Passive Leg Raising Research Articles

Effects of adiabatic index on the sonic surface and time variability of low angular momentum accretion flows

We study the role of adiabatic index in determining the critical points in the transonic low angular momentum accretion flow onto a black hole. We present the general relativistic 2D hydrodynamic simulations of axisymmetric, inviscid accretion flows in a fixed Kerr black hole gravitational field. A relativistic fluid where its bulk velocity is comparable to the speed of light, flowing in the accretion disk very close to the horizon can be described by an adiabatic index of 4/3 < {\gamma} < 5/3. The time dependent evolution of the shock position and respective effects on mass accretion rate and oscillation frequency with varying adiabatic index is discussed in the context of the observed microquasars.

Experimental investigation of shock-induced separation and flow control in a transonic compressor cascade

The influence of transition control on shock-induced flow separation was investigated in a highly loaded transonic compressor cascade at an inlet Mach number of 1.21 and a chord-based Reynolds number of $$1.4 \times 10^6$$ . Transition was influenced by raising the free-stream turbulence from 0.5 to 2.5%. Two further cases employed either air-jet vortex generators (AJVG) or a surface roughness patch as transition control devices. Velocity fields in the vicinity of the unsteady transonic separation were captured by particle image velocimetry (PIV). Blade flexure induced by the unsteady aerodynamic loading was tracked for each image and compensated individually prior to PIV processing. The captured flow fields indicate shape variations of the separation region, while the shock foot moves within a range of up to 20% of chord. The frequency of separation for each investigated case was assessed on the number of vectors with negative velocity in each PIV sample. To further quantify the size of the separation region, the statistically independent PIV samples were conditionally averaged for various passage shock positions at a resolution of 1% chord length. Insight to the dynamics and frequency of the passage shock motion was further provided by high-speed shadowgraphy. Large bubble separation occurs if the turbulence of the incoming flow is low. The size of separation region decreases when AJVGs are applied but still exhibits bubble separation as the passage shock moves downstream. The size of the separation region is significantly reduced either if a roughness patch is applied or if the turbulence level of the incoming flow is high. The flow conditions showing bubble separation in the mean flow also exhibit distinct spectral peaks indicating periodic shock oscillations.

Comparison of the effect of different degrees of passive leg raising on the internal jugular vein cross-sectional area in patients before thoracic surgery

BackgroundThis study investigated the effect of different degrees of passive leg raising (PLR) on the internal jugular vein (IJV) cross-sectional area (CSA) and on the success rate of IJV cannulation in patients waiting for thoracic surgery, to analyze whether body mass index (BMI), gender, age, fasting time and preoperative rehydration have any impact on changes in the IJV CSA.MethodsEighty-two patients scheduled for selective thoracic surgery were enrolled in this study. Patients were randomly assigned based on a computer-generated randomization sequence into 3 groups: 0, 30, and 50 degrees (n = 32, 25, and 25 patients, respectively). The right IJV CSA in the sequence of 0-degree (supine position), 30-degree and 50-degree PLR positions was recorded in all patients using an ultrasound probe. The relationship of BMI, gender, age, fasting time and preoperative rehydration to the IJV CSA was analyzed. Then, each patient was returned to a supine position. After waiting for at least 5 min, patients were placed in a PLR position at 0, 30, or 50 degrees, and then IJV cannulation was performed without ultrasound guidance. The success rate of IJV catheterization at different PLR angles was compared.ResultsThe average CSA of the right IJV in the supine position, 30-degree PLR position and 50-degree PLR position was 1.39 ± 0.63 cm2, 1.65 ± 0.73 cm2, and 1.68 ± 0.71 cm2, respectively. These results showed gradual increases in the IJV CSA of 18.5% (30-degree PLR) and 20.2% (50-degree PLR) when compared to that in the supine position (P = 0.045 and 0.025, respectively). However, only fasting time had a significant impact on the increase in the right IJV CSA at different PLR angles (P = 0.026). Other factors, such as BMI, gender, age and preoperative rehydration, had no significant effects. The success rates of IJV catheterization at angles of 0, 30 and 50 degrees were 84.3, 88 and 92%, respectively; however, there were no significant differences among the three groups (P = 0.674).ConclusionsPLR increases the CSA of the right IJV, especially for patients with long fasting times before thoracic surgery. The effect of the 30-degree PLR position is similar to that of the 50-degree PLR position. However, the success rate of right IJV catheterization was not enhanced in this study using landmark-guided puncture, even though the CSA of the right IJV was increased.Trial registrationClinical trial registration number: ChiCTR1800015051. Date of registration: March 2018.

