of NCC implant. The body weight gain
decreased from 1.76 to 0.46 g/day after 4 months of NCC
implant. The fasting glucose decreased from 87.7 to 75.3 mg/
dl at terminal day. The duodenal muscle layer covered by the
NCC increased from 0.133 to 0.334 mm. After 4 weeks of
NCC removal, the food intake, body weight gain, and fasting
glucose recovered to 36.2, 2.51 g/day, and 83.9 mg/dl. The
duodenal muscle layer covered by the NCC decreased to
0.217 mm.
Conclusion
The NCC implant placed on the proximal duode-
num is safe in rats for a 4-month period. The efficacy of the
NCC implant is significant for decrease in food intake, body
weight gain, and fasting glucose in a normal rat model. The
removal of NCC implant confirmed a cause-effect relation
with food intake and hence body weight
Protein Kinase C inhibition ameliorates functional endothelial insulin resistance and Vascular Smooth Muscle Cell hypersensitivity to insulin in diabetic hypertensive rats
<p>Abstract</p> <p>Objective</p> <p>Insulin resistance, diabetes, and hypertension are considered elements of metabolic syndrome which is associated with vascular dysfunction. We investigated whether inhibition of protein kinase C (PKC) would affect vascular function in diabetic hypertensive (DH) rats.</p> <p>Methods</p> <p>A combination of type 2 diabetes and arterial hypertension was produced in male Sprague Dawley rats by intrauterine protein deprivation (IUPD) followed by high salt diet. At the age of 32 weeks, DH rats were treated for 2 weeks with the angiotensin-converting enzyme inhibitor captopril (Capto, 30 mg/kg), PKC inhibitor ruboxistaurin (RBX, 50 mg/kg) or vehicle (n = 8 per group) and blood pressure was monitored using telemetry. At the end of experiments, femoral arteries were dissected, and vascular reactivity was evaluated with isovolumic myography.</p> <p>Results</p> <p>The IUPD followed by high salt diet resulted in significant elevation of plasma glucose, plasma insulin, and blood pressure. Endothelium-dependent vascular relaxation in response to acetylcholine was blunted while vascular contraction in response to phenylephrine was enhanced in the DH rats. Neither Capto nor RBX restored endothelium-dependent vascular relaxation while both suppressed vascular contraction. Ex-vivo incubation of femoral arteries from control rats with insulin induced dose-response vasorelaxation while insulin failed to induce vasorelaxation in the DH rat arteries. In the control arteries treated with endothelial nitric oxide synthase inhibitor L-NAME, insulin induced vasoconstriction that was exacerbated in DH rats. Capto and RBX partially inhibited insulin-stimulated vascular contraction.</p> <p>Conclusion</p> <p>These findings suggest that PKC inhibition ameliorates functional endothelial insulin resistance and smooth muscle cell hypersensitivity to insulin, but does not restore acetylcholine-activated endothelium-dependent vasodilation in DH rats.</p
Cannabis and the Brain: Friend or Foe?
Legalization of cannabis in the US and other countries highlight the need to understand the health consequences of this substance use. Research indicates that some cannabis ingredients may play beneficial role in treating various medical conditions while other ingredients may pose health risks. This review is focused on the brain and mental health effects of cannabis use. The rationale for examining cannabis use in behavioral and neural conditions is that these conditions are highly widespread in the US and account for high level of medical healthcare and associated cost. The purpose of this review is to provide an overview of the known medicinal benefits of selected cannabis cannabinoids in conditions like pediatric epilepsy, attention deficit hyperactivity disorder, autism spectrum disorder, and the known side effects or contraindications in conditions such as addiction, cognition, and psychosis. Several recommendations are made as to studies that will help further understanding the increasing role of cannabis in neuropsychiatric health and disease
Endothelial actin depolymerization mediates NADPH oxidase-superoxide production during flow reversal
Slow moving blood flow and changes in flow direction, e.g., negative wall shear stress, can cause increased superoxide (O2·−) production in vascular endothelial cells. The mechanism by which shear stress increases O2·− production, however, is not well established. We tested the hypothesis that actin depolymerization, which occurs during flow reversal, mediates O2·− production in vascular endothelial cells via NADPH oxidase, and more specifically, the subunit p47phox. Using a swine model, we created complete blood flow reversal in one carotid artery, while the contralateral vessel maintained forward blood flow as control. We measured actin depolymerization, NADPH oxidase activity, and reactive oxygen species (ROS) production in the presence of various inhibitors. Flow reversal was found to induce actin depolymerization and a 3.9 ± 1.0-fold increase in ROS production as compared with forward flow. NADPH oxidase activity was 1.4 ± 0.2 times higher in vessel segments subjected to reversed blood flow when measured by a direct enzyme assay. The NADPH oxidase subunits gp91phox (Nox2) and p47phox content in the vessels remained unchanged after 4 h of flow reversal. In contrast, p47phox phosphorylation was increased in vessels with reversed flow. The response caused by reversed flow was reduced by in vivo treatment with jasplakinolide, an actin stabilizer (only a 1.7 ± 0.3-fold increase). Apocynin (an antioxidant) prevented reversed flow-induced ROS production when the animals were treated in vivo. Cytochalasin D mimicked actin depolymerization in vitro and caused a 5.2 ± 3.0-fold increase in ROS production. These findings suggest that actin filaments play an important role in negative shear stress-induced ROS production by potentiating NADPH oxidase activity, and more specifically, the p47phox subunit in vascular endothelium
