Transient pressure at closing of a monoleaflet mechanical heart valve prosthesis: mounting compliance effect.

An in vitro experimental study was performed to investigate the mounting compliance effect on the occluder closing dynamics and the transient pressure at the closing of the mitral Medtronic Hall (MH) mechanical heart valve (MHV). The closing velocity and the transient pressure were simultaneously measured at heart rates of 70, 90, 120, and 140 beats/minute with cardiac outputs of 5.0, 6.

Asynchronous closure and leaflet impact velocity of bileaflet mechanical heart valves.

The effect of gravitational field on the asynchronous closure of four different types of bileaflet heart valves (BHV) were investigated in an in vitro mock circulation system. The experimental study involved the 29 mm St. Jude Medical Standard, 29 mm CarboMedics, 29mm Edwards-Duromedics and 29 mm Edwards-Tekna BHVs.

Ventricular pressure slope and bileaflet mechanical heart valve closure.

The maximum left ventricular pressure slope (dP/dt) value has been used by several investigators as the criterion for studying mitral valve closure. In this article, the relationship between the ventricular pressure slope (dP/dt) and the leaflet closing behavior of bileaflet mechanical heart valves (BMV) is investigated. Two current BMVs, the St.

The closing velocity of mechanical heart valve leaflets.

The closing motion of the occluder leaflets in bileaflet type mechanical heart valves (MHV) was monitored with a laser sweeping technique. The angular displacements of the leaflets were registered with precision of 0.2 microsecond steps.

A squeeze flow phenomenon at the closing of a bileaflet mechanical heart valve prosthesis.

In vivo cavitation in cardiovascular flow fields may occur under very unusual circumstances as a localized transient phenomenon which are confined to very small regions in the vicinity of the valve body or leaflet surface. The violent collapse of cavitation bubbles induces local erosion that may lead to structural damage. The fluid mechanical factors that may cause in vivo cavitation inception in mechanical heart valve (MHV) prostheses are investigated.

On the transport of a suspended particle in flow through the entrance region of a tube.

The motion of a single, spherical particle, released at different radial positions at the inlet of the entrance region of a straight circular laminar flow tube (Re = 260), was studied theoretically. Radial migration of the particle, either toward the tube center or toward the tube wall, was predicted. Based on the hypothesis that the particle experienced a lift force which was produced by the vorticity in the boundary layer and a velocity difference between the center of the suspended particle and the fluid medium, an inertia-vorticity fluid dynamic model was formulated to analyze the particle radial motions.

The closing behavior of Medtronic Hall mechanical heart valves.

The rapid deceleration of mechanical heart valve leaflets or discs at closure, and their rebound after impact between the leaflets or discs and housing may produce conditions that favor cavitation inception. Precision measurements of the disc closing velocity using a laser sweeping technique (LST) were made on two Medtronic Hall (Med Hall) mitral valve models, the 29 mm Standard and D-16 Med Hall valves. The experiment was carried out in a pulsatile mock flow loop (PFL) by installing the tested valve in the mitral position of the PFL.

An experimental-computational analysis of MHV cavitation: effects of leaflet squeezing and rebound.

A combined experimental-computational study was performed to investigate the flow mechanics which could cause cavitation during the squeezing and rebounding phases of valve closure in the 29 mm mitral bileaflet Edwards-Duromedics (ED) mechanical heart valve (MHV). Leaflet closing motion was measured in vitro, and input into a computational fluid mechanics software package, CFD-ACE, to compute flow velocities and pressures in the small gap space between the occluder tip and valve housing. The possibility of cavitation inception was predicted when fluid pressures dropped below the saturated vapor pressure for blood plasma.

Occluder closing behavior: a key factor in mechanical heart valve cavitation.

A laser sweeping technique developed in this laboratory was found to be capable of monitoring the leaflet closing motion with microsecond precision. The leaflet closing velocity was measured inside the last three degrees before impact. Mechanical heart valve (MHV) leaflets were observed to close with a three-phase motion; the approaching phase, the decelerating phase, and the rebound phase, all of which take place within one to two milliseconds.

Closing behavior of a new bileaflet mechanical heart valve.

Recently, the in vivo cavitation potential has become a primary concern among manufacturers of new mechanical heart valves (MHV). An experimental/computational program was designed to investigate each of the flow parameters involved. It was established that the closing velocity of the leaflet holds the key to MHV cavitation.

Phase Equilibria and Crystal Chemistry in Portions of the System SrO-CaO-BiO-CuO, Part IV- The System CaO-BiO-CuO.

New data are presented on the phase equilibria and crystal chemistry of the binary systems CaO-BiO and CaO-CuO and the ternary CaO-BiO-CuO. Symmetry data and unit cell dimensions based on single crystal and powder x-ray diffraction measurements are reported for several of the binary CaO-BiO phases, including corrected compositions for CaBiO and CaBiO. The ternary system contains no new ternary phases which can be formed in air at ~700-900 °C.

Effect of prefrontal cooling on levels of glutamate, DOPAC and 5-HIAA in nucleus accumben and striatum in vivo.