Infrared dust arcs around stars – I. Effect of the radiation pressure

In this paper we consider the distribution of the interstellar dust in the vicinity of the star under an influence of the stellar gravitation and radiation pressure. This study is applicable to the stars with relatively weak stellar wind and strong radiation, when the stellar radiation swept out the interstellar dust much further from the star than the position of the bow shock created by an interaction of the stellar and interstellar plasma flows. In this case the number density of dust for a certain dust grains radius can be calculated analytically based on the classical `cold model'. The dust density distribution for the mixture of dust grains with different radii is calculated. We also calculated intensity maps of the thermal infrared emission at 24~$\mu$m from dust due to heating by the stellar radiation. It is shown that the obtained maps of the infrared emission extremely depends on the model parameters: material of dust grains, dust size distribution assumed in the interstellar medium, the approach used to calculate the dust temperature. The bright distinct arc at the intensity maps is seen for graphite dust grains and almost disappears for silicates. Absolute values of intensity in the case of graphite are several order of magnitudes larger than for silicates due to more intensive heating of graphite. Possible application of the presented theory is proposed as an algorithm for analysis of the observational images of the infrared arc around the star.

Passive leg raising combined with echocardiography could evaluate volume responsiveness in patients with septic shock

To assess the value of passive leg raising (PLR) combined with echocardiography in predicting volume responsiveness in patients with septic shock. Thirty septic shock patients with spontaneous respiration admitted to intensive care unit (ICU) of Tianjin First Center Hospital from July 2016 to August 2018 were enrolled. PLR and volume expansion (VE) were performed successively. The hemodynamic parameters including left ventricular end-diastolic volume (LVEDV), left ventricular end-systolic volume (LVESV), stroke volume (SV) and left ventricular ejection fraction (LVEF) before PLR (baseline level), after PLR, immediately after VE were examined by echocardiography, and the central venous pressure (CVP) was monitored. The patients with increase in SV after VE (ΔSV) ≥ 15% were served as reaction group, while ΔSV < 15% were served as non-reaction group. The changes in LVEDV, LVESV, SV, LVEF and CVP at baseline level, after PLR and after VE were compared between the two groups. Pearson correlation method was used to analyze the correlation between ΔSV, increase in LVEF (ΔLVEF) after PLR and ΔSV, and ΔLVEF after VE. Receiver operating characteristic (ROC) curve was plotted to evaluate the predictive value of ΔSV and ΔLVEF after PLR for volume responsiveness. PLR and VE were successfully performed in 30 patients, of which 23 patients (76.7%) were enrolled in the reaction group, and 7 patients (23.3%) in the non-reaction group. Compared with baseline levels, LVEDV, SV, and LVEF in the reaction group were significantly increased after PLR [LVEDV (mL): 83.5±9.6 vs. 77.1±6.2, SV (mL): 48.5±5.6 vs. 43.2±4.9, LVEF: 0.58±0.04 vs. 0.56±0.06, all P < 0.05], and CVP was significantly increased after VE [cmH2O (1 cmH2O = 0.098 kPa): 7.4±3.3 vs. 4.6±0.7, P < 0.01], however, there was no significant change in LVESV. In the non-reaction group, SV and LVEF were significantly increased after PLR as compared with those at baseline levels [SV (mL): 42.7±3.7 vs. 40.6±3.1, LVEF: 0.52±0.05 vs. 0.50±0.05, both P < 0.05], while LVEDV and CVP were significantly increased after VE as compared with those at baseline levels [LVEDV (mL): 84.4±4.1 vs. 80.6±5.9, CVP (cmH2O): 10.6±3.5 vs. 7.6±0.5, both P < 0.05], however, there was no significant change in LVESV. Pearson correlation analysis showed that ΔSV and ΔLVEF after PLR were positively correlated with ΔSV and ΔLVEF after VE (r1 = 0.86, r2 = 0.65, both P < 0.01). ROC curve analysis showed that the area under ROC curve (AUC) of PLR-induced ΔSV and ΔLVEF for predicting volume responsiveness was 0.85 and 0.66 respectively. When the cut-off value of ΔSV after PLR was 10.6%, the sensitivity was 78.2%, the specificity was 82.3%; when the cut-off value of ΔLVEF after PLR was 3.6%, the sensitivity was 78.2%, and the specificity was 73.2%. ΔSV and ΔLVEF measured by PLR combined with echocardiography can be used to evaluate the volume responsiveness in patients with septic shock and can guide fluid therapy.

