Probing deep lung regions using a new 6-electrode tetrapolar impedance method

Probing deep regions of the lung using electrical impedance is very important considering the need for a low cost and simple technique, particularly for the low and medium income countries. Because of complexity and cost, Electrical Impedance Tomography is not suitable for this envisaged application. The simple Tetrapolar Impedance Measurement (TPIM) technique employing four electrodes is the age old technique for bioelectrical measurements. However, it has its limitations in respect of organ localisation and depth sensitivity using skin surface electrodes. Recently, a new 6-electrode TPIM with two current electrodes but two pairs of appropriately connected potential electrodes positioned on the front and back of the thorax, proposed by one of the authors, came with a promise. However, this work gave a qualitative proposal based on concepts of physics and lacked a quantitative evaluation. In order to evaluate the method quantitatively, the present work employed finite element method based COMSOL Multiphysics software and carried out simulation studies using this new 6-electrode TPIM and compared the results with those from 4-electrode TPIM, with electrodes applied either on the front or at the back of the thorax for the latter. Initially, it carried out a sensitivity distribution study using a simple rectangular volume conductor which showed that the 6-electrode TPIM gives better depth sensitivity throughout the lung region. Next it used a near life like thorax model developed by another of the authors earlier. Using this model, extensive studies were carried out to quantify the overall sensitivity over a target lung region, the contribution of the target lung to the total measured impedance, and several other parameters. Through these studies, the 6-electrode TPIM was established on a stronger footing for probing deep regions of the lungs

The sensitivity of focused electrical impedance measurements

One of the problems with tetrapolar impedance measurements is the lack of spatial sensitivity within the measured volume. In this paper we compare the sensitivity of tetrapolar measurements and the focused impedance measurements (FIM) proposed by Rabbani et al (1999 Ann. New York Acad. Sci. 873 408-20), which give an improved sensitivity profile. Using a previously validated model of sensitivity based on Geselowitz's lead theory, the sensitivity of FIM using eight, six and four electrodes was investigated. All electrode configurations showed a maximum in the average sensitivity of a plane at a depth of one-third of the drive-receive electrode spacing. No difference was found in the sensitivity value of this maximum between electrode configurations having the same drive-receive electrode spacing. The six-and eight-electrode configurations showed negative sensitivity regions down to half of the drive-receive electrode spacing, whilst the four-electrode measurement showed negative sensitivity regions down to one-third of the drive-receive electrode spacing. The single peak in sensitivity beneath the centre of the electrode configuration became dominant at 0.56, 1.4 and 0.14 of the receive electrode spacing for the eight-, six- and four-electrode configurations respectively. Thus, the four-electrode FIM configuration gives a single peak closest to the surface

The role of risk perception in reducing cholera vulnerability

This article highlights multiple aspects of risk perception in relation to cholera control and infectious disease risk reduction in Beira, Mozambique. Findings suggest that risk perceptions vary over time and are interpreted on the basis of visible contamination, cognition and context. Risk perceptions influence the efficacy of risk reduction strategies. Although risk is viewed as a communal problem, notions of individual, community and institutional responsibilities structure the perceptions and attitudes to local hygiene and infectious disease reduction strategies. Perceived risk variously acts as a motivator in the adoption of risk management approaches. However, a lack of infectious disease interventions by other community members and local institutions devalues individual motivation to combat risk of cholera. Community involvement in addressing vulnerability to disease requires knowledge of multiple influences on risk perceptions and governance contexts that facilitate collective control and responsibility