Fluid Volume Estimation by Bioimpedance: Methodological Caveats and Clinical Interpretation.

Measurement of whole body bioimpedance provides a non-invasive and practical approach to estimate extracellular volume (ECV) in man. However, recent data indicate that ECV cannot be treated as a homogeneous compartment without obtaining paradoxical results. Therefore, bioimpedance measurements should include measurements of body segments such as the arm, the trunk, and the leg. A digital switch was developed and used to consecutively select different body segments for the continuous measurement of whole body and segmental bioimpedance at a minimum sampling period of 3 seconds. Bioimpedance data were modeled to determine the resistance of the ECV in the segments and in the whole body for a period of 30 minutes where subjects were in supine body position followed by a 30 minute standing phase. During supine body position modeled extracellular resistance increased in the leg, the arm, and in the whole body but slightly increased in the trunk. Changes in extracellular resistance reversed with subjects assuming a standing position. These measurements reflect the shifts in ECV between segments to be expected with changes in body position. Simultaneous measurement of bioimpedance in different body segments utilizing this approach might be useful to analyze the nature of fluid shifts in clinical applications such as hemodialysis and ultrafiltration.

Observational studies have found associations between urinary sodium (UNa) with obesity, body shape and composition; but the findings may be biased by residual confounding. The objective of this two-sample Mendelian randomization (MR) study was to analyze their causal associations in both sex-combined and sex-specific models. Genome-wide association studies of UNa, body mass index (BMI), BMI-adjusted waist-to-hip ratio (WHR), body fat (BF) percentage and estimated glomerular filtration rate (eGFR) were identified. We initially extracted fifty SNPs associated with UNa at significance level of 5 × 10–8, but further removed those SNPs with potential horizontal pleiotropy. Univariable and multivariable MR with adjustment for eGFR were performed. Inverse-variance weighted MR was performed as the primary analysis, with MR-Egger methods as sensitivity analysis. The potential bidirectional association between BMI and UNa was investigated. All exposure and outcomes were continuous, and the effect measure was regression coefficients (beta) and their 95% confidence intervals (95% CI). The total sample size was up to 322 154. UNa was causally associated with increased BMI in both men [eGFR-adjusted beta 0.443 (0.163–0.724)] and women [0.594 (0.333–0.855)]. UNa caused BF percentage increase in men [0.622 (0.268–0.976)] and women [0.334 (0.007–0.662)]. UNa significantly elevated BMI-adjusted WHR in men [0.321 (0.094–0.548)], but not in women [0.170 (− 0.052 to 0.391)]. Additionally, we found that BMI causally increased UNa [0.043 (0.023–0.063)]. UNa increased BMI and BF percentage. Salt intake affects male body shape by increasing BMI-adjusted WHR, but showed no effects on female body shape. The bidirectional association between BMI and UNa suggested that salt reduction measures and weight reduction measures should be implemented simultaneously to break the vicious cycle and gain more health benefits.

Ingestions constitute a common problem in pediatric emergency medicine. Management decisions are frequently based on parental assessments of the amount of the ingested material. The purpose of this study was to examine the accuracy of parental estimates of fluid volumes. One hundred parents of children seen in an outpatient clinic and emergency department were asked to estimate fluid volumes in four containers. There were no significant differences (P greater than 0.05) in the accuracy of fluid volume assessment between younger and older parents, between participants with and without high school education, or between parents with one or more children. While most parents are accurate in their fluid volume estimates, 14.5% of the assessments were overestimates of over 300% of the actual volume. In view of our findings, caution should be used when management decisions are being based on parental fluid volume estimates.

Segmental eight-point bioimpedance has been increasingly used in practice. However, whether changes in bioimpedance analysis components before and after hemodialysis (HD) using this technique in a standing position is comparable to traditional whole-body wrist-to-ankle method is still unclear. We aimed to investigate the differences between two eight-point devices (InBody 770 and Seca mBCA 514) and one wrist-to-ankle (Hydra 4200) in HD patients and healthy subjects in a standing position. Thirteen HD patients were studied pre- and post-HD, and 12 healthy subjects once. Four measurements were performed in the following order: InBody; Seca; Hydra; and InBody again. Electrical equivalent models by each bioimpedance method and the fluid volume estimates by each device were also compared. Overall, total body water (TBW) was not different between the three devices, but InBody showed lower extracellular water (ECW) and higher intracellular water (ICW) compared to the other two devices. When intradialytic weight loss was used as a surrogate for changes in ECW (∆ECW) and changes in TBW (∆TBW), ∆ECW was underestimated by Hydra (-0.79 ± 0.89 L, p < 0.01), InBody (-1.44 ± 0.65 L, p < 0.0001), and Seca (-0.32 ± 1.34, n.s.). ∆TBW was underestimated by Hydra (-1.14 ± 2.81 L, n.s.) and InBody (-0.52 ± 0.85 L, p < 0.05) but overestimated by Seca (+0.93 ± 3.55 L, n.s.). Although segmental eight-point bioimpedance techniques provided comparable TBW measurements not affected by standing over a period of 10-15 min, the ECW/TBW ratio appeared to be significantly lower in InBody compared with Seca and Hydra. Results from our study showed lack of agreement between different bioimpedance devices; direct comparison of ECW, ICW, and ECW/TBW between different devices should be avoided and clinicians should use the same device to track the fluid status in their HD population in a longitudinal direction.