Investigation of supersonic turbulent flows over a sphere by fully resolved direct numerical simulation

In this work, a fully resolved direct numerical simulation study of the interaction between supersonic turbulent flow and inertial particle is carried out. For the compressible flow, an eighth-order bandwidth optimization weighted essentially nonoscillatory scheme is used for shock capturing, and the central finite difference scheme is used for the spatial discretization of diffusion terms. The three-dimensional ghost zone immersed boundary method is adopted for solid-fluid interface identification. These numerical schemes are integrated in a direct numerical simulation solver, and its validation is demonstrated by comparing to several benchmark cases. Such a developed method is then used to attack the problem of an upstream supersonic turbulent flow over a spherical particle. Three cases with different inflow turbulence intensities are studied. It is shown that with the turbulence intensity increasing the drag force coefficient presents a smaller relative increase compared to the incompressible situation. Analysis of the bow shock-turbulence interaction is also reported. Similar to the normal shock-turbulence interaction, both the Kolmogorov and Taylor scales decrease after being compressed by the shock. Moreover, both the streamwise and transverse Reynolds stresses have a peak at the shock position. These results indicate the significance of taking the effects of shock into consideration when modeling the modulation of a solid particle to the compressible turbulence.

БЕССТОЛКНОВИТЕЛЬНОЕ ВЗАИМОДЕЙСТВИЕ В ПЛАЗМЕ: КАК МАГНИТОПАУЗА ВЗАИМОДЕЙСТВУЕТ С УДАРНОЙ ВОЛНОЙ?

Our analysis of a sunward Poynting flux throughout magnetosheath and foreshock (directly measured byINTERBALL-1, CLUSTER-4 and DOUBLE STAR TC1), for the first time clearly demonstrates, how the resonances in the magnetospheric boundary layers are transmitted back wards the bow shock: the short pulses of the sunward Poynting flux initiate the strongest (&gt;80%!) 3-wave interactions with the incident dynamic pressure. They start in the foreshock, regulate the bow shock position and oscillations, and then another near- magnetopause 3-wave strong interactions assist plasma flow extra deflections and acceleration downstream the magnetopause.

Research progress in monitoring methods of fluid responsiveness

Accurate evaluation of fluid responsiveness in the body has been a hot topic in clinical researches. Dynamic indexes are widely concerned due to the inaccuracy and innovation of static indexes. However, each dynamic index has its own scope of application and most of the dynamic indicators are applicable to the evaluation of capacity reactivity under mechanical ventilation. With the development of medicine, the research of non-invasive and easy to use ultrasonic measurement index and dynamic index caused by autologous volume load test is the hottest. This paper reviews the relevant research of various dynamic indicators so as to provide reference for clinical liquid therapy. Key words: Fluid responsiveness; Assessment; Monitoring; Dynamic indicators; Passive leg raising test; End-expiratory occlusion test

From outburst to quiescence: spectroscopic evolution of V1838 Aql imbedded in a bow-shock nebula

