Electrical Velocimetry Research Articles

Investigations of Porosity Changes during Granular Silo Flow Using Electrical Capacitance Tomography (ECT) and Particle Image Velocimetry (PIV)

AbstractThe paper presents results of measurements of porosity changes in sand during granular flow in model silos using two different non‐invasive methods, i.e., Electrical Capacitance Tomography (ECT) and Particle Image Velocimetry (PIV). The experiments in model silos are carried out with different initial unit weights of sand and silo wall roughness. Advantages and disadvantages of both methods are outlined.

Comparison of electrical velocimetry and thermodilution techniques for the measurement of cardiac output

To compare a new method of non-invasive determination of cardiac output based on electrical velocimetry (EV-CO) with invasive thermodilution methods. Fifty critically ill patients were enrolled into the study. EV-CO was compared with cardiac output measured by a pulmonary artery catheter (PA-CO) in one group (n= 25) and by a femoral artery catheter (PiCCO-CO) in a second group (n= 25), by simultaneous measurements. Standard electrocardiography electrodes were used for non-invasive measurements, and EV-CO was calculated using the Bernstein-Osypka equation. The invasive measurements of PA-CO and PiCCO-CO were made by the injection of iced 0.9% saline and the recording of thermodilution curves. The precision values of EV-CO, PA-CO and PiCCO-CO measurements were +/- 0.46 [95% confidence interval (95% CI), +/- 0.06], +/- 0.57 (95% CI, +/- 0.09) and +/- 0.48 l/min (95% CI, +/- 0.08 l/min), respectively. The mean differences between EV-CO and PA-CO or PiCCO-CO were -0.05 +/- 0.71 and 0.22 +/- 0.78 l/min, respectively. The lower and upper limits of agreement for the comparison of EV-CO with PA-CO were -1.47 and 1.37 l/min (95% CI, +/- 0.25 l/min), respectively. In the comparison of EV-CO and PiCCO-CO, lower and upper limits of -1.34 and 1.78 l/min (95% CI, +/- 0.27 l/min) were found. The percentage errors between EV-CO and PA-CO or PiCCO-CO were 26.5% and 26.4%, respectively. The values of cardiac output were statistically comparable between the groups. Therefore, electrical velocimetry is a suitable method to evaluate haemodynamic variables with clinically acceptable accuracy.

Cardiac output measurements with electrical velocimetry in patients undergoing CABG surgery

The purpose was to study the agreement between cardiac output measurements with electrical velocimetry vs. intermittent thermodilution before and after coronary artery bypass graft surgery. Cardiac output was measured simultaneously with electrical velocimetry and intermittent thermodilution before and immediately after coronary artery bypass graft surgery, and in the intensive care unit. Measurements were performed in three different body positions. The results were analysed according to Bland and Altman. The mean bias of all 150 paired measurements in 16 patients was 0.21 +/- 0.78 L min(-1), and the mean error was 40%. Before skin incision the mean bias was 0.04 +/- 0.41 L min(-1), and the mean error was 25%. After skin closure the mean bias was 0.57 +/- 0.92 L min(-1), and the mean error was 42%. In the intensive care unit the mean bias was 0.26 +/- 0.68 L min(-1), and the mean error was 32%. The agreement between cardiac output measurements with electrical velocimetry and intermittent thermodilution was clinically acceptable only before skin incision in coronary artery bypass graft surgery. The mean error was unacceptably high immediately after skin closure and was at a borderline level in the intensive care unit. Thus, the overall accuracy of cardiac output measurements with the electrical velocimetry technique during coronary artery bypass graft surgery is not clinically unacceptable.

Lack of agreement between thermodilution and electrical velocimetry cardiac output measurements

The modified algorithm for the non-invasive determination of cardiac output (CO) by electrical bioimpedance-electrical velocimetry (EV)-has been reported to give reliable results in comparison with echocardiography and pulmonary arterial thermodilution (PA-TD) in patients either before or after cardiac surgery. The present study was designed to determine whether EV-CO measurements reflect intraindividual changes in CO during cardiac surgery. Prospective, observational study. Operating room (OR) and intensive care unit (ICU) of a university hospital. Twenty-nine patients undergoing elective cardiac surgery. None. CO was determined simultaneously by PA-TD and EV after induction of anesthesia (t1) and 4.9+/-3.5 h after ICU admission (t2). TD-CO was 3.9+/-1.4 and 5.4+/-1.1 l/min at t1 and t2 (p < 0.0001). EV-CO was 4.3+/-1.1 and 4.9+/-1.5 l/min at t1 and t2 (p = 0.013). Bland-Altman analysis showed a bias of -0.4 l/min and 0.4 l/min and a precision of 3.2 and 3.6 l/min (34.3% and 67.4%) at t1 and t2, respectively. Analysis of the individual pre- to postoperative changes in CO with both methods revealed bidirectional changes in n = 12 patients and unidirectional changes with a difference greater than 50% and less than 50% in n = 9 and n = 8 patients, respectively. The disagreement between PA-TD and EV-CO measurements after anesthesia induction and after ICU admission, as well as the fact that thoracic bioimpedance did not adequately reflect pre- to postoperative changes in CO, questions the reliability of EV-CO measurements in cardiac surgery patients and contrasts sharply with previous studies.

