Passive Leg Raising Research Articles

Unsteady Shock Motion in a Transonic Flow over a Wall-Mounted Hemisphere

Particle image velocimetry measurements have been conducted for a Mach 0.8 flow over a wall-mounted hemisphere with a strongly separated wake. The shock foot was found to typically sit just forward of the apex of the hemisphere and move within a range of about . Conditional averages based upon the shock foot location show that the separation shock is positioned upstream along the hemisphere surface when reverse velocities in the recirculation region are strong and is located downstream when they are weaker. The recirculation region appears smaller when the shock is located farther downstream. No correlation was detected of the incoming boundary layer with the shock position nor with the wake recirculation velocities. These observations are consistent with recent studies concluding that, for large, strong separation regions, the dominant mechanism is the instability of the separated flow rather than a direct influence of the incoming boundary layer.

Phosphorus-bearing molecules in solar-type star-forming regions: first PO detection

As part of the Large Program ASAI (Astrochemical Surveys At IRAM), we have used the IRAM 30m telescope to lead a systematic search for the emission of rotational transitions of P-bearing species between 80 and 350 GHz towards L1157-B1, a shock position in the solar-type star forming region L1157. We report the detection of several transitions of PN and, for the first time, of prebiotic molecule PO. None of these species are detected towards the driving protostar of the outflow L1157-mm. Analysis of the line profiles shows that PN arises from the outflow cavity, where SiO, a strong shock tracer, is produced. Radiative transfer analysis yields an abundance of 2.5e-9 and 0.9e-9 for PO and PN, respectively. These results imply a strong depletion (approx 100) of Phosphorus in the quiescent cloud gas. Shock modelling shows that atomic N plays a major role in the chemistry of PO and PN. The relative abundance of PO and PN brings constraints both on the duration of the pre-shock phase, which has to be about 1 Myr, and on the shock parameters. The maximum temperature in the shock has to be larger than 4000K, which implies a shock velocity of 40 km/s.

Global MHD simulations of Neptune's magnetosphere

AbstractA global magnetohydrodynamic (MHD) simulation has been performed in order to investigate the outer boundaries of Neptune's magnetosphere at the time of Voyager 2's flyby in 1989 and to better understand the dynamics of magnetospheres formed by highly inclined planetary dipoles. Using the MHD code Gorgon, we have implemented a precessing dipole to mimic Neptune's tilted magnetic field and rotation axes. By using the solar wind parameters measured by Voyager 2, the simulation is verified by finding good agreement with Voyager 2 magnetometer observations. Overall, there is a large‐scale reconfiguration of magnetic topology and plasma distribution. During the “pole‐on” magnetospheric configuration, there only exists one tail current sheet, contained between a rarefied lobe region which extends outward from the dayside cusp, and a lobe region attached to the nightside cusp. It is found that the tail current always closes to the magnetopause current system, rather than closing in on itself, as suggested by other models. The bow shock position and shape is found to be dependent on Neptune's daily rotation, with maximum standoff being during the pole‐on case. Reconnection is found on the magnetopause but is highly modulated by the interplanetary magnetic field (IMF) and time of day, turning “off” and “on” when the magnetic shear between the IMF and planetary fields is large enough. The simulation shows that the most likely location for reconnection to occur during Voyager 2's flyby was far from the spacecraft trajectory, which may explain the relative lack of associated signatures in the observations.

Flow Field Analysis on the Stagnation Streamline of a Blunt Body

The hypersonic flow on the stagnation streamline of a blunt body is analyzed with quasi one-dimensional (1-D) Navier-Stokes equations approximated by adopting the local similarity to the two-dimensional (2-D)/axisymmetric Navier-Stokes equations. The governing equations are solved using the implicit finite volume method. The computational domain is confined from the stagnation point to the shock wave, and the shock fitting method is used to find the shock position. We propose a boundary condition at the shock, which employs the shock wave angle in the vicinity of the stagnation streamline using the shock shape correlation. As a result of numerical computation conducted for the hypersonic flow over a sphere, the proposed boundary condition is shown to improve the accuracy of the prediction of the shock standoff distance. The quasi 1-D Navier-Stokes code is efficient in computing time and is reliable for the flow analysis along the stagnation streamline and the prediction of heat flux at the stagnation point in the hypersonic blunt body flow.

