Biomedical subjects

Y S Morsi

Publications and source records attributed to Y S Morsi.

6 recordsLinked to original sources

PubMed2006

The effect of angle on wall shear stresses in a LIMA to LAD anastomosis: numerical modelling of pulsatile flow.

The purpose of this study was to examine the effect of anastomotic angle on the flow patterns and wall shear distributions at the distal anastomosis of a left interior mammary artery (LIMA) graft to the left anterior descending artery (LDA). It is now well recognized that abnormal wall shear stress distributions along the anastomotic bed, around the toe, and around the heel can contribute to the focal development of intimal hyperplasia. However, the exact nature of the interaction between the dominant pulsing flow and the anastomotic angle on wall shear stresses has not been fully investigated numerically. In this study a commercial CFD package was used for three-dimensional flow analysis where the pulsatile waveforms and flowrates used as the boundary conditions are representative of an anastomosed left internal mammary artery and a stenosed left anterior descending coronary artery (intermediate, <70 per cent diameter narrowing). The flow patterns and distributions of time-averaged wall shear stress (TAWSS) and the oscillatory shear index (OSI) for three anastomotic angles of 20, 40, and 60 degrees were evaluated and compared with other published data. The findings indicated that transient, highly disturbed flow patterns occurred in localized regions of the proximal and distal native segments and in the anastomotic domain including recirculation zones, moving points of stagnation, and oscillating wall shear stresses mainly on the bed, at the toe, and at the heel. Moreover, higher anastomotic angles resulted in more extreme variations in TAWSS and OSI values, particularly around the toe and along the bed. In addition, the effect of anastomotic angle on OSI values at the heel followed the same pattern whereas the TAWSS values along the graft at the heel showed a significant increase at the lowest anastomotic angle of 20 degrees.

Anastomosis, Surgical↗

PubMed2004

Artificial aortic valves: an overview.

This review discusses strategies that may address some of the limitations associated with replacing diseased or dysfunctional aortic valves with mechanical or tissue valves. These limitations range from structural failure and thromboembolic complications associated with mechanical valves to a limited durability and calcification with tissue valves. In pediatric patients there is an issue with the inability of substitutes to grow with the recipient. The emerging science of tissue engineering potentially provides an attractive alternative by creating viable tissue structures based on a resorbable scaffold. Morphometrically precise, biodegradable polymer scaffolds may be fabricated from data obtained from scans of natural valves by rapid prototyping technologies such as fused deposition modelling. The scaffold provides a mechanical profile until seeded cells produce their own extra cellular matrix. The microstructure of the forming tissue may be aligned into predetermined spatial orientations via fluid transduction in a bioreactor. Although there are many technical obstacles that must be overcome before tissue engineered heart valves are introduced into routine surgical practice these valves have the potential to overcome many of the shortcomings of current heart valve substitutes.

Animals↗

PubMed2003

Effect of environmental fluctuations on the dynamic composition of engineered cartilage: a deterministic model in stochastic environment.

Dynamics of extracellular matrix (ECM) deposition and scaffold degradation in cell-polymer constructs have been studied in a random fluctuating environment created due to the applications of growth factors into the in vitro generation of cartilaginous constructs. Existing models of cell-polymer constructs for the design of engineered cartilage have been discussed and then a new deterministic scheme in random environment proposed taking into account the effects of growth factors as the environmental variability in the form of Gaussian white noise. Steady-state probability distribution of each individual component of the ECM in its homeostasis is found explicitly. The computer-simulated results of the model have been discussed and then compared with the data from a variety of scaffold systems and culture conditions.

Animals↗

PubMed2000

Hydrodynamic evaluation of three artificial aortic valve chambers.

The effect of chamber geometry on the characteristics of turbulent steady flow through a newly designed artificial heart valve, "the jellyfish valve," has been investigated for flow rates matching those of peak systole. Laser Doppler Anemometry (LDA) was employed to determine the velocity and shear stress distributions at various locations downstream of the jellyfish valve. Three geometrically different aortic valve chambers have been investigated: namely, a chamber with sinuses of Valsalva, an ellipsoidal chamber, and a cylindrical chamber. The results of this investigation indicated that the aorta with sinuses of Valsalva model had the highest turbulent shear stresses whereas the ellipsoidal model gave the highest-pressure drops. However, for the various flow rates examined, including the systole peak value of 26 L/min, it appears that the ellipsoidal model displays better hydrodynamic characteristics in terms of shear stress and uniformity of axial velocity distributions downstream of the jellyfish valve.

Aortic Valve↗

PubMed2000

Flow characteristics past jellyfish and St. Vincent valves in the aortic position under physiological pulsatile flow conditions.

Thrombus formation and hemolysis have been linked to the dynamic flow characteristics of heart valve prostheses. To enhance our understanding of the flow characteristics past the aortic position of a Jellyfish (JF) valve in the left ventricle, in vitro laser Doppler anemometry (LDA) measurements were carried out under physiological pulsatile flow conditions. The hemodynamic performance of the JF valve was then compared with that of the St. Vincent (SV) valve. The comparison was given in terms of mean systolic pressure drop, back flow energy losses, flow velocity, and shear stresses at various locations downstream of both valves and at cardiac outputs of 3.5 L/min, 4.5 L/min, and 6.5 L/min respectively. The results indicated that both valves created disturbed flow fields with elevated levels of turbulent shear stress as well as higher levels of turbulence in the immediate vicinity of the valve and up to 1 diameter of the pipe (D) downstream of the valve. At a location further downstream, the JF valve showed better flow characteristics than the SV in terms of velocity profiles and turbulent shear stresses. The closure volume of the SV valve was found to be 2.5 times higher than that of the JF valve. Moreover, the total back flow losses and mean systolic pressure drop also were found to be higher in the SV than the JF valve.

Aortic Valve↗

PubMedDate not supplied

Analysis of regurgitation, mean systolic pressure drop and energy losses for two artificial aortic valves.

The work reported here is related to the hydrodynamic performance of a Jellyfish valve and St Vincent valve in terms of total energy losses, mean systolic pressure drop and regurgitation. The in vitro experimental investigation was conducted at cardiac outputs of 3.5, 4.5 and 6.51 min-1 across the two valves and under pulsatile flow condition. It was found that the closure volume of the St Vincent valve was about 2.5 times higher than that of the Jellyfish valve. The total back flow losses on the other hand were found to be in the range of 36.5 to 107.1 and 85.5 to 192.5 mJ for the Jellyfish valve and St Vincent valve respectively. Moreover, the mean systolic pressure drop of the St Vincent valve was found to be higher than that of the Jellyfish valve. However, for all the operating conditions tested here, the Jellyfish valve showed superior hydrodynamic performance in terms of backflow and mean systolic pressure as well as energy losses.

Aortic Valve↗