Impedance analyser module for EIT and spectroscopy using undersampling

Validation of Low-Cost Impedance Analyzer via Nitrate Detection

Impedance spectroscopy is a widely used electrochemical technique with a wide variety of applications. Many of these applications benefit from the additional accessibility provided by low-cost impedance devices. With this in mind, a low-cost impedance device was designed for a high performance-to-cost ratio. The performance of this analyzer was validated against a high-performance DropSens µStat-i 400s potentiostat by performing an application-based experiment. Nitrate detection provides a relevant experiment because of the importance of maintaining precise nitrate concentrations to mitigate the impact of nitrate fluctuations on the environment. Dissolved nitrate samples of different concentrations, in the range 3-1000 mg/L, were confirmed colorimetrically and measured with both instruments. A calibration curve of the real impedance matched a sigmoidal transfer, with a linear region for concentrations below 10 mg/L. The device under investigation exhibited an average magnitude error of 1.28% and an average phase error of 0.96∘ relative to the high-performance standard, which validates the performance of the low-cost device. A cost analysis is presented that highlights some of the complexities of cost comparisons.

The effectiveness of quarter turn from prone in maintaining respiratory function in premature infants

AIM

The aim of this study was to determine the effectiveness of quarter turn from prone compared with supine and prone positioning in maintaining respiratory function in premature infants managed in a neonatal intensive care unit.

METHODS

The study was a prospective, randomised, cross-over trial with concealed allocation and intention to treat analysis. Fifty-four infants ≤32 weeks gestation were randomly allocated to the order of the positions supine, prone and quarter turn from prone. Distribution of ventilation was assessed by measurement of regional impedance amplitude, global inhomogeneity index and phase angle analysis using electrical impedance tomography 30 min after each position change. Physiological characteristics of heart rate, respiratory rate (RR), oxygen saturation and inspired oxygen were also measured.

RESULTS

There was a significant difference between positions for RR with the RR in quarter turn from prone significantly lower than for supine (mean difference 6.53 breaths/min; 2.04-11.02), but not compared with the prone position. No significant differences between positions were found for any of the other outcomes measured.

CONCLUSION

This study demonstrated that quarter turn from prone had an immediate positive positional effect on the RR of premature infants. The position of quarter turn from prone was comparable with prone in the maintenance of lung function and had a superior effect over supine on RR. These findings support the view that a quarter turn from prone can be confidently used in neonatal nurseries to manage premature infants.

Effect of body position on ventilation distribution in ventilated preterm infants

RATIONALE

Positioning is considered vital to the maintenance of good lung ventilation by optimizing oxygen transport and gas exchange in ventilated premature infants. Previous studies suggest that the prone position is advantageous; however, no data exist on regional ventilation distribution for this age group.

OBJECTIVES

To investigate the effect of body position on regional ventilation distribution in ventilated and nonventilated preterm infants using electrical impedance tomography.

DESIGN

Randomized crossover study design.

SETTING

Neonatal ICU.

PATIENTS

A total of 24 ventilated preterm infants were compared with six spontaneously breathing preterm infants.

INTERVENTIONS

Random assignment of the order of the positions supine, prone, and quarter prone.

MEASUREMENTS AND MAIN RESULTS

Ventilation distribution was measured with regional impedance amplitudes and global inhomogeneity indices using electrical impedance tomography. In the spontaneously breathing infants, regional impedance amplitudes were increased in the posterior compared with the anterior lung (p < 0.01) and in the right compared with the left lung (p = 0.03). No differences were found in the ventilated infants. Ventilation was more inhomogeneous in the ventilated compared with the healthy infants (p < 0.01). Assessment of temporal regional lung filling showed that the posterior lung filled earlier than the anterior lung in the spontaneously breathing infants (p < 0.02) whereas in the in the ventilated infants the right lung filled before the left lung (p < 0.01).

CONCLUSIONS

In contrast to previous studies showing that ventilation is distributed to the nondependent lung in infants and children, this study shows that gravity has little effect on regional ventilation distribution.

Design of a complex bioimpedance spectrometer using DFT and undersampling for neural networks diagnostics

Electrical impedance spectroscopy offers many applications in the medical field due the fast response, non-invasiveness and low cost. One promising area is the use of this method for diagnostics. This paper describes the design and experimental evaluation of a multifrequencial complex bioimpedance analyzer. Impedance amplitude and phase were calculated using Discrete Fourier Transform (DFT) and high frequency signals were measured with undersampling. The prototype was able to measure values from 1 Ω to 50 kΩ (frequency range from 50 Hz to 500 kHz). The accuracy of the technique was compared with a commercial equipment. The analysis of passive components resulted in a mean error of 2.9% for the magnitude and 0.69 degrees for the phase. Besides, an initial study for head and neck cancer detection through neural networks is shown. One used bioimpedance values as well as gender, age and body mass index as inputs. The network used 120 training and 40 validation data and was able to simulate 77.5% of the two types of diagnostic correctly.

A simple method to measure phase difference between sinusoidal signals

In this paper, a novel and simple method to measure the phase difference between two sinusoidal signals is presented. Basically, the method consists of subtracting two sinusoidal signals with same frequencies and measuring the resulting signal amplitude: this amplitude being a minimum whenever there is a coincidence between both signal phases. In order to test this method, an adjustable phase reference signal has been generated using a direct digital synthesizer device. Employing this reference signal, it can be demonstrated that the phase difference between two signals can be evaluated with errors smaller than 0.3° for signals with frequencies up to 1.25 MHz.

Impedance analyzer for in vivo electroporation studies

Electroporation, the permeabilization of the cell membrane with electrical pulses, is being used for in vivo gene therapy, drug therapy and minimally invasive tissue ablation. Applying electrical pulses across cells can have a variety of outcomes; from no effect to reversible electroporation to irreversible electroporation. For reliable in vivo use of electroporation it is important to have real time feedback on the outcome of the application of the electrical pulse. Recently, it has been proposed that measuring the electrical properties of electroporated tissues in temporal relation to the applied pulses could provide this feedback. To generate fundamental data on the in vivo electrical properties of electroporated tissues we have developed a fast spectroscopic impedance analyzer that measures electrical properties of tissues in vivo in conjunction with commercial electroporation pulse generators. Here we describe the apparatus and illustrate its use with an experiment on reversible electroporation in a rat liver.