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.

Cerebroplacental ratio for prediction of adverse intrapartum and neonatal outcomes in a term uncomplicated pregnancy

Background Fetal hypoxia is one of the major causes of high perinatal morbidity and mortality rates. Doppler ultrasound tests such as cerebroplacental ratio (CPR) evaluation are commonly used to assess blood flow disturbances in placento-umbilical and feto-cerebral circulations. A low cerebroplacental ratio has been shown to be associated with an increased risk of stillbirth regardless of the gestation or fetal weight. We conducted this study to assess the fetal cerebroplacental ratio in prediction of adverse intrapartum and neonatal outcomes in a term, uncomplicated pregnancy to reduce fetal and neonatal morbidity and mortality. Results It was found that neonates with CPR ≤1.1 had significantly higher frequencies of cesarean delivery (CS) for intrapartum fetal compromise compared to those with CPR >1.1 (p=0.043). Neonates with CPR ≤1.1 had significantly lower Apgar score at 1 min and 5 min than those with CPR >1.1 (p=0.004) and (p=0.003), respectively. Neonates with CPR ≤1.1 had significantly higher rates of NICU admission than those with CPR <1.1 (p=0.004). Conclusion The cerebroplacental ratio shows the highest sensitivity in the prediction of fetal heart rate abnormalities and adverse neonatal outcome in uncomplicated pregnancies at term. The cerebroplacental ratio index is useful in clinical practice in antenatal monitoring of these women in order to select those at high risk of intra- and postpartum complications.

Revisited Hyperoxia Pathophysiology in the Perioperative Setting: A Narrative Review

The widespread use of high-dose oxygen, to avoid perioperative hypoxemia along with WHO-recommended intraoperative hyperoxia to reduce surgical site infections, is an established clinical practice. However, growing pathophysiological evidence has demonstrated that hyperoxia exerts deleterious effects on many organs, mainly mediated by reactive oxygen species. The purpose of this narrative review was to present the pathophysiology of perioperative hyperoxia on surgical wound healing, on systemic macro and microcirculation, on the lungs, heart, brain, kidneys, gut, coagulation, and infections. We reported here that a high systemic oxygen supply could induce oxidative stress with inflammation, vasoconstriction, impaired microcirculation, activation of hemostasis, acute and chronic lung injury, coronary blood flow disturbances, cerebral ischemia, surgical anastomosis impairment, gut dysbiosis, and altered antibiotics susceptibility. Clinical studies have provided rather conflicting results on the definitions and outcomes of hyperoxic patients, often not speculating on the biological basis of their results, while this review highlighted what happens when supranormal PaO2 values are reached in the surgical setting. Based on the assumptions analyzed in this study, we may suggest that the maintenance of PaO2 within physiological ranges, avoiding unnecessary oxygen administration, may be the basis for good clinical practice.

Pressure and velocity measurements of air flow past a proposed generic Aircraft carrier geometry

Research on the air flow disturbances in the aircraft carrier environment has gained prominence in recent times. However, there is presently no representative carrier model analogous to the Simplified Frigate Shape (SFS) which is generic naval frigate for air flow investigation. In the present study, a Generic Aircraft Carrier (GAC) model is proposed, as a simplified, benchmark model for aerodynamic research. With the motivation to provide validation data for future CFD studies, baseline experimental data is generated in the wind tunnel, in terms of pressure distribution over the deck, for two variants, namely, a complete flat deck configuration with no island and secondly, with the island in the baseline position of the GAC. Effect of the island in modifying the flow is discussed by a comparison between the two variants. Particle Image Velocimetry (PIV) is employed to record velocity and turbulence levels in the GAC environment, highlighting regions of velocity deficits, and unsteady flow which may hinder the landing procedure of an approaching pilot. Comprehensive database of experimental data is presented as baseline data for future work and for validation of numerical models. Traditional tuft and smoke visualization studies are also conducted to provide corroboratory qualitative insights.

Study on viscosity induced contrast in ultrasound color flow imaging of carotid atherosclerosis

Efficient imaging of blood flow disturbances resulted from carotid atherosclerosis plays a vital role clinically to predict brain stroke risk. Carotid atherosclerosis and its development is closely linked with raised blood viscosity. Therefore, study of viscosity changing hemodynamic effect has importance and it might be useful for improved examination of carotid atherosclerosis incorporating the viscosity induced contrast in conventional ultrasound imaging. This work considered the design of realistic models of atherosclerotic carotid artery of different stages and solved to compute the hemodisturbances using computational fluid dynamics (CFD) by finite element method (FEM) to investigate viscosity changes effect. Ultrasound color flow image of velocities of blood have been constructed using phase shift information estimated with autocorrelation of Hilbert transformed simulated backscattered radiofrequency (RF) signals from moving blood particles. The simulated ultrasound images have been compared with CFD simulation images and identified a good match between them. The atherosclerosis stages of the models have been investigated from the estimated velocity data. It has been observed that the blood velocities increase noticeably in carotid atherosclerotic growths and velocity distribution changes with viscosity variations. It is also found importantly that the viscosity induced contrast associated to atherosclerosis is detectable in ultrasound color flow imaging. The findings of this work might be useful for better investigation of carotid atherosclerosis as well as prediction of its progression to reduce the stroke risk.