ObjectivesTo evaluate the reliability of physician gestalt estimation of pelvic free fluid volume on pediatric Focused Assessment with Sonography for Trauma (FAST). To determine a reliable cut‐off volume and characteristics associated with small pelvic free fluid.MethodsOur study assessed the ability of 2 ultrasound‐trained pediatric emergency medicine (PEM) physicians and 2 pediatric radiologists to characterize pelvic free fluid in a retrospective convenience sample of archived FAST from a Level 1 pediatric trauma center, April 2018–June 2020. Inter‐ and intra‐rater reliability were measured to determine the most reliable volume cut‐off. Chi‐squared and Fisher's exact tests determined characteristics associated with physiologic fluid and fluid volume.ResultsEighty‐one (10.2%) of 797 FAST had pelvic fluid and met inclusion criteria. Volume estimates using none/trace/small versus moderate/large classifications were moderately reliable by the PEM physicians (κ = 0.65 [95% CI, 0.63–0.66]; raw agreement = 92%) and radiologists (κ = 0.48 [95% CI, 0.47–0.49]; raw agreement = 91%). This volume cut‐off demonstrated higher reliability for both groups and greater agreement for PEM physicians than none/trace versus small/moderate/large. Girls (P = .005), isoechoic (P = .045), and location posterior to bladder (P < .001) were associated with physiologic fluid and hyperechoic (P = .019) with non‐physiologic fluid. Hyperechoic (P < .001), anterior (P < .001), lateral (P = .04), or “other” location (P < .001) relative to the bladder were associated with moderate/large volume.ConclusionsUltrasound‐trained PEM physicians and pediatric radiologists can reliably use gestalt estimation to distinguish moderate or large fluid from smaller pelvic fluid volumes on pediatric FAST.

Multi-frequency bioelectrical impedance analysis (MFBIA) is becoming more widely used to assess hydration status and body composition in haemodialysis patients. Most centres only measure MFBIA pre dialysis when patients are overhydrated. We wished to determine whether body composition assessments change post dialysis following fluid removal. Lean body and fat mass were measured by MFBIA pre and post haemodialysis in 676 stable outpatients. Weight fell post dialysis from 72.9 ± 17.8 to 70.9 ± 19.9 kg, P<0.001, soft lean mass from 48.2 ± 12.1 to 45.4 ± 11.0 kg and fat-free mass from 51.8 ± 19.2 to 48.1 ± 11.8 kg, P<0.001, whereas percentage body fat (PBF) increased from 28.8 ± 11.9 to 30.8 ± 12.1% post dialysis, P<0.001, with a mean increase post dialysis of 2.0% (95% confidence limits 1.55 to 2.45). There were correlations between the fall in total body water and extracellular water and skeletal muscle mass (r=0.826, P<0.001 and r=0.711, P<0.001, respectively), and negative correlation between the fall in total body water and ICW and the increase in PBF (r=-0.72, P<0.001, and -0.72, P<0.001, respectively). The relative changes were greater for the arms compared with the legs. Although more convenient for both patients and staff to undertake bioimpedance measurements pre dialysis, overhydration over estimates muscle mass and under estimates fat. For more reliable and reproducible assessments of nutritional status, we suggest that bioimpedance measurements of body composition should be made when patients are closer to their target weight than when overhydrated.

