Effect of lower extremity amputation on cardiovascular hemodynamic environment: An in vitro study.

Lower extremity amputation (LEA) was associated with a greater risk of cardiovascular disease, but its hemodynamic mechanisms have not been fully studied. Therefore, to clarify the interrelationship between them, and figure out the potential pathogenesis, the exploration of the hemodynamic environment change of patients after LEA was premeditatedly executed. A near-physiological mock circulatory system (MCS) was employed in the present work to replicate the cardiovascular circulation after LEA in a short time and the unsteady-state numerical simulation was utilized as an auxiliary method to observe the changes of the hemodynamic environment inside the blood vessel. Higher severity of LEA leads to higher peripheral vascular impedance, higher blood pressure, and more obvious redistribution of blood perfusion volume. In addition, higher severity of LEA leads to lower wall shear stress (WSS), higher oscillatory shear index (OSI), and higher relative residence time (RRT) appeared in the infrarenal abdominal aorta and the iliac artery, while these changes are closely related to the higher probability of cardiovascular diseases. Results showed that different degrees of LEA (varying heights, unilateral/bilateral) have diverse effects on the patient's hemodynamic environment. This study explained the potential pathogenesis of cardiovascular diseases after LEA from a hemodynamic perspective and provided a certain reference value for the improvement of the cardiovascular hemodynamic environment and the prevention of cardiovascular diseases in lower extremity amputees.

Morphology display and hemodynamic testing using 3D printing may aid in the prediction of LVOT obstruction after mitral valve replacement.

AIMS: Left ventricular outflow tract(LVOT) obstruction after mitral valve replacement can be life-threatening once occur. We simulated mitral valve replacement preoperatively using dynamic, three-dimensional(3D) printed models to help predict LVOT obstruction in this study. METHODS: 56 patients who underwent mitral valve replacement were included. Prediction of LVOT obstruction in vitro was based on the data from 4 sources: digital, anatomical, flexible, and dynamic model. Digital 3D models were designed based on computed tomography (CT) image dataset and printed with photopolymer resin to create a 3D anatomical model, which contributed to the morphology display. Then, flexible models were made from specialized silicone, which is similar to cardiac tissue in terms of its softness and elasticity. Dynamic function was achieved by coupling flexible models to a mock circulatory system (MCS). Besides, surgery simulation and hemodynamic testing was done using dynamic 3D printed model and patients were regrouped based on hemodynamic change. Finally, different methods for prediction of LVOT obstruction as well as classification based on two-dimensional image data and dynamic model were compared with surgical results as golden standard. RESULTS: (1)Qualitatively, the prediction of LVOT obstruction using the dynamic 3D model was the most accurate and was consistent with clinical outcomes. In the four patients who developed LVOT obstruction after surgery, only two were at a high risk based on the other three models. (2)Quantitatively, the area of neo-LVOT predicted by the digital, anatomical, and flexible models was higher compared with the dynamic models and in-vivo after surgery. (3)Classification based on traditional criteria(two-dimensional image data) was different from surgical results. While the difference between dynamic model and surgical results was not statistically different. CONCLUSIONS: After coupling the flexible model with the mock circulatory system, the dynamic 3D model predicted LVOT obstruction more accurately with hemodynamic testing compared with morphological evaluation. 3D printing can assist surgeons to better plan mitral valve replacement than traditional image data.

Three-dimensional printing for cardiovascular diseases: from anatomical modeling to dynamic functionality.

Three-dimensional (3D) printing is widely used in medicine. Most research remains focused on forming rigid anatomical models, but moving from static models to dynamic functionality could greatly aid preoperative surgical planning. This work reviews literature on dynamic 3D heart models made of flexible materials for use with a mock circulatory system. Such models allow simulation of surgical procedures under mock physiological conditions, and are; therefore, potentially very useful to clinical practice. For example, anatomical models of mitral regurgitation could provide a better display of lesion area, while dynamic 3D models could further simulate in vitro hemodynamics. Dynamic 3D models could also be used in setting standards for certain parameters for function evaluation, such as flow reserve fraction in coronary heart disease. As a bridge between medical image and clinical aid, 3D printing is now gradually changing the traditional pattern of diagnosis and treatment.