We analyse new optical spectroscopic, direct-image and X-ray observations of the recently discovered a high proper motion cataclysmic variable V1838 Aql. The data were obtained during its 2013 superoutburst and its subsequent quiescent state. An extended emission around the source was observed up to 30 days after the peak of the superoutburst, interpreted it as a bow--shock formed by a quasi-continuous outflow from the source in quiescence. The head of the bow--shock is coincident with the high--proper motion vector of the source ($v_{\perp}=123\pm5$ km s$^{-1}$) at a distance of $d=202\pm7$ pc. The object was detected as a weak X-ray source ($0.015\pm0.002$ counts s$^{-1}$) in the plateau of the superoutburst, and its flux lowered by two times in quiescence (0.007$\pm$0.002 counts s$^{-1}$). Spectroscopic observations in quiescence we confirmed the orbital period value $P_{\rm{orb}}=0.0545\pm 0.0026$ days, consistent with early-superhump estimates, and the following orbital parameters: $\gamma= -21\pm3$ km s$^{-1}$ and $K_1 = 53\pm3$ km s$^{-1}$. The white dwarf is revealed as the system approaches quiescence, which enables us to infer the effective temperature of the primary $T_{eff}=11,600\pm400$K. The donor temperature is estimated $\lesssim 2200$K and suggestive of a system approaching the period minimum. Doppler maps in quiescence show the presence of the hot spot in HeI line at the expected accretion disc-stream shock position and an unusual structure of the accretion disc in H$\alpha$.

Clinical value of early liquid resuscitation guided by passive leg-raising test combined with transthoracic echocardiography in patients with septic shock

To explore the clinical value of early fluid resuscitation guided by passive leg-raising test (PLR) combined with transthoracic echocardiography (TTE) in patients with septic shock. A prospective randomized controlled trial (RCT) was conducted. Seventy-four patients with septic shock admitted to China-Japan Friendship Hospital from January 2017 to October 2018 were enrolled. The patients were randomly divided into control group and experimental group with 37 patients in each group. Both groups of patients were treated with broad-spectrum antibiotics empirically, while received fluid resuscitation via the subclavian vein catheter. The patients of control group were given rapid fluid replacement, and those of experimental group received fluid replacement according to result of PLR combined with TTE. The stroke volume (SV) was measured by TTE before and after PLR, volumetric response of patients was judged by stroke volume variation (SVV). If the SVV ≥ 15%, it was considered that there was a volume responsiveness, and fluid loading was given. If SVV < 15%, it was considered that there was no volume shortage, and the restrictive fluid replacement was given. The goal of fluid resuscitation in both groups were to simultaneously meet the central venous pressure (CVP) of 8-12 mmHg (1 mmHg = 0.133 kPa), mean arterial pressure (MAP) ≥ 65 mmHg, urine volume ≥ 0.5 mL×kg-1×h-1, and central venous blood oxygen saturation (ScvO2) ≥ 0.70 within 6 hours. Vasoactive drugs were used when the patients could not achieve the treatment goals. The MAP, lactic acid (Lac), oxygenation index (PaO2/FiO2) and ScvO2 of the patients were determined at 6 hours of treatment, and serum C-reactive protein (CRP) and chest CT were reviewed at 48 hours of treatment, and compared with those before treatment. The total hospital stay and the mortality were recorded. There was no significant difference in gender, age, body weight and etiological structure between the two groups, which indicated that the baseline data were generally balanced. There was no statistical difference in MAP, Lac, PaO2/FiO2, ScvO2 and CRP before infusion between the two groups. After 6 hours of treatment, the MAP, Lac, PaO2/FiO2 and ScvO2 of the two groups were all better than those before infusion. Except for the difference in MAP between the experimental group and the control group (mmHg: 78.76±5.22 vs. 76.35±6.66, P > 0.05), the other three parameters in the experimental group were significantly better than those in the control group [Lac (mmol/L): 2.52±1.15 vs. 3.89±1.42, PaO2/FiO2 (mmHg): 338.14±27.47 vs. 303.35±22.52, ScvO2: 0.70±0.04 vs. 0.63±0.05, all P < 0.01]. After 48 hours of treatment, CRP levels of both groups were lower than those before infusion, and the experimental group was better than the control group (mg/L: 110.12±39.80 vs. 137.98±31.23, P < 0.01). Chest CT showed that the incidence of pulmonary edema in the experimental group was significantly lower than that in the control group [13.5% (5/37) vs. 37.8% (14/37), P < 0.01]. The hospital stay of the experimental group was shorter than that of the control group (days: 21.47±5.58 vs. 28.33±4.93, P < 0.01), but no significant difference in mortality was found between the two groups [18.9% (7/37) vs. 18.9% (7/37), P > 0.05]. Compared with the traditional rapid fluid replacement, early fluid resuscitation treatment strategies guided by the PLR combined with TTE, could better improve perfusion and oxygenation level of tissues and organs, avoid pulmonary edema caused by rapid fluid replacement, shorten the hospital stay in patients with septic shock, but had no significant effect on hospital mortality.

