Mean Flow Velocity Research Articles

The Diagnostic Accuracy of Transcranial Color-Coded Doppler Ultrasound Technique in Stratifying Intracranial Cerebral Artery Stenoses in Cerebrovascular Disease Patients: A Systematic Review and Meta-Analysis.

The early and accurate stratification of intracranial cerebral artery stenosis (ICAS) is critical to inform treatment management and enhance the prognostic outcomes in patients with cerebrovascular disease (CVD). Digital subtraction angiography (DSA) is an invasive and expensive procedure but is the gold standard for the diagnosis of ICAS. Over recent years, transcranial color-coded Doppler ultrasound (TCCD) has been suggested to be a useful imaging method for accurately diagnosing ICAS. However, the diagnostic accuracy of TCCD in stratifying ICASs among patients with CVD remains unclear. Therefore, this systematic review and meta-analysis aimed at evaluating the diagnostic accuracy of TCCD in the stratification of intracranial steno-occlusions among CVD patients. A total of six databases-Embase, CINAHL, Medline, PubMed, Google Scholar, and Web of Science (core collection)-were searched for studies that assessed the diagnostic accuracy of TCCD in stratifying ICASs. The meta-analysis was performed using Meta-DiSc 1.4. The Quality Assessment of Diagnostic Accuracy Studies tool version 2 (QUADAS-2) assessed the risk of bias. Eighteen studies met all of the eligibility criteria. TCCD exhibited a high pooled diagnostic accuracy in stratifying intracranial steno-occlusions in patients presenting with CVD when compared to DSA as a reference standard (sensitivity = 90%; specificity = 87%; AUC = 97%). Additionally, the ultrasound parameters peak systolic velocity (PSV) and mean flow velocity (MFV) yielded a comparable diagnostic accuracy of "AUC = 0.96". In conclusion, TCCD could be a noble, safe, and accurate alternative imaging technique to DSA that can provide useful diagnostic information in stratifying intracranial steno-occlusions in patients presenting with CVD. TCCD should be considered in clinical cases where access to DSA is limited.

Very short time Fourier transform for turbulent analysis

Nominally stationary acoustic sensors, e.g., buoy suspended or bottom anchored, are subject to various environmental flows. Direct numerical simulation of hydrodynamic flow around the acoustic sensor housing show turbulence along the housing surface. Time-space analysis of pressure variation along the surface of the housing shows significant acoustic-like surface interaction at low frequencies, even at very low mean flow velocity. In this case turbulence manifests as intermittently generated, irregular, coherent vortex structures that separate from the surface of the housing and advect downstream. These structures drive rapid surface pressure transients that propagate within the housing to the acoustic sensors as noise. Fractional Fourier Analysis provides joint time-frequency methods to extract transient features of turbulence. Use of Hermite-Gauss functions and phase relations are of particular interest. [This research is supported by 6.2 NRL base program sponsored by the Office of Naval Research. Distribution Statement A: Approved for public release. Distribution unlimited.]

Effect of continuous 2MHz transcranial ultrasound as an adjunct to tenecteplase thrombolysis in acute anterior circulation ischemic stroke patients: an open labeled non-randomized clinical trial.

The treatment of acute ischemic stroke has improved in last few decades. While meta-analyses of several trials have established the safety and efficacy of Intravenous (IV) Tenecteplase thrombolysis, concomitant continuous transcranial doppler (TCD) ultrasound administration has not been assessed in any clinical trial. The aim of this study was to determine the effects of continuous 2MHz TCD ultrasound during IV Tenecteplase thrombolysis for Middle cerebral artery (MCA) stroke. A total of 19 patients were included, 13 received TCD ultrasound and 6 sham TCD with IV Tenecteplase. TCD spectrum and difference in Pre and post TCD parameters were measured. Asymptomatic hemorrhagic transformation of infarct wasseen in two patients. There was no mortality or clinical worsening in thesonothrombolysis group as against sham sonothrombolysis group. Median of peak systolic velocity wasincreased in both thesonothrombolysis (P = 0.0002) and sham sonothrombolysis group (P-value = 0.001). The difference in change in mean flow velocity between two groups, sonothrombolysis (11cm/sec)and sham sonothrombolysis (3.5cm/sec) were also significantly different (P = 0.014). This pilot work has established safety of continuous 30min TCD application along with IV Tenecteplase thrombolysis and it concludes thatconcomitant 2MHz TCD ultrasound administration significantly increased the MCA blood flow compared to chemothrombolysis alone.CTRI Registered Number: CTRI/2021/02/031418.

