A Di Molfetta

A cardiovascular simulator tailored for training and clinical uses

OBJECTIVE In the present work a cardiovascular simulator designed both for clinical and training use is presented. METHOD The core of the simulator is a lumped parameter model of the cardiovascular system provided with several modules for the representation of baroreflex control, blood transfusion, ventricular assist device (VAD) therapy and drug infusion. For the training use, a Pre-Set Disease module permits to select one or more cardiovascular diseases with a different level of severity. For the clinical use a Self-Tuning module was implemented. In this case, the user can insert patients specific data and the simulator will automatically tune its parameters to the desired hemodynamic condition. The simulator can be also interfaced with external systems such as the Specialist Decision Support System (SDSS) devoted to address the choice of the appropriate level of VAD support based on the clinical characteristics of each patient. RESULTS The Pre-Set Disease module permits to reproduce a wide range of pre-set cardiovascular diseases involving heart, systemic and pulmonary circulation. In addition, the user can test different therapies as drug infusion, VAD therapy and volume transfusion. The Self-Tuning module was tested on six different hemodynamic conditions, including a VAD patient condition. In all cases the simulator permitted to reproduce the desired hemodynamic condition with an error<10%. CONCLUSIONS The cardiovascular simulator could be of value in clinical arena. Clinicians and students can utilize the Pre-Set Diseases module for training and to get an overall knowledge of the pathophysiology of common cardiovascular diseases. The Self-Tuning module is prospected as a useful tool to visualize patients status, test different therapies and get more information about specific hemodynamic conditions. In this sense, the simulator, in conjunction with SDSS, constitutes a support to clinical decision - making.

Towards a personalized and dynamic CRT-D. A computational cardiovascular model dedicated to therapy optimization.

BACKGROUND In spite of cardiac resynchronization therapy (CRT) benefits, 25-30% of patients are still non responders. One of the possible reasons could be the non optimal atrioventricular (AV) and interventricular (VV) intervals settings. Our aim was to exploit a numerical model of cardiovascular system for AV and VV intervals optimization in CRT. METHODS A numerical model of the cardiovascular system CRT-dedicated was previously developed. Echocardiographic parameters, Systemic aortic pressure and ECG were collected in 20 consecutive patients before and after CRT. Patient data were simulated by the model that was used to optimize and set into the device the intervals at the baseline and at the follow up. The optimal AV and VV intervals were chosen to optimize the simulated selected variable/s on the base of both echocardiographic and electrocardiographic parameters. RESULTS Intervals were different for each patient and in most cases, they changed at follow up. The model can well reproduce clinical data as verified with Bland Altman analysis and T-test (p > 0.05). Left ventricular remodeling was 38.7% and left ventricular ejection fraction increasing was 11% against the 15% and 6% reported in literature, respectively. CONCLUSIONS The developed numerical model could reproduce patients conditions at the baseline and at the follow up including the CRT effects. The model could be used to optimize AV and VV intervals at the baseline and at the follow up realizing a personalized and dynamic CRT. A patient tailored CRT could improve patients outcome in comparison to literature data.

Application of a user-friendly comprehensive circulatory model for estimation of hemodynamic and ventricular variables

Purpose Application of a comprehensive, user-friendly, digital computer circulatory model to estimate hemodynamic and ventricular variables. Methods The closed-loop lumped parameter circulatory model represents the circulation at the level of large vessels. A variable elastance model reproduces ventricular ejection. The circulatory model has been modified embedding an algorithm able to adjust the model parameters reproducing specific circulatory conditions. The algorithm reads input variables: heart rate, aortic pressure, cardiac output, and left atrial pressure. After a preliminary estimate of circulatory parameters and ventricular elastance, it adjusts the amount of circulating blood, the value of the systemic peripheral resistance, left ventricular elastance, and ventricular rest volume. Input variables and the corresponding calculated variables are recursively compared: the procedure is stopped if the difference between input and calculated variables is within the set tolerance. At the procedure end, the model produces an estimate of ventricular volumes and Emaxl along with systemic and pulmonary pressures (output variables). The procedure has been tested using 4 sets of experimental data including left ventricular assist device assistance. Results The algorithm allows the reproduction of the circulatory conditions defined by all input variable sets, giving as well an estimate of output variables. Conclusions The algorithm permits application of the model in environments where the simplicity of use and velocity of execution are of primary importance. Due to its modular structure, the model can be modified adding new circulatory districts or changing the existing ones. The model could also be applied in educational applications.

