Biomedical subjects

P Metherall

Publications and source records attributed to P Metherall.

3 recordsLinked to original sources

PubMed1999

Can we optimize electrode placement for impedance pneumography?

In this paper, we discuss issues involved in defining an optimum placement of four electrodes for impedance pneumography. We observed a general trend where the change in impedance (delta Z) decreased while the sensitivity (delta Z/Z) increased with distance between the drive and receive electrode pairs. However, the theoretical study indicated that delta Z/Z should decrease with distance. The scatter of points in the plots indicated that sensitivity was influenced by factors other than distance. The correlation coefficient between the theoretical and measured delta Z/Z was low, but significant. This suggested that the best electrode configuration can be derived from the theoretical data. High delta Z/Z was obtained when the drive and receive electrode pairs were placed close to the lungs and in different horizontal planes.

Adult↗

PubMed1996

Three-dimensional electrical impedance tomography.

The electrical resistivity of mammalian tissues varies widely and is correlated with physiological function. Electrical impedance tomography (EIT) can be used to probe such variations in vivo, and offers a non-invasive means of imaging the internal conductivity distribution of the human body. But the computational complexity of EIT has severe practical limitations, and previous work has been restricted to considering image reconstruction as an essentially two-dimensional problem. This simplification can limit significantly the imaging capabilities of EIT, as the electric currents used to determine the conductivity variations will not in general be confined to a two-dimensional plane. A few studies have attempted three-dimensional EIT image reconstruction, but have not yet succeeded in generating images of a quality suitable for clinical applications. Here we report the development of a three-dimensional EIT system with greatly improved imaging capabilities, which combines our 64-electrode data-collection apparatus with customized matrix inversion techniques. Our results demonstrate the practical potential of EIT for clinical applications, such as lung or brain imaging and diagnostic screening.

Algorithms↗

PubMedDate not supplied

Posture control using electrical stimulation biofeedback: a pilot study.

The investigation studied the effects of biofeedback on the sitting posture of a 14 year old girl with cerebral palsy. The subject's posture was quantified using a video analysis technique which established the threshold of poor posture at 30 degrees from the vertical plane. A stimulator system was designed using an adapted drop foot stimulator and a custom made controller with a mercury tilt switch as the posture angle transducer. If posture became greater than 30 degrees tactile electrical stimulation was administered to the subject's lower back. Repetitive stimuli occurred on non-correction of posture, with a maximum of 4 consecutive stimuli, upon which an alarm was activated. 10 training sessions of 20 min duration were completed over a 4 week period, monitored using a data logger. Following initial improvement the daily results show a gradual deterioration in posture, whilst post-trial video analysis indicates a significant improvement in posture. An improved response to the alarm stimulus is observed. Reasons for these conflicting findings are discussed.

Adolescent↗