Sequential Coupling Shows Minor Effects of Fluid Dynamics on Myocardial Deformation in a Realistic Whole-Heart Model

Background: The human heart is a masterpiece of the highest complexity coordinating multi-physics aspects on a multi-scale range. Thus, modeling the cardiac function in silico to reproduce physiological characteristics and diseases remains challenging. Especially the complex simulation of the blood's hemodynamics and its interaction with the myocardial tissue requires a high accuracy of the underlying computational models and solvers. These demanding aspects make whole-heart fully-coupled simulations computationally highly expensive and call for simpler but still accurate models. While the mechanical deformation during the heart cycle drives the blood flow, less is known about the feedback of the blood flow onto the myocardial tissue.Methods and Results: To solve the fluid-structure interaction problem, we suggest a cycle-to-cycle coupling of the structural deformation and the fluid dynamics. In a first step, the displacement of the endocardial wall in the mechanical simulation serves as a unidirectional boundary condition for the fluid simulation. After a complete heart cycle of fluid simulation, a spatially resolved pressure factor (PF) is extracted and returned to the next iteration of the solid mechanical simulation, closing the loop of the iterative coupling procedure. All simulations were performed on an individualized whole heart geometry. The effect of the sequential coupling was assessed by global measures such as the change in deformation and—as an example of diagnostically relevant information—the particle residence time. The mechanical displacement was up to 2 mm after the first iteration. In the second iteration, the deviation was in the sub-millimeter range, implying that already one iteration of the proposed cycle-to-cycle coupling is sufficient to converge to a coupled limit cycle.Conclusion: Cycle-to-cycle coupling between cardiac mechanics and fluid dynamics can be a promising approach to account for fluid-structure interaction with low computational effort. In an individualized healthy whole-heart model, one iteration sufficed to obtain converged and physiologically plausible results.

Hemodynamics Challenges for the Navigation of Medical Microbots for the Treatment of CVDs

Microbots have been considered powerful tools in minimally invasive medicine. In the last few years, the topic has been highly studied by researchers across the globe to further develop the capabilities of microbots in medicine. One of many applications of these devices is performing surgical procedures inside the human circulatory system. It is expected that these microdevices traveling along the microvascular system can remove clots, deliver drugs, or even look for specific cells or regions to diagnose and treat. Although many studies have been published about this subject, the experimental influence of microbot morphology in hemodynamics of specific sites of the human circulatory system is yet to be explored. There are numerical studies already considering some of human physiological conditions, however, experimental validation is vital and demands further investigations. The roles of specific hemodynamic variables, the non-Newtonian behavior of blood and its particulate nature at small scales, the flow disturbances caused by the heart cycle, and the anatomy of certain arteries (i.e., bifurcations and tortuosity of vessels of some regions) in the determination of the dynamic performance of microbots are of paramount importance. This paper presents a critical analysis of the state-of-the-art literature related to pulsatile blood flow around microbots.

Cardiovascular Disease Recognition Based on Heartbeat Segmentation and Selection Process

Assessment of heart sounds which are generated by the beating heart and the resultant blood flow through it provides a valuable tool for cardiovascular disease (CVD) diagnostics. The cardiac auscultation using the classical stethoscope phonological cardiogram is known as the most famous exam method to detect heart anomalies. This exam requires a qualified cardiologist, who relies on the cardiac cycle vibration sound (heart muscle contractions and valves closure) to detect abnormalities in the heart during the pumping action. Phonocardiogram (PCG) signal represents the recording of sounds and murmurs resulting from the heart auscultation, typically with a stethoscope, as a part of medical diagnosis. For the sake of helping physicians in a clinical environment, a range of artificial intelligence methods was proposed to automatically analyze PCG signal to help in the preliminary diagnosis of different heart diseases. The aim of this research paper is providing an accurate CVD recognition model based on unsupervised and supervised machine learning methods relayed on convolutional neural network (CNN). The proposed approach is evaluated on heart sound signals from the well-known, publicly available PASCAL and PhysioNet datasets. Experimental results show that the heart cycle segmentation and segment selection processes have a direct impact on the validation accuracy, sensitivity (TPR), precision (PPV), and specificity (TNR). Based on PASCAL dataset, we obtained encouraging classification results with overall accuracy 0.87, overall precision 0.81, and overall sensitivity 0.83. Concerning Micro classification results, we obtained Micro accuracy 0.91, Micro sensitivity 0.83, Micro precision 0.84, and Micro specificity 0.92. Using PhysioNet dataset, we achieved very good results: 0.97 accuracy, 0.946 sensitivity, 0.944 precision, and 0.946 specificity.

