The rapid spread of SARS-COV-2 Omicron variant in Italy reflected early through wastewater surveillance.

The SARS-CoV-2 Omicron variant emerged in South Africa in November 2021, and has later been identified worldwide, raising serious concerns. A real-time RT-PCR assay was designed for the rapid screening of the Omicron variant, targeting characteristic mutations of the spike gene. The assay was used to test 737 sewage samples collected throughout Italy (19/21 Regions) between 11 November and 25 December 2021, with the aim of assessing the spread of the Omicron variant in the country. Positive samples were also tested with a real-time RT-PCR developed by the European Commission, Joint Research Centre (JRC), and through nested RT-PCR followed by Sanger sequencing. Overall, 115 samples tested positive for Omicron SARS-CoV-2 variant. The first occurrence was detected on 7 December, in Veneto, North Italy. Later on, the variant spread extremely fast in three weeks, with prevalence of positive wastewater samples rising from 1.0% (1/104 samples) in the week 5-11 December, to 17.5% (25/143 samples) in the week 12-18, to 65.9% (89/135 samples) in the week 19-25, in line with the increase in cases of infection with the Omicron variant observed during December in Italy. Similarly, the number of Regions/Autonomous Provinces in which the variant was detected increased from one in the first week, to 11 in the second, and to 17 in the last one. The presence of the Omicron variant was confirmed by the JRC real-time RT-PCR in 79.1% (91/115) of the positive samples, and by Sanger sequencing in 66% (64/97) of PCR amplicons. In conclusion, we designed an RT-qPCR assay capable to detect the Omicron variant, which can be successfully used for the purpose of wastewater-based epidemiology. We also described the history of the introduction and diffusion of the Omicron variant in the Italian population and territory, confirming the effectiveness of sewage monitoring as a powerful surveillance tool.

Electrospun bioresorbable heart valve scaffold for tissue engineering.

Currently marketed mechanical or biological prosthetic heart valves are regarded as valid substitutes for native heart valves suffering from degenerative pathologies. These devices require strict follow-up due to dysfunctions or post-surgical complications. Potential drawbacks of these medical devices are calcification, tearing of the cusps, thromboembolism and hemolysis. In this context, a tissue engineering approach offers a promising alternative scenario. In this paper, a trileaflet poly(epsilon-caprolactone) (PCL) heart valve scaffold prototype has been manufactured by electrospinning technique using a custom-made rotating target. Process parameters were selected in order to achieve suitable microstructure and mechanical performance. The electrospun heart valve prototype was functionally characterized by means of a pulse duplicator in order to evaluate the mechanical/hydraulic response to the imposed testing conditions. Leaflets synchronously opened in the ejection phase and the proper apposition of the leaflets prevented high leakage volumes in the diastolic phase. This preliminary study suggests a successful perspective for the proposed approach in designing a novel tissue engineered bioresorbable heart valve.

Time-resolved PIV technique for high temporal resolution measurement of mechanical prosthetic aortic valve fluid dynamics.

Prosthetic heart valves (PHVs) have been used to replace diseased native valves for more than five decades. Among these, mechanical PHVs are the most frequently implanted. Unfortunately, these devices still do not achieve ideal behavior and lead to many complications, many of which are related to fluid mechanics. The fluid dynamics of mechanical PHVs are particularly complex and the fine-scale characteristics of such flows call for very accurate experimental techniques. Adequate temporal resolution can be reached by applying time-resolved PIV, a high-resolution dynamic technique which is able to capture detailed chronological changes in the velocity field. The aim of this experimental study is to investigate the evolution of the flow field in a detailed time domain of a commercial bileaflet PHV in a mock-loop mimicking unsteady conditions, by means of time-resolved 2D Particle Image Velocimetry (PIV). The investigated flow field corresponded to the region immediately downstream of the valve plane. Spatial resolution as in "standard" PIV analysis of prosthetic valve fluid dynamics was used. The combination of a Nd:YLF high-repetition-rate double-cavity laser with a high frame rate CMOS camera allowed a detailed, highly temporally resolved acquisition (up to 10000 fps depending on the resolution) of the flow downstream of the PHV. Features that were observed include the non-homogeneity and unsteadiness of the phenomenon and the presence of large-scale vortices within the field, especially in the wake of the valve leaflets. Furthermore, we observed that highly temporally cycle-resolved analysis allowed the different behaviors exhibited by the bileaflet valve at closure to be captured in different acquired cardiac cycles. By accurately capturing hemodynamically relevant time scales of motion, time-resolved PIV characterization can realistically be expected to help designers in improving PHV performance and in furnishing comprehensive validation with experimental data on fluid dynamics numeric modelling.