In vitro testing of an intra-ventricular assist device.

A novel pulsatile assist device, intra-ventricular assist device, was proposed to address various disadvantages existing in conventional pulsatile assist device, such as the large size, accessories and reduced pulsatility. The assist device was designed, fabricated and implanted into the sac from left ventricular apex in a home-designed mock circulatory system. In vitro test was carried out and results demonstrated that the response time did not vary with the heart rate, and co-pulsatiled synchronously with native heart by electrocardiograph. The key parameter, stroke volume of proposed device was precisely measured under different afterloads (60, 80, 100, and 120 mmHg), drive pressure (from 90 to 300 mmHg at 30 mmHg intervals), and heart rate (45-150 beats per minute). The measurement results revealed that the output characteristics of device, stroke volume increased with increasing drive pressure but decreased with increasing peripheral resistance, were consistent with the native heart. The proposed pump was then coupled with mock system that was set to a heart failure mode and the circulatory responses were tested. Results showed that the device improved left ventricular pressure from 106 to 158 mmHg, and stroke volume from 25.5 to 44 ml at 90 bpm.

Finite state machine implementation for left ventricle modeling and control.

BACKGROUND: Simulation of a left ventricle has become a critical facet of evaluating therapies and operations that interact with cardiac performance. The ability to simulate a wide range of possible conditions, changes in cardiac performance, and production of nuisances at transition points enables evaluation of precision medicine concepts that are designed to function through this spectrum. Ventricle models have historically been based on biomechanical analysis, with model architectures constituted of continuous states and not conducive to deterministic processing. Producing a finite-state machine governance of a left ventricle model would enable a broad range of applications: physiological controller development, experimental left ventricle control, and high throughput simulations of left ventricle function. METHODS: A method for simulating left ventricular pressure-volume control utilizing a preload, afterload, and contractility sensitive computational model is shown. This approach uses a logic-based conditional finite state machine based on the four pressure-volume phases that describe left ventricular function. This was executed with a physical system hydraulic model using MathWorks' Simulink® and Stateflow tools. RESULTS: The approach developed is capable of simulating changes in preload, afterload, and contractility in time based on a patient's preload analysis. Six pressure-volume loop simulations are presented to include a base-line, preload change only, afterload change only, contractility change only, a clinical control, and heart failure with normal ejection fraction. All simulations produced an error of less than 1 mmHg and 1 mL of the absolute difference between the desired and simulated pressure and volume set points. The acceptable performance of the fixed-timestep architecture in the finite state machine allows for deployment to deterministic systems, such as experimental systems for validation. CONCLUSIONS: The proposed approach allows for personalized data, revealed through an individualized clinical pressure-volume analysis, to be simulated in silico. The computational model architecture enables this control structure to be executed on deterministic systems that govern experimental left ventricles. This provides a mock circulatory system with the ability to investigate the pathophysiology for a specific individual by replicating the exact pressure-volume relationship defined by their left ventricular functionality; as well as perform predictive analysis regarding changes in preload, afterload, and contractility in time.

Development of an adaptive pulmonary simulator for in vitro analysis of patient populations and patient-specific data.