Conventional echocardiography—basic principles

Echocardiography is an imaging technique that enables accurate assessment of cardiac structures and cardiac function. Conventional echocardiography involves different modalities—especially the M-mode, the 2D, and colour Doppler, as well as the pulsed-wave and continuous wave Doppler. The M-mode illustrates the reflections of a single sound beam plotted against time. 2D echocardiography enables the documentation of views, which represent characteristic sectional planes of the moving heart during one heart cycle. Colour Doppler echocardiography adds the information of blood flow to the 2D cineloop. Pulsed-wave Doppler is the acquisition of a local blood flow spectrum of a defined region represented by the dimension of the sample volume, whereas continuous wave Doppler displays the blood flow spectrum of all measured blood flow velocities along a straight line sound beam from its beginning to the end. The handling of the transducer has to be target-oriented, stable with respect to the imaging targets, and coordinated with respect to angle differences between the defined views to use all these modalities correctly to get optimal image quality of the cineloops and spectra. Thus, the focus of this chapter will be a mainly practically oriented description of scanning technique in transthoracic and transoesophageal echocardiography.

End-to-end heart sound segmentation using deep convolutional recurrent network

Heart sound segmentation (HSS) aims to detect the four stages (first sound, systole, second heart sound and diastole) from a heart cycle in a phonocardiogram (PCG), which is an essential step in automatic auscultation analysis. Traditional HSS methods need to manually extract the features before dealing with HSS tasks. These artificial features highly rely on extraction algorithms, which often result in poor performance due to the different operating environments. In addition, the high-dimension and frequency characteristics of audio also challenge the traditional methods in effectively addressing HSS tasks. This paper presents a novel end-to-end method based on convolutional long short-term memory (CLSTM), which directly uses audio recording as input to address HSS tasks. Particularly, the convolutional layers are designed to extract the meaningful features and perform the downsampling, and the LSTM layers are developed to conduct the sequence recognition. Both components collectively improve the robustness and adaptability in processing the HSS tasks. Furthermore, the proposed CLSTM algorithm is easily extended to other complex heart sound annotation tasks, as it does not need to extract the characteristics of corresponding tasks in advance. In addition, the proposed algorithm can also be regarded as a powerful feature extraction tool, which can be integrated into the existing models for HSS. Experimental results on real-world PCG datasets, through comparisons to peer competitors, demonstrate the outstanding performance of the proposed algorithm.

Pulsatile Aortic Blood Flow - a Critical Assessment of Boundary Conditions

Patient specific (PS) blood flow studies have become popular in recent years but have thus far had limited clinical impact. This is possibly due to uncertainties and errors in the underlying models and simulations set-up. This study focuses on the sensitivity of simulation results due to in- and outflow boundary conditions (BC:s). Nine different inlet- and seven different outlet BC:s were applied to two variants of a healthy subject's thoracic aorta. Temporal development of the flow is essential for the formation and development of helical/spiralling flow where the commonly observed clockwise helical motion may change direction during the heart-cycle. The sensitivity to temporal and spatial variations in the inlet conditions is significant both when expressed in terms of mean and maximal wall shear stress (WSS) and its different averaged variables, e.g. Time-Averaged WSS (TAWSS), Oscillating Shear Index (OSI) and Relative Residence Time (RRT). The simulation results are highly sensitive to BC. For example, the maximal WSS the results may vary over 3 orders of magnitude (1 to 1000 Pa) depending on particular combinations of BC:s. Moreover, certain formulations of outlet boundary conditions may be inconsistent of the computed flow field if the underlying assumptions of the space-time dependence are violated. The results of this study show that CFD simulations can reveal flow details that can enhance understanding of blood flows. However, the results also demonstrate the potential difficulties in mimicking blood flow in clinical situations.

Pulmonary arteriovenous fistula diagnosed by contrast echocardiography: a case report of a daughter and a mother

Background Pulmonary arteriovenous fistula is a rare disease with a direct connection between the pulmonary artery and the vein, and in most cases is congenital. In a proportion of patients, it can cause hypoxemia, cyanosis and dyspnea. The golden standard for the diagnosis of PAVF is pulmonary angiography. We experienced two cases of a daughter and a mother with PAVF diagnosed by contrast echocardiography, which is simple and sensitive for the detection of pulmonary arteriovenous fistula. Case presentation Case 1:A 22-year-old female was admitted to hospital because of "unconsciousness for 3 hours after sudden seizures".CT showed left frontal cerebral arteriovenous malformation with hemorrhage, a nodule of upper lobe of left lung, arteriovenous malformation possible.Intracranial hematoma removal, arteriovenous malformation resection were performed urgently. Postoperatively, the patient presented severe hypoxemia. Contrast echocardiography showed continuous dense bubbles were visualized in the left heart from the third heart cycle following imaging in the right heart, , suggesting pulmonary arteriovenous fistula. Case 2 : The mother of the first patient, 44-year-old female, with no history of dyspnea, cyanosis,and stroke, was medically screened for suspected pulmonary arteriovenous fistula due to her daughter’s disease. Contrast echocardiography also indicated pulmonary arteriovenous fistula. Conclusions Contrast echocardiography is an excellent tool for the detection of pulmonary arteriovenous fistula. Patients with suspected pulmonary arteriovenous fistula should be examined by chest radiography combined with contrast echocardiography as first line screening tests, especially in patients with severe condition.