The effect of pre-frontal cooling of the cortex (PFC) on monoaminergic metabolites (DOPAC and 5-HIAA) and excitatory amino acids (glutamate (Glu) and aspartate (Asp)) was investigated using microdialysis in rat striatum (Str) and nucleus accumben (NuAc). The cooling profoundly decreased Glu and elevated DOPAC and 5-HIAA in both Str and NuAc for a long period of time. However, the time course of the detection of each compound appeared different between Str and NuAc.

Fluid mechanics of left ventricular assist system outflow housings.

Using the Novacor (Baxter Novacor, Oakland, CA) Left Ventricular Assist System (LVAS) as a test bed, phasic flow patterns were analyzed for three outflow valve housing designs: 1) a triple sinus; 2) an axisymmetric concentric sinus (CS); and 3) a modified triple sinus (MS). The 21 mm Carpentier-Edwards trileaflet pericardial heart valve prosthesis was used for all experiments done on the three housing designs. The LVAS was actuated by a laboratory model of the Novacor LVAS control console, and it was connected to a mock flow loop with an adjustable afterload system to provide physiologic pressures and flows (Pao, 120/80 mmHg; pump output [PO], 2-6 L/min).

In vitro performance of venous valve prostheses. An experimental model study.

The performance of fresh and glutaraldehyde fixed bovine jugular vein valves (10 mm diameter) was investigated in an experimental flow loop that provides adjustable flow rates and a downstream oscillatory pressure. Three different venous valve (VV) conduit geometries (curved [C], straight [S], and tapered [T]), were tested. The flow loop consisted of two independently adjustable components, with the mean flow generated by adjusting the elevation difference between the head tank and outflow chamber.

On transport of suspended particulates in tube flow.

Blood cells suspended in shear flows exhibit much larger dispersive motions than those predicted by the Stokes-Einstein formula for Brownian diffusion. The lateral migration and the erratic motions of the 8 microns red blood cells (RBC) is thought to be analogous to a diffusive process. It is shown that the often cited convective-diffusion theory may not be an adequate model for describing the transverse migration of suspended cells in blood flow.

Venturi pressure cannot cause cavitation in mechanical heart valve prostheses.

Surface pitting of certain mechanical heart valve (MHV) explants has prompted investigation into possible causes of cavitation during MHV operation. Leaflets of a 29 mm MHV were glued shut with B-datum (BD) gaps fixed at 0.0089, 0.

Haemodynamics of angioaccess venous anastomoses.

A large percentage of arteriovenous haemodialysis angioaccess loop grafts (AVLG) fail within the first year after surgery, the occlusive lesions being found predominantly at the venous anastomosis site. This paper presents a detailed flow dynamic study of the AVLG system using three elastic, transparent bench-top flow models, which were based on the geometry of silicone rubber casts obtained at different times from a chronic animal model. Each model thus represented a different stage of the lesion development.

Laser assessment of leaflet closing motion in prosthetic heart valves.

The dynamics of leaflet motion in heart valve prostheses (HVP), and in particular the closing velocity, is believed to be related to the valve sound and possibly to the phenomenon of valve cavitation. This paper describes a non-intrusive laser sweeping technique enabling the study of leaflet motion. The principle of measurement and the equipment involved are presented, together with the results of two commercially available, 29 mm bileaflet mitral valves, a St.

Estimation of the rotational undamped natural frequency of bileaflet cardiac valve prostheses.

The angular momentum balance is solved numerically for a size 29 mm CarboMedics prosthetic heart valve. The lift force is estimated from potential flow theory, while the drag force is estimated from the lift force and a blunt body empiricism. Buoyancy and gravitational effects are calculated based on the assumption of homogeneous leaflets.

The closing velocity of Baxter Duromedic heart valve prostheses.

The closing velocity of a mechanical heart valve (MHV) leaflet has been conventionally related to the valve sound, and possibly to recently observed MHV cavitation phenomenon. Presently, the MHV leaflet terminal closing velocity has been indirectly assessed either by listening to the valve sound and/or averaging over the closing period. Leaflet motion during the closing phase is not uniform.

Graft compliance and anastomotic flow patterns.

The oscillatory flow patterns at the venous anastomosis of a hemodialysis angioaccess loop graft system were studied using two new compliant vascular prostheses: a longitudinally compliant polytetrafluoroethylene-composite (Baxter Ultraflex PTFE-Plus) graft (BA) and a radially compliant ultrafine polyester fiber (TORAY-UFPF) graft (TR). A non-compliant Gore-Tex polytetrafluoroethylene graft was used as the control. The experimental grafts were 8 mm inside diameter x 25 cm long.

Vortex shedding in bileaflet heart valve prostheses.

A dynamic study of two geometrically similar bileaflet heart valve prostheses (HVP) was performed using a physiologic mock circulatory flow loop. The HVPs studied were the 25 mm St. Jude Medical (SJM) and the 25 mm Carbomedics (CMI) in the aortic position and the 27 mm SJM and 27 mm CMI in the mitral position.