BACKGROUND AND OBJECTIVE: Patient-specific modeling (PSM) is gaining more attention from researchers due to its ability to potentially improve diagnostic capabilities, guide the design of intervention procedures, and optimize clinical management by predicting the outcome of a particular treatment and/or surgical intervention. Due to the hemodynamic diversity of specific patients, an adaptive pulmonary simulator (PS) would be essential for analyzing the possible impact of external factors on the safety, performance, and reliability of a cardiac assist device within a mock circulatory system (MCS). In order to accurately and precisely replicate the conditions within the pulmonary system, a PS should not only account for the ability of the pulmonary system to supply blood flow at specific pressures, but similarly consider systemic outflow dynamics. This would provide an accurate pressure and flow rate return supply back into the left ventricular section of the MCS (i.e. the initial conditions of the left heart). METHODS: Employing an embedded Windkessel model, a control system model was developed utilizing MathWorks' Simulink® Simscape™. Following a verification and validation (V&V) analysis approach, a PI-controlled closed-loop hydraulic system was developed using Simscape™. This physical system modeling tool was used to (1) develop and control the in silico system during verification studies and (2) simulate pulmonary performance for validation of this control architecture. RESULTS: The pulmonary Windkessel model developed is capable of generating the left atrial pressure (LAP) waveform from given pulmonary factors, aortic conditions, and systemic variables. Verification of the adaptive PS's performance and validation of this control architecture support this modeling methodology as an effective means of reproducing pulmonary pressure waveforms and systemic outflow conditions, unique to a particular patient. Adult and geriatric with and without Heart Failure and a Normal Ejection Fraction (HFNEF) are presented. CONCLUSIONS: The adaptability of this modelling approach allows for the simulation of pulmonary conditions without the limitations of a dedicated hardware platform for use in in vitro investigations.

Effects of an intra-ventricular assist device on the stroke volume of failing ventricle: Analysis of a mock circulatory system.

BACKGROUND: A novel intra-ventricular assist device (iVAD) was established as a new pulsatile assist device to address various disadvantages, such as bulky configuration and reduced arterial pulsatility, observed in conventional ventricular assist devices. OBJECTIVE: Analyzed the native left ventricular stroke volume (SV) after iVAD support in vitro. METHODS: The SV of iVAD was examined in a home-designed mock circulatory system (MCS) at different heart rates and drive pressures and the SV of a failure ventricle was examined with iVAD at 75, 90, 120 bpm and 120-180 mmHg drive pressure after iVAD support. Data pertaining to native left ventricular SV before and after iVAD support were compared. RESULTS: The native ventricular SV was improved by iVAD when its drive pressure (DP) was slightly greater than that of the mock system. Conversely, the native ventricular SV was decreased when DP was much greater than that (150 mmHg) of MCS. A high DP had a significant effect on SV. CONCLUSIONS: The proposed device improved the dysfunctional native left ventricular SV when DP of iVAD was slightly greater than that of MCS. However, iVAD reduced the SV when the drive pressure was greater than that of MCS.

A Review on Mock Circulatory Systems for in vitro Hemodynamic Performance Evaluation of Ventricular Assist Devices / 医用生物力学

Mock circulatory system (MCS) is an experimental platform for simulating hemodynamic performance of human circulatory system, and has been widely used in in-vitro hemodynamic performance evaluation of passive devices such as ventricular assist devices (VADs), artificial valves, as well as hemodynamic responses of mock circulation loop. MCSs are capable of simulating various physiological conditions, including health, exercise, and heart failure, by adjusting drive element of heart simulator and lumped-parameter element of vasculature components. Since 1 960 s, the research and development target of MSCs has evolved from meeting the basic performance evaluation requirement of VADs and mechanical valve to mimicking local hemodynamic characteristics in vital organs. This review summarizes the design principles, system construction of MCSs as well as its research progress and future prospects.

[A correction method for calculating resistance of Westerhof 's resistor].