Mechanics of the influx phase in the jet regurgitant mode of a powered resonance tube

Time-resolved visualisation of shock wave motion within a powered resonant tube (PRT) is presented for the regurgitant mode of operation. Shock position and velocity are measured as functions of both time and space from ultra-high-speed schlieren visualisations. The shock wave velocity is seen to vary across the resonator length for both the incident and reflected waves. Three mechanisms are explored as explanations for the variation in velocity: change in local fluid velocity, variation in shock strength and variations in local temperature. For the incident wave, local fluid velocity and shock strength are extracted from the data and both are demonstrated to contribute to the observed variation, with a non-trivial remainder likely explained by variation in temperature.

The influence of an oscillating wall on the position of oblique shocks in a 2D channel

In the paper we solve the problem of supersonic gas flow in a two-dimensional channel with the moving upper wall making oscillations according to the harmonic law. In order to obtain a numerical solution for gas dynamics equations we have implemented two difference schemes: the scheme with the space and time approximation of the first order and the scheme with the space approximation of the second order. The fluxes were computed using Van Leer’s method. A special form of fluxes in the gas dynamics equations is given, which enables to calculate fluxes on cell faces of difference mesh using Van Leer’s method. Depending on a type of the harmonic law and initial gas inflow conditions, the peculiarities of oblique-shock wave propagation in moving curvilinear domains have been investigated. It has been determined that under a particular oscillation frequency the presence of wall oscillation practically doesn’t have an effect on the flow regime inside the domain. The convergence of the obtained solution is shown by calculations using difference grids with different numbers of cells. While comparing the numerical solution obtained due to our program with the one obtained with Ansys Fluent solver we found that the constructed code operates correctly.

External-Compression Supersonic Inlet Free from Violent Buzz

To greatly improve the supersonic inlet stability at low cost of structural weight and complexity, a novel buzz suppression strategy based on fixed-geometry air bleed is developed. It is designed to have plenty of narrow flush slots that are widely distributed along the compression surface. Using the natural pressure gradient varying with the terminal shock position, it is capable of creating self-adaptive bypass flow removal upstream of the internal duct. A strong stabilizing effect can be thus automatically produced on the subcritical flowfield by eliminating shock-induced separation and discharging excessively captured airflow. Simultaneously, the undesired air leakage at the critical regime can be naturally restricted to prevent a prohibitive performance penalty during normal operation. To verify the effectiveness, an external-compression inlet model is specially designed and carefully tested at freestream Mach numbers of 2.0 and 2.5 with an almost full exit throttle range considered (0–99.1%). Results indicate that the subcritical stable-flow range is remarkably extended from a throttle threshold of 53.7% to that of 86.4% and 73.7%, respectively, after the usage of the proposed bleed method. Moreover, intense flow instability is totally eliminated, even when the duct exit is almost closed. Further analysis reveals that the bleed flow rate at the near-critical state is not beyond 1% of the inlet flow rate for both freestream conditions. It actually causes no obvious loss of the inlet flow rate. Also, the following total pressure drop and drag increase are below 0.4%. Additionally, the observed unique buzz flow implies that the buzz origin is not necessarily limited to the two known sources, as opposed to the long-established understanding.