Introduction: Metabolic acidosis is a common problem in patients with Chronic Kidney Disease (CKD) and those on maintenance haemodialysis. In resource-poor countries, financial constraints adversely affect the frequency of dialysis and compliance with medication. This leads to a worsening clinical condition for patients and an increased need for inhospital care, often requiring intensive care, which further drives up treatment costs. Metabolic acidosis also has implications for bone and muscle health. Aim: To assess the changes in body composition (fat percentage and lean body mass), changes in third space fluid, biochemical parameters, the number of admissions and the requirement for blood transfusions before and after the correction of metabolic acidosis. Materials and Methods: This was a prospective, interventional study conducted in a tertiary care centre, Western India, in which 40 patients on maintenance haemodialysis were included. Bioelectrical Impedance Analysis (BIA) and biochemical parameters (Complete Blood Counts (CBC), renal function tests, serum calcium and phosphorus, liver function tests and blood gas analysis) were conducted at baseline before starting bicarbonate supplementation. The number of admissions and blood transfusions in the three months prior to the initiation of bicarbonate supplementation was noted. Oral bicarbonate supplementation was increased based on the baseline blood gas analysis. The same parameters were assessed after three months and analysed. Results: At the end of three months, a significant reduction (p-value &lt;0.05) in creatinine, Extracellular Water (ECW) and lean body mass, along with an increased body fat percentage. There was a reduction in third space fluid and ECW, with no significant changes (p-value &gt;0.1) in the weight and Body Mass Index (BMI) of patients was observed. Additionally, there was a significant improvement (p-value &lt;0.05) in the serum protein and albumin levels of these patients. The number of hospitalisations decreased from 28 to 13 and the number of blood transfusions required also decreased from 31 to 13. Conclusion: The correction of acidosis improved metabolic parameters, resulting in an increase in fat percentage and a reduction in ECW and third space water without intracellular dehydration. There was a significant reduction in urea and creatinine values, as well as a significant decrease in hospitalisations and the number of blood transfusions required.

This study presents the hydrodynamic characteristics of different adult male swimmer's body shape using computational fluid dynamics method. This simulation strategy is carried out by CFD fluent code with solving the 3D incompressible Navier-Stokes equations using the RNG k-ε turbulence closure. The water free surface is captured by the volume of fluid (VOF) method. A set of full body models, which is based on the anthropometrical characteristics of the most common male swimmers, is created by Computer Aided Industrial Design (CAID) software, Rhinoceros. The analysis of CFD results revealed that swimmer's body shape has a noticeable effect on the hydrodynamics performances. This explains why male swimmer with an inverted triangle body shape has good hydrodynamic characteristics for competitive swimming.

The primary aim was to appraise the relationship between body fat percentage and the inflammatory markers C-reactive protein (CRP) and orosomucoid in a population of young, non-smoking, healthy, Swedish adults, without any chronic diseases. A secondary aim was to compare whether these associations differed between the women using estrogen contraceptives and those who did not. We assessed the association in linear regression models between body fat percentage based on a bio-impedance measurement and plasma concentrations of CRP and orosomucoid in men and women aged 18–26 years, n = 834. Statistically significant associations were found between body fat percentage and both biomarkers of inflammation, with β coefficients of 0.30 (95% CI 0.24–0.37) and 0.28 (0.22–0.35) for CRP and orosomucoid, respectively (p < .001). Adjustment for established risk factors marginally lowered the effects sizes (partial betas, 0.28 and 0.20, respectively), while the strong statistically significant associations remained. In the female cohort, estrogen and non-estrogen using subpopulations did not significantly differ in the correlations between body fat percentage and the inflammatory biomarkers, even adjusted for established cardiometabolic risk factors. In conclusion, in healthy young adults, higher levels of body fat percentage are associated with elevations in plasma biomarkers of inflammation, suggesting that a systemic inflammatory process, promoting atherosclerosis, may commence already at this early stage in life. CRP and orosomucoid plasma concentrations differed between users and non-users of estrogen contraceptives, but both subgroups showed similar correlations between increasing body fat percentage and increasing plasma concentrations of the biomarkers of inflammation.

Amniotic fluid volume estimation and the biophysical profile: a confusion of criteria

