Comparison of three implant systems under preload loss: A finite element analysis validated by digital image correlation methods.

PURPOSE: This study evaluated the effects of screw preload loss on three implant systems, both in silico and in vitro. METHODS: Three finite element analysis (FEA) models of implant restorations were created using bone-level (BL, 4.8×12 mm; BLX, 4.5×12 mm) and tissue-level (TL, 4.8×12 mm) implant systems. The screws in each group were subjected to preloads of 100 N and 200 N, with an additional 130 N load applied to the crown tops. An in vitro study of the principal strain was conducted using digital image correlation (DIC) under the same conditions as for the FEA models. The results were evaluated for von Mises stress, principal strain, and sensitivity index. RESULTS: During loading, the highest stress levels were observed in the implants and screws. In the BL group, the screws experienced the highest von Mises stress at 466.04 MPa and 795.26 MPa in the 100 N and 200 N groups, respectively. The BLX group showed the highest von Mises stress at 439.33 MPa and 780.88 MPa in the implants in the 100 N and 200 N groups. Sensitivity analysis revealed that the screws and abutments in the TL group were significantly more affected by the preload changes. CONCLUSIONS: The abutment in the TL group was particularly sensitive to preload changes compared with those in the BL and BLX groups. Variations in the preload significantly affect the stress distribution in implants and screws. Maintaining screw preload stability under loading is crucial in clinical practice to prevent mechanical failure.

Passive leg raising test versus rapid fluid challenge in critically ill medical patients.

BACKGROUND: The passive leg raising (PLR) test is a simple test to detect preload responsiveness. However, variable fluid doses and infusion times were used in studies evaluating the effect of PLR. Studies showed that the effect of fluid challenge on hemodynamics dissipates in 10 min. This prospective study aimed to compare PLR and a rapid fluid challenge (RFC) with a 300-ml bolus infused within 5 min in adult patients with a hemodynamic compromise. MATERIALS AND METHODS: Critically ill medical patients with signs of systemic hypoperfusion were included if volume expansion was considered. Hemodynamic status was assessed with continuous measurements of cardiac output (CO), when possible, and mean arterial pressure (MAP) at baseline, during PLR, and after RFC. RESULTS: A total of 124 patients with a median age of 65.0 years were included. Their acute physiology and chronic health evaluation (APACHE) II score was 19.7 ± 6.0, with a sequential organ failure assessment (SOFA) score of 9.0 ± 4.4. Sepsis was diagnosed in 73.3%, and 79.8% of the patients were already receiving a norepinephrine infusion. Invasive MAP monitoring was established in all patients, while continuous CO recording was possible in 42 patients (33.9%). Based on CO changes, compared with those with RFC, the false positive and false negative rates with PLR were 21.7 and 36.8%, respectively, with positive and negative predictive values of 70.6 and 72.0%, respectively. Based on MAP changes, compared with those with RFC, the false positive and false negative rates with PLR compared to RFC were 38.2% and 43.3%, respectively, with positive and negative predictive values of 64.4 and 54.0%, respectively. CONCLUSION: This study demonstrated a moderate agreement between PLR and RFC in hemodynamically compromised medical patients, which should be considered when testing preload responsiveness.

Increased preload and echocardiographic assessment of diastolic function.

AIMS: Echocardiographic diastolic parameters are used to diagnose and monitor increased left ventricular filling pressure (LVFP) and we hypothesized that increased loading conditions cause increased E/e'. Our aim was to assess the effect of preload augmentation on diastolic parameters among both healthy subjects and subjects with known cardiac disease. METHODS AND RESULTS: We included 129 subjects merged from two cohorts; one dialysis cohort (n = 47) and one infusion cohort (n = 82). Echocardiography was performed immediately before and after hemodialysis (HD) or saline infusion, under low and high loading conditions. Elevated LVFP was defined as septal E/e' ≥ 15 and/or lateral E/e' ≥ 13 at high-loading conditions. The population was divided according to elevated LVFP (n = 31) and normal LVFP (n = 98). The load difference for the population was 972 ± 460 mL, with no differences in load difference between elevated and normal LVFP (p NS). The subjects with elevated LVFP were older (63 ± 11 vs. 46 ± 16 years, p < .001), and had lower LV ejection fraction (50 ± 14 vs. 59 ± 8.1%, p < .01). After augmented preload, EDV increased in the normal LVFP group (p < .01) but remained unchanged in the elevated LVFP group (p NS). Both E and e' increased among the subjects with normal LVFP, whereas E/e' remained unchanged (∆E/e' +.1 [-.5-1.2]), p NS). Among the subjects with elevated, LVFP we observed increased E but not e', resulting in significantly increased E/e' (∆ average E/e' +2.4 [0-4.0], p < .01). CONCLUSION: Augmented preload does not seem to affect E/e' among subjects with normal LVFP, whereas E/e' seems to increase significantly among subjects with elevated LVFP.