Numerical Simulation on Interfacial Characteristics in Supersonic Steam–water Injector Using Particle Model Method

Steam–water injectors have been widely applied in various industrial fields because of their compact and passive features. Despite its straightforward mechanical design, the internal two-phase condensing flow phenomena are extremely complicated. In present study, a numerical model has been developed to simulate steam–water interfacial characteristics in the injectors based on Eulerian–Eulerian multiphase model in ANSYS CFX software. A particle model is available for the interphase transfer between steam and water, in which a thermal phase change model was inserted into the model as a CFX Expression Language (CEL) to calculate interphase heat and mass transfer. The developed model is validated against a test case under a typical operating condition. The numerical results are consistent with experimental data both in terms of axial pressure and temperature profiles, which preliminarily demonstrates the feasibility and accuracy of particle model on simulation of gas–liquid interfacial characteristics in the mixing chamber of injector. Based on the dynamic equilibrium of steam supply and its condensation, interfacial characteristics including the variation of steam plume penetration length and steam–water interface have been discussed under different operating conditions. The numerical results show that steam plume expands with steam inlet mass flow rate and water inlet temperature increasing, while it contracts with the increase of water inlet mass flow rate and backpressure. Besides this, the condensation shock position moves upstream with the backpressure increasing.

Plasma-Assisted Control of Supersonic Flow over a Compression Ramp

This study considers the effect of an electric discharge on the flow structure near a 19.4° compression ramp in Mach-2 supersonic flow. The experiments were conducted in the supersonic wind tunnel SBR-50 at the University of Notre Dame. The stagnation temperature and pressure were varied in a range of 294–600 K and 1–3 bar, respectively, to attain various Reynolds numbers ranging from 5.3 × 105 to 3.4 × 106 based on the distance between the exit of the Mach-2 nozzle and the leading edge of the ramp. Surface pressure measurements, schlieren visualization, discharge voltage and current measurements, and plasma imaging with a high-speed camera were used to evaluate the plasma control authority on the ramp pressure distribution. The plasma being generated in front of the compression ramp shifted the shock position from the ramp corner to the electrode location, forming a flow separation zone ahead of the ramp. It was found that the pressure on the compression surface reduced almost linearly with the plasma power. The ratio of pressure change to flow stagnation pressure was also an increasing function of the ratio of plasma power to enthalpy flux, indicating that the task-related plasma control effectiveness ranged from 17.5 to 25.

Pulse Pressure and Carotid Artery Doppler Velocimetry as Indicators of Maternal Volume Status: A Prospective Cohort Study

(Anesth Analg. 2018;127:457–464) Not only is pregnancy associated with numerous physiological cardiovascular changes that influence maternal volume status, but neuraxial analgesia also significantly alters the maternal hemodynamic profile. Noninvasive techniques to assess intravascular volume are thereby critical to intrapartum fluid management in the obstetric population. Neither pulse pressure nor the carotid artery Doppler response to passive leg raise (PLR) has been prospectively evaluated in an obstetric population for the assessment of volume status. Therefore, the authors of the present study tested the hypothesis that carotid artery Doppler response to PLR is greater in women with a narrow pulse pressure, indicating relative hypovolemia.

Hybrid passive-active control method of a swept shock wave-supersonic wake interaction

In the present study, a hybrid passive-active flow control method is used to investigate the interaction between a swept shock wave (SSW) generated by a swept compression wall, and a supersonic wake formed by a wake generator (WG), using a three-dimensional finite volume code. In order to detect the turbulence in the flow behavior, the Reynolds stress model (RSM) is used. Furthermore, dynamic mesh adaptation (DMA) and full multigrid (FMG) techniques are used to better predict the flow structure. The numerical simulations are validated with available data and acceptable agreements are found. After ensuring the accuracy of the numerical code, the effects of the variations in the wake generator's height and temperature, as a hybrid passive-active flow control method, on a swept shock wave and a supersonic wake are investigated. The results indicate that any change in the height and temperature of the wake generator affects the Mach number distribution, the static and the stagnation pressures, as well as the shock's position.

