Right ventricular (RV) failure in response to pulmonary hypertension (PH) is a severe disease that remains poorly understood. PH-induced pressure overload leads to changes in the RV free wall (RVFW) that eventually results in RV failure. While the development of computational models can benefit our understanding of the onset and progression of PH-induced pressure overload, detailed knowledge of the underlying structural and biomechanical events remains limited. The goal of the present study was to elucidate the structural and biomechanical adaptations of RV myocardium subjected to sustained pressure overload in a rat model. Hemodynamically confirmed severe chronic RV pressure overload was induced in Sprague-Dawley rats via pulmonary artery banding. Extensive tissue-level biaxial mechanical and histomorphological analyses were conducted to assess the remodeling response in the RV free wall. Simultaneous myofiber hypertrophy and longitudinal re-orientation of myo- and collagen fibers was observed, with both fiber types becoming more highly aligned. Transmural myo- and collagen fiber orientations were co-aligned in both the normal and diseased state. The overall tissue stiffness increased, with larger increases in longitudinal versus circumferential stiffness. Interestingly, estimated myofiber stiffness increased while the collagen fiber stiffness remained unchanged. The latter was attributed to longitudinal fiber re-orientation, which increased the degree of anisotropy. Increased mechanical coupling between the two axes was attributed to the increased fiber alignment. The increased myofiber stiffness was consistent with clinical results showing titin-associated increased sarcomeric stiffening observed in PH patients. These results further our understanding of the underlying adaptive and maladaptive remodeling mechanisms and may lead to improved techniques for prognosis, diagnosis, and treatment for PH.
A better understanding of the biomechanical properties of the arterial wall provides important insight into arterial vascular biology under normal (healthy) and pathological conditions. This insight has potential to improve tracking of disease progression and to aid in vascular graft design and implementation. In this study, we use linear and nonlinear viscoelastic models to predict biomechanical properties of the thoracic descending aorta and the carotid artery under ex vivo and in vivo conditions in ovine and human arteries. Models analyzed include a four-parameter (linear) Kelvin viscoelastic model and two five-parameter nonlinear viscoelastic models (an arctangent and a sigmoid model) that relate changes in arterial blood pressure to the vessel cross-sectional area (via estimation of vessel strain). These models were developed using the framework of Quasilinear Viscoelasticity (QLV) theory and were validated using measurements from the thoracic descending aorta and the carotid artery obtained from human and ovine arteries. In vivo measurements were obtained from ten ovine aortas and ten human carotid arteries. Ex vivo measurements (from both locations) were made in eleven male Merino sheep. Biomechanical properties were obtained through constrained estimation of model parameters. To further investigate the parameter estimates we computed standard errors and confidence intervals and we used analysis of variance to compare results within and between groups. Overall, our results indicate that optimal model selection depends on the arterial type. Results showed that for the thoracic descending aorta (under both experimental conditions) the best predictions were obtained with the nonlinear sigmoid model, while under healthy physiological pressure loading the carotid arteries nonlinear stiffening with increasing pressure is negligible, and consequently, the linear (Kelvin) viscoelastic model better describes the pressure-area dynamics in this vessel. Results comparing biomechanical properties show that the Kelvin and sigmoid models were able to predict the zero-pressure vessel radius; that under ex vivo conditions vessels are more rigid, and comparatively, that the carotid artery is stiffer than the thoracic descending aorta; and that the viscoelastic gain and relaxation parameters do not differ significantly between vessels or experimental conditions. In conclusion, our study demonstrates that the proposed models can predict pressure-area dynamics and that model parameters can be extracted for further interpretation of biomechanical properties.
Background Pulmonary arterial hypertension (PAH) is a severe and progressive disease, a hallmark of which is pulmonary vascular remodeling. Nicotinamide phosphoribosyltransferase (NAMPT), is a cytozyme which regulates intracellular NAD levels and cellular redox state, regulates histone deacetylases, promotes cell proliferation and inhibits apoptosis. We hypothesized that NAMPT promotes pulmonary vascular remodeling, and that inhibition of NAMPT could attenuate pulmonary hypertension. Methods Plasma and mRNA and protein levels of NAMPT were measured in the lungs and isolated pulmonary artery endothelial cells (PAECs) from PAH patients, as well as in lungs of rodent models of pulmonary hypertension (PH). Nampt+/− mice were exposed 10% hypoxia and room air for 4 weeks and the preventive and therapeutic effects of NAMPT inhibition were tested in the monocrotaline and Sugen-hypoxia models of PH. The effects on NAMPT activity on proliferation, migration, apoptosis and calcium signaling were tested in human pulmonary artery smooth muscle cell (hPASMC). Results Plasma and mRNA and protein levels of NAMPT were increased in the lungs and isolated pulmonary artery endothelial cells (PAECs) from PAH patients, as well as in lungs of rodent models of pulmonary hypertension (PH). Nampt+/− mice were protected from hypoxia-mediated PH. NAMPT activity promoted human pulmonary artery smooth muscle cell (hPASMC) proliferation via a paracrine effect. In addition, recombinant NAMPT stimulated hPASMC proliferation via enhancement of store-operated calcium entry by enhancing expression of Orai2 and STIM2. Finally, inhibition of NAMPT activity attenuated monocrotaline and Sugen hypoxia induced PH in rats. Conclusions Our data provide evidence that NAMPT plays a role in pulmonary vascular remodeling and its inhibition could be a potential therapeutic target for PAH.
In this paper, we analyze how elastic and viscoelastic properties differ across seven locations along the large arteries in 11 sheep. We employ a two-parameter elastic model and a four-parameter Kelvin viscoelastic model to analyze experimental measurements of vessel diameter and blood pressure obtained in vitro at conditions mimicking in vivo dynamics. Elastic and viscoelastic wall properties were assessed via solutions to the associated inverse problem. We use sensitivity analysis to rank the model parameters from the most to the least sensitive, as well as to compute standard errors and confidence intervals. Results reveal that elastic properties in both models (including Young's modulus and the viscoelastic relaxation parameters) vary across locations (smaller arteries are stiffer than larger arteries). We also show that for all locations, the inclusion of viscoelastic behavior is important to capture pressure-area dynamics.
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