[Functional hemodynamic monitoring]. / Funktionelles hämodynamisches Monitoring.

BACKGROUND: Critically ill patients in the intensive care unit require intensified monitoring to control the treatment with volume and/or vasoactive substances. RESEARCH QUESTION: What role does functional hemodynamic monitoring play in controlling treatment and what techniques are used to manage this? MATERIAL AND METHODS: Review of the current literature. RESULTS AND DISCUSSION: Precise knowledge of the physiology of the cardiovascular system as well as the pathophysiology of individual clinical pictures and the possibilities of invasive and noninvasive monitoring are the prerequisites for the indications, implementation and interpretation of functional hemodynamic monitoring. An understanding of the heart-lung interaction and the influence of invasive ventilation on the volumetric target parameters, such as stroke volume variation, systolic pressure variation and pulse pressure variation as well as sonography of the inferior vena cava are indispensable prerequisites for the question of volume responsiveness. Other maneuvers, such as the passive leg raising test, can be very helpful when deciding on volume administration in everyday clinical practice. Static parameters such as central venous pressure generally play no role and if any only a subordinate one.

Effects of submersion on VO2: comparing maximum aerobic exertion on land and underwater.

Introduction: Submersion results in blood redistribution into the pulmonary circulation, causing changes in pulmonary compliance and increased cardiac preload. Few studies have compared incremental exercise to exhaustion (VO2 max testing) in a dry environment with exercise underwater. We hypothesized that the physiological effects of submersion would result in lower heart rate (HR), minute ventilation (VE), and peak oxygen uptake (VO2 peak) compared with dry conditions. Methods: Fourteen male and four female volunteers completed two VO2 peak testing sessions with approximately two hours between trials: first in the dry laboratory on a cycle ergometer and second while fully submersed in a prone position with zero static lung load. HR was monitored via ECG, and inspiratory and expiratory gas compositions were recorded using a metabolic cart. The tests were terminated once the subject reached exhaustion. Results: Absolute VO2 peak was lower in the submersed VO2 max trial (37.1 ± 7.0 mL•kg-1•min-1) compared with dry exercise (45.8 ± 8.9 mL•kg-1•min-1) p < 0.001. HR and VE were also lower in the submersed trial. Conclusions: VO2 peak while submersed is reduced relative to dry VO2 peak, which may be partly due to a decrease in heart rate and a reduction in VE.

Seismocardiography and echocardiography: the correlation in the systolic complex.

Aim. This study aimed to investigate the correlation between seismocardiographic and echocardiographic systolic variables and whether a decrease in preload could be detected by the seismocardiography (SCG).Methods. This study included a total of 34 subjects. SCG and electrocardiography were recorded simultaneously followed by echocardiography (echo) in both supine and 30◦head-up tilted position. The SCG signals was segmented into individual heartbeats and systolic fiducial points were defined using a detection algorithm. Statistical analysis included correlation coefficient calculations and paired sample tests.Results. SCG was able to measure a decrease in preload by almost all of the examined systolic SCG variables. It was possible to correlate certain echo variables to SCG time intervals, amplitudes, and peak to peak intervals. Also, changes between supineand tilted position of some SCG variables were possible to correlate to changes in echo variables. LVET, IVCT, S', strain, SR, SV, and LVEF were significantly correlated to relevant SCG variables.Conclusion. This study showed a moderate correlation, between systolic echo and systolic SCG variables. Additionally, systolic SCG variables were able to detect a decrease in preload.