Static and Functional Hemodynamic Profiles of Women with Abnormal Uterine Artery Doppler at 22-24 Weeks of Gestation.

ObjectiveTo compare cardiac function, systemic hemodynamics and preload reserve of women with increased (cases) and normal (controls) uterine artery (UtA) pulsatility index (PI) at 22–24 weeks of gestation.Materials and MethodsA prospective cross-sectional study of 620 pregnant women. UtA blood flow velocities were measured using Doppler ultrasonography, and PI was calculated. Mean UtA PI ≥ 1.16 (90th percentile) was considered abnormal. Maternal hemodynamics was investigated at baseline and during passive leg raising (PLR) using impedance cardiography (ICG). Preload reserve was defined as percent increase in stroke volume (SV) 90 seconds after passive leg raising compared to baseline.ResultsMean UtA PI was 1.49 among cases (n = 63) and 0.76 among controls (n = 557) (p < 0.0001). Eighteen (28.6%) cases and 53 (9.5%) controls developed pregnancy complications (p <0.0001). The mean arterial pressure and systemic vascular resistance were 83 mmHg and 1098.89±293.87 dyne s/cm5 among cases and 79 mmHg and 1023.95±213.83 dyne s/cm5 among controls (p = 0.007 and p = 0.012, respectively). Heart rate, SV and cardiac output were not different between the groups. Both cases and controls responded with a small (4–5%) increase in SV in response to PLR, but the cardiac output remained unchanged. The preload reserve was not significantly different between two groups.ConclusionPregnant women with abnormal UtA PI had higher blood pressure and systemic vascular resistance, but similar functional hemodynamic profile at 22–24 weeks compared to controls. Further studies are needed to clarify whether functional hemodynamic assessment using ICG can be useful in predicting pregnancy complications.

Shape and position of Earth’s bow shock near-lunar orbit based on ARTEMIS data

Abstract Earth’s bow shock is the result of interaction between the supersonic solar wind and Earth’s magnetopause. However, data limitations mean the model of the shape and position of the bow shock are based largely on near-Earth satellite data. The model of the bow shock in the distant magnetotail and other factors that affect the bow shock, such as the interplanetary magnetic field (IMF) B y , remain unclear. Here, based on the bow shock crossings of ARTEMIS from January 2011 to January 2015, new coefficients of the tail-flaring angle α of the Chao model (one of the most accurate models currently available) were obtained by fitting data from the middle-distance magnetotail (near-lunar orbit, geocentric distance - 20 R E> X > - 50 R E). In addition, the effects of the IMF B y on the flaring angle α were analyzed. Our results showed that: (1) the new fitting coefficients of the Chao model in the middle-distance magnetotail are more consistent with the observed results; (2) the tail-flaring angle α of the bow shock increases as the absolute value of the IMF B y increases. Moreover, positive IMF B y has a greater effect than negative IMF B y on flaring angle. These results provide a reference for bow shock modeling that includes the IMF B y .

Assessment of fluid responsiveness with end-tidal carbon dioxide using a simplified passive leg raising maneuver: a prospective observational study.