Beat to beat analysis of mechanical heart valves by means of return map.

Three mechanical heart valves (two bileaflet prostheses and a tilting one) were investigated in a basic hardware setup in order to evaluate with a hydrophone their opening and closing action in time and in amplitude of each beat. The recorded signal was then segmented into the series of cycles xi(t) having a temporal duration equal to the working period imposed on the valve. Two return maps were defined, in order to evaluate the degree of dispersion of the resulting scatter plot: (i) the amplitude map xi(t) versus xi+1(t); (ii) the delay map for the closure of the valve within each beat versus the successive ones. To evaluate the results obtained, two indices were proposed based on both the degree of dispersion and the deviation of the regression line of the resulting scatter plot with respect to the bisector of the map plane. The tilting disc valve showed a lower degree of dispersion, both in the amplitude signal and in the closure time delays, with respect to the other two bileaflet heart valves. The methodology proposed here could be regarded as an alternative non-invasive tool to investigate the dynamic behaviour of prosthetic heart valves, especially in the case of their suspected failure.

Time dependent non-Newtonian numerical study of the flow field in a realistic model of aortic arch.

A three-dimensional time dependent numerical simulation was performed in a geometric model of aortic arch complete with a realistic aortic root and major branches originating from the arch, for a peak Reynolds number set at 2200 and Womersley number set at 20.4. The computational fluid dynamic analysis was aimed to provide spatial and temporal distribution of the shear stress all along the entire model together with the velocity patterns, related both to the non planar geometry of the aortic system here considered and to the pulsatility imposed on the numerical model to simulate physiologic conditions. A non-Newtonian evolving fluid was considered to account for the actual rheological nature of blood; a comparison on the incidence of wall shear stress, implementing a Newtonian fluid, was also made as reference. The spatial shear stress pattern, within the cardiac cycle, was shown to have higher values in correspondence to the inner wall of the aortic arch and the sites where the major vessels originated from the arch itself. The velocity patterns, on transversal sections of the aorta, resulted in highly skewed morphology. The resulting complex fluid dynamics, established in the aortic arch and in its branches, can be related to the possible endothelium response to mechanical stimuli, induced by wall shear stress, in the promotion of inflammatory events.

SWIFT (sequence-wide investigation with Fourier transform): a software tool for identifying proteins of a given class from the unannotated genome sequence.

BACKGROUND: The ever increasing number of sequenced genomes calls for new analysis techniques, which can benefit from the methodologies developed in the field of signal processing. METHODS: The present paper addresses the question of searching a pattern of amino acids (not necessarily completely specified) by means of the cross-correlation of complex sequences, obtained after suitable coding of the original amino acid sequence. Subsequently, the proposed algorithm provides a flexible strategy in setting the border between the accepted and rejected ORFs, by means of the k-means clustering of the candidate ORFs. The search for the class of proteins specified by the pattern is carried out from the most basic level, i.e. the DNA sequence, without sifting through an ensemble of previously determined ORFs. Thus, an exhaustive examination of all the occurrences of the pattern in the genome is performed. RESULTS: The application of the method to the search of surface proteins in Gram-positive bacteria witnesses its efficacy, in terms of both sensitivity and specificity. The comparison with the usual (and somewhat arbitrary) choice of setting a fixed value for the threshold length of the putative ORF confirms the validity of the proposed approach.

Morphological analysis of in vivo velocity field in the alteration of the vasomotor tone.