The effects of bolus isosorbide dinitrate on pulmonary hypertension with cardiopulmonary comorbidities.

Lowering mean pulmonary arterial pressure (mPAP) without reducing cardiac output is essential in treating pulmonary hypertension (PH). Isosorbide dinitrate (ISDN) potentially achieves this in post-capillary PH but can decrease cardiac output and blood pressure (BP), especially in pre-capillary PH. However, post-capillary PH and pre-capillary PH can overlap, and their clear discrimination is difficult. The aim of the study was to examine to what extent bolus ISDN injection reduces mPAP and BP, and changes mixed venous oxygen saturation (SvO2), an indicator of cardiac output in PH with various cardiopulmonary comorbidities in the context of treatment modifications. We retrospectively examined the hemodynamic effects of bolus ISDN injection in patients with PH who underwent right heart catheterization and their subsequent treatment modification. Our sample comprised 13 PH patients. In seven with pre-capillary PH, ISDN significantly lowered mPAP from the median 34 (interquartile range 32-39) to 28 (28-30) mmHg and the mean BP (mBP) from 90 (79-92) to 72 (68-87) mmHg. In six with post-capillary PH, ISDN lowered mPAP from 40 (29-44) to 27 (23-31) mmHg and mBP from 91 (87-110) to 87 (82-104) mmHg. There was a significant decrease in SvO2 from 69.8% (64.9%-78.1%) to 63.9% (60.5%-71.5%) in pre-capillary PH, but not in post-capillary PH including combined post- and pre-capillary PH and some patients showed a large increase in SvO2. In all patients showing an SvO2 increase, diuretics or hemodialysis were up-titrated or continued. Bolus ISDN injection lowered mPAP. However, in pre-capillary PH, it caused a significant decrease in SvO2 and a notable reduction in blood pressure. In post-capillary PH, including combined post- and pre-capillary PH, it clarified whether systemic preload and afterload reduction increased or decreased SvO2 in each patient, which may aid in treatment modification.

Myocardial strain is regulated by cardiac preload in the early stage of sepsis.

BACKGROUND: Owing to a lack of data, this study aimed to explore the effect of cardiac preload on myocardial strain in patients with sepsis. METHODS: A total of 70 patients with sepsis in intensive care unit (ICU) of a tertiary teaching hospital in China from January 2018 to July 2019 and underwent transthoracic echocardiography were enrolled. Echocardiographic data were recorded at ICU admission and 24 h later. Patients were assigned to low left ventricular end-diastolic volume index (LVEDVI) and normal LVEDVI groups. We assessed the impact of preload on myocardial strain between the groups and analyzed the correlation of echocardiographic parameters under different preload conditions. RESULTS: Thirty-seven patients (53%) had a low LVEDVI and 33 (47%) a normal LVEDVI. Those in the low LVEDVI group had a faster heart rate (121.7 vs. 95.3, p < 0.001) and required a greater degree of fluid infusion (3.67 L vs. 2.62 L, P = 0.019). The left ventricular global strain (LVGLS) (-8.60% vs. -10.80%, p = 0.001), left ventricular global circumferential strain (LVGCS) (-13.83% vs. -18.26%, p = 0.006), and right ventricular global longitudinal strain (RVGLS) (-6.9% vs. -10.60%, p = 0.001) showed significant improvements in the low LVEDVI group after fluid resuscitation. However, fluid resuscitation resulted in a significantly increased cardiac afterload value (1172.00 vs. 1487.00, p = 0.009) only in the normal LVEDVI group. Multivariate backward linear regression showed that LVEDVI changes were independently associated with myocardial strain-related improvements during fluid resuscitation. The baseline LVEDVI was significantly negatively correlated with the LVGLS and RVGLS (r = -0.44 and - 0.39, respectively) but not LVGCS. LVEDVI increases during fluid resuscitation were associated with improvements in the myocardial strain degree. CONCLUSIONS: Myocardial strain alterations were significantly influenced by the cardiac preload during fluid resuscitation in sepsis.