Passive leg raising in out-of-hospital cardiac arrest

BackgroundThe use of passive leg raising (PLR) in cardiopulmonary resuscitation (CPR) is sometimes discussed and even recommended. The effect of this intervention has never been properly addressed. We planned to determine whether PLR in out-of-hospital cardiac arrest (OHCA) is associated with an improved survival to 30 days. MethodsIn eight districts in western Sweden, we introduced PLR within five minutes after the start of CPR, among patients with OHCA. Patients in whom PLR was not performed, within the same district, served as a control group. Thirty-day survival was the primary endpoint. A propensity score analysis, as well as a standard multivariate analysis, was used to assess possible differences between the two groups. ResultsWe identified 3554 patients with OHCA from the eight districts. Forty-four percent were treated with PLR during CPR. Patients who received PLR differed from those who did not, by having more risk factors for an adverse outcome (fewer crew-witnessed cases, more OHCA at home, a greater need for medication and prolonged delays to treatment). The overall survival to 30 days was 7.9% among patients who received PLR versus 13.5% among those who did not. A comparison of the groups, using propensity score matching, revealed a 30 -day survival of 8.6% in the PLR group versus 8.2% in the control group (odds ratio 1.07; 95% confidence interval 0.80–1.44). ConclusionIn an observational study, we introduced PLR as an addition to standard treatment in patients with OHCA. We did not find any evidence that this treatment improves survival to 30 days.

The effects of spinal manipulative therapy on lower limb neurodynamic test outcomes in adults: a systematic review

ABSTRACTObjective: Spinal Manipulative Therapy (SMT) is a routinely applied treatment modality for various musculoskeletal conditions, including low back pain. The precise mechanisms by which SMT elicits its effects are largely unknown, but recent research supports a multi-system explanation recognizing both biomechanical and neurophysiological mechanisms. Although the evaluation of changes in clinical presentation is complex, objective neurophysiological measures of sensitivity to movement (e.g. neurodynamic tests) can be a valuable clinical indicator in evaluating the effects of SMT. This review aimed to synthesize current literature investigating the effects of SMT on lower limb neurodynamics.Method: Eight electronic databases were systematically searched for randomized controlled trials (RCT) that applied SMT (against any control) and evaluated lower limb neurodynamics (Passive Straight Leg Raise or Slump Test). Selection and data extraction were conducted by one researcher, reviewed by a second author. Risk of bias (RoB) was assessed using the Cochrane Back Review Group criteria.Results: Eight RCTs were included, one with high RoB. SMT produced a clinically meaningful (≥6⁰) difference in five of these studies compared with inert control, hamstring stretching, and as an adjunct to conventional physiotherapy, but not compared with standard care, as an adjunct to home exercise and advice, or when comparing different SMT techniques. Findings compared to sham were mixed. When reported, effects tentatively lasted up to 6 weeks post-intervention.Conclusion: Limited evidence suggests SMT-improved range of motion and was more effective than some other interventions. Future research, using standardized Neurodynamic tests, should explore technique types and evaluate longer-term effects.Level of Evidence: 1a

Wall-Resolved Large-Eddy Simulations of Transonic Shock-Induced Flow Separation

Wall-resolved implicit large-eddy simulations based on spatial filtering are performed for shock-induced flow separation over an axisymmetric bump at a Mach number of 0.875 and a chord-based Reynolds number of 2.763 million. The incoming boundary layer has a momentum thickness Reynolds number of 6600 at 1.5 chords upstream of the bump. The calculations, which employ up to 24 billion grid points, simulate the experimental model of Bachalo and Johnson (“Transonic, Turbulent Boundary-Layer Separation Generated on an Axisymmetric Flow Model,” AIAA Journal, Vol. 24, No. 3, 1986, pp. 437–443), except that the tunnel walls are ignored and free air is assumed. The effects of domain span and grid resolution are examined along with main flowfield features. The predicted shock position as well as separation and reattachment locations agree well with experiment. Grid convergence is observed in the attached region well upstream of separation. Two-point azimuthal correlations suggest that a span of at least 20 deg is needed in the attached region, whereas a 120 deg span appears insufficient for correlations to completely decay to zero by midspan in the separation/reattachment region. Computed rms surface pressure fluctuations display a sharp primary peak at the shock foot and a broader secondary peak near the reattachment location. Simulations reveal evidence of low-frequency shock unsteadiness; however, a longer statistical sample is needed to investigate this phenomenon.