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in vitro Conditioning of Engineered Tissues
Published in Claudio Migliaresi, Antonella Motta, Scaffolds for Tissue Engineering, 2014
Aaron S. Goldstein, Patrick Thayer
Perfusion bioreactors have also been used to develop cardiac neo-tissues. In particular, pulsatile flow mechanically stimulates cardiomyocytes, while convection improves the delivery of nutrients and oxygen. For example, Kofidis et al.59 showed that pulsatile perfusion (100 ml/h, 2 Hz) increased cardiomyocyte viability throughout three-dimensional scaffolds compared with nonperfused scaffolds. In another study, Brown et al.60 demonstrated that pulsatile flow (1 Hz) conditioning resulted in neo-tissues with a lower excitation threshold, higher capture rate, and higher contraction amplitude than statically cultured neo-tissues.
Chapter 22 Safety-Critical Systems And Engineering Design: Cardiac And Blood-Related Devices
Published in B H Brown, R H Smallwood, D C Barber, P V Lawford, D R Hose, Medical Physics and Biomedical Engineering, 2017
Pulsatile flow testing is carried out using hydrodynamic test rigs, or pulse duplicators. These model the left side of the heart with varying levels of sophistication and attention to anatomical variation. There is no single universally accepted design and many involve a compromise between accurate simulation and ease of use. It is likely that, in the future, the use of in vitro techniques will be superseded by computational fluid-dynamic analyses (CFD).
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Published in Splinter Robert, Illustrated Encyclopedia of Applied and Engineering Physics, 2017
[biomedical, fluid dynamics] Many systems have a periodic flow pattern based on the mechanism of action of the device providing the energy for the flow. In biological applications, the pulsatile flow is provided by the beating heart. The flow process in biological systems is very complex due to the compliance of the system (vascular dilation/stretch), and downstream resistance that can be influenced by mechanical and hormonal functions (e.g., muscle contraction and adrenaline). Other mechanical pulsatile systems are piston pumps, rotary pumps, and for instance windmills with a paddle system operating with angular velocity (ω = ν2π, where ν represent the alternation frequency). The flow in mechanical systems can be analyzed using the (time-dependent) Navier-Stokes equation (ρ(∂u/∂t) = −(∂P/∂z) + μ{∂2u/∂t2) + [(1/r)(∂u/∂r)]},with the boundary condition (∂u/∂z) = 0) assuming that the fluid is incompressible (constant density ρ); the tubes are rigid with constant radius r, for laminar flow at flow velocity u, driven by an applied pressure (P) gradient as a function of the axial direction z. Developing the pressure gradient in a series will prove to be beneficial: (∂P/∂z)=∑n=1NCneinωt, disregarding the steady-state background flow that can be incorporated in various ways (e.g., n = 0) and the velocity is directly in line with the pressure fluctuations (also seeblood flow) (see Figure P.175).
Structure and motion design of a mock circulatory test rig
Published in Journal of Medical Engineering & Technology, 2018
Yuhui Shi, Theodosios Korakianitis, Zhongjian Li, Yubing Shi
Three pressure transducers and two flow-rate transducers are installed in each loop, to measure the pressure in the atrium, the ventricle and the main artery, and the flow rates in the artery and the vein. The operating range of the pressure transducers is chosen as , in case there may be temporary pressure overload in the system. Electromagnetic type or ultrasound type flow transducers are good candidates for the measurement of the pulsatile flow in the systematic artery and the pulmonary artery positions. Considering that the normal cardiac output is and it may raise to about in the maximum exercise condition [39], the operating range of the flow transducer can be set as . Flows in the simulated systematic and pulmonary vein positions are much steady, so the rotameters can be used in these locations to save the expense.
Quantification of error between the heartbeat intervals measured form photoplethysmogram and electrocardiogram by synchronisation
Published in Journal of Medical Engineering & Technology, 2018
Srinivas Kuntamalla, Ram Gopal Reddy Lekkala
The pulsatile flow of blood in the arteries is produced through the circulatory pumping action of the heart by means of ventricular systole and diastole. The ventricular systole is produced by the contraction of left ventricular myocardium during its electrical excitation through Purkinje fibres, which are recorded as R-peaks in ECG. The causal relationship between the R-peaks in ECG and the systolic peaks in PPG representing the systolic phase in pulsatile blood flow in arteries is a well-known physiologically established fact [9]. It, therefore, obviates the need for any statistical analysis to explore the relationship between them. The peak to peak intervals in PPG and R–R intervals in ECG, both measure the same physiological parameter, the heart beat interval, which can be seen in Figure 1.
In silico modelling of aortic valve implants – predicting in vitro performance using finite element analysis
Published in Journal of Medical Engineering & Technology, 2022
Robert Whiting, Elizabeth Sander, Claire Conway, Ted J. Vaughan
To evaluate the hydrodynamic performance of each valve, in vitro bench testing was performed using a Vivitro Pulse Duplicator (Figure 2(a)) (Vivitro Labs, Inc. Victoria, B.C.) according to ISO 5840. Valves were sealed in a mounting ring and placed in the aortic position between the ventricular sac and aorta of the flow rig. This flow rig reproduced cardiac pulsatile flow by compressing the ventricular sac, ejecting fluid through the aortic valve according to assigned stroke volume, systolic waveform and heart rate. Pressure transducers recorded the aortic, ventricular and atrial pressures while a flow probe positioned directly below the valve took flow measurements during each cycle, as shown in Figure 2(b). Valves were submerged in water for 2 h prior to testing in 0.9% NaCl solution at room temperature (20ᵒC). To investigate the hydrodynamic performance across a range of conditions, each valve was tested at increasing cardiac outputs of 2, 3, 4, 5, 6 and 7 L/min, while maintaining a constant mean aortic pressure of 100 mmHg, heart rate of 70 bpm and a systolic waveform occupying 35% of the cardiac cycle. High-speed images were captured using a Sony RX100 Mark IV camera (Figure 2(a)) at a frame rate of 1000fps to visualise open and closing configurations of valves during testing. Vivitest software (Vivitro Labs, Inc. Victoria, B.C.) recorded pressure and flow measurements over 10 consecutive cycles, which were used to calculate several hydrodynamic parameters, namely the EOA, RF and transvalvular ΔP. The EOA is defined as the minimal cross-sectional area of the jet formed downstream of the aortic valve [31,32]. It is often used during cardiac catheterisation to assess the severity of aortic stenosis in patients [8,33]. It is calculated using the Gorlin Formula [34] given by where is the root mean squared forward flow (ml/sec), is the mean transvalvular pressure drop (mmHg) and is the density of the test fluid (g/cm3). The RF is a measure of aortic valve leakage and is calculated by the regurgitant volume () as a fraction of the stroke volume (), as in Eq. (2) where is the sum of the closing volume and leakage volume (Figure 2(b)). The transvalvular ΔP, shown in Figure 2(b), refers to the pressure gradient across the valve during systole where the ventricles contract ejecting blood into the aorta and pulmonary artery. It is calculated as the mean pressure difference between the start and end of the systole positive pressure drop. It is used to assess aortic stenosis, with pressure drops of greater than 40 mmHg being considered severe [35]. In the design of replacement valves, low-pressure drops indicate ease of opening, which translates to a more efficient valve.