The objective of the mock circulatory system (MCS) is to construct the characteristics of cardiovascular hemodynamics. Westerhof 's resistor that often regarded as the laminar flow resistance in the MCS, is commonly used to simulate the peripheral resistance of the cardiovascular system. However, the theoretical calculation value of fluid resistance of the Westerhof 's resistor shows distinguished difference with the actual needed value. If the theoretical resistance is regarded as the actual needed one and be used directly in the experiment, the experimental accuracy would not be acceptable. In order to improve the accuracy, an effective correction method for calculating the resistance of Westerhof 's resistor was proposed in this paper. Simulation software was also developed to compute accurately the capillary number, total length and resistance. The results demonstrate the proposed method is able to reduce the difficulty and complexity of the design of the resistor, which would obviously increase the manufactured precision of the Westerhof 's resistor. Simulation software would provide great support to the construction of various MCSs.

A Mock Circulatory System Incorporating a Compliant 3D-Printed Anatomical Model to Investigate Pulmonary Hemodynamics.

A realistic mock circulatory system (MCS) could be a valuable in vitro testbed to study human circulatory hemodynamics. The objective of this study was to design a MCS replicating the pulmonary arterial circulation, incorporating an anatomically representative arterial model suitable for testing clinically relevant scenarios. A second objective of the study was to ensure the system's compatibility with magnetic resonance imaging (MRI) for additional measurements. A latex pulmonary arterial model with two generations of bifurcations was manufactured starting from a 3D-printed mold reconstructed from patient data. The model was incorporated into a MCS for in vitro hydrodynamic measurements. The setup was tested under physiological pulsatile flow conditions and results were evaluated using wave intensity analysis (WIA) to investigate waves traveling in the arterial system. Increased pulmonary vascular resistance (IPVR) was simulated as an example of one pathological scenario. Flow split between right and left pulmonary artery was found to be realistic (54 and 46%, respectively). No substantial difference in pressure waveform was observed throughout the various generations of bifurcations. Based on WIA, three main waves were identified in the main pulmonary artery (MPA), that is, forward compression wave, backward compression wave, and forward expansion wave. For IPVR, a rise in mean pressure was recorded in the MPA, within the clinical range of pulmonary arterial hypertension. The feasibility of using the MCS in the MRI scanner was demonstrated with the MCS running 2 h consecutively while acquiring preliminary MRI data. This study shows the development and verification of a pulmonary MCS, including an anatomically correct, compliant latex phantom. The setup can be useful to explore a wide range of hemodynamic questions, including the development of patient- and pathology-specific models, considering the ease and low cost of producing rapid prototyping molds, and the versatility of the setup for invasive and noninvasive (i.e., MRI) measurements.

In vitro simulation experimental study of a fully magnetically levitated ventricular assist device based on mock circulatory system / 医用生物力学

Objective To investigate the circulatory supporting effect of the third generation fully magnetically levitated China Heart ventricular assist device (CH-VAD) under heart failure (HF) condition.Methods An in vitro mock circulatory system (MCS) was developed.This system could simulate a healthy adult under resting state and a patient with heart failure,and incorporate the CH-VAD to evaluate the assisting performance under continuous flow mode.Furthermore,CH-VAD was equipped with a pulsatile flow controller and its initial performance was accessed.The pulsatile mode was obtained by using sinusoidal velocity waveform of the pump which synchronized the CH-VAD with the ventricle simulator of the MCS.Results CH-VAD under continuous flow mode could recover the hemodynamic parameters (arterial pressure and cardiac output) under HF condition to normal range.Preliminary pulsatile test results showed that amplitude of current pulse speed had a minor influence on the hemodynamic performance.CH-VAD under continuous flow and pulsatile flow mode could obtain comparable mean arterial pressure,systolic arterial pressure,diastolic arterial pressure and mean flow.Conclusions CH-VAD can generate a certain degree of speed pulse via appropriate pulsatility control,so as to provide sufficient support on ventricular function.Further optimization on pulsatile controller of CH-VAD is required to conform to natural physiology.The developed MCS can be utilized as an effective and controllable in vitro platform for design,optimization and verification of VADs or other mechanical circulatory support devices.