Comparison of Pressure vs Volume Overload Ventricular Wall Stress in Patients With Valvular Heart Disease.

BACKGROUND: Aortic stenosis (AS) and mitral regurgitation (MR) result in different patterns of left ventricular remodeling and hypertrophy. OBJECTIVES: We characterized left ventricular wall stress (LVWS) profiles in pressure and volume-overloaded systems, examined the relationship between baseline LVWS and cardiac remodeling, and assessed the acute effects of valve intervention on LVWS using invasive pressures combined with cardiac magnetic resonance (CMR) imaging measures of left ventricular volumes/mass. METHODS: A total of 47 patients with severe AS undergoing transcatheter aortic valve replacement (TAVR) and 15 patients with severe MR undergoing MitraClip (MC) underwent a 6-minute walk test (6MWT), transthoracic echocardiogram, and CMR before their procedures. Catheters in the left ventricle were used to record hemodynamic changes before and after valve/clip deployment. This was integrated with CMR data to calculate LVWS before and after intervention. RESULTS: The TAVR group demonstrated significant reductions in systolic LVWS post procedure (median 24.7 Pa [IQR: 14 Pa] pre vs median 17.3 Pa [IQR: 12 Pa] post; P < 0.001). The MC group demonstrated significant reductions in diastolic LVWS (median 6.4 Pa [IQR: 5 Pa] pre vs median 4.3 Pa [IQR: 4.1 Pa] post; P = 0.021) with no significant change in systolic LVWS (30.6 ±1.61 pre vs 33 ±2.47 Pa post; P = 0.16). There was an inverse correlation between baseline systolic LVWS and 6MWT in the TAVR group (r = -0.31; P = 0.04). CONCLUSIONS: TAVR results in significant reductions in systolic LVWS acutely. MC results in significant reductions in diastolic LVWS. Higher baseline systolic LVWS in TAVR is associated with shorter 6MWT suggesting that in AS, LVWS may be a useful marker of early decompensation.

Preload responsiveness-guided fluid removal in mechanically ventilated patients with fluid overload: A comprehensive clinical-physiological study.

This study investigated fluid removal strategies for critically ill patients with fluid overload on mechanical ventilation. Traditionally, a negative fluid balance (FB) is aimed for. However, this approach can have drawbacks. Here, we compared a new approach, namely removing fluids until patients become fluid responsive (FR) to the traditional empiric negative balance approach. Twelve patients were placed in each group (n = 24). FR assessment was performed using passive leg raising (PLR). Both groups maintained stable blood pressure and heart function during fluid management. Notably, the FR group weaned from the ventilator significantly faster than negative FB group (both for a spontaneous breathing trial (14 h vs. 36 h, p = 0.031) and extubation (26 h vs. 57 h, p = 0.007); the difference in total ventilator time wasn't statistically significant (49 h vs. 62 h, p = 0.065). Additionally, FR group avoided metabolic problems like secondary alkalosis and potential hypokalemia seen in the negative FB group. FR-guided fluid-removal in fluid overloaded mechanically ventilated patients was a feasible, safe, and maybe superior strategy in facilitating weaning and disconnection from mechanical ventilation than negative FB-driven fluid removal. FR is a safe endpoint for optimizing cardiac function and preventing adverse consequences during fluid removal.

Plasma catecholamines in patients undergoing invasive cardiopulmonary exercise test for exercise intolerance.

