Comparison of electrical field plethysmography with electrical impedance plethysmography

Electrical impedance plethysmography technique in estimating pulmonary function status

An attempt has been made to study the appropriateness of electrical impedance plethysmography (EIP) in detecting pulmonary health status. A feasibility study was conducted on normal, obstructive and restrictive subjects aged between 20 and 60 years. Quantitative assessment of pulmonary function was made by way of both EIP and pulmonary function tests (PFT). Amongst the various EIP parameters, a statistically significant difference was observed for the respiratory band power, between normal (129.7) and obstructive (35.8) subjects, indicating that this EIP variable can be used to distinguish between the two pulmonary function states. A significant positive correlation was observed between a spirometry parameter, peak expiratory flow rate (PEFR), and an EIP parameter, respiratory amplitude (r = 0.372, p < 0.05), thereby indicating that EIP information by way of respiratory amplitude is comparable to that provided by PEFR. Hence, both respiratory amplitude and respiratory band power were seen to provide useful information on pulmonary health status.

Origin of changes in the epigastric impedance signal as determined by a three-dimensional model

The impedance technique can be used for the noninvasive monitoring of the stomach, with the epigastric impedance signal being a function of the position and configuration of the electrodes. The changes observed could be due to meal resistivity, meal volume and contractions of the gastric smooth muscles. The effect of these various factors on the epigastric impedance signal was determined for several electrode configurations using a three-dimensional model of the abdomen. When the voltage sensing electrodes are located close to the current electrodes, the signal varies linearly with meal volume. The relationship between meal resistivity and the epigastric impedance signal is nonlinear. The impedance signal varies linearly with the contractions of the circular smooth muscles of the stomach.