Changes In Wall Geometry Research Articles

A novel ultrasound-derived index of intra-myocardial work, utilizing automated AI segmentation, quantifies energy stored in systole and used for diastolic recoil during isovolumic relaxation

Abstract Introduction The commonly used Pressure-Volume loops focus on the cavity volume and quantify the cardiac systolic work. We focused on changes in wall geometry and have hypothesized that pressure-wall area relationships, in short-axis, relate to the intra-myocardial work (IMW) that is stored during systole and released during early diastole. Purpose The study aims to validate the novel IMW concept and to test its ability to quantify the severity of diastolic dysfunction in a model of myocardial injury during inflammation. Materials and Methods Short-axis ultrasound cines were continuously acquired (12MHz, 40-70 fps) in Langendorff perfused isolated rat hearts (N=7), with unique preload and afterload control of both ventricles. Dedicated artificial intelligence segmentation model was developed for fast and accurate quantification of both Pressure-Volume loops and IMWs. Inflammatory myocardial injury was emulated by adding MMP8 (secreted by activated macrophages and neutrophils) to the perfusion. Results 120,000 echocardiographic images of isolated rat hearts (n=7) were analyzed. The wall dynamics generated counterclockwise loops on the pressure-wall area plane that consisted of three phases: (1) Initial fast and large wall thickening, with 74±15% of the total wall area increase and only 7.79±6.44% of the total systolic pressure development. (2) The main (94.71±8.01%) systolic pressure upstroke, with only minor further changes in wall area. (3) Closure of the IMW loop during the diastolic isovolumic relaxation. This phase describes the fast energy release, when moving over the hypotenuse of the triangle-like loop, from end-systole to the end of the isovolumic relaxation. The IWM generated during the two systolic phases and released during diastole was of the same order as the systolic external work. MMP perfusion led to progressive shift of the end-diastolic pressure cavity-volume relationship to lower volumes, with marked decrease in end-diastolic volume (-20.0±17.2%, p=0.04) at the same filling pressure. There were insignificant changes in the systolic maximal elastance, hence, the progressive decline in myocardial recoil was associated with decrease in the external work. In parallel, there was conspicuous drop in the IMW (-60.82±19.44%, p=0.03). While the e` tracks the motion of a single point on the mitral annulus, the suggested IWM is based on monitoring a large myocardial mass and is easier to be acquired. The major fast changes in the IMW loops occurred at the isovolumic contraction and relaxation phases, and they relate to myocardial twist and recoil and to fast changes in myocardial shape. Conclusions The novel IMW is easily derived from short-axis echocardiographic images, and describes the systolic-to-diastolic energy conversion. The matrix plays a key role as the main energy storage element for myocardial recoil. IMW may play important roles in cardiac recoil and in assessment of diastolic dysfunction.Intra-myocardial work - MMP8 perfusion

Loss of the hyaluronan receptor RHAMM prevents constrictive artery wall remodeling

Constrictive extracellular matrix (ECM) remodeling contributes significantly to restenosis after arterial reconstruction, but its molecular regulation is poorly defined. Hyaluronan (HA) accumulates within ECM at sites of injury where it is thought to facilitate smooth muscle cell (SMC) trafficking and collagen remodeling analogous to its role in cutaneous wound healing. SMC receptors for HA include receptor for hyaluronan-mediated motility (RHAMM), which mediates HA-induced migration. We hypothesized RHAMM would also mediate SMC-matrix interactions to alter the extent of constrictive remodeling. We studied the role of RHAMM in SMC attachment to collagen, migration, and contraction of collagen gels using blocking antibodies and SMC from RHAMM -/- knockout mice. We then determined the role of RHAMM in constrictive artery wall remodeling by comparing changes in wall geometry in RHAMM -/- vs wild-type (WT) RHAMM +/+ controls 1 month after carotid ligation. HA increased SMC attachment to collagen-coated plates, but blocking RHAMM reduced adhesion (P = .025). RHAMM -/- SMC also demonstrated reduced adhesion (% adherent: 36.1 ± 2.2 vs 76.3 ± 1.9; P < .05). SMC contraction of collagen gels was enhanced by HA and further increased by RHAMM blockade (P < .01) or knockout (gel diameter, mm: RHAMM -/-, 6.7 ± 0.1 vs WT 9.8 ± 0.1; P < .01). RHAMM promoted constrictive remodeling in vivo as carotid artery size was significantly larger in knockout mice 1 month after ligation. Neointimal thickening, however, was not affected in RHAMM -/- (P = NS vs WT), but lumen size was significantly larger (lumen area, μm(2): 52.4 ± 1.4 × 10(3) vs 10.4 ± 1.8 × 10(3); P = .01) because artery size constricted less (external elastic lamina area, μm(2): RHAMM -/-, 92.4 ± 4.7 × 10(3) vs WT, 51.3 ± 5.9 × 10(3); P = .015). Adventitial thickening and collagen deposition were also more extensive in ligated RHAMM -/- carotids (adventitial thickness, μm: 218 ± 12.2 vs 109 ± 7.9; P = .01). HA activation of RHAMM significantly impacts SMC-ECM adhesive interactions and contributes to constrictive artery wall remodeling in mice. Strategies to block RHAMM at sites of vessel injury may prove useful in the prevention of clinical restenosis.

Inverse design of 2-D subsonic ducts using flexible string algorithm

The duct inverse design in fluid flow problems usually involves finding the wall shape associated with a prescribed distribution of wall pressure or velocity. In this investigation, an iterative inverse design method for 2-D subsonic ducts is presented. In the proposed method, the duct walls shape is changed under a novel algorithm based on the deformation of a virtual flexible string in flow. The deformation of the string due to the local flow conditions resulting from changes in wall geometry is observed until the target shape satisfying the prescribed wall's pressure distribution is reached. The flow field at each step is analysed using Euler equations and the advection upstream splitting method method. Some validation test cases and a design example are presented here which show the robustness and flexibility of the method in handling complex geometries. The method is a physical and quick converging approach and can efficiently utilize commercial flow analysis software.

Lipoteichoic acid from Bacillus subtilis subsp. niger WM: isolation and effects on cell wall autolysis and turnover.

Lipoteichoic acid (LTA) was extracted by means of hot aqueous phenol from Bacillus subtilis subsp. niger WM cells grown under various conditions in chemostat culture. The extracts were partially purified by nuclease treatment and gel permeation chromatography. Chemical analyses revealed a composition consistent with a polyglycerol phosphate polymer. The influence on autolysis of the LTAs thus obtained was studied with both whole cells and autolysin-containing native walls of B. subtilis subsp. niger WM. Lysis rates of phosphate-limited cells could be reduced to about 40% of the control rate by the addition of LTA, whereas lysis of cells grown under phosphate-sufficient conditions was affected to a much lesser extent. The lysis of native walls prepared from variously grown cells proved to be fairly insensitive to the addition of LTA. The effect of LTA on wall turnover was studied by following the release of radioactively labeled wall material during exponential growth. The most obvious effect of LTA was a lowered first-order rate of release of labeled wall material; calculations according to the model for cell wall turnover in Bacillus spp. formulated by De Boer et al. (W. R. De Boer, F. J. Kruyssen, and J. T. M. Wouters, J. Bacteriol. 145:50-60, 1981) revealed changes in wall geometry and not in turnover rate in the presence of LTA.