Vessel wall remodeling is involved in atherogenesis and in several important vascular diseases affecting mainly aged and prosthetic implanted patients. This adaptive response to pathological states in arterial hemodynamics strongly suggests that flow-derived stresses act as mechanical stimuli to the release of endothelium-derived vasoactive factors, leading to vascular alterations. As the correlation of intimal hyperplasia (IH) with blood flow alterations in arteries has been shown to be significant, and as it is well-known that clinical procedures carry a substantial risk of development of vascular disease, the relevance of local hemodynamics must be investigated to describe changes in compliance matching in prosthetic applications. The aim of our research is to investigate the use of principal components analysis, together with varimax rotation, in the individuation process of morphological characteristics of real time ultrasound in in vivo recordings of blood flow velocities, as provided by two different carotid perivascular manipulations. This would be of use in the clinical assessment of atherogenesis, hypertension, prosthetic replacement or more in general in all applications in which vascular tone may be impaired. Data recordings refer to previous animal experiments where the Moncada model was investigated by means of an ultrasound profilometer. The present study confirms the feasibility of the proposed analysis to follow vascular pathology evolution, distiguishing between an in progress and a static situation.

Proposal for a quantitative description of blood spiral flow in medical devices.

The association between specific blood flow patterns and blood behaviour through medical devices suggests that a Lagrangian study may be a useful instrument for the evaluation of the thrombogenic and/or hemolytic potential of certain devices' geometries and biomaterials. In this study a description of blood particle trajectories in terms of their spiral contents is proposed; such a mathematical description for blood spiral flow, computed along several pathlines, is tested for a quantitative determination of the spiralled motion of blood flow into two three-dimensional numerical models, having different design characteristics, of venous cannula inserted in a vessel. As the influence of vortical flow conditions have been observed to have both beneficial and detrimental influence on blood behaviour in terms of blood-device interaction, of the degradation of its components, and of the efficiency of mass-exchange (in red cells oxygenation and plasma filtration, for example), the herein proposed method for the description of spiral laminar motion may be a helpful instrument to build up a tool to investigate, for example, the existence of correlations between level of spiral flow and geometry (as in the present investigated test case), rather than the effects of blood-surface contact. The results obtained in this test case investigation, confirm the effectiveness of the proposed function for a quantitative analysis of spiral flow in medical devices.

Endovascular stents: market vigilance and risk factors.

With the aim of enhancing the safety and reliability level of coronary stents, we analyzed data collected from accident reports drawn from the MAUDE database (Manufacturer and User Facility Device Experience Database) of the FDA from 1996 to 2000. This analysis allowed us to highlight problems related to the use of coronary stents by means of the analysis of these reports at different levels, beginning from the causes that can lead to a certain type of accident up to the possible complication related to that event. Moreover we analyzed the procedure outcomes in terms of stent position inside the patient's body and the possible therapies adopted to solve the problems. The results showed that the most probable event that can lead to an accident is the stent separation from the balloon which, alone, turns up in a number of cases equal to the sum of all the others. This result highlights the importance of the technical skill of the operators accomplished by special training and of the importance of clarity and completeness in the instructions for the use of the device. Another critical point is the reliability of the device which must guarantee an adequate safety level when it is used according to the instructions.

Pathological patient in protocol definition for bench testing of mechanical cardiac support system.

Clinical techniques for the restoration of a failing heart are mainly based on the use of mechanical assist devices. In recent years, with the growing need for mechanical circulatory support, these devices have been shown to be a useful therapeutic tool, thanks to their intrinsic capability to unload the failing ventricle, allowing the heart to recover. Mechanical circulatory support systems (MCSS) require an accurate biomechanical characterization of the complex interaction that occurs between the patient and the mechanical support. A protocol for MCSS testing is proposed which takes into account several working conditions, in a modified test mock loop apparatus able to mimic various pathological conditions. Both physiological and pathological conditions can be replicated to show the actual efficacy of a MCSS device in correctly supporting a wide spectrum of ventricular conditions. The test bench is able to simulate the recovery of the pathological condition quite accurately, showing, at the same time, that this set up can be a reliable choice to characterize cardiac support devices. Thus the results of this experimentation can be useful to clinicians in forecasting the response of the heart affected by a cardiac disease and to set appropriate parameters for suitable assistance.

Numerical simulation of a realistic total cavo-pulmonary connection: effect of unbalanced pulmonary resistances on hydrodynamic performance.