Assessing fluid responsiveness is important in the management of patients with hemodynamic instability. Passive leg raising (PLR) is a validated dynamic method to induce a transient increase in cardiac preload and predict fluid responsiveness. Variations in end-tidal carbon dioxide (ETCO2) obtained by capnography correlate closely with variations in cardiac output when alveolar ventilation and carbon dioxide production are kept constant. In this prospective observational study, we tested the hypothesis that variations in ETCO2induced by a simplified PLR maneuver can track changes in the cardiac index (CI) and thus predict fluid responsiveness. A five-minute standardized PLR maneuver was performed in 90 paralyzed hemodynamically stable cardiac surgical patients receiving mechanical ventilation. Cardiac index was measured by thermodilution before and one minute after PLR. End-tidal CO2measurements using capnography were obtained during the entire PLR maneuver. Fluid responsiveness was defined as a 15% increase in the CI. The Chi square test and Student's t test were used to compare responders and non-responders. Logistic regression analyses were then performed to determine factors of responsiveness. There were no differences between responders and non-responders in demographic and baseline hemodynamic variables. Fluid responsiveness was associated with an ETCO2 variation (ΔETCO2) of ≥ 2 mmHgduring PLR [odds ratio (OR), 7.3; 95% confidence interval (CI), 2.7 to 20.2; P < 0.01; sensitivity 75%]. A low positive predictive value (54%) and a high negative predictive value (NPV) (86%) were observed. No other clinical or hemodynamic predictors were associated with fluid responsiveness. A logistic regression model established that a combination of ΔETCO2 ≥ 2 mmHg and a change in systolic blood pressure ≥ 10 mmHg induced by passive leg raising was predictive of fluid responsiveness (OR, 8.9; 95% CI, 2.5 to 32.2; P = 0.005). Use of a passive leg raising maneuver to induce variation in ETCO2is a noninvasive and useful method to assess fluid responsiveness in paralyzed cardiac surgery patients receiving mechanical ventilation. Given its high NPV, fluid responsiveness is unlikely if a passive leg raising maneuver induces ΔETCO2 of < 2 mmHg.

Intra-examiner reliability of lumbar spine and neuro-dynamic flexibility measurements in an older and overweight healthy asymptomatic population.

Measurement of lumbar spine movement and neuro-dynamic flexibility is fundamental to clinical examination and forms part of most systems or protocols used to classify patients with low back pain. However, the increased age and body mass index reported in the chronic low back pain subgroup, may compromise the reliability of these measurements. Specifically, this relates to greater soft tissue excursion relative to the underlying bony landmarks used for these clinical tests. The objective of this research was to determine the intra-examiner reliability for six lumbar spine and two neuro-dynamic examination tests in older and overweight individuals selected to represent a similar age and body mass index of a chronic low back pain population. Nineteen volunteers (56.00 ± 7.62 years) performed sets of eight lumbar spine examination tests. Five repetitions of each set of tests were conducted with rest periods between sets. One examiner measured lumbar flexion, extension, right and left lateral flexion and rotation using a tape measure. A goniometer was used to measure Slump and Passive Straight Leg Raise (PSLR) test. Intra-class correlation coefficients (ICCintra) were calculated to evaluate the reliability of measurement for each test. The eight tests showed ICC ranges between `Large' and `Nearly Perfect' (0.68-0.99). Measurement of lateral flexion and rotation had the highest reliability and extension the lowest. This study was conducted on an asymptomatic older, overweight population and the ICC results support the suitability of these methods and tools for measurement in a clinical setting for this population demographic. Measurement reliability in the study population was comparable with previous research in populations of contrasting demographics. Accordingly, further investigation specifically in a chronic low back pain population is indicated as the paucity of previous literature for some of the movement tests disallowed comparisons, and the reliability reported in this study may not be directly transferable to a chronic low back pain population.

Osher Flux with Entropy Fix for Two-Dimensional Euler Equations

AbstractWe compare in this paper the properties of Osher flux with O-variant and P-variant (Osher-O flux and Osher-P flux) in finite volume methods for the two-dimensional Euler equations and propose an entropy fix technique to improve their robustness. We consider both first-order and second-order reconstructions. For inviscid hypersonic flow past a circular cylinder, we observe different problems for different schemes: A first-order Osher-O scheme on quadrangular grids yields a carbuncle shock, while a first-order Osher-P scheme results in a dislocation shock for high Mach number cases. In addition, a second-order Osher scheme can also yield a carbuncle shock or be unstable. To improve the robustness of these schemes we propose an entropy fix technique, and then present numerical results to show the effectiveness of the proposed method. In addition, the influence of grid aspects ratio, relative shock position to the grid and Mach number on shock stability are tested. Viscous heating problem and double Mach reflection problem are simulated to test the influence of the entropy fix on contact resolution and boundary layer resolution.

