Arterial Load and Norepinephrine Are Associated With the Response of the Cardiovascular System to Fluid Expansion

BackgroundFluid responsiveness has been extensively studied by using the preload prism. The arterial load might be a factor modulating the fluid responsiveness. The norepinephrine (NE) administration increases the arterial load and modifies the vascular properties. The objective of the present study was to determine the relationship between fluid responsiveness, preload, arterial load, and NE use. We hypothesized that as a preload/arterial load, NE use may affect fluid responsiveness.MethodsThe retrospective multicentered analysis of the pooled data from 446 patients monitored using the transpulmonary thermodilution before and after fluid expansion (FE) was performed. FE was standardized between intensive care units (ICUs). The comparison of patients with and without NE at the time of fluid infusion was performed. Stroke volume (SV) responsiveness was defined as an increase of more than 15% of SV following the FE. Pressure responsiveness was defined as an increase of more than 15% of mean arterial pressure (MAP) following the FE. Arterial elastance was used as a surrogate for the arterial load.ResultsA total of 244 patients were treated with NE and 202 were not treated with NE. By using the univariate analysis, arterial elastance was correlated to SV variations with FE. However, the SV variations were not associated with NE administration (26 [15; 46]% vs. 23 [10; 37]%, p = 0.12). By using the multivariate analysis, high arterial load and NE administration were associated with fluid responsiveness. The association between arterial elastance and fluid responsiveness was less important in patients treated with NE. Arterial compliance increased in the absence of NE, but it did not change in patients treated with NE (6 [−8; 19]% vs. 0 [−13; 15]%, p = 0.03). The changes in total peripheral and arterial elastance were less important in patients treated with NE (−8 [−17; 1]% vs. −11 [−20; 0]%, p < 0.05 and −10 [−19; 0]% vs. −16 [−24; 0]%, p = 0.01).ConclusionThe arterial load and NE administration were associated with fluid responsiveness. A high arterial load was associated with fluid responsiveness. In patients treated with NE, this association was lower, and the changes of arterial load following FE seemed to be driven mainly by its resistive component.

Extracting the Resistive Current Component from a Surge Arrester’s Leakage Current without Voltage Reference

This article presents the development of the theoretical background and the design of an electronic device for monitoring the condition of a gapless Metal Oxide Surge Arrester (MOSA). The device is intended to be used online. Because of the inaccessibility and possible remote location of most surge arresters, it is equipped with a communication system, allowing for the device to convey the measurement of the surge arrester characteristics under any conditions. It is possible to determine the condition of the MOSA by gathering measurements of the surge arrester’s resistive component of leakage current. The leakage current information is sent via data transfer unit to a server and, after interpretation, will be forwarded to the authorised personnel through the surge arrester control centre.

Determination of the attenuation coefficients from the measured frequency characteristics of the windings of power transformers. Part 1. Theoretical consideration

To model high-frequency processes and determine the stresses on the internal insulation of transformer windings, reliable high-frequency models of power transformers are required. The accuracy of modeling high-frequency resonance processes in the windings depends on how correctly the model reproduces the natural frequencies and damping of free oscillations in the windings. To construct and verify high-frequency models of power transformers, it is necessary to have experimentally obtained data on the values of damping factors. There is a known method for determining the winding damping factors based on measurements of the voltage transfer functions at the internal points of the windings and their subsequent processing using the vector fitting technique, but its application is not always possible in practice. The article presents the results of theoretical studies performed for a simplified transformer winding equivalent circuit. It is shown that the damping factors can be estimated from the width of the resonance peaks of the frequency responses of the voltage modulus and reactive component at the midpoint of the equivalent circuit, and from the input admittance resistive component and current in the neutral of the considered resonance circuit.

Electrical impedance to easily discover undeclared freeze-thaw cycles in slaughtered bovine meat

A portable electrical impedance spectroscopy device was developed to monitor the bioimpedance resistive component of bovine meat by injecting a sinusoidal current of 1 mA at 65 kHz. Both right and left longissimus dorsi muscles were trimmed from 4 slaughtered cows. The left muscle portions were frozen to −18 °C for 7 days while the right ones were meantime maintained at 5 °C. Mean value of impedance per length (Ω/cm) of frozen and thawed left samples was 31% lower than that of right non-frozen one (P = 0.0001). It was concluded that the device is reliable for monitoring the maturation of beef meat in situ with the possibility of revealing undeclared freeze-thaw cycles.

Pulsatile and resistive systolic loads as determinants of left ventricular remodelling after physical training

Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): British Heart Foundation Barts Cardiovascular Biomedical Research Centre onbehalf The Marathon Study Consortium Introduction Cardiovascular function depends on the inter-relation between heart and vasculature. The contribution of aorta and peripheral vessels to the total systolic load of the left ventricle (LV) can be represented respectively by a "pulsatile" and a "resistive" component. We sought to understand their interrelation by exploring how LV remodelling occurred with altered load associated with an external stimulus (training). Methods: 237 untrained healthy male and female subjects volunteering for their first-time marathon were recruited. At baseline and after 6 months of unsupervised training, race completers underwent 1.5T cardiac magnetic resonance, brachial and non-invasive central blood pressure assessment. For analysis, runners were divided into 4 groups according to the variation (positive versus null or negative) in Total Arterial Compliance Index (TACi), representing the pulsatile component of the LV load, and in Systemic Vascular Resistance Index (SVRI), representing the resistive component of the LV load. Results: 138runners (age 21-69 years; F: 51%) completed the race. Data are reported for each variable as Δ mean [95% Confidence Interval]. In the whole cohort, training was associated with a small increase in LV mass index (+3g/m2, [0, 6 g/m2]), indexed LV end-diastolic volume (EDVi) (+3ml/m2, [-2, 5 3ml/m2]), in LV mass/LVEDV ratio (+0.02g/ml, [0.00, 0.04 g/ml]) and in TACi (+0.02ml/m2, [0.02, 0.38 ml/m2]). SVRi mildly fell (-43dyn·s/cm2[-103, 17dyn·s/cm2]). TACi increase was associated with LVEDVi increase and no change in LV mass/EDV (eccentric remodelling). On the other hand, both TACi reduction and SVRi increase were associated with increase in LV mass/EDV and no significant change in LVEDVi (concentric remodelling). A similar increase in LV mass was observed in all groups. See Table. Conclusion: Cardiac remodelling observed after mild, medium term, unsupervised training seems to be related to the modifications of aorta and peripheral vessels. In particular, a reduction in pulsatile load seems associated with eccentric LV remodelling, while an increase in both pulsatile and resistive with concentric LV remodelling. Further research is needed to understand the interaction between TACi and SVRi. Table 1 LV EDVi (ml/m2) LV mass index (g/m2) LV mass/EDV TACi increase (n = 75) +4 [0, 9] +3 [0, 7] 0 [-0.03, 0.03] TACi decrease (n = 62) -1 [-6, 4] +3 [0, 8] 0.04 [0.01, 0.07] SVRi increase (n = 63) 0 [-4,4] +3 [0, 7] +0.03 [0, 0.06] SVRi decrease (n = 73) +3 [-3, 7] +3 [-1, 6] +0.01 [-0.02, 0.04]

Circuit-based method for extracting the resistive leakage current of metal oxide surge arrester

Resistive leakage current based condition assessment of metal oxide surge arrester (MOSA) is one of the most extensively employed technique to monitor its degradation. An extraction method is customarily required to extract the resistive component from the total leakage current. The existing methods to extract the resistive current are complex and less accurate. Therefore, this paper describes a simple and accurate circuit-based method to extract the resistive current using equivalent model and measured leakage current of the arrester. The accuracy of the proposed method is validated through experimental results on ABB’s 120 kV surge arrester, EMTP and QuickField software simulations. The performance of the method is also analyzed and verified experimentally on 72, 180 and 240 kV rated ABB’s surge arresters. The obtained results of resistive leakage current have shown the maximum error of 0.001%. Simple and easier computational steps with higher accuracy are the key benefits of the proposed technique.

Strain sensors based on conducting poly(acrylamide) hydrogels

ABSTRACTA simple model system towards an impedance-probing strain sensor based on conducting tough hydrogels is demonstrated. A poly(acrylamide) hydrogel, cross-linked with N,N’-methylene-bis(acrylamide) was contacted with carbon fibres for electrical impedance analysis. The conductivity of the salt-containing hydrogel was determined to be 114 ± 10 mS/cm. Upon stretching the hydrogel samples to their fourfold initial length, the impedance response increased according to a power law. This was used to establish a sensing equation for the relation between the resistive component of the impedance signal and the applied mechanical strain under tension. This work contributes to the development of highly stretchable and soft strain sensors for applications in soft robotics.

IMPULSE OSCILLOMETRY FOR DIAGNOSIS OF EARLY CHANGES IN THE RESPIRATORY SYSTEM FUNCTIONAL STATE IN PATIENTS WITH MILD ASTHMA

Currently, the analysis of respiratory function of lungs at suspicion of obstructive pulmonary diseases is recommended to start with spirometry as the most sensitive method of obstruction detection. However, data on informative value and specificity of a method are contradictory. To obtain reliable results good cooperation of the patient and health professionals is necessary. Impulse oscillometry is a noninvasive method of general respiratory resistance assessment, which does not require forced exhalations. The sensitivity and specificity of this method remain undecided as well as the obtained parameter interpretation. The objective of this work was to study opportunities of impulse oscillometry in diagnostics of early respiratory dysfunctions of ist most informative indicators correlating with parameters of spirometry and body plethysmography.Materials and methods. Patients with the established diagnosis of mild asthma (n=68) were examined. In 71% of patients, obstructive respiratory dysfunction was revealed. In the control group (n=41) there were no abnormalities.Results. In most of patients with revealed via spirometry and body plethysmography obstructive disturbances the increase in indicators of absolute frequency dependence of the resistive component of the respiratory impedance at the oscillation frequency of 5 and 20 Hz (Rrs5-Rrs20) and the reactance area (AX). Increase in Rrs5-Rrs20 was revealed in 48 (71%) patients and the increase in AX was observed in 44 (65%) of the surveyed, patients with 42 (61%) patients without the increase of reactance (Xrs5) and resistance (Rrs5).Conclusion. The absolute frequency dependence of Rrs5-Rrs20 and AX are the most informative parameters of impulse oscillometry. In some patients the IOM findings were more significant in comparison with spirometry ones.