Experimental investigation on the effects of transverse injection distribution scheme on dual flame dynamics subjected to flow disturbances

Combustion instability has become a major problem in low-emission annular gas turbine combustors. It is of practical importance to investigate the effects of transverse nozzle distribution scheme on multi-flame dynamics subjected to external acoustic perturbations. In this study, the responses of heat release rate perturbations from dual propane/air laminar premixed flames to axial acoustic perturbations have been experimentally measured. Specifically, the velocity disturbance upstream the flame base has been measured by two-microphone method and the flame heat release rate perturbation is obtained by the photomultiplier tube with CH* filter lens. The dynamic evolution of dual flames is captured by the high-speed camera and then analyzed with the proper orthogonal decomposition (POD) method. Results indicate that there is a critical distribution distance, where the peak gain of the dual flame transfer function is the largest. And the direct injection dual flame transfer function can behave as the low-pass filter. Furthermore, the dual flame transfer function behaves nonlinearly with the increase of the injection angle. The dual flame transfer function for large injection angle can behave as the hybrid mode of the low-pass filter and the band-pass filter. The POD analysis reveals that the coupling effect of gas thermal expansion and stretch effect would contribute to the interaction between dual flame front dynamics. The transverse injection distribution scheme (dual flame distance and injection angle) has a significant effect on the dual flame front dynamics, which in turn affects the flame heat release rate disturbance. The bulk mean flow velocity can enhance the interaction effect between dual flame front dynamics.

Predictive value of intracranial pressure-related parameters and coagulation on the prognosis in patients with traumatic brain injury.

This study investigated the factors affecting the prognosis of patients with traumatic brain injury (TBI) and assessed the predictive value of intracranial pressure-related parameters and coagulation on prognosis. Seventy TBI patients admitted between January 2020 and January 2021 were catego-rized into good prognosis (n=42) and poor prognosis (n=28) groups according to the Glasgow Outcome Scale (GOS) score upon discharge. Factors affecting prognosis were analyzed, and differences in intracranial pressure and coagula-tion between the two groups were compared. The receiver operating charac-teristic curve (ROC) was used to calculate the predictive value of intracranial pressure-related parameters and coagulation function on prognosis. Within 24 h postoperatively, the good prognosis group had lower levels of intracra-nial pressure (ICP) and partial pressure of oxygen in brain tissue (PbtO2) and higher cerebral perfusion pressure (CPP) and cerebral hemodynamic param-eters than the poor prognosis group (p<0.05). The good prognosis group had significantly lower prothrombin time (PT), activated partial thromboplastin time (aPTT),and prothrombin time (TT) levels and higher platelets (PLT) and fibrinogen (Fib) levels than the poor prognosis group (p<0.05). Regression analysis revealed that CPP, systolic blood flow velocity (Vs), end-diastolic blood flow velocity (Vd), mean blood flow velocity (Vm), PLT, Fib were independent protective factors for the prognosis, and ICP, PbtO2, PT, APTT, and TT were risk factors for prognosis. The ROC revealed that ICP, CPP, PbtO2, Vs, Vd, Vm, APTT, PLT, Fib exhibited high diagnostic value for poor prognosis (AUC=0.732, 0.940, 0.796, 0.706, 0.914, 0.729, 0.876, 0.709, 0.866), with ICP showing the highest diagnostic sensitivity and Vd showing the highest diagnostic specificity. Intracranial pressure-related parameters and coagulation indicators are prog-nosis-related indexes in patients with TBI, and the prognosis and survival can be improved by controlling intracranial pressure and improving coagulation.