BACKGROUND: Invasive cardiopulmonary exercise testing (iCPET) combines traditional cardiopulmonary exercise testing with invasive hemodynamic measurements to assess exercise intolerance, which can be caused by preload insufficiency (PI), characterized by low ventricular filling pressures and reduced cardiac output during exertion. We hypothesize that plasma catecholamine levels at rest and during exercise correlate with hemodynamic parameters in PI. METHODS: We included adult patients who underwent iCPET for exercise intolerance and had plasma catecholamines measured at rest and peak exercise. RESULTS: Among 84 patients, PI was identified in 57 (67.8 %). Compared to patients without PI, those with PI were younger [median (IQR) 37 (28, 46) vs 47 (39,55) years, p = 0.005] and had lower workload at peak exercise [81 (66, 96) vs 95 (83.5, 110.50) Watts, p = 0.006]. Patients with PI had higher heart rates at rest and peak exercise [87 (78, 97) vs 79 (74, 87) bpm, p = 0.04; and 167 (154, 183) vs 156 (136, 168) bpm, p = 0.01, respectively]. In all patients, epinephrine and norepinephrine at peak exercise directly correlated with peak workload (r:0.41, p < 0.001 and r:0.47, p < 0.001, respectively). Resting epinephrine was higher in patients with PI [136 (60, 210) vs 77 (41, 110) pg/mL, p = 0.02]. There was no significant difference in the change in catecholamines from rest to peak exercise between patients with or without PI. CONCLUSION: PI patients exhibited elevated heart rate and epinephrine at rest, indicating increased sympathetic activity. We did not find strong associations between catecholamines and cardiac filling pressures, suggesting that catecholamine levels are predominantly influenced by peak workload.

Preload Influence on the Dynamic Properties of a Polyurethane Elastomeric Foam.

Polymeric foams are widely used in engineering applications for vibration attenuation. The foams usually work preloaded and it is known that the dynamic properties and attenuation ability of these polymers depend on the preload. In this paper, experimental characterization of a polyurethane elastomeric foam is performed in a frequency range between 1 and 60 Hz, a temperature range between -60 and 30 °C and a preload range between 2 and 12 N, using a Dynamic Mechanical Analyzer. When going from the minimum to the maximum preload, results show the linear viscoelastic range increases 57%. In the frequency sweeps, the storage modulus increases 58% on average, while the loss factor remains unaffected by preload. Moreover, the glassy transition temperature of the material decreases for greater preloads. From the curve-fitting of a four-parameter fractional derivative model using the experimental data, a seven-parameter mathematical model is developed, reducing the number of parameters needed to describe the influence of frequency and preload on the dynamic properties of the material. Hence, it has been established that the relaxation time, relaxed modulus and unrelaxed modulus depend on the exponential of the squared prestress. In contrast, the fractional parameter does not depend on preload for the range under study.

Bias, trending ability and diagnostic performance of a non-calibrated multi-beat analysis continuous cardiac output monitor to identify fluid responsiveness in critically ill patients.

Objective: To evaluate the accuracy of non-calibrated multi-beat analysis continuous cardiac output (CCOMBA), against calibrated pulse-contour analysis continuous cardiac output (CCOPCA) during a passive leg raise (PLR) and/or a fluid challenge (FC). Design: Observational, single-centre, prospective study. Setting: Tertiary academic medical intensive care unit, Lyon, France. Participants: Adult patients receiving norepinephrine, monitored by CCOPCA, and in which a PLR and/or a FC was indicated. Main outcome measures: CCOMBA and CCOPCA were recorded prior to and during the PLR/FC to evaluate bias and evaluate changes in CCOMBA and CCOPCA (∆%CCOMBA and ∆%CCOPCA). Fluid responsiveness was identified by an increase >15% in calibrated cardiac output after FC, to identify the optimal ∆%CCOMBA threshold during PLR to predict fluid responsiveness. Results: 29 patients (median age 68 [IQR: 57-74]) performed 28 PLR and 16 FC. The bias between methods increased with higher CCOPCA values, with a percentage error of 64% (95%confidence interval: 52%-77%). ∆%CCOMBA adequately tracked changes in ∆%CCOPCA with an angular bias of 2 ± 29°. ∆%CCOMBA during PLR had an AUROC of 0.92 (P < 0.05), with an optimal threshold >14% to predict fluid responsiveness (sensitivity: 0.99, specificity: 0.87). Conclusions: CCOMBA showed a non-constant bias and a percentage error >30% against calibrated CCOPCA, but an adequate ability to track changes in CCOPCA and to predict fluid responsiveness.

PMUT-Based System for Continuous Monitoring of Bolted Joints Preload.

