Indirect measurement of lung density and air volume from electrical impedance tomography (EIT) data.

This paper describes a method for estimating lung density, air volume and changes in fluid content from a non-invasive measurement of the electrical resistivity of the lungs. Resistivity in Ω m was found by fitting measured electrical impedance tomography (EIT) data to a finite difference model of the thorax. Lung density was determined by comparing the resistivity of the lungs, measured at a relatively high frequency, with values predicted from a published model of lung structure. Lung air volume can then be calculated if total lung weight is also known. Temporal changes in lung fluid content will produce proportional changes in lung density. The method was implemented on EIT data, collected using eight electrodes placed in a single plane around the thorax, from 46 adult male subjects and 36 adult female subjects. Mean lung densities (±SD) of 246 ± 67 and 239 ± 64 kg m(-3), respectively, were obtained. In seven adult male subjects estimates of 1.68 ± 0.30, 3.42 ± 0.49 and 4.40 ± 0.53 l in residual volume, functional residual capacity and vital capacity, respectively, were obtained. Sources of error are discussed. It is concluded that absolute differences in lung density of about 30% and changes over time of less than 30% should be detected using the current technology in normal subjects. These changes would result from approximately 300 ml increase in lung fluid. The method proposed could be used for non-invasive monitoring of total lung air and fluid content in normal subjects but needs to be assessed in patients with lung disease.

Tactile information transfer: a comparison of two stimulation sites.

Two experiments on the discrimination of time-varying tactile stimuli were performed, with comparison of stimulus delivery to the distal pad of the right index finger and to the right wrist (palmar surface). Subjects were required to perceive differences in short sequences of computer-generated stimulus elements (experiment 1) or differences in short tactile stimuli derived from a speech signal (experiment 2). The pulse-train stimuli were distinguished by differences in frequency (i.e., pulse repetition rate) and amplitude, and by the presence/absence of gaps (approximately 100-ms duration). Stimulation levels were 10 dB higher at the wrist than at the fingertip, to compensate for the lower vibration sensitivity at the wrist. Results indicate similar gap detection at wrist and fingertip and similar perception of frequency differences. However, perception of amplitude differences was found to be better at the wrist than at the fingertip. Maximum information transfer rates for the stimuli in experiment 1 were estimated at 7 bits s(-1) at the wrist and 5 bits s(-1) at the fingertip.

Detection of cervical intraepithelial neoplasia using impedance spectroscopy: a prospective study.

OBJECTIVE: To compare cervical impedance spectrometry in the cervical epithelium of women with cervical intraepithelial neoplasia (CIN) and normal epithelium. DESIGN: Prospective observational study. SETTING: Colposcopy clinic, Jessop Wing, Royal Hallamshire Hospital, Sheffield, UK. POPULATION: Eighty-seven women referred to colposcopy with a moderate or severely dyskaryotic smear. METHODS: A pencil probe incorporating four gold electrodes was used to measure an electrical impedance spectrum from cervical epithelium. Colposcopy examinations, including probe positioning, were recorded by video to allow for correlation between results obtained from colposcopic impression, histopathological examination of colposcopically directed punch biopsies and the impedance measurements. MAIN OUTCOME MEASURES: Cervical impedance derived parameters R, S and C were assessed to see if there was a significant difference in values obtained in CIN and normal squamous epithelium. Analysis was based upon matching the electrical components measured to those identified by cellular modelling as being most sensitive for premalignancy. RESULTS: From normal epithelium through CIN 1 to CIN 2/3, R decreased by a factor of 4.5, S increased by a factor of 2.5 but C remained unchanged. CONCLUSIONS: Cervical impedance spectrometry provides a potentially promising screening tool with similar sensitivity and specificity to currently used screening tests, but with the potential advantage of providing instant results. Further work is currently being undertaken to improve the probe in its clinical use.