Tailoring the hybrid palliation for hypoplastic left heart syndrome: A simulation study using a lumped parameter model

The results of Hybrid procedure (HP) for the hypoplastic left heart syndrome (HLHS) depend on several variables: pulmonary artery banding tightness (PAB), atrial septal defect size (ASD) and patent ductus arteriosus stent size (PDA). A HP complication could be the aortic coarctaction (CoAo). The reverse Blalock-Taussig shunt (RevBT) placement was proposed to avoid CoAo effects. This work aims at developing a lumped parameter model (LPM) to investigate the effects of the different variables on HP haemodynamics. A preliminary verification was performed collecting measurements on a newborn HLHS patient to calculate LPM input parameters to reproduce patients baseline. Results suggest that haemodynamics is affected by ASD (ASD: 0.15-0.55 cm, pulmonary to systemic flow ratio Qp/Qs: 0.73-1, cardiac output (CO): 1-1.5 l/min and ventricular stroke work SW: 336-577 ml mmHg) and by the PAB diameter (PAB: 0.07-0.2 cm, Qp/Qs: 0.46-2.1, CO: 1.3-1.6 l/min and SW: 591-535 ml mmHg). Haemodynamics was neither affected by RevBT diameter nor by PDA diameter higher than 0.2 cm. RevBT implantation does not change the HP haemodynamics, but it can make the CoAo effect negligible. LPM could be useful to support clinical decision in complex physiopathology and to calibrate and personalise the parameters that play a role on flow distribution.

Experimental integration of Autoregulation Unit for left ventricular assist devices in a cardiovascular hybrid simulator

In this paper, an Autoregulation Unit (ARU) for left ventricular sensorized assist devices (LVAD) has been used with a cardiovascular hybrid simulator mimicking physiological and pathological patient conditions. The functionalities of the ARU have been demonstrating for the successful receiving and visualization of system parameters, sending of commands for LVAD speed changes, and enabling of the autonomous flow control algorithm. Experiments of speed changes and autoregulation are reported, showing the feasibility of the approach for both local and remote control of a LVAD.

Stem cell therapy: Numerical simulation of In Vivo nutrient transport and cells growth

Stem cell therapy, like cell cardiomyoplasty, is an innovative therapy for patients affected by advanced heart failure. Predicting of the exact amount of implantable cells is one of the most important limitations of this therapy. This parameter must be calculated considering cells metabolism and histological environment (damage, O2 and CO2 concentration, residual microcirculation, temperature, pH, etc.) closed to ischemic area where stem cells will be implanted.

A hybrid cardiovascular simulator as test bench for VAD autoregulation control

Aim: Doppler ultrasound is standard for measurements of blood velocity. Aninherent limitation is that Doppler methods only measure the velocity parallelto the ultrasound beam. In Ultrasound Image Velocimetry (UIV) regions of two sequential B-mode images are cross-correlated to calculate 2-D velocity vectors. UIV results were compared with Doppler and transit-time flow measurements.Methods: In vitro experiments were performed in a pulsatile flow loop. Theworking fluid was water/glycerol with ultrasound contrast agent (microbubbles).The latex tube was imaged using an Ultrasonix RP500 and a novelimaging sequence was used to interleave two ultrasound frames, enabling ashort and variable (0.3-39 ms) interframe time separation (δt). A rabbit wasanaesthetised and imaged through the abdomen, with microbubbles administered via the ear vein. Radiofrequency data were post-processed offlineusing in-house code which calculates the local correlation between successiveframes, then sums correlation results for identical phases of all cardiaccycles.Results: Peak velocities >2 m/s were accurately measured across the entirefield-of-view in vitro, while peak systolic velocities in the rabbit were 0.99 m/sand 1.04 m/s with UIV and Doppler respectively. As δt was increased flow instability during deceleration caused the UIV velocity measurement to drop to zero. Comparing velocity measurements of decelerating flow with different values of δt leads to a new method for investigating flow instability.Conclusions: With short δt UIV and derived flow rates agreed excellently withDoppler and transit time flow rates.Aim: Topical application of ophthalmic drugs is very inefficient; contact lenses used as drug delivery devices could minimize the drug loss and side effects. Styrene-maleic acid copolymers (PSMA) can form polymer-phospholipid complexes with dipalmitoyl phosphatidylcholine (DMPC) in the form of nanometric vesicles, which can easily solubilise hydrophobic drugs. They can be dispersed on very thin contact lens coatings to immobilize the drug on their surface. Methods: Two types of complexes stable at different pH values (5 and 7 respectively) where synthesized and loaded with drugs of different hydrophilicities during their formation process. The drug release was studied in vitro and compared to the free drug. Results: The mean sizes of the complexes obtained by light scattering were 50 nm and 450 nm respectively with low polydispersities. However, they were affected by the drugs load and release. An increase was observed in the duration of the release in the case of hydrophobic drugs, from days to weeks, avoiding initial “burst” and with a lesser amount of total drug released due to the interaction of the drug with the phospholipid core. The size and charge of the different drugs and the complexes nature also affected the release profile. Conclusions: Polymer-phospholipid complexes in the form of nanoparticles can be used to solubilise and release hydrophobic drugs in a controlled way. The drug load and release can be optimised to reach therapeutic values in the eye.