Comparison of electrical velocimetry and transpulmonary thermodilution for measuring cardiac output in piglets

Monitoring of cardiovascular function is essential during major pediatric and pediatric cardiac surgery. Invasive monitoring of cardiac output (CO) and oxygen delivery is expensive and sometimes associated with adverse events. Therefore, we investigated the accuracy of a new noninvasive CO monitoring device using electrical velocimetry (EV) in comparison with the more invasive transpulmonary thermodilution (TPTD) method. In five fasted, anesthetized and mechanically ventilated piglets, CO was measured simultaneously using EV and TPTD under normal conditions, volume loading, inotropic support and exsanguination. In five piglets, 169 measurements could be performed. The correlations between EV-CO and TPTD-CO were significant for absolute values (P < 0.0001, r = 0.82) and relative changes from baseline (P < 0.0001, r = 0.93). The receiver operating characteristic (ROC) curve analysis of the relative changes of the EV-CO values in relation to the first EV-CO measurement showed a sensitivity of 91% and specificity of 94% (AUC 0.974, 95% CI 0.96-0.99). Changes in TPTD-CO greater than 15% lead to a change of EV-CO in the same direction in 93%. Bland-Altman analysis showed a mean difference between the two methods of -0.63 l x min(-1) with an sd of 0.64 l x min(-1). The lower and upper limits of agreement were -1.88 and 0.62 l x min(-1), percentage limit of agreement was +/-82.8%. The results show that EV is a safe, simple, noninvasive and cost-effective method for continuous trend monitoring of CO in piglets. The agreement of the EV-CO with TPTD-CO is not good enough to replace the standard method in our animal model. A correction factor for body habitus in piglets may be beneficial.

Electrical velocimetry compared with ficks principle for cardiac output measurement in children undergoing cardiac catheterisation

Electrical velocimetry compared with ficks principle for cardiac output measurement in children undergoing cardiac catheterisation

Noninvasive cardiac output measurement in cardiovascular ICU-patients – comparison of conventional impedance cardiography, electrical velocimetry and thermodilution methods

Noninvasive cardiac output measurement in cardiovascular ICU-patients – comparison of conventional impedance cardiography, electrical velocimetry and thermodilution methods

Comparison of electrical velocimetry and transoesophageal Doppler echocardiography for measuring stroke volume and cardiac output

Impedance cardiography (ICG) has been used extensively to estimate stroke volume (SV) and cardiac output (CO) from changes of thoracic electrical bioimpedance (TEB). However, studies comparing ICG with reference methods have questioned the reliability of this approach. Electrical velocimetry (EV) provides a new algorithm to calculate CO from variations in TEB. As the transoesophageal Doppler echocardiographic quantification of CO (TOE-CO) has emerged as a reliable method, the purpose of this study was to determine the limits of agreement between CO estimations using EV (EV-CO) and TOE-CO. Standard ECG electrodes were used for non-invasive EV-CO measurements. These were placed on 37 patients scheduled for coronary artery surgery necessitating transoesophageal echocardiography monitoring. Simultaneous EV-CO and TOE-CO measurements were recorded after induction of anaesthesia. EV-CO was calculated using the Bernstein-Osypka equation. TOE-CO was measured across the aortic valve using continuous-wave Doppler echocardiography and a triangular orifice model. A significant high correlation was found between the TOE-CO and the EV-CO measurements (r2=0.86). Data were related linearly. The slope of the line (1.10 (se 0.07)) was not significantly different from unity, and the point at which it intersected the ordinate (-0.46 (0.32) litre min(-1)) was not significantly different from zero. Bland-Altman analysis revealed a bias of 0.18 litre min(-1) with narrow limits of agreement (-0.99 to 1.36 litre min(-1)). The agreement between EV-CO and TOE-CO is clinically acceptable, and these two techniques can be used interchangeably.

Comparative study of cardiac output (CO) measurement using thermodilution (TD) and electrical velocimetry (EV) techniques in patients undergoing CABG surgery

Comparative study of cardiac output (CO) measurement using thermodilution (TD) and electrical velocimetry (EV) techniques in patients undergoing CABG surgery

Accurate analytical measurements in the atomic force microscope: a microfabricated springconstant standard potentially traceable to the SI

Calibration of atomic force microscope (AFM) cantilevers is necessary for the measurementof nanonewton and piconewton forces, which are critical to analytical applications of AFMin the analysis of polymer surfaces, biological structures and organic molecules at nanoscalelateral resolution.We have developed a compact and easy-to-use reference artefact for this calibration, usinga method that allows traceability to the SI (Système International). Traceability is crucial toensure that force measurements by AFM are comparable to those made by optical tweezersand other methods. The new non-contact calibration method measures the springconstant of these artefacts, by a combination of electrical measurements andDoppler velocimetry. The device was fabricated by silicon surface micromachining.The device allows AFM cantilevers to be calibrated quite easily by the ‘cantilever-on-reference’method, with our reference device having a spring constant uncertainty of around ± 5% at one standard deviation. A simple substitution of the analogue velocimeterused in this work with a digital model should reduce this uncertainty to around ± 2%.Both are significant improvements on current practice, and allow traceability to the SI forthe first time at these nanonewton levels.