Biomedical subjects

J M Gross

Publications and source records attributed to J M Gross.

21 records · Page 2Linked to original sources

PubMedDate not supplied

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, 0.0174, and 0.0219 cm. Each BD gap setting was tested in a steady flow chamber, with leakage flow established at transvalvular pressures (delta P) of 20 to 200 mmHg. Laser Doppler velocimeter (LDV) velocity measurements were recorded 220 microns distal to the BD, along with leakage flowrates. Maximum LDV velocities were compared with those calculated using the mass conservation equation. At identical P, the LDV flow velocities for the three BD settings were found to be approximately equal. This indicates a geometric independence of the leakage flow velocity. At atmospheric pressure, the local velocity necessary to cavitate blood as a liquid is approximately 13 m/sec. These results demonstrate that the leakage velocity is insufficient to cause cavitation. A simplified theoretical model is proposed to illustrate the necessary delta P to produce Venturi related cavitation.

Blood Flow Velocity↗

PubMedDate not supplied

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. All data were collected at a heart rate of 70 beats/min and a cardiac output of 5.0 L/min. Flow visualization was conducted in the transparent flow chambers of the pulsatile mock circulatory flow loop using a 15 mW He-Ne laser light source. A cylindrical lens and optics system converted the incident laser beam into a thin parallel light plane, and 420 microns tracer particles were suspended in the testing fluid to illuminate the flow field at selected planes. Frame-by-frame analysis of the 16 mm high-speed cine provides detailed phasic flow patterns in the vicinity of the HVP. A series of still photographs of flow patterns, taken at approximately 22.5 degrees phase intervals, are sequentially presented for each HVP. In the aortic position, a Karman-like vortex pattern appears downstream of the SJM at the end of the ejection phase. The CMI exhibits a rather symmetrical ejection flow pattern that turns into random motion immediately after the onset of ejection. In the mitral position, the SJM again exhibits a strong core flow during ventricular filling, whereas the CMI produces a more diffuse pattern during the same period. A pair of vortices shed from both the SJM and CMI are clearly visible toward the end of the ventricular filling phase. The vortex mechanisms are discussed in light of leaflet boundary layer formation.

Aortic Valve↗

PubMedDate not supplied

A non-invasive technique to quantify in vitro bioprosthetic valvular coaptation.

The functional relationship between valvular leaflet stress and coaptive geometry may provide insight into a bioprosthetic heart valve's ability to maintain coaptation under a broad range of physiologic operating conditions. Previous investigators have only indirectly measured coaptation geometry. A non-invasive in vitro technique is demonstrated to directly quantify the coaptive geometry of bioprosthetic heart valves. A discussion is provided detailing the use of this information in a finite element model to determine the functional relationship between valvular leaflet stress and coaptation geometry. Video images of the stent post deflections and coaptive geometry for size 21 mm, 23 mm, and 25 mm Hancock Aortic Pericardial heart valves are obtained based on back light illumination of each valve's coaptive area at discrete back pressures. The resulting images are analyzed using image processing and motion analysis techniques. Results indicate that at back pressures greater than 50-75 mmHg the coaptive area remains constant. There is a decrease in coaptive depth at the valve's periphery, whereas the point of maximum coaptation maintains position approximately midway along the free margin. Good agreement is found between the experimentally determined and finite element model's predicted coaptation geometry.

Aortic Valve↗