In this paper, we present a bolt preload monitoring system, including the system architecture and algorithms. We show how Finite Element Method (FEM) simulations aided the design and how we processed signals to achieve experimental validation. The preload is measured using a Piezoelectric Micromachined Ultrasonic Transducer (PMUT) in pulse-echo mode, by detecting the Change in Time-of-Flight (CTOF) of the acoustic wave generated by the PMUT, between no-load and load conditions. We performed FEM simulations to analyze the wave propagation inside the bolt and understand the effect of different configurations and parameters, such as transducer bandwidth, transducer position (head/tip), presence or absence of threads, as well as the frequency of the acoustic waves. In order to couple the PMUT to the bolt, a novel assembly process involving the deposition of an elastomeric acoustic impedance matching layer was developed. We achieved, for the first time with PMUTs, an experimental measure of bolt preload from the CTOF, with a good signal-to-noise ratio. Due to its low cost and small size, this system has great potential for use in the field for continuous monitoring throughout the operative life of the bolt.

Comparison of Left Ventricular End-Diastolic Volume Approximated from Mean Blood Pressure and Stroke Volume and End-Diastolic Volume Calculated from Left Ventricular-Aortic Coupling.

Objectives: The purpose of this study was to compare left ventricular end-diastolic volume (EDV), derived from left ventricular arterial coupling (Ees/Ea), and mean arterial blood pressure. Both of these methods of measuring EDV require some invasive procedure. However, the method of measuring EDV approximate is less invasive than the EDV coupling measuring method. This is because EDV approximate only requires arterial pressure waveform as an invasive procedure. Methods: This study included 14 patients with normal cardiac function who underwent general anesthesia. The point when blood pressure stabilized after the induction of anesthesia was taken as a baseline according to the study protocol. At the point when systolic arterial blood pressure fell 10% or more from the baseline blood pressure, 300 mL of colloid solution was administered over 15 min. EDV approximate and EDV coupling were calculated for each of the 14 patients at three points during the course of anesthetic. Each value was obtained by calculating a 5 min average. The timing of these three points was 5 min before, 5 min during, and 5 min after infusion loading. Results: The total number of comparable points was 42; 3 points were taken from each of the 14 participants. Both EDV approximate and EDV coupling increased through the infusion load testing. Scatter plots were prepared, and regression lines were calculated from the obtained values. A high correlation was shown between EDV approximate and EDV coupling (R2 = 0.96, p < 0.05). Conclusions: In patients with good cardiac function, EDV approximate can be substituted for EDV coupling, suggesting the possibility that EDV can be continuously and less invasively calculated under the situation of general anesthesia.

Vasoconstriction with phenylephrine increases cardiac output in preload dependent patients.

General Anaesthesia (GA) is accompanied by a marked decrease in sympathetic outflow and thus loss of vasomotor control of cardiac preload. The use of vasoconstriction during GA has mainly focused on maintaining blood pressure. Phenylephrine (PE) is a pure α1-agonist without inotropic effects widely used to correct intraoperative hypotension. The potential of PE for augmenting cardiac stroke volume (SV) and -output (CO) by venous recruitment is controversial and no human studies have explored the effects of PE in preload dependent circulation using indicator dilution technique. We hypothesized that PE-infusion in patients with cardiac stroke volume limited by reduced preload would restore preload and thus augment SV and CO. 20 patients undergoing GA for gastrointestinal surgery were monitored with arterial catheter and LiDCO unity monitor. Upon stable haemodynamics after induction patients were placed in head-up tilt (HUT). All patients became preload responsive as verified by a stroke volume variation (SVV) of > 12%. PE-infusion was then started at 15-20mikrg/min and adjusted until preload was restored (SVV < 12%). Li-dilution cardiac output (CO) was initially measured after induction (baseline), again with HUT in the preload responsive phase, and finally when preload was restored with infusion of PE.At baseline SVV was 10 ± 3% (mean ± st.dev.), CI was 2,6 ± 0,4 L/min*m2, and SVI 43 ± 7mL/m2. With HUT SVV was 19 ± 4%, CI was 2,2 ± 0,4 L/min*m2, SVI 35 ± 7mL/m2. During PE-infusion SVV was reduced to 6 ± 3%, CI increased to 2,6 ± 0,5 L/min*m2, and SVI increased to 49 ± 11mL/m2. All differences p < 0,001. In conclusion: Infusion of phenylephrine during preload dependency increased venous return abolishing preload dependency as evaluated by SVV and increased cardiac stroke volume and -output as measured by indicator-dilution technique. (ClinicalTrials.gov NCT05193097).