Total cavo pulmonary connection (TCPC) is one of the surgical techniques adopted to compensate the failure of the right heart in pediatric patients. The main goal of this procedure is the realization of a configuration for the caval veins and for the pulmonary arteries that can guarantee as low as possible pressure losses and appropriate lung perfusion. Starting from this point of view, a realistic TCPC with extracardiac conduit (TECPC) is investigated by means of Computational Fluid Dynamics (CFD) to evaluate the pressure loss under different pressure conditions, simulating different vessel resistances, on the pulmonary arteries. A total flow of 3 L/min, with a distribution between the inferior vena cava (IVC) and the superior vena cava (SVC) equal to 6/4, was investigated; three different boundary conditions for the pressure were imposed, resulting in three simulations in steady-state conditions, to the right pulmonary artery (RPA) and to the left pulmonary artery (LPA), simulating a balanced (deltaP(LPA-RPA) = 0 mmHg) and two unbalanced pulmonary resistances to blood flow (a pressure difference deltaP(LPA-RPA) = +/- 2 mmHg, respectively). The geometry for the TECPC was realized according to MRI derived physiological values for the vessels and for the configuration adopted for the anastomosis (the extra-cardiac conduit was inclined 22 degrees towards the left pulmonary artery with respect to the IVC axis). The computed power losses agree with previous in vitro Particle Image Velocimetry investigations. The results show that a higher resistance on the LPA causes the greater pressure loss for the TECPC under study, while the minimum pressure loss can be achieved balancing the pulmonary resistances, subsequently obtaining a balanced flow repartition towards the lungs.

Computational model of the fluid dynamics of a cannula inserted in a vessel: incidence of the presence of side holes in blood flow.

Vascular access methods, performed by the insertion of cannulae into vessels, may disturb the physiological flow of blood, giving rise to non-physiological pressure variations and shear stresses. To date, the hydrodynamic behaviour of the cannulae has been evaluated comparing their pressure loss-flow rate relationships, as obtained from in vitro experiments using a monodimensional approach; this methodology neither furnish information about the local fluid dynamics nor the established flow field in specific clinical work conditions. Since the shear stress is a critical factor in the design of artificial circulatory devices, more knowledge should be necessary about the local values assumed by the haemodynamic parameters during cannulation. An alternative way to investigate the fluid dynamic as accurately as possible is given by numeric studies. A 3D model of cannula concentrically placed in a rigid wall vessel is presented, with the finite element methodology used to numerically simulate the steady-state flow field in two different venous cannulation case studies, with two cannulae having a central hole and two or four side holes, respectively, with the same boundary conditions. Lower velocity and shear stress peak values have been computed for the model with four side holes upstream of the central hole, in the region of the cannula where the inlet flows meet and towards cannula's outlet, due to the increased flow symmetry and inlet area with respect to the model with two side holes. Starting from the investigation of different cannula designs, numerically assessing the local fluid dynamics, indications can be drawn to support both the design phase and the device optimal clinical use, in order to limit risks of biomechanical origin. Thus the presence of four side holes implied, as a consequence of the greater inlet area and of the increased symmetry, a less disturbed blood flow, together with reduced shear stress values. Furthermore, results show that the numerical simulations furnished useful informations on the interaction between vessel and cannula, e.g. on the fluid dynamics establishing in the free luminal space left, in the vessel, by the inserted cannula.

Potential mechanical blood trauma in vascular access devices: a comparison of case studies.

Since vascular access devices may cause disturbances in blood flow, possibly damaging red blood cells (RBCs), the correlated risk of lysis must be assessed. The monodimensional approach for the evaluation of cannulae hydrodynamic behaviour (in vitro measured flow curves) does not furnish information on the local flow field occurring in specific clinical conditions. Researchers consider the prediction of blood trauma, induced by mechanical loading, to optimize the design phase, and to furnish indications on their optimal clinical use. In this study, a model of cannula inserted in a non compliant wall vessel was used as a test bench in a Computational Fluid Dynamics (CFD) problem. By means of CFD the flow field was 3D analysed to achieve information on velocity and shear stress local values, when cannula is used for inflow and outflow cannulation. A prediction of potential blood corpuscle damage, based on a power law, quantified the potential blood damage. Several numerical simulations, with different cannula/vessel flow rate ratios were provided, to investigate the incidence of local sites in the design on blood damaging potential during cannulation. Several regions appeared to be sensitive to the flow rate not only inside the cannula but also in the space between cannula and vessel, suggesting new indications for the assessment of a quality factor based on the evaluation of induced blood cells injury.