In vitro simulation experimental study of a fully magnetically levitated ventricular assist device based on mock circulatory system / 医用生物力学

Objective To investigate the circulatory supporting effect of the third generation fully magnetically levitated China Heart ventricular assist device (CH-VAD) under heart failure (HF) condition.Methods An in vitro mock circulatory system (MCS) was developed.This system could simulate a healthy adult under resting state and a patient with heart failure,and incorporate the CH-VAD to evaluate the assisting performance under continuous flow mode.Furthermore,CH-VAD was equipped with a pulsatile flow controller and its initial performance was accessed.The pulsatile mode was obtained by using sinusoidal velocity waveform of the pump which synchronized the CH-VAD with the ventricle simulator of the MCS.Results CH-VAD under continuous flow mode could recover the hemodynamic parameters (arterial pressure and cardiac output) under HF condition to normal range.Preliminary pulsatile test results showed that amplitude of current pulse speed had a minor influence on the hemodynamic performance.CH-VAD under continuous flow and pulsatile flow mode could obtain comparable mean arterial pressure,systolic arterial pressure,diastolic arterial pressure and mean flow.Conclusions CH-VAD can generate a certain degree of speed pulse via appropriate pulsatility control,so as to provide sufficient support on ventricular function.Further optimization on pulsatile controller of CH-VAD is required to conform to natural physiology.The developed MCS can be utilized as an effective and controllable in vitro platform for design,optimization and verification of VADs or other mechanical circulatory support devices.

In vitro simulation experimental study of a fully magnetically levitated ventricular assist device based on mock circulatory system / 医用生物力学

Objective To investigate the circulatory supporting effect of the third generation fully magnetically levitated China Heart ventricular assist device (CH-VAD) under heart failure (HF) condition.Methods An in vitro mock circulatory system (MCS) was developed.This system could simulate a healthy adult under resting state and a patient with heart failure,and incorporate the CH-VAD to evaluate the assisting performance under continuous flow mode.Furthermore,CH-VAD was equipped with a pulsatile flow controller and its initial performance was accessed.The pulsatile mode was obtained by using sinusoidal velocity waveform of the pump which synchronized the CH-VAD with the ventricle simulator of the MCS.Results CH-VAD under continuous flow mode could recover the hemodynamic parameters (arterial pressure and cardiac output) under HF condition to normal range.Preliminary pulsatile test results showed that amplitude of current pulse speed had a minor influence on the hemodynamic performance.CH-VAD under continuous flow and pulsatile flow mode could obtain comparable mean arterial pressure,systolic arterial pressure,diastolic arterial pressure and mean flow.Conclusions CH-VAD can generate a certain degree of speed pulse via appropriate pulsatility control,so as to provide sufficient support on ventricular function.Further optimization on pulsatile controller of CH-VAD is required to conform to natural physiology.The developed MCS can be utilized as an effective and controllable in vitro platform for design,optimization and verification of VADs or other mechanical circulatory support devices.

In vitro simulation experimental study of a fully magnetically levitated ventricular assist device based on mock circulatory system / 医用生物力学

Objective To investigate the circulatory supporting effect of the third generation fully magnetically levitated China Heart ventricular assist device (CH-VAD) under heart failure (HF) condition. Methods An in vitro mock circulatory system (MCS) was developed. This system could simulate a healthy adult under resting state and a patient with heart failure, and incorporate the CH-VAD to evaluate the assisting performance under continuous flow mode. Furthermore, CH-VAD was equipped with a pulsatile flow controller and its initial performance was accessed. The pulsatile mode was obtained by using sinusoidal velocity waveform of the pump which synchronized the CH-VAD with the ventricle simulator of the MCS. Results CH-VAD under continuous flow mode could recover the hemodynamic parameters (arterial pressure and cardiac output) under HF condition to normal range. Preliminary pulsatile test results showed that amplitude of current pulse speed had a minor influence on the hemodynamic performance. CH-VAD under continuous flow and pulsatile flow mode could obtain comparable mean arterial pressure, systolic arterial pressure, diastolic arterial pressure and mean flow. Conclusions CH-VAD can generate a certain degree of speed pulse via appropriate pulsatility control, so as to provide sufficient support on ventricular function. Further optimization on pulsatile controller of CH-VAD is required to conform to natural physiology. The developed MCS can be utilized as an effective and controllable in vitro platform for design, optimization and verification of VADs or other mechanical circulatory support devices.