Numerical continuation and stability of nonlinear systems with distributed delays: Application to fluid-induced impacts of tubes in cross-flow

Fluid–elastic instability is the main source of concern during the design of heat-exchanger tube bundles. The associated research has focused on the understanding of the physical mechanisms behind this phenomenon and the establishing of models capable of predicting its onset; also some concomitant work has been done to establish post-instability behaviour and to prevent from excessive wear in possible sliding contacts. Moreover, the existing studies make use of time-integration methods alone for this purpose, through which it is difficult to get a comprehensive insight of global dynamics. Continuation methods, which give access to unstable branches and precise bifurcation information, are a precious tool to unfold the attainable dynamic regimes. In this paper, the parametric behaviour of two representative systems under cross-flow excitation is explored through pseudo arc-length continuation with mean flow velocity as a main driving parameter, wherein the nonlinear modal equations of motion are solved by harmonic balance at each step. As the quasi-unsteady model used for fluid–elastic coupling introduces convolution integrals, this approach is quite natural and we show that, despite some difficulties regarding the treatment of stiff intermittent contacts, it allows for a thorough exploration of the system’s response. For the first case -a benchmark model-, increasingly complex dynamics arise as more modes are kept in the truncated modal basis, which is due to a series of modal interactions as the impacts distribute mechanical energy from the linearly-unstable first mode to the higher ones. This can be anticipated by studying the nonlinear normal modes of the system, as they expose the allowed internal resonances. In the second case, consisting of a realistic heat-exchanger tube configuration, a similar pattern is observed.

A Comparative Study of Transcranial Color-Coded Doppler (TCCD) and Transcranial Doppler (TCD) Ultrasonography Techniques in Assessing the Intracranial Cerebral Arteries Haemodynamics.

Cerebrovascular disease (CVD) poses a major public health and socio-economic burden worldwide due to its high morbidity and mortality rates. Accurate assessment of cerebral arteries' haemodynamic plays a crucial role in the diagnosis and treatment management of CVD. The study compared a non-imaging transcranial Doppler ultrasound (TCD) and transcranial color-coded Doppler ultrasound (with (cTCCD) and without (ncTCCD)) angle correction in quantifying middle cerebral arteries (MCAs) haemodynamic parameters. A cross-sectional study involving 50 healthy adults aged ≥ 18 years was conducted. The bilateral MCAs were insonated via three trans-temporal windows (TTWs-anterior, middle, and posterior) using TCD, cTCCD, and ncTCCD techniques. The MCA peak systolic velocity (PSV) and mean flow velocity (MFV) were recorded at proximal and distal imaging depths that could be visualised on TCCD with a detectable spectral waveform. A total of 152 measurements were recorded in 41 (82%) subjects with at least one-sided open TTW across the three techniques. The mean PSVs measured using TCD, ncTCCD, and cTCCD were 83 ± 18 cm/s, 81 ± 19 cm/s, and 93 ± 21 cm/s, respectively. There was no significant difference in PSV between TCD and ncTCCD (bias = 2 cm/s, p = 1.000), whereas cTCCD yielded a significantly higher PSV than TCD and ncTCCD (bias = -10 cm/s, p < 0.001; bias = -12 cm/s, p ≤ 0.001, respectively). The bias in MFV between TCD and ncTCCD techniques was (bias = -0.5 cm/s; p = 1.000), whereas cTCCD demonstrated a higher MFV compared to TCD and ncTCCD (bias = -8 cm/s, p < 0.001; bias = -8 cm/s, p ≤ 0.001, respectively). TCCD is a practically applicable imaging technique in assessing MCA blood flow velocities. cTCCD is more accurate and tends to give higher MCA blood flow velocities than non-imaging TCD and ncTCCD techniques. ncTCCD is comparable to non-imaging TCD and should be considered in clinical cases where using both TCD and TCCD measurements is needed.

