Measuring bioimpedance in the human uterine cervix: towards early detection of preterm labor

Abstract

We have created a bioimpedance probe designed to detect subtle changes in human cervical tissue composition in vivo, and thereby detect the onset of cervical remodeling in a noninvasive manner sooner than existing clinical methods allow. Our cervical bioimpedance measurement device, which can be used during a routine pelvic examination, is composed of a contoured probe with disposable tip and, within the probe's handle, a bioimpedance sensor equipped with an integrated chip capable of generating sinusoidal voltage of varying frequencies. A constant force spring assures consistent measurements through a range of contact forces applied. An activation switch allows the operator to control the application of current. The sensor can be synchronized with a computer data storage and analysis system, which interfaces with the device. With the probe placed in contact with a collagen gels of varying concentration, the relationship between measured bioimpedance and collagen concentration is verified to be positive exponential (R/sup 2/=0.94) and repeatability in saline solution showed that measurements varied by less than +/-10% over 20 trials. Finally, a variety of user-applied forces showed that impedance values plateau when forces exceed 1N.

Towards BirthAlert—A Clinical Device Intended for Early Preterm Birth Detection

“…3 show the fluorescent excitation/emission peaks for collagen lie around 370 nm/420 nm. Changes in fluorescence counts, impedance magnitude, and impedance phase are a function of collagen concentration, and the range of values is in concordance with the literature [15], [24], [33]–[35], [39], [41]–[43], [50]–[52]. …”

“…The cup-like design for the tip of the intravaginal probe was a consequence of arranging electrodes on both the bottom and sides of the cup to generate spatial diversity in impedance measurements. Furthermore, whereas other researchers have used loaded-spring mechanisms in pencil-probe designs to saturate force-dependent variability in impedance measurements, we exploited the elasticity of the bulk silicone material itself via the form-fitting cup-like design to accomplish the same goal [52]. …”

Preliminary results