Pre-arterialization of coronary veins prior to retroperfusion of ischemic myocardium: percutaneous closure device
BackgroundChronic coronary retroperfusion to treat myocardial ischemia has previously failed due to edema and hemorrhage of coronary veins suddenly exposed to arterial pressures. The objective of this study was to selectively adapt the coronary veins to become arterialized prior to coronary venous retroperfusion to avoid vascular edema and hemorrhage.Methods and resultsIn 32 animals (Group I = 19 and Group II = 13), the left anterior descending (LAD) artery was occluded using an ameroid occlusion model. In Group I, the great cardiac vein was blocked with suture ligation (Group IA = 11) or with occlusion device (Group IB = 8) to arterialize the venous system within 2 weeks at intermediate pressure (between arterial and venous levels) before a coronary venous bypass graft (CVBG) was implemented through a left internal mammary artery (LIMA) anastomosis. Group II only received the LAD artery occlusion and served as control. Serial echocardiograms showed recovery of left ventricular (LV) function with this adaptation-arterialization approach, with an increase in ejection fraction (EF) in Group I from 38% ± 5% after coronary occlusion to 53% ± 7% eight weeks after CVBG, whereas in Group II the EF never recovered (41% ± 2%–33% ± 7%). The remodeling of the venous system not only allowed restoration of myocardial function when CVBG was implemented but possibly promoted a novel form of “collateralization” between the native arterioles and the newly arterialized venules, which revascularized the ischemic myocardium.ConclusionsThese findings form a potential rationale for a venous arterialization-revascularization treatment for the refractory angina and the “no-option” patients using a hybrid percutaneous (closure device for arterialization)/surgical approach (CVBG) to revascularize the myocardium
Distension-Induced Gastric Contraction is Attenuated in an Experimental Model of Gastric Restraint
Background
Gastric distension has important implications
for motility and satiety. The hypothesis of this study was
that distension affects the amplitude and duration of gastric
contraction and that these parameters are largely mediated
by efferent vagus stimulation.
Methods
A novel isovolumic myograph was introduced to
test these hypotheses. The isovolumic myograph isolates
the stomach and records the pressure generated by the
gastric contraction under isovolumic conditions. Accordingly,
the phasic changes of gastric contractility can be
documented. A group of 12 rats were used under in vivo
conditions and isolated ex vivo conditions and with two
different gastric restraints (small and large) to determine the
effect of degree of restraint.
Results
The comparison of the in vivo and ex vivo
contractility provided information on the efferent vagus
mediation of gastric contraction, i.e., the in vivo amplitude
and duration reached maximum of 12.6±2.7 mmHg and
19.8±5.6 s in contrast to maximum of 5.7±0.9 mmHg and
7.3±1.3 s in ex vivo amplitude and duration, respectively. The
comparison of gastric restraint and control groups highlights
the role of distension on in vivo gastric contractility. The
limitation of gastric distension by restraint drastically reduced
the maximal amplitude to below 2.9±0.2 mmHg.
Conclusions
The results show that distension-induced
gastric contractility is regulated by both central nervous
system and local mechanisms with the former being more
substantial. Furthermore, the gastric restraint significantly
attenuates gastric contractility (decreased amplitude and
shortened duration of contraction) which is mediated by the
efferent vagus activation. These findings have important
implications for gastric motility and physiology and may
improve our understanding of satiety
Which diameter and angle rule provides optimal flow patterns in a coronary bifurcation?
The branching angle and diameter ratio in epicardial coronary artery bifurcations are two important determinants of atherogenesis. Murray's cubed diameter law and bifurcation angle have been assumed to yield optimal flows through a bifurcation. In contrast, we have recently shown a 7/3 diameter law (HK diameter model), based on minimum energy hypothesis in an entire tree structure. Here, we derive a bifurcation angle rule corresponding to the HK diameter model and critically evaluate the streamline flow through HK and Murray-type bifurcations. The bifurcations from coronary casts were found to obey the HK diameter model and angle rule much more than Murray's model. A finite element model was used to investigate flow patterns for coronary artery bifurcations of various types. The inlet velocity and pressure boundary conditions were measured by ComboWire. Y-bifurcation of Murray type decreased wall shear stress-WSS (10%-40%) and created an increased oscillatory shear index-OSI in atherosclerosis-prone regions as compared with HK-type bifurcations. The HK-type bifurcations were found to have more optimal flow patterns (i.e., higher WSS and lower OSI) than Murray-type bifurcations which have been traditionally believed to be optimized. This study has implications for changes in bifurcation angles and diameters in percutaneous coronary intervention
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