Fluid volume estimates may help predict functional status and thereby improve sarcopenia diagnosis. Bioimpedance-derived fluid volume, combined with DXA, improves identification of jump power over traditional measures. DXA-measured lean mass should be corrected for fluid distribution in older populations; this may be a surrogate of muscle quality. Sarcopenia, the age-related loss of muscle mass and function, negatively impacts functional status, quality of life, and mortality. We aimed to determine if bioimpedance spectroscopy (BIS)-derived estimates of body water compartments can be used in conjunction with dual-energy X-ray absorptiometry (DXA) measures to aid in the prediction of functional status and thereby, ultimately, improve the diagnosis of sarcopenia. Participants (≥ 70years) had physical and muscle function tests, DXA, and BIS performed. Using a BMI correction method, intracellular water (ICWc), extracellular water (ECWc), and ECWc to ICWc (E/Ic) ratio was estimated from standard BIS measures. Jump power was assessed using jump mechanography. The traditional measure used to diagnose sarcopenia, DXA-derived appendicular lean mass (ALM) corrected for height (ALM/ht2), was the least predictive measure explaining jump power variability (r2 = 0.31, p < 0.0001). The best measure for explaining jump power was a novel variable combining DXA ALM and BIS-derived E/Ic ratio (ALM/(E/Ic); r2 = 0.70, p < 0.0001). ALM/(E/Ic) and ICWc had the highest correlation with jump power and grip strength, specifically jump power (r = 0.84 and r = 0.80, respectively; p < 0.0001). The creation of a novel variable (ALM/(E/Ic)) improved the ability of DXA to predict jump power in an older population. ALM/(E/Ic) substantially outperformed traditional lean mass measures of sarcopenia and could well be an improved diagnostic approach to predict functional status. DXA-measured ALM should be corrected for fluid distribution, i.e., ALM/(E/Ic); this correction may be considered a surrogate of muscle quality.

A benchmark study is conducted using isoAdvection as the interface description method. In different studies for the simulation of the thermal phase change of nanofluids, the Volume of Fluid (VOF) method is a contemporary standard to locate the interface position. One of the main drawbacks of VOF is the smearing of the interface, leading to the generation of spurious flows. To solve this problem, the VOF method can be supplemented with a recently introduced geometric method called isoAdvection. We study four benchmark cases that show how isoAdvection affects the simulation results and expose its relative strengths and weaknesses in different scenarios. Comparisons are made with VOF employing the Multidimensional Universal Limiter for Explicit Solution (MULES) limiter and analytical data and experimental correlations. The impact of nanoparticles on the base fluid are considered using empirical equations from the literature. The benchmark cases are 1D and 2D boiling and condensation problems. Their results show that isoAdvection (with isoAlpha reconstruct scheme) delivers a faster solution than MULES while maintaining nearly the same accuracy and convergence rate in the majority of thermal phase change scenarios.

Correct estimation of peritoneal fluid volume is the prerequisite to control the infusion and the removal of dialysate solution into and from the peritoneal cavity during peritoneal dialysis. A new approach using segmental bioimpedance measurements, a special placement of electrodes, and a correction for inhomogeneous distribution of current considerably improved the estimation of peritoneal fluid volume in 11 studies with two subsequent peritoneal fluid exchanges.

Changes, observed in rats after bilateral nephrectomy, in blood pressure and in the relation betwen plasma volume-extracellular fluid volume or plasma volume-interstitial fluid volume, are consistent with the postulation that the kidney secretes a substance that regulates, to some degree, the compliance of the interstitial space. In order to evaluate the possibility that this also occurs in humans, we have carried out a retrospective analysis of measurements of extracellular fluid volume, plasma volume, and blood volume made prior to and after bilateral nephrectomy in a group of 9 patients. It was observed that significant increases had occurred in both the plasma-extracellular fluid volume ratio (0.22 before, 0.26 after) and in the blood-extracellular fluid volume ratio (0.27 before, 0.32 after). These data are consistent with a reduction in compliance of the interstitial compartment caused by bilateral nephrectomy in man, even though other explanations cannot be excluded.

Until an accurate fluid saturation tool is designed, the lack of a solid link between the petrophysical properties of reservoir rock and fluid is a real problem. The reservoir water saturation models are normally based on the standard Archie model to calculate fluid volumes. However, in tight carbonate reservoirs with heterogeneous wettability this model may present unrealistic results for the fluid volume (e.g., water/oil/gas) estimates. An integrated model using resistivity and NMR logs is introduced to quantify the movability of hydrocarbons in the reservoir transition zone. Pay zones may be missed in low-resistivity reservoirs (i.e., transition zones) due to the high water volume estimated from conventional logs. New synthetic resistivity logs are made in both the invaded and non-invaded zones based on assumptions made on the basis of pore and fluid interaction in the NMR log T2 distribution. The differences between the original and synthetic resistivity logs in connection with other log data are dominant signatures of the fluid volumes and movability in the formation. The new approach is developed on basis of exploration well data from a complex and heterogeneous carbonate reservoir in the Norwegian Barents Sea. The estimated fluid movability results are in agreement with the wireline formation tester (WFT) measurements of the well. This model, in addition to the transition zone, can also be applied for hydrocarbon bearing intervals which contain connate water. This approach shows that the reservoir wettability signature can also be identified by comparing the measured and constructed resistivity logs.