Experimental, numerical and deep learning modeling study of heat transfer in turbulent pulsating pipe flow

Pulsating heat transfer is important in many engineering applications but is not fully understood or easily modeled. This work helps understand the phenomenon and demonstrates the efficacy and utility of deep learning modeling for pulsating heat transfer. The convective heat transfer coefficient (HTC) of pulsating flow through a copper tube was experimentally investigated at seventy-seven different operating conditions (500,000 time-series data points were collected at each operating condition) corresponding to different pulsating waveforms, frequencies, mass flow rates and pressures. The intensity of pulsation ranged from mild to strong enough to cause reverse flow. The literature on pulsating HTC is mixed, with several researchers reporting increased heat transfer and several other reporting decreased heat transfer relative to steady flow. The experimental data showed that both could be true depending on the ratio of the amplitude to mean flow velocity (amplitude ratio AR). The enhancement ratio (ER) of pulsating HTC relative to steady-flow HTC was measured to vary between 0.48 and 2.18 for AR ranging from 0.64 to14.42. A numerical study showed that this was only a (positive) correlation; fundamentally the overall pulsating HTC could be approximately explained by the variation of instantaneous Reynold’s number (Re) during the pulsating cycle. The distribution of instantaneous Re and hence the ER is primarily determined by the pulsating waveform, and this explains the disparate observations by different researchers. Long Short-Term Memory (LSTM) networks have been used to model pulsating HTC as a function of pulsating waveforms occuring across a measurement orifice. The ‘Toy Model’ concept where physics-based variables are used to increase generalization was implemented with the LSTMs for increased model robustness. These models could be used to maximize pulsating heat transfer by optimizing the waveform.

Numerical study on flow characteristics in the primary side of a once-through steam generator under ocean conditions

The flow characteristics of the primary side of the helical coil once-through steam generator (OTSG) have a significant impact on the safe operation of the reactor. Different from the land-based stationary working conditions, the flow of the primary side of the OTSG is influenced by sea waves and winds under ocean conditions. The rigid body motion model is used to calculate the flow of the primary side under different ocean conditions, including heeling, trimming, rolling, pitching, heaving, and combined conditions. The results show that under heeling and trimming conditions, the static pressure of the primary side is different from that under vertical conditions due to the influence of gravity, but its impact on the flow field is relatively small. Under rolling and pitching conditions, the mean flow velocity and pressure drop change periodically with the movement of the OTSG, and the smaller the sway angle, the smaller the variation amplitude of the mean flow velocity and pressure drop. Under the heaving condition, the variation amplitude of the mean flow velocity is greater than that under rolling and pitching conditions, and reverse flow occurs. Under the combined heaving and rolling condition, the mean flow velocity and pressure drop are influenced by the period and amplitude of both the two motions.

Correlation between Morphological and Hemodynamic Parameters of Carotid Arteries and Cerebral Vasomotor Reactivity.

The function of cerebral small vessels can be assessed using cerebral vasomotor reactivity (VMR). Our aim in this retrospective cross-sectional study was to investigate a correlation between carotid artery stenosis measured through ultrasonographic morphological and hemodynamic parameters and cerebral VMR. A total of 285 patients (125 males; mean age 54) were included. The breath-holding index (BHI) was used to evaluate cerebral VMR. Ultrasonographic carotid artery parameters were collected: the presence and characteristics of carotid plaques, the degree of carotid diameter stenosis, intima-media thickness (IMT), peak systolic velocity (PSV), and end diastolic velocity (EDV). Additionally, hemodynamic parameters of the middle cerebral artery (MCA) were evaluated, including the mean flow velocity (MFV) and pulsatility index (PI). The following was collected from patients' medical histories: age, gender, and vascular risk factors. A negative correlation between the BHI and age (r = -0.242, p < 0.01), BHI and the presence of carotid plaques, BHI and IMT (r = -0.203, p < 0.01), and BHI and the PI of MCA on both sides (r = -0.268, p < 0.01) was found. We found a positive correlation between the BHI in the left MCA and EDV in the left internal carotid artery (r = 0.121, p < 0.05). This study shows the correlation between cerebral VMR and carotid stenosis but indicates a higher influence of morphological parameters on VMR values.