The Effect of Positive End-Expiratory Pressure on Pulmonary Vascular Resistance Depends on Lung Recruitability in Patients with Acute Respiratory Distress Syndrome.

Rationale: A U-shaped relationship should exist between lung volume and pulmonary vascular resistance (PVR), with minimal PVR at FRC. Thus, positive end-expiratory pressure (PEEP) in patients with acute respiratory distress syndrome (ARDS) should increase PVR if it induces significant lung distension compared with recruitment. However, this has never been proved in patients. Objectives: To study the effects of PEEP on PVR according to lung recruitability, evaluated by the recruitment-to-inflation (R/I) ratio. Methods: In patients with ARDS, we measured hemodynamic (pulmonary artery catheter), echocardiographic, and ventilatory variables (including esophageal pressure) at both low PEEP and higher PEEP by 10 cm H2O. Preload responsiveness was assessed by the passive leg-raising test at high PEEP. Measurements and Main Results: We enrolled 23 patients, including 10 low recruiters (R/I <0.5) and 13 high recruiters (R/I ⩾0.5). Raising PEEP from 4 (2-5) to 14 (12-15) cm H2O increased PVR in low recruiters (from 160 [120-297] to 243 [166-380] dyn·s/cm5; P < 0.01), whereas PVR was unchanged in high recruiters (from 224 [185-289] to 235 [168-300] dyn·s/cm5; P = 0.55). Right-to-left ventricular end-diastolic area ratio simultaneously increased in low recruiters (from 0.54 [0.50-0.59] to 0.64 [0.56-0.70]; P < 0.01) while remaining stable in high recruiters (from 0.70 [0.65-0.79] to 0.68 [0.58-0.80]; P = 0.48). Raising PEEP decreased cardiac index only in preload responsive patients. Conclusions: PEEP increases PVR only when it induces significant lung distension compared with recruitment according to the R/I ratio. Tailoring PEEP on this recruitability index should mitigate its hemodynamic effects.

Differential Cardiac Responses after Passive Leg Raising.

This study retrospectively examined the hemodynamic effects of passive leg raising (PLR) in mechanically ventilated patients during fluid removal before spontaneous breathing trials. In previous studies, we noticed varying cardiac responses after PLR completion, particularly in positive tests. Using a bioreactance monitor, we recorded and analyzed hemodynamic parameters, including stroke volume and cardiac index (CI), before and after PLR in post-acute ICU patients. We included 27 patients who underwent 60 PLR procedures. In preload-unresponsive patients, no significant CI changes were observed (CI_t-6 = 3.7 [2.6; 4.7] mL/min/m2 vs. CI_t9 = 3.3 [2.5; 3.4] mL/min/m2; p = 0.306), while in preload-responsive patients, two distinct CI response types to PLR were identified: a transient peak with immediate return to baseline (CI_t-6 = 2.7 [2.5; 3.1] mL/min/m2 vs. 3.3 [2.6; 3.8] L/min/m2; p = 0.119) and a sustained CI elevation lasting beyond the PLR maneuver (CI_t-6 = 2.8 [2.3; 2.9] L/min/m2 vs. 3.3 [2.8; 3.9] ml/min/m2; p = 0.034). The latter was particularly noted when ΔCI during PLR exceeded 25%. Our findings suggest that in certain preload-responsive patients, PLR can induce a more sustained increase in CI, indicating a possible persistent hemodynamic effect. This effect could be due to a combination of autotransfusion and sympathetic activation affecting venous return and vascular tone. Further research in larger cohorts and more comprehensive hemodynamic assessments are warranted to validate these observations and elucidate the possible underlying mechanisms.The Fluid unLoading On Weaning (FLOW) study was prospectively registered under the ID NCT04496583 on 2020-07-29 at ClinicalTrials.gov.