Binary Repetitive Model Predictive Active Flow Control Applied to an Annular Compressor Stator Cascade with Periodic Disturbances

Novel pressure gain combustion concepts invoke periodic flow disturbances in a gas turbine&#39;s last compressor stator row. This contribution presents studies of mitigation efforts on the effects of periodic disturbances on an annular compressor stator rig. The passages were equipped with pneumatic active flow control influencing the stator blade&#39;s suction side, and a rotating throttling disc downstream of the passages inducing periodic disturbances. For steady blowing, it is shown that with increasing actuation amplitudes $c_\mu$, a hub corner vortex's extension deteriorating the suction side flow can be reduced, resulting in an increased static pressure rise coefficient~$C_p$ of a passage. The effects of the induced periodic disturbances could not be addressed, by using steady blowing actuation. Considering a corrected total pressure loss coefficient $\zeta^*$, which includes the actuation effort, the stator row&#39;s efficiency decreases with higher $c_\mu$. Therefore, a closed-loop approach is presented to address the effects of the disturbances more specifically, thus lowering the actuation effort. For this, a Repetitive Model Predictive Control (RMPC) was applied, taking advantage of the disturbance's periodic nature. The presented RMPC formulation is restricted to a binary control domain to account for the used solenoid valves&#39; switching character. An efficient implementation of the optimization within the RMPC is presented, which ensures real-time capability. As a result, $C_p$ increases in a similar magnitude but with a lower actuation mass flow of up to 66\,\%, resulting in a much lower~$\zeta^*$ for similar values of $c_\mu$.

Association of VEGF and KDR polymorphisms with the development of schizophrenia

Aim: Several approaches indicate different blood flow disturbances in schizophrenia (Scz). Vascular endothelial growth factor (VEGF) is widely recognized as one of the key molecules implicated in the angiogenesis process through mainly its receptor KDR. The current work was designed to investigate the potential association between three polymorphisms (rs699947; rs833061 and rs3025039) in VEGF gene and two SNPs (rs2305948 and rs1870377) within KDR gene and predisposition to Scz among the Tunisian population. Methods: We carried-out a case-control study composed of 200 schizophrenic patients and 200 healthy subjects using RFLP-PCR. Results: Of all analyzed polymorphisms, only rs3025039, rs833061 and rs1870377 showed a significant risk for Scz. Following the stratified analysis, rs833061 was more prevalent among undifferentiated form. Yet, rs1870377 was especially correlated with paranoid subtype. We found also that rs699947 and rs833061 had an impact on patients' symptomatology. Haplotype analysis unveiled a strong LD between rs833061 and rs3025039 only for undifferentiated patients. Moreover, the -2578/-460/+936 CTT haplotype, with only one mutated allele +936T, conferred a high risk to Scz and, in particular, to undifferentiated and paranoid forms. Among the last-mentioned subgroup, we noticed another overrepresented haplotype (ATT). Furthermore, the +1192/+1719 GT haplotype carrying the minor allele +1719T displayed increased frequencies in schizophrenics as well as in paranoid patients. Conclusion: Our results show that all SNPs associated with the development or the severity of schizophrenia, were subsequently correlated with a decrease in the VEGF levels or influence VEGFR-2 binding affinity. Nevertheless, these data need to be strengthened by further independent analyses.

PIV measurement of complex flow characteristics in open-cell metal foam replica

Time-resolved 2-D particle image velocimetry was used to study on turbulent flow characteristics inside an open-cell metal foam under the laminar and turbulent inlet conditions. A study on the effect of Reynolds number was conducted with different three channel Reynolds numbers, 1000, 5000 and 10000. Uniform upstream flow is divided by the pore network of metal foam and it is found that there are flow disturbances induced by metal foam structure even at a laminar inlet condition. It is confirmed that there is a similarity of the preferred flow path flows take regardless of Reynolds number.

Acoustic-Convective Interference in Transfer Functions of Methane/Hydrogen and Pure Hydrogen Flames

We investigate the occurrence of modulations in the gain and phase of flame transfer functions (FTF) measured in CH4/H2 and pure H2 flames. These are shown to be caused by flow disturbances originating from the screws used to centre the bluff body indicative of a more generalised phenomenon of convective wave propagation. Velocity measurements are performed around the injector dump plane, inside the injector pipe, and in the wake of the bluff body to provide detailed insight into the flow. Peaks corresponding to natural shedding frequencies of the screws appear in the unforced velocity spectra and the magnitude of these convective modes depends on the screws’ location. Flame imaging and PIV measurements show that these disturbances do not show up in the mean velocity and flame shape which appear axisymmetric. However, the rms fields capture a strong asymmetry due to convective disturbances. To quantify the role of these convective disturbances, hydrodynamic transfer functions are constructed from the forced cold flow, and similar modulations observed in the FTFs are found. A strong correlation is obtained between the two transfer functions, subsequently, the modulations are shown to be centered on the vortex shedding frequency corresponding to the first convective mode. For acoustic-convective interaction to be possible, the shedding (convective) frequency needs to be lower than the cut-off frequency of the flame response. This condition is shown to be more relevant for hydrogen flames compared to methane flames due to their shorter flame lengths and thus increased cut-off frequency.