The four-electrode impedance technique: a method for investigation of compliance in luminal organs.

A probe for measurement of related values of cross-sectional area (CA) and pressure has been developed to record characteristics of the walls in luminal organs. The aim of this study was to test the probe in vitro. CA was measured in the range 0.17 to 7.07 cm2 by means of the field gradient principle. Pressure was measured in the range 0 to 20 kPa (150 mmHg) by external transducers. After calibration both the pressure and the CA measuring system did measure the parameters adequately. The CA measuring system was dependent on the temperature and electrolyte concentration of the fluid, but was not affected by the size and form outside the excitation electrodes. The upper frequency limits for recordings of CA and pressure were 15.7 and 0.44 Hz, respectively. These in vitro results indicate that the tube assembly has characteristics sufficient for simultaneous measurement of CA and pressure in sphincter regions. These two variables can be used to describe mechanical wall properties such as compliance, hysteresis and creep.