Bioprosthetic valve thrombosis has been considered uncommon, but recent studies have shown that it is more frequent than previously thought. Insufficient washout of the aortic sinus is believed to be a risk factor for bioprosthetic valve thrombosis. The objective of this in vitro experiment was to investigate the impact of aortic root morphology on blood flow in the aortic sinus and to relate these results to in vivo data obtained in patients with a transcatheter aortic valve implant. Two compliant aortic root phantoms with different morphologies (symmetrical and patient-specific) were fabricated with silicone. A bioprosthetic aortic valve was inserted in both phantoms. Haemodynamic measurements were performed in a pulsatile flow-loop replicating physiological flow and pressure conditions. The flow in the aortic root was visualized by injecting contrast agent (CA). The distribution of the CA was captured by a high-speed camera, and image post-processing was performed to quantify CA distribution in the aortic sinus. The results were compared with angiographic images after a transcatheter aortic valve implant. Blood flow in the aortic root and the washout of the sinus portion are significantly affected by aortic root morphology. CA arrives at the aortic sinus of the 2 phantoms at 0.09 s and 0.16 s after the valve opens in the symmetrical and the patient-specific phantoms, respectively. Delayed CA arrival was also observed in the patients with a transcatheter aortic valve implant. Aortic root morphology affects the blood flow in the aortic sinus and may be a factor in bioprosthetic valve thrombosis. Therefore, patient-specific aortic root morphology should be considered when selecting and positioning a prosthesis.

OBJECTIVES In this study, the influence of aortic root distensibility on the haemodynamic parameters and valve kinematics of a bioprosthetic aortic valve was investigated in a controlled in vitro experiment. METHODS An Edwards INTUITY Elite 21 mm sutureless aortic valve (Edwards Lifesciences, Irvine, CA, USA) was inserted in three transparent aortic root phantoms with different wall thicknesses (0.55, 0.85 and 1.50 mm) mimicking different physiological distensibilities. Haemodynamic measurements were performed in an in vitro flow loop at heart rates of 60, 80 and 100 bpm with corresponding cardiac outputs of 3.5, 4.0 and 5.0 l/min and aortic pressures of 100/60, 120/90 and 145/110 mmHg, respectively. Aortic valve kinematics were assessed using a high-speed camera. The geometric orifice area (GOA) was measured by counting pixels in the lumen of the open aortic valve. The effective orifice area (EOA) was calculated from the root-mean-square value of the systolic aortic valve flow rate and the mean systolic trans-valvular pressure gradient. RESULTS The tested aortic root phantoms reproduce physiological distensibilities of healthy individuals in age groups ranging from 40 to 70 years (±10 years). The haemodynamic results show only minor differences between the aortic root phantoms: the trans-valvular pressure gradient tends to increase for stiffer aortic roots, whereas the systolic aortic valve flow rate remains constant. As a consequence, the EOA decreased slightly for less distensible aortic roots. The GOA and the aortic valve opening and closing velocities increase significantly with reduced distensibility for all haemodynamic measurements. The resulting mean systolic flow velocity in the aortic valve orifice is lower for the stiffer aortic root. CONCLUSIONS Aortic root distensibility may influence GOA and aortic valve kinematics, which affects the mechanical load on the aortic valve cusps. Whether these changes have a significant effect on the onset of structural valve deterioration of bioprosthetic heart valves needs to be further investigated.

Human motion analysis is a valuable tool for assessing disease progression in persons with conditions such as multiple sclerosis or Parkinson’s disease. Human motion tracking is also used extensively for sporting technique and performance analysis as well as for work life ergonomics evaluations. Wearable inertial sensors (e.g., accelerometers, gyroscopes and/or magnetometers) are frequently employed because they are easy to mount and can be used in real life, out-of-the-lab-settings, as opposed to video-based lab setups. These distributed sensors cannot, however, measure relative distances between sensors, and are also cumbersome when it comes to calibration and drift compensation. In this study, we tested an ultrasonic time-of-flight sensor for measuring relative limb-to-limb distance, and we developed a combined inertial sensor and ultrasonic time-of-flight wearable measurement system. The aim was to investigate if ultrasonic time-of-flight sensors can supplement inertial sensor-based motion tracking by providing relative distances between inertial sensor modules. We found that the ultrasonic time-of-flight measurements reflected expected walking motion patterns. The stride length estimates derived from ultrasonic time-of-flight measurements corresponded well with estimates from validated inertial sensors, indicating that the inclusion of ultrasonic time-of-flight measurements could be a feasible approach for improving inertial sensor-only systems. Our prototype was able to measure both inertial and time-of-flight measurements simultaneously and continuously, but more work is necessary to merge the complementary approaches to provide more accurate and more detailed human motion tracking.