In Vitro Assessment of the Assisted Bidirectional Glenn Procedure for Stage One Single Ventricle Repair.

This in vitro study compares the hemodynamic performance of the Norwood and the Glenn circulations to assess the performance of a novel assisted bidirectional Glenn (ABG) procedure for stage one single ventricle surgery. In the ABG, the flow in a bidirectional Glenn procedure is assisted by injection of a high-energy flow stream from the systemic circulation using an aorta-caval shunt with nozzle. The aim is to explore experimentally the potential of the ABG as a surgical alternative to current surgical practice. The experiments are directly compared against previously published numerical simulations. A multiscale mock circulatory system was used to measure the hemodynamic performance of the three circulations. For each circulation, the system was tested using both low and high values of pulmonary vascular resistance. Resulting parameters measured were: pressure and flow rate at left/right pulmonary artery and superior vena cava (SVC). Systemic oxygen delivery (OD) was calculated. A parametric study of the ratio of ABG nozzle to shunt diameter was done. We report time-based comparisons with numerical simulations for the three surgical variants tested. The ABG circulation demonstrated an increase of 30-38% in pulmonary flow with a 2-3.7 mmHg increase in SVC pressure compared to the Glenn and a 4-14% higher systemic OD than either the Norwood or the Glenn. The nozzle/shunt diameter ratio affected the local hemodynamics. These experimental results agreed with those of the numerical model: mean flow values were not significantly different (p > 0.05) while mean pressures were comparable within 1.2 mmHg. The results verify the approaches providing two tools to study this complicated circulation. Using a realistic experimental model we demonstrate the performance of a novel surgical procedure with potential to improve patient hemodynamics in early palliation of the univentricular circulation.

Selective reduction of afterload in right heart assist therapy: a mock loop study†.

OBJECTIVES: The treatment of right ventricular failure is closely linked to effects on pulmonary vascular resistance and thus the right ventricular (RV) afterload. Medical therapy includes afterload-decreasing drugs such as nitric oxide and prostacycline. However, current devices for mechanical unloading of the right ventricle aim at a decrease in preload increasing the pulmonary volume loading. In our concept study, we tested a minimally invasive right ventricular assist device (MIRVAD) that specifically reduces the afterload. METHODS: The MIRVAD is supposed to be a foldable device for temporary transvascular placement in the pulmonary artery. We incorporated a MIRVAD prototype into a mock circulatory loop that can reproduce haemodynamic interaction between the pump and the physiological system. Pulmonary hypertension (PH), right heart failure (RHF) and MIRVAD-assisted cases were simulated. The key haemodynamic parameters for RV unloading were recorded. RESULTS: Mock loop simulation attested to a sufficient right ventricular unloading by serial application of a miniaturized impeller pump in the pulmonary artery. The afterload, represented by the pulmonary arterial root pressure, was recovered to the healthy range (32.62-10.93 mmHg) for the simulated PH case. In the simulated RHF case, the impaired pulmonary perfusion increased from 43.4 to 88.8% of the healthy level and the total ventricular work reduced from 0.381 to 0.197 J at a pump speed of 3500 rpm. At pump speeds higher than 3500 rpm, the pulmonary valve remains constantly open and the right ventricular configuration changes into a simple perfused hollow body. CONCLUSIONS: The feasibility of RV unloading by a selective decrease in RV afterload was proved in principle. By alternation of the pump speed, gradual reloading in sense of a myocardial training may be achieved. The results will be validated by future animal trials where the relationship between the level of support and pulmonary vascular pressure can be investigated in vivo. Further device design concerning foldable impeller leaflets will be carried out. At a final stage, the crimped version is supposed to reach a size below 1 cm to facilitate minimally invasive insertion.

