Comparison of Bioimpedance Versus Pulse Contour Analysis for Intraoperative Cardiac Index Monitoring in Patients Undergoing Kidney Transplantation

Background: Cardiac index (CI; cardiac output indexed to body surface area) is routinely measured during kidney transplant surgery. Bioimpedance cardiometry is a transthoracic impedance as the non-invasive alternative for hemodynamic monitoring, using semi-invasive uncalibrated pulse wave or contour (UPC) analysis. Objectives: We performed a cross-sectional observational study on 50 kidney transplant patients to compare the CI measurement agreement, concordance rate, and trending ability between bioimpedance and UPC analysis. Methods: For each patient, CI was measured by bioimpedance analysis (ICONTM) and UPC analysis (EV1000TM) devices at three time points: after induction, during incision, and at reperfusion. The device measurement accuracy was assessed by the bias value, limit of agreement (LoA), and percentage error (PE) using Bland-Altman analyses. Trending ability was assessed by angular bias and polar concordance through four-quadrant and polar plot analyses. Results: From each time point and pooled measurement, the correlation coefficients were 0.267, 0.327, 0.321, and 0.348. Bland-Altman analyses showed mean bias values of 1.18, 1.06, 1.48, and 1.30, LoA of -1.35 to 3.72, -1.39 to 3.51, -1.07 to 4.04, and -1.17 to 3.78, and PE of 82.21, 78.50, 68.74, and 74.58%, respectively. Polar plot analyses revealed angular bias values of -10.37º, -15.01º, -18.68º, and -12.62º, with radial LoA of 89.79º, 85.86º, 83.38º, and 87.82º, respectively. The four-quadrant plot concordance rates were 70.77, 67.35, 65.90, and 69.79%. These analyses showed poor agreement, weak concordance, and low trending ability of bioimpedance cardiometry to UPC analysis. Conclusions: Bioimpedance and UPC analysis for CI measurements were not interchangeable in patients undergoing kidney transplant surgery. Cardiac index monitoring using bioimpedance cardiometry during kidney transplantation should be interpreted cautiously because it showed poor reliability due to low accuracy, precision, and trending ability for CI measurement.

Bioreactance Cardiac Output Trending Ability in Preterm Infants: A Single Centre, Longitudinal Study

<b><i>Introduction:</i></b> It is unknown whether bioreactance (BR) can accurately track cardiac output (CO) changes in preterm neonates. <b><i>Methods:</i></b> A prospective observational longitudinal study was performed in stable preterm infants (&#x3c;37 weeks) during the first 72 h of life. Stroke volume (SV) and CO, as measured by BR and transthoracic echocardiography, were compared. <b><i>Results:</i></b> The mean gestational age (GA) was 31.3 weeks and mean birth weight (BW) was 1,563 g. Overall, 690 measurements were analysed for trending ability by 4-quadrant and polar plots. For non-weight-indexed measurements, 377 (54.6%) lay outside the 5% exclusion zone, the concordance rate was poor (77.2%) with a high mean angular bias (28.6°), wide limits of agreement and a poor angular concordance rate (17.4%). Neither GA, BW nor respiratory support mode affected trending data. Patent ductus arteriosus, postnatal age, and CO level had variable effects on trending data. Trending data for 5 and 10% exclusion zones were also compared. <b><i>Conclusion:</i></b> The ability of BR to track changes in CO is not interchangeable with CO changes as measured by echocardiography. BR, as a trend monitor for changes in CO or SV to determine clinical decisions around interventions in neonatology, should be used with caution.

Angular Bias Errors in Three-Component Laser Velocimeter Measurements

For three-component laser velocimeter systems, the change in projected area of the coincident measurement volume for different flow directions will introduce an “angular” bias in naturally sampled data. In this study, the effect of turbulence level and orientation of the measurement volumes on angular bias errors was examined. The operation of a typical three-component laser velocimeter was simulated using a Monte Carlo technique. Results for the specific configuration examined show that for turbulence levels less than 10 percent no significant bias errors in the mean velocities will occur and errors in the root-mean-square (r.m.s.) velocities will be less than 3 percent for all orientations. For turbulence levels less than 30 percent, component mean velocity bias errors less than 5 percent of the mean velocity vector magnitude can be attained with proper orientation of the measurement volume; however, the r.m.s. velocities may be in error as much as 10 percent. For turbulence levels above 50 percent, there is no orientation which will yield accurate estimates of all three mean velocities; component mean velocity errors as large as 15 percent of the mean velocity vector magnitude may be encountered.

Optical Diffraction Analysis for Estimating Foliage Angle Distribution in Grassland Canopies

A non-destructive, rapid technique utilizing horizontal in situ ground photographs for estimating foliage angle distributions is discussed. Optical diffraction patterns generated from orthogonal photographs are analysed for angular bias by wedge sampling. Probability distributions for planar projections of foliage orientations are derived from these measurements and mathematically convo- luted to determine the actual three-space probability distribution function for foliage angles. The method is particularly appropriate for dense canopies which are difficult to measure by other tech- niques. The diffraction technique is evaluated for abstract canopies and for a canopy of Western wheat grass (Agropyron smithii). It also yields physically consistent interpretations for the phenolo- gical development of domestic Satanta wheat (Triticum aestivum).