Analysis of Retinal Vessel Pulsation with Electrographic Gating – Pulsation Amplitude and the Influence of Hyperoxia

Purpose To analyse the amplitude of vessel pulsation in the retina and to determine whether constriction of the vessels by oxygen would decrease their pulsation amplitude and could thus be used to quantify the rigidity of the retinal vessels. Patients and Methods The study included 20 healthy young subjects. With the RVA (retinal vessel analyser), we aimed to quantify vessel pulsations under normal and hyperoxic conditions. Electrocardiographic (ECG)-gated RVA was used for this purpose, with change in vessel pulsation as the primary endpoint and shift in vessel pulsation during the heart cycle as the secondary endpoint. Furthermore, we assessed the correlation between the amplitude of retinal vessel wall pulsation and blood pressure. Descriptive statistics, paired t-tests, and correlation analysis were applied. Results Retinal veins in proximity to the optic disc demonstrated the highest pulsation amplitude under all conditions. All retinal vessels significantly constricted under hyperoxic conditions. There was no significant change in the amplitude of vessel pulsation nor a significant shift in the pulsation cycle under hyperoxic conditions in the examined cohort. No correlation was found between systemic blood pressure parameters and amplitude of retinal vessel wall pulsation or any change in this. Conclusion ECG-gated RVA recording is not able to detect any relevant change in vessel pulsation behaviour under oxygen, despite clearly observed vasoconstriction in retinal vessels. New approaches are necessary to reliably quantify the rigidity of the retinal vessels.

INSTRUMENTAL MARKERS OF THE RIGHT VENTRICLE FUNCTIONAL CONDITION WITH TISSUE DOPPLER IN CHILDREN WITH TETRALOGY OF FALLOT AFTER SURGICAL CORRECTION AND THEIR CONNECTION WITH VALVULAR FUNCTION OF PULMONARY ARTERY

The aim: To improve efficacy of the right ventricle functional condition evaluation in children with tetralogy of Fallot after surgical correction by estimation of instrumental markers of myocardial dysfunction. Materials and methods: We completely examined 35 children with tetralogy of Fallot after their surgical correction at the age of 3 – 17 years. For all the patients was presented tissue doppler. We evaluated peak myocardial velocities of right ventrical in different phases of the heart cycle (S, E`, A`), tricuspid annular plane systolic excursion (TAPSE), diastolic myocardial velocities ratio (E/E`), peak myocardial velocity during isovolumic contraction (IVV), isovolumic relaxation time (IVRT). Results: All children of the study group had pulmonary insufficiency of different severity with main predominance of mild pulmonary regurgitation (20 patients, 57,14±8,36 %). Children with tetralogy of Fallot after surgical correction were admitted with: decreased TAPSE up to 1,39±0,28 cm, decreased S` up to 8,00±1,90 cm/s, and decreased IVV up to 5,69±0,95 cm/s that is significantly lower results of the healthy children. Severe pulmonary regurgitation usually followed by high chances of the right ventricle systolic dysfunction, exactly with: decresed TAPSE<1,5 cm (OR=0,500; 95% CI 0,323 – 0,775), S`<8,1 cm/s (OR=0,600; 95% CI 0,420 – 0,858) and IVV<5,9 cm/s (OR=0,250; 95% CI 0,117 – 0,534). As well we admitted significant decline of the velocities in earl and end diastole periods to compare with the results of the control group (E`= 12,11±1,22, A`= 4,56±0,92 cm/s (Р=0,009 and P=0.0002)), boost of the E/E` ratio – 7,96±2,33 (P=0.01) and decline of the RV IVRT up to 43,49±6,04 ms (P=0.017). Severe pulmonary regurgitation followed by high chances of the right ventricle systolic dysfunction development with TAPSE <1,5 cm (OR=0,500; 95% CI 0,323 – 0,775), S`<8,1 cm/s (OR=0,600; 95% CI 0,420 – 0,858) and IVV<5,9 cm/s (OR=0,250; 95% CI 0,117 – 0,534). As well we noticed high chances of the E/E`ratio > 6,0 in 1,5 times (95% CI 1,072 – 1,903) and decreased E` <12,2 cm/s (OR=0,200; 95% CI 0,083 – 0,481). Conclusions: Apart of clinical symptoms of the heart failure in children with tetralogy of Fallot after surgical correction markers of the right ventricle myocardial dysfunction are presented by indices of myocardial velocities, received during tissue doppler in different phases of the heart cycle.