The passive leg raising test to guide fluid removal in critically ill patients.

BackgroundTo investigate whether haemodynamic intolerance to fluid removal during intermittent renal replacement therapy (RRT) in critically ill patients can be predicted by a passive leg raising (PLR) test performed before RRT.MethodsWe included 39 patients where intermittent RRT with weight loss was decided. Intradialytic hypotension was defined as hypotension requiring a therapeutic intervention, as decided by the physicians in charge. Before RRT, the maximal increase in cardiac index (CI, pulse contour analysis) induced by a PLR test was recorded. RRT was then started.ResultsUltrafiltration rate was similar in patients with and without intradialytic hypotension. Thirteen patients presented intradialytic hypotension, while 26 did not. In patients with intradialytic hypotension, it occurred 120 min [interquartile range 60–180 min] after onset of RRT. In the 26 patients without intradialytic hypotension, the PLR test induced no significant change in CI. Conversely, in patients with intradialytic hypotension, PLR significantly increased CI by 15 % [interquartile range 11–36 %]. The PLR-induced increase in CI predicted intradialytic hypotension with an area under the ROC curve of 0.89 (95 % interval confidence 0.75–0.97) (p < 0.05 from 0.50). The best diagnostic threshold was 9 %. The sensitivity was 77 % (95 % confidence interval 46–95 %), the specificity was 96 % (80–100 %), the positive predictive value was 91 % (57–100 %), and the negative predictive value was 89 % (72–98 %). Compared to patients without intolerance to RRT, CI decreased significantly faster in patients with intradialytic hypotension, with a slope difference of −0.17 L/min/m2/h.ConclusionThe presence of preload dependence, as assessed by a positive PLR test before starting RRT with fluid removal, predicts that RRT will induce haemodynamic intolerance.Electronic supplementary materialThe online version of this article (doi:10.1186/s13613-016-0149-1) contains supplementary material, which is available to authorized users.

Large Scale Earth’s Bow Shock with Northern IMF as Simulated by PIC Code in Parallel with MHD Model

In this paper, we propose a 3D kinetic model (Particle-in-Cell PIC ) for the description of the large scale Earth's bow shock. The proposed version is stable and does not require huge or extensive computer resources. Because PIC simulations work with scaled plasma and field parameters, we also propose to validate our code by comparing its results with the available MHD simulations under same scaled Solar wind ( SW ) and ( IMF ) conditions. We report new results from the two models. In both codes the Earth's bow shock position is found to be ~14.8 RE along the Sun-Earth line, and ~ 29 RE on the dusk side. Those findings are consistent with past in situ observations. Both simulations reproduce the theoretical jump conditions at the shock. However, the PIC code density and temperature distributions are inflated and slightly shifted sunward when compared to the MHD results. Kinetic electron motions and reflected ions upstream may cause this sunward shift. Species distributions in the foreshock region are depicted within the transition of the shock (measured ~2 c/{\omega}pi for {\Theta}Bn =90o and MMS =4.7 ) and in the downstream. The size of the foot jump in the magnetic field at the shock is measured to be (1.7 c/{\omega}pi ). In the foreshocked region, the thermal velocity is found equal to 213 km.sec-1 at 15 RE and is equal to 63 km.sec-1at 12 RE (Magnetosheath region). Despite the large cell size of the current version of the PIC code, it is powerful to retain macrostructure of planets magnetospheres in very short time, thus it can be used for a pedagogical test purposes. It is also likely complementary with MHD to deepen our understanding of the large scale magnetosphere

ULF/ELF Atmospheric Radiation in Possible Association to the 2011 Tohoku Earthquake as Observed in China