Hydraulic functional characterisation of aortic mechanical heart valve prostheses through lumped-parameter modelling.

Lumped-parameter modelling techniques are proposed as a method for studying the hydraulic characteristics of mechanical prosthetic heart valves (PHVs). The global hydraulic behaviour of PHVs in the open position was modelled by taking into account the (nonlinear) resistive and (linear) inertial factors governing the time-dependent relationship between transvalvular pressure drop and fluid flow rate, and neglecting the leaflets' opening and closure transient phenomena. Statistically defined indices associated to the parameters' values attest how properly the model describes PHV hydraulic behaviour. Local fluid dynamics is not modelled with this approach. The proposed method was implemented in a software program and applied to the characterisation of the aortic StJude Medical, StJude Medical Hemodynamic Plus and CarboMedics PHVs, basing on steady- and pulsatile-flow hydraulic-bench experimental data. The results showed that reliable parameters expressing hydraulic resistance can be derived from steady-flow data (R(2)>0.995). Inertance parameters derived from pulsatile-flow experiments are liable to a degree of uncertainty (confidence intervals up to 17%), however, comparing the reconstructed vs. measured pressure drop during systolic time demonstrates that this deficiency is mostly due to the missing description of initial, transient oscillations presumably related to the leaflets' opening (not modelled).

Flow on the symmetry plane of a total cavo-pulmonary connection.

The flow inside a total cavo-pulmonary connection, a bypass operation of the right heart adopted in the presence of congenital malformation, is here studied for a specific geometry which has been recently introduced in clinics. The analysis has been performed by preliminary experimental observation and a novel Navier-Stokes formulation on the symmetry plane. This method, once some basic hypotheses are verified, allows to reproduce the flow on the symmetry plane of a three-dimensional field by using an extension of the two-dimensional approach. The analysis has confirmed the existence of a central vortex showing that it is not a real vortex (i.e. a place with accumulation of vorticity) but, rather, a weakly dissipative recirculating zone. It is surrounded by a shear layer that becomes spontaneously unsteady at moderately high Reynolds number. The topological changes and energy dissipation have been analysed in both cases of unbalanced and of balanced pulmonary artery and caval flows.

A mathematical model of the fetal cardiovascular system based on genetic algorithms as identification technique.

The development of fetal cardiac surgery, considered the ultimate goal in the treatment of congenital cardiac malformations, needs to be supported by detailed knowledge of the blood circulation in the fetal cardiovascular system. The hemodynamic behavior in distal territories is usually inferred from vessel resistance indices, which give limited physiological information. This study presents a mathematical model of the human fetal global cardiovascular system, developed to clarify the relationships and differences existing between upper and lower body circulation. We modelled the heart with two time-varying capacitances, each representing the respective ventricle's pressure-volume relationship. The fetal vascular system was represented using two six-element Windkessel models, for the upper and lower body respectively. We obtained the identification of the set of circuital and elastance function parameters of the model using Genetic Algorithms (GAs), which follow the laws of evolutionary theory. We compared the results of our numerical study on the model identified with data collected from measurements and literature, to validate the proposed global cardiovascular system model of the human fetus. This model is intended as an instrument to investigate the differences in blood distribution between the different vascular districts in the upper and lower fetal body and the role of the aortic isthmus, the small tract of vessel connecting upper and lower fetal vascular beds; it may also represent a useful tool in the assessment of dynamic balance during mechanical assistance of circulation.

The influence of the leaflets' curvature on the flow field in two bileaflet prosthetic heart valves.

A successful mechanical prosthetic heart valve design is the bileaflet valve, which has been implanted for the first time more than 20 years ago. A key feature of bileaflet valves is the geometry of the two leaflets, which can be very important in determining the flow field. Laser Doppler anemometry (LDA) was used to perform an accurate study of the velocity and turbulence shear stress peak values (TSS(max)) fields at four distances from the valve plane. TSS(max) is a relevant parameter to assess the risk of hemolysis and platelet activation associated to the implantation of a prosthetic device, continuously interacting with blood. Two bileaflet valves were tested: the St. Jude HP and the Sorin Bicarbon, of the same nominal size (19mm). The former has flat leaflets, whereas the latter's leaflets have a cylindrical surface. A high regime (CO: 6l/min) was imposed, in order to test the two valves at maximum Reynolds number and consequent turbulence generation. The flat-leaflet design of the St. Jude generates a TSS field constant with distance; on the contrary, the Bicarbon's shear stress field undergoes an evident development, with an unexpected central peak at a distance comparable to the valve's dimensions (21mm). The two bileaflet valves tested, although very similar in design, behave very differently as for their turbulence properties. In particular, the concept of curved wake leads to conclude that the curvature of the leaflets' surface must be identified as an important parameter, which deserves careful attention in PHV design and development.