Ventricular contractility and compliance measured during axial flow blood pump support: in vitro study.

End-systolic elastance and end-diastolic compliance have been used to quantify systolic and diastolic function of the left ventricle (LV). In this study, the effective end-systolic elastance, (EES )eff , end-systolic volume intercept, (V0 )eff , and end-diastolic compliance of the LV were assessed at various levels of left ventricular assist device (LVAD) support. We tested the hypothesis that (EES )eff and (V0 )eff vary as a function of LVAD speed, while compliance does not change. The Penn State in vitro cardiac simulator was used in two heart conditions (control and heart failure [HF]) with the HeartMate II axial flow LVAD. The LVAD speed was linearly increased from 6000 to 11 000 rpm, with 500-rpm increments. The end-systolic and end-diastolic pressure-volume relationships were estimated at each LVAD speed. Acute LVAD support itself showed pseudo-improvement of ventricular contractility. The (EES )eff and (V0 )eff in HF were found to be dependent on the LVAD speed. The effective compliance for both control and HF was independent of the LVAD speed. Therefore, when examining the time-course cardiac recovery induced by the LVAD support, LV performance should be measured immediately before and after LVAD support while keeping LVAD speed consistent to avoid potential overestimation of long-term cardiac recovery.

Basic Performance of a Miniature Intraventricular Axial Pump.

A miniature intraventricular axial pump for left ventricular (LV) support is under development. This pump was designed for placement in the LV cavity by insertion through the LV apex with the outlet located at the ascending aorta via the aortic valve. The basic hydro-dynamic characteristics represented as a relationship between pump head (H) and flow (Q) showed a negative linear relationship under a constant head. This characteristic was generally the same as that obtained by other axial rotation pumps. However, the actual H-Q relationship was represented as anticlockwise "loops" caused by the contraction of the natural LV. The comparative in vitro data on these H-Q loops showed that the shape of the loops was changed drastically by the connecting condition between the pump and natural cardiovascular system.

In vitro pressure drop comparison between two mechanical valve prostheses

An hemodynamic evaluation of two mechanical heart valves is presented. A tilting disc valve and a bileaflet valve were incorporated in a mock circulatory system which consists of a closed flow loop with a pneumatically driven flexible diaphragm to simulate the physiologic pulsatile flow. Comparisons between the valves were made on the aortic pressure, ventricular pressure, as well as mean pressure gradient at a systolic duration of 45% and a heart rate of 90 beats per minute. The results showed that the tilting disc valve has higher ventricular pressure and mean pressure gradient than that of the bileaflet valve. This indicates that the tilting disc valve has higher transvalvular flow resistance and energy loss than that of the bileaflet valve. From this study it is demonstrated that the mock circulatory system can be a very useful device to evaluate the prosthetic heart valves in vitro.

In vitro sound spectral analysis of prosthetic heart valves by mock circulatory system

A comparative study was made of the sounds produced by normal prosthetic valves (St. Jude Medical, Bjork-Shiley, polymer) with those produced by the same valves but having simulated thrombosis at the stent, hinge, or strut. Comparisons of the closing sound were made for the power frequency spectra associated with individual valves. We used periodogram approach to obtain the spectral characteristics of the valve prostheses. The closing sound of the abnormal mechanical valves displayed lower apparent peak frequency. But the abnormal polymer valve produced higher apparent peak frequency. The results showed that frequency spectra gave information pertinent to the simulated malfunction. Sound spectral analysis is believed to be a simple and a good diagnostic tool for detection of prosthetic valve malfunction. Also it seemed to be superior to other methods such as phonocardiography and echocardiography.