Recordings of a search-coil magnetometer located in Yongsheng in the Yunnan province of China have been used to find atmospheric ULF/ELF precursors to the 2011 Tohoku earthquake (EQ) with M=9 which occurred on 11 March 2011 with a large epicentral distance of about 4100 km. The combined characteristics of the horizontal magnetic fields, the ratio of tangential and radial field components in the numerator and root mean square of ellipticity in the denominator, were used to detect seismo-related ULF/ELF signals. This value is found to increase before the EQ, and then to decrease during a few weeks, with a reliable maximum on 8 March (3 days before the EQ). We also analyzed azimuth distributions of pulsed radiation in the frequency range 2-5 Hz during the previous week before the main shock. This radiation reached a maximal value on 10 March - one day before the EQ date, and the azimuth of its source is estimated to coincide with the position of the main shock. The results are further compared with the ULF/ELF precursors of the same EQ observed at 3 stations in Japan by Ohta et al. (2013).

The effects of passive leg raising and ultrafiltration stopping on blood pressure in hemodialysis patients.

Hemodialysis-associated hypotension, one of the more serious issues in hemodialysis patients, can be treated by passive leg raising (PLR) and ultrafiltration (UF) stopping. We investigated the effects of PLR and UF stopping on blood pressure in hemodialysis patients. The study was conducted in 76 end-stage renal disease patients. After the second hour of dialysis, systolic and diastolic blood pressure (SBP and DBP) of the patients who did not develop intradialytic hypotension (IDH) were measured in the supine position. Thereafter, PLR was performed by raising the legs 20°; and after 3min, SBP and DBP were measured again. UF was then stopped in the PLR position; SBP and DBP were repeated 3min later. The same procedure was performed during IDH in the patients that developed IDH. A mean 5-mmHg (p<0.05) increase in SBP and a mean 2-mmHg increase in DBP (p<0.05) were observed by PLR in the supine position. UF stopping during PLR increased SBP by a mean of 1mmHg (p<0.05) while no change was observed in DBP (p=ns). IDH occurred in 19 (25%) patients. PLR positioning increases SBP and DBP by a mean of 8mmHg (p<0.05) and 3mmHg (p<0.05), respectively, in the supine position during IDH. During IDH, UF stopping in the PLR position did not significantly increase SBP and DBP in patients as compared to the PLR position. SBP and DBP increase during PLR. UF stopping during PLR does not lead to a higher increase in blood pressure as compared to PLR positioning.

Effects of Ischemic Reperfusion Injury and Remote Conditioning on Passive Leg Raising-Induced Brachial-Artery Dilation

Objectives: Passive leg raising (PLR) has been proposed to assess arterial vasodilator reserve and possibly endothelial function. Since endothelial function is sensitive to ischemic-reperfusion (I-R) injury, we determined the effects of I-R injury and ischemic conditioning on PLR-induced brachial-artery dilation (BAD), i.e. PLR-BAD. Methods: We induced PLR-BAD before and after ipsilateral arm I-R injury (7.5 min of occlusion) in 20 healthy males aged 29 ± 6 years. The protocol was repeated in combination with remote conditioning stimuli (3 × 30 s of contralateral arm occlusions). Results: PLR resulted in significant BAD (3.85%, p < 0.001) before but not after prolonged ischemia (0.25%, p = 0.38). I-R injury, along with either preischemic or postischemic conditioning restored the PLR-BAD response (before: 3.11%, p < 0.001 and after: 3.74%, p < 0.001). Conclusions: I-R injury blunts the BAD induced by PLR. Remote pre- and postconditioning restore this response. These findings are similar to those previously reported using hyperemia and ultrasound to assess BAD.

