A Comparison of Flow Field Structures of Two Tri-Leaflet Polymeric Heart Valves

Abstract

Polymeric heart valves have the potential to reduce thrombogenic complications associated with current mechanical valves and overcome fatigue-related problems experienced by bioprosthetic valves. In this in vitro study, the velocity fields inside and downstream of two different prototype tri-lealfet polymeric heart valves were studied. Experiments were conducted on two 23 mm prototype polymeric valves, provided by AorTech Europe, having open or closed commissure designs and leaflet thickness of 120 and 80 microm, respectively. A two-dimensional LDV system was used to measure the velocity fields in the vicinity of the two valves under simulated physiological conditions. Both commissural design and leaflet thickness were found to affect the flow characteristics. In particular, very high levels of Reynolds shear stress of 13,000 dynes/cm2 were found in the leakage flow of the open commisure design. Maximum leakage velocities in the open and closed designs were 3.6 m/s and 0.5 m/s respectively; the peak forward flow velocities were 2.0 m/s and 2.6 m/s, respectively. In both valve designs, shear stress levels exceeding 4,000 dyne/cm2 were observed at the trailing edge of the leaflets and in the leakage and central orifice jets during peak systole. Additionally, regions of low velocity flow conducive to thrombus formation were observed in diastole. The flow structures measured in these experiments are consistent with the location of thrombus formation observed in preliminary animal experiments.

Fluid Dynamic Assessment of Three Polymeric Heart Valves Using Particle Image Velocimetry

“…Previous studies with prototypes A and B using two component Laser Doppler Velocimetry (LDV) also showed the flow splitting characteristic, which was attributed to the combined influence of the closing dynamics of the valve and the persistent oscillation of the valve during diastole. 16 The persistence of the observed oscillation was believed to be due to the combined effect of both the leaflet thickness and the flexibility of the valve frame. 16 LDV measurements near the frames of the three polymeric valves showed that the stent posts oscillate at a frequency of approximately 12-14 Hz during diastole.…”

“…16 The persistence of the observed oscillation was believed to be due to the combined effect of both the leaflet thickness and the flexibility of the valve frame. 16 LDV measurements near the frames of the three polymeric valves showed that the stent posts oscillate at a frequency of approximately 12-14 Hz during diastole. 16 …”

“…A detailed description of the flow loop can be found in literature. 16 Figure 4 shows the resulting physiological flow and pressure waveforms.…”

“…The flow loop, driven by a pulse generator, consisted of tubing, a mechanical valve in the mitral position, a flow transducer, ventricular and aortic pressure transducers, a bulb pump, compliance, and resistance. 16 Variation of the compliance and resistance sections of the loop allowed additional control in order to produce physiological flow and pressure waveforms. The heart rate was set at 70 beats/min with a cardiac output of 5.0 L/min, a peak systolic flow rate of 25.0 L/min, a mean aortic pressure of 90-100 mmHg and a systolic flow phase duration of approximately 35% of the cardiac cycle time.…”

In vitro hemodynamic investigation of the embryonic aortic arch at late gestation

“…The bulb pump is driven through a pneumatic circuit that consists of a computer controlled pulse duplicator, compressor and solenoid valves (Leo et al, 2005). In the present arrangement, the pulsatile bulb pump was used solely to create the pulsatile flow component and had little effect on influencing the total flow rate which was adjusted with the steady pump to the desired level generating the physiological flow waveform, Fig 2. LVOT and RVOT flow rates are measured using ultrasonic clamp-on flow probes (Model T108, Transonic Inc, NY).…”