Cold stimulation of the oral cavity redistributes blood towards the brain in healthy volunteers.

The aim of this study was to analyze cold stimulation-induced changes in cerebral and cardiac hemodynamics. Upon ingestion of an ice cube, the changes in resistance index, mean flow velocity and flow index of the middle cerebral arteries (MCA) were assessed using transcranial Doppler sonography. Extracranial duplex sonography was used to measure the mean flow velocity and resistance index of the right internal carotid artery (ICA). The change in mean arterial pressure, heart rate, root mean square of successive differences (RMSSD) and end-tidal carbon dioxide pressure were analyzed additionally. These changes were compared to sham stimulation. Compared with sham stimulation, cooling of the oral cavity resulted in significant changes in cerebral and cardiac hemodynamics. The cold stimulation decreased the resistance index in the MCA (-4.5% ± 5.4%, p < 0.0001) and right ICA (-6.3% ± 15.6%, p = 0.001). This was accompanied by an increase in mean flow velocity (4.1% ± 8.0%, p < 0.0001) and flow index (10.1% ± 43.6%, p = 0.008) in the MCA. The cardiac effects caused an increase in mean arterial pressure (1.8% ± 11.2%, p = 0.017) and RMSSD (55% ± 112%, p = 0.048), while simultaneously decreasing the heart rate (-4.3% ± 9.6%, p = 0.0001). Cooling of the oral cavity resulted in substantial changes in cerebral and cardiac hemodynamics resulting in a blood flow diversion to the brain.

Predictive Value of Quantitative Electroencephalogram Combined with Transcranial Doppler Ultrasound in Delayed Cerebral Ischemia after Subarachnoid Hemorrhage

ObjectiveTo explore the predictive value of transcranial Doppler ultrasound (TCD) combined with quantitative electroencephalogram (QEEG) in delayed cerebral ischemia (DCI) caused by aneurysmal subarachnoid hemorrhage (aSAH). MethodsThe subjects were 105 patients with aSAH from June 2020 to December 2022. Patients were divided into DCI group (n=34) and non-DCI group (n=71) according to the presence of DCI 14d after onset. Further comparison was conducted on the baseline data as well as the parameters of QEEG and TCD within 24h after admission. Multivariate logistic analysis was performed to investigate risk factors related to DCI within 14 days of admission in aSAH patients. ResultsThere were significant differences in the comparison of the proportion of Hunt-Hess grading, relative δ power (RDP), relative α power (RAP), relative α/β power ratio (ADR), as well as peak systolic velocity (Vs), mean blood flow velocity (MBFV) and pulsatility index (PI) of middle cerebral artery between the two groups (P<0.05). Furthermore, Logistic regression analysis revealed that ADR [OR=1.668, 95%CI (1.369, 4.345)] and MBFV of middle cerebral artery [OR=3.279, 95%CI (2.332, 6.720)] were risk factors for the occurrence of DCI in aSAH patients (P<0.05). In addition, evaluation of the predictive value revealed that combined use of the two indicators showed the highest predictive value (AUC: 0.959, 95%CI: 0.896∼0.993). ConclusionPatients with aSAH complicated by DCI have relatively higher MBFV of middle cerebral artery and ADR. Combined use of the two indicators can provide reference for early prediction of DCI in aSAH patients.