Comparison of positive end-expiratory pressure–induced increase in central venous pressure and passive leg raising to predict fluid responsiveness in patients with atrial fibrillation

BackgroundPositive end-expiratory pressure (PEEP)–induced increase in central venous pressure (CVP) has been suggested to be a robust indicator of fluid responsiveness, with heart rhythm having minimal influence. We compared the ability of PEEP-induced changes in CVP with passive leg raising (PLR)–induced changes in stroke volume index (SVI) in patients with atrial fibrillation after valvular heart surgery. MethodsIn 43 patients with atrial fibrillation after cardiac surgery, PEEP was increased from 0 to 10 cm H2O for 5 min and changes in CVP were assessed. After returning the PEEP to 0 cm H2O, PLR was performed for 5 min and changes in SVI were recorded. Finally, 300 ml of colloid was infused and haemodynamic variables were assessed 5 min after completion of a fluid challenge. Fluid responsiveness was defined as an increase in SVI ≥10% measured by a pulmonary artery catheter. ResultsFifteen (35%) patients were fluid responders. There was no correlation between PEEP-induced increases in CVP and changes in SVI after a fluid challenge (β coefficient −0.052, P+0.740), whereas changes in SVI during PLR showed a significant correlation (β coefficient 0.713, P<0.001). The area under the receiver operating characteristic curve of the PEEP-induced increase in CVP and changes in SVI during PLR for fluid responsiveness was 0.556 [95% confidence interval (CI) 0.358–0.753, P+0.549) and 0.771 (95% CI 0.619–0.924, P+0.004), respectively. ConclusionsA PEEP-induced increase in CVP did not predict fluid responsiveness in patients with atrial fibrillation after cardiac surgery, but increases in SVI during PLR seem to be a valid predictor of fluid responsiveness in this subset of patients.

Prevalence and risk factors of hypotension associated with preload-dependence during intermittent hemodialysis in critically ill patients.

BackgroundHypotension is a frequent complication of intermittent hemodialysis (IHD) performed in intensive care units (ICUs). Passive leg raising (PLR) combined with continuous measurement of cardiac output is highly reliable to identify preload dependence, and may provide new insights into the mechanisms involved in IHD-related hypotension. The aim of this study was to assess prevalence and risk factors of preload dependence-related hypotension during IHD in the ICU.MethodsA single-center prospective observational study performed on ICU patients undergoing IHD for acute kidney injury and monitored with a PiCCO® device. Primary end points were the prevalence of hypotension (defined as a mean arterial pressure below 65 mm Hg) and hypotension associated with preload dependence. Preload dependence was assessed by the passive leg raising test, and considered present if the systolic ejection volume increased by at least 10 % during the test, as assessed continuously by the PiCCO® device.ResultsForty-seven patients totaling 107 IHD sessions were included. Hypotension was observed in 61 IHD sessions (57 %, CI95%: 47–66 %) and was independently associated with inotrope administration, higher SOFA score, lower time lag between ICU admission and IHD session, and lower MAP at IHD session onset. Hypotension associated with preload dependence was observed in 19 % (CI95%: 10–31 %) of sessions with hypotension, and was associated with mechanical ventilation, lower SAPS II, higher pulmonary vascular permeability index (PVPI) and dialysate sodium concentration at IHD session onset. ROC curve analysis identified PVPI and mechanical ventilation as the only variables with significant diagnostic performance to predict hypotension associated with preload dependence (respective AUC: 0.68 (CI95%: 0.53–0.83) and 0.69 (CI95%: 0.54–0.85). A PVPI ≥ 1.6 at IHD session onset predicted occurrence of hypotension associated with preload dependence during IHD with a sensitivity of 91 % (CI95%: 59–100 %), and a specificity of 53 % (CI95%: 42–63 %).ConclusionsThe majority of hypotensive episodes occurring during intermittent hemodialysis are unrelated to preload dependence and should not necessarily lead to reduction of fluid removal by hemodialysis. However, high PVPI at IHD session onset and mechanical ventilation are risk factors of preload dependence-related hypotension, and should prompt reduction of planned fluid removal during the session, and/or an increase in session duration.Electronic supplementary materialThe online version of this article (doi:10.1186/s13054-016-1227-3) contains supplementary material, which is available to authorized users.