Pulsatile flow and atherogenesis: results from in vivo studies.

Compliance mismatch between prosthetic vascular replacement (possibly stented) and native artery is considered to be an important factor in implant failure due, e.g., to vascular remodeling, tissutal growth or intimal hyperplasia (IH). From an in vivo study involving altered vascular mechanics (and, consequently, compliance mismatch), carried out using the Moncada model of atherosclerosis development and smooth muscle cell (SMC) proliferation, the hemodynamic assessment was followed by means of real-time multigated ultrasound profilometry, of collared carotid artery using two different models: non-constrictive and constrictive plastic collars, wrapped around the vessel. The experiments provided the real-time measurement of velocity profiles in vivo and the subsequent estimation of wall shear stresses, locally responsible for the altered hemodynamics. Endothelium modifications were correlated with local hemodynamic alterations by using statistical regression analysis of the development of intimal hyperplasia and the mechanical stimulus applied to the endothelium by means of the two different manipulation models. Different correlations were found between wall shear rate and IH in the two models, showing the importance of the vascular pulsatility in determining SMC proliferation. This result could be useful in minimizing the negative consequences of clinical interventions such as graft and/or stent implantation.

Particle image velocimetry analysis of the flow field in the total cavopulmonary connection.

The total cavopulmonary connection (TCPC) is a common operation, meant to restore a proper pulmonary blood flow in heart defects with only one functional ventricle. It consists of the direct connection of the venae cavae to the pulmonary arteries in a cross-shaped disposition which entails a peculiar hemodynamics: Side effects can occur, such as recirculation zones and pressure drop across the connection. Our study is aimed at the quantitative investigation of the flow field of a successful Fontan-type operation, in view of the clinical importance of assuring a nearly physiological pulmonary blood flow, especially if one considers that many pediatric patients are eligible for this operation. A glass-blown TCPC phantom, realized according to nuclear magnetic resonance data, was employed in a steady-flow loop. Thus, a realistic model of this Fontan-type operation was realized using materials which enable advanced measurement techniques such as particle image velocimetry (PIV). The mean flow rates at each branch of the cavopulmonary shunt could be independently varied with a vertical shift of the corresponding upstream reservoir. The PIV technique was used successfully in identifying the flow field characteristics. The flow field in this TCPC topology was shown to be well organized and regulated by the presence of a vortex at the confluence of the venae cavae. The effect of different loading conditions, which realistically can be found in vivo, is studied with a high spatial resolution, showing the possibility to use pulmonary resistance as a parameter in designing the surgical geometry.

Hemodynamic performance of small-size bileaflet valves: pressure drop and laser Doppler anemometry study comparison of three prostheses.

Laser Doppler anemometry (LDA) is a single-point technique which is unparalleled to detect accurately the local properties of the velocity field in a turbulent flow, such as that generated by a prosthetic heart valve (PHV). We propose a correlation between the structure of the flow field in three 19 mm bileaflet PHVs (Sorin Bicarbon, St. Jude Standard, St. Jude HP), investigated at peak systole (6 L/min cardiac output [CO]) with LDA, in kinematic and geometric similarity, and the global parameter of transvalvular pressure drop measured in both steady and pulsatile conditions. The pressure transducers of the same apparatus were used to characterize pressure drops at different flow rates whereas the steady-flow case was studied with a highly accurate tester built in our laboratory. The 2 St. Jude models rank according to their internal orifice diameter (ID) with the standard model (with a smaller ID) providing higher pressure drops for each flow rate. Sorin Bicarbon, due to its leaflet geometry, generates a more complex flow field with respect to the 2 St. Jude flat-leaflet models and shows improved hemodynamical behavior in pulsatile conditions with respect to the stationary case due to differences in pressure recovery. This study can provide insights into a PHV's local flow structure and global hemodynamical parameters.