Assessing the effects of pressure variations on combustion dynamics in vortex-tube flows

In our investigation, we scrutinize combustion stability in vortex-tube combustion at high operating pressures by examining stability limits, flame configurations, and pressure oscillations. Our examination deeply probes the intricacies of flow and flame behaviors in terms of aerodynamic, thermodynamic, and flamedynamic aspects to identify the fundamental reasons behind stability variances at different pressure levels. The findings indicate that combustion instability escalates with rising operating pressures, marked by increased variability in flame patterns and a monotonic upsurge in pressure oscillation amplitudes. Although aerodynamic and thermodynamic stabilities remain unaffected, the thermoacoustic stability is compromised at elevated pressures. This is evidenced by the strong link between the Rayleigh criterion and the amplitude of pressure fluctuations, with an increased “gain” in the flame transfer function as pressure mounts. The core of the observed thermoacoustic instability is traced back to heightened density variations and mean flow velocities at high pressures, leading to amplified momentum flux oscillations.

Transcranial ultrasonographic evaluation of effect of ventriculoperitoneal shunt on intracranial dynamics: A prospective observational study

BackgroundTranscranial sonographic (TCS) evaluation of optic nerve sheath diameter (ONSD), third ventricular diameter (TVD) and mean flow velocities (Vm) and pulsatility index (PI) of middle cerebral artery (MCA) can provide important insights to the change in intracranial dynamics following ventriculo-peritoneal (VP) shunt surgery. The primary objective of this study was to observe changes in ONSD values following VP shunt at 12 h, compared to pre-VP shunt values. MethodsAfter obtaining ethical approval, patients admitted with a diagnosis of hydrocephalus posted for a VP shunt surgery were prospectively enrolled. TCS evaluation was done before induction of anesthesia and 12-hour post-VP shunt surgery. We recorded the values of ONSD, TVD and Vm and PI MCA at both time points. ResultsThirty-four patients (19 male) were evaluated for ONSD and for the improvement of symptoms. Transtemporal window could not be obtained in six patients. At 12 h following VP shunt, bilateral median ONSD values reduced significantly from their pre-VP shunt values [right ONSD- 0.62 (0.59–0.64) to 0.53 (0.5–0.54) mm (p < 0.001); left ONSD- 0.62 (0.59–0.63) to 0.53 (0.5–0.54) mm (p < 0.001)]. Similarly, the median TVD at 12 h post-VP shunt reduced significantly from its pre-VP shunt measurements [0.97 (0.85–1.09) to 0.74 (0.7–0.84) cm]. PI MCA values reduced significantly, while Vm MCA values increased significantly from the pre-VP shunt values. ConclusionVP shunt reduced the ONSD, TVD, PI MCA and increased the Vm MCA after shunt surgery as early as 12hrs.

Levenberg–Marquardt backpropagation neural networking (LMB-NN) analysis of hydrodynamic forces in fluid flow over multiple cylinders

The mathematical formulation of the flowing liquid stream around and through confined multiply connected domains brings a complex differential system. Due to this, one cannot provide a complete description of flow field properties. The current pagination provides a numerical remedy by the use of artificial intelligence in this direction. To be more precise, fluid is considered in the rectangular channel. The circular, square, and triangular-shaped cylinders are positioned as an obstacle to the continuous fluid. The channel’s left wall is viewed as an inlet and two different velocity profiles are introduced at an inlet that are constant and parabolic profile. To discretize the computational domain, hybrid meshing is used. The variance in basic variables, namely, the velocity of the liquid and the distribution of the liquid pressure, is recorded via graphs. The nine different meshed grades are tested for the drag and lift coefficients around the right-angle triangle, square, and circular barrier. The neural networking model is constructed by using 99 datasets of sample values for drag coefficient when characteristic length, the density of fluid, the dynamic viscosity of the fluid, and mean flow velocity are taken as inputs. The training of the neural network takes up 69 slots (about 70%), while the testing and validation of the neural network each take up 15 slots (15%). The Levenberg–Marquardt backpropagation algorithm is used for training. We have observed that for the parabolic profile, the drag coefficient is higher in intensity for each obstacle compared to the constant profile, while the lift coefficient shows opposite patterns.

Abstract WP121: Cerebral Hemodynamics in the First Week Postpartum in Healthy Women and Women With Preeclampsia

Objective: Standard adult normative data for transcranial Doppler (TCD)-based cerebral hemodynamic measures, such as mean and peak cerebral blood flow velocity (mCBFV, pCBFV), are used to identify pathological conditions such as postpartum angiopathy. However, little is known about cerebral hemodynamics during the early postpartum period, particularly in patients with preeclampsia (PEC). We characterized cerebral hemodynamics using TCD in the first week postpartum in patients with and without PEC. Methods: We prospectively recruited women with PEC and normotensive pregnant women delivering at an urban academic medical center. We measured CBFV in the bilateral middle cerebral arteries with TCD and calculated systolic mCBFV and pCBFV as well as pulsatility index (PI) and PI-derived noninvasive intracranial pressure (nICP). We compared systolic mCBFV and pCBFV between postpartum women with and without PEC, and historical data from non-pregnant young adult female controls. Results: Subjects were 51 women with PEC, 19 normotensive postpartum women, and 28 non-pregnant historical controls. In the PEC group, median mCBFV was 75.0 cm/s (IQR 65.2-99.1) and median pCBFV was 106.9 cm/s (IQR 92.7-130.8). In the normotensive postpartum group, median mCBFV was 77.1 cm/s (IQR 66.0-92.3) and median pCBFV was 107.9 cm/s (IQR 96.6-127.4). In the non-pregnant female control group, median mCBFV was 62.0 cm/s (IQR 48.5-67.9) and median pCBFV was 83.6 cm/s (IQR 69.3-95.2) (p&lt;0.0001 for mean and peak 3-way comparisons; see Figure). PI and nICP were within normal range in both postpartum groups and did not differ significantly between groups. Conclusion: Postpartum women with and without PEC had mCBFV and pCBFV significantly higher than non-pregnant controls, and many fell outside the standard normal range for healthy adults, but PI and nICP were within normal range. Standard ranges of CBFV for healthy adults may not apply in the postpartum period.

Abstract WP194: Quantified Effects of Intra-Arterial Vasodilatory Therapy for Cerebral Vasospasm

Introduction: Cerebral vasospasm is a major cause of morbidity and mortality after aneurysmal subarachnoid hemorrhage (aSAH). Though used routinely in clinical practice, objective metrics to evaluate effectiveness of intra-arterial vasodilatory treatment (IAT) have not been identified. To quantify effects of IAT on flow dynamics in cerebral vasospasm, we retrospectively compared Lindegaard ratios (LR) of aSAH patients pre-and post-IAT. Methods: Subjects included 24 aSAH patients undergoing IAT in the bilateral middle cerebral arteries (MCA) for cerebral vasospasm, diagnosed by standard clinical and radiographic criteria. Subjects were excluded if balloon angioplasty was performed prior to/within 2 days of the index procedure. All subjects received 10 mg IA milrinone, a non-catecholamine phosphodiesterase inhibitor drug, per MCA. Transcranial doppler (TCD) ultrasound was measured pre-IAT (D0) and at D+1 and D+2 post-IAT. LR was calculated as the ratio of mean flow velocities in the middle cerebral artery (MCA) to the ipsilateral extracranial internal carotid artery. Standard threshold for vasospasm is defined as LR&gt;3. Results: Right and left LR were aggregated, total N=48. Average pre-IAT LR was 2.96 (R 2.67/L 3.25±1.29). Post-IA LR were 2.72±1.12 and 3.15±1.55 at D+1 and D+2, respectively. Subjects with pre-IA LR&gt;3 showed an average LR decrease of 21% post-IAT D+1 (p=0.01) and an 8% decrease at D+2 (p=0.16) [Fig.1A]. Subjects with pre-IAT&lt;3 experienced an average LR increase of 28% by D+2 (p=0.02) [Fig 1B]. Conclusion: Subjects with TCD confirmed vasospasm (LR&gt;3) at D0 showed a significant improvement in cerebral blood flow one day after therapy. Subjects who did not meet TCD threshold for vasospasm (LR&lt;3) showed little change one day post-IAT but worsening cerebral blood flow by day two post-IAT. Further study is needed to determine whether LR can be used to predict benefit or objectively assess effectiveness of IAT in aSAH patients with cerebral vasospasm.

Clinical Profile and middle cerebral artery velocity of children with sickle cell anaemia seen in UUTH, Uyo, Akwa Ibom state, Nigeria.

The risk of stroke in individuals with Sickle Cell Anaemia (SCA) can be assessed by routine non-invasive measurement of their cerebral blood flow using a Transcranial Doppler (TCD) ultrasound scan. This study aimed to determine the difference in blood flow velocity parameters in the middle cerebral artery (MCA) of children with sickle cell anaemia compared to a normal age-matched population. This was a hospital-based comparative cross-sectional study among 40 SCA patients aged 3-16 years, in steady state and 40 age and sex-matched HbAA healthy subjects. This study lasted from June to October 2019. Medical history was retrieved using a structured questionnaire. The time-averaged mean of maximum velocity (TAMMV) of the right and left MCA was measured using non-imaging TCD. The mean age ± SD of the SCA patients was 9.1 ± 4.4 years. The SCA patients and sex and age-matched HbAA group consisted of 23 (57.5%) males and 17 (42.5%) females respectively. SCA patients had a significantly lower mean ± SD haemoglobin (Hb) than the controls (7.1 ± 1.1g/dl vs 11.1 ± 1.4g/dl; p<0.001). The right MCA of the patients with SCA had a significantly higher mean flow velocity compared to the controls (94.1 ± 23.1 vs 55.0 ± 8.8cm/sec, p<0.001). The mean TAMMV recorded in the SCA subjects were significantly higher than that of the non-SCA subjects. There is a need to ensure that TCD ultrasound is employed as a routine screening tool for stroke risk among SCA patients in Nigerian tertiary health institutions.

Mixed Averaging Procedures

The statistical operators typically applied in postprocessing numerical databases for statistically steady turbulence are a mixture of physical averages in homogeneous spatial directions and in time. Alternative averaging operators may involve phase or ensemble averages over different simulations of the same flow. In this paper, we propose straightforward metrics to assess the relative importance of these averages, employing a mixed averaging analysis of the variance. We apply our novel indicators to two statistically steady turbulent flows that are homogeneous in the spanwise direction. In addition, this study highlights the local effectiveness of the averaging operator, which can vary significantly depending on the mean flow velocity and turbulent length scales. The work can be utilized to identify the most effective averaging procedure in flow configurations featuring at least two homogeneous directions. Thus, this will contribute to achieving better statistics for turbulent flow predictions or reducing computing time.

Nonlinear dynamics of a circular curved cantilevered pipe conveying pulsating fluid based on the geometrically exact model

Due to the novel applications of flexible pipes conveying fluid in the field of soft robotics and biomedicine, the investigations on the mechanical responses of the pipes have attracted considerable attention. The fluid-structure interaction (FSI) between the pipe with a curved shape and the time-varying internal fluid flow brings a great challenge to the revelation of the dynamical behaviors of flexible pipes, especially when the pipe is highly flexible and usually undergoes large deformations. In this work, the geometrically exact model (GEM) for a curved cantilevered pipe conveying pulsating fluid is developed based on the extended Hamilton’s principle. The stability of the curved pipe with three different subtended angles is examined with the consideration of steady fluid flow. Specific attention is concentrated on the large-deformation resonance of circular pipes conveying pulsating fluid, which is often encountered in practical engineering. By constructing bifurcation diagrams, oscillating shapes, phase portraits, time traces, and Poincare maps, the dynamic responses of the curved pipe under various system parameters are revealed. The mean flow velocity of the pulsating fluid is chosen to be either subcritical or supercritical. The numerical results show that the curved pipe conveying pulsating fluid can exhibit rich dynamical behaviors, including periodic and quasi-periodic motions. It is also found that the preferred instability type of a cantilevered curved pipe conveying steady fluid is mainly in the flutter of the second mode. For a moderate value of the mass ratio, however, a third-mode flutter may occur, which is quite different from that of a straight pipe system.