Shock wave bifurcation in convergent–divergent channels of rectangular cross section

This work addresses two- and three-dimensional turbulent flow in simple channels, modeling the air intakes of rectangular cross section. Flow regimes with a supersonic free stream and supersonic velocities at the throat or immediately downstream of the throat are considered. Bifurcations of the shock wave arising ahead of the cowl are studied numerically. Solutions of the Reynolds-averaged Navier–Stokes equations are obtained with a finite-volume solver of second-order accuracy on fine computational meshes. The solutions reveal jumps of the shock leg position with variations of the free-stream Mach number. The dependence of the shock position on the cowl slope and streamwise location of the throat is examined.

Understanding the passive leg raising test.

Understanding the passive leg raising test.

Passive leg raising for predicting fluid responsiveness: a systematic review and meta-analysis

We performed a systematic review and meta-analysis of studies investigating the passive leg raising (PLR)-induced changes in cardiac output (CO) and in arterial pulse pressure (PP) as predictors of fluid responsiveness in adults. MEDLINE, EMBASE and Cochrane Database were screened for relevant original and review articles. The meta-analysis determined the pooled area under the ROC curve, the sensitivity, specificity and threshold for the PLR test when assessed with CO and PP. Twenty-one studies (991 adult patients, 995 fluid challenges) were included. CO was measured by echocardiography in six studies, calibrated pulse contour analysis in six studies, bioreactance in four studies, oesophageal Doppler in three studies, transpulmonary thermodilution or pulmonary artery catheter in one study and suprasternal Doppler in one study. The pooled correlation between the PLR-induced and the fluid-induced changes in CO was 0.76 (0.73-0.80). For the PLR-induced changes in CO, the pooled sensitivity was 0.85 (0.81-0.88) and the pooled specificity was 0.91 (0.88-0.93). The area under the ROC curve was 0.95±0.01. The best threshold was a PLR-induced increase in CO≥10±2%. For the PLR-induced changes in PP (8 studies, 432 fluid challenges), the pooled sensitivity was 0.56 (0.49-0.53), the pooled specificity was 0.83 (0.77-0.88) and the pooled area under the ROC curve was 0.77±0.05. Sensitivity and subgroup analysis were consistent with the primary analysis. PLR-induced changes in CO very reliably predict the response of CO to volume expansion in adults with acute circulatory failure. When PLR effects are assessed by changes in PP, the specificity of the PLR test remains acceptable but its sensitivity is poor.

Assessing Fluid Responsiveness in Spontaneously Breathing Patients.

The primary objective of this study was to test if fasting volunteers exhibit fluid responsiveness using noninvasive hemodynamic measurements. The secondary objective was to test a passive leg raise (PLR) maneuver as a diagnostic predictor of fluid responsiveness. This was a quasi-experimental design involving healthy volunteers. Subjects were excluded for pregnancy and congestive heart failure. Following a 12-hour fast, subjects had baseline hemodynamic monitoring recorded using noninvasive, continuous pulse contour analysis. Subjects then had a PLR maneuver performed, followed by an intravenous bolus of crystalloid. A rise in stroke volume ≥ 10% from baseline with the bolus was considered consistent with fluid responsiveness, and the same rise with a PLR was consistent with a positive PLR maneuver. The primary outcome was the change in stroke volume with a fluid bolus. Univariate analysis assessed changes in hemodynamic parameters. Logistic regression analysis determined the test characteristics of the PLR in predicting subjects who were ultimately fluid responsive. Forty subjects completed the study. The mean change in stroke volume with a crystalloid bolus was 19% (95% confidence interval [CI] = 16% to 21%). Thirty-six (90%) subjects were fluid responsive. The mean PLR response for the overall cohort was 16% (95% CI = 12% to 19%), and 26 (65%) subjects had a positive PLR maneuver. The PLR was 72% sensitive (95% CI = 55% to 85%) and 100% specific (95% CI = 40% to 100%) for predicting the presence of fluid responsiveness. Noninvasive assessment of fluid responsiveness in healthy volunteers and prediction of this response with a PLR maneuver is achievable. Further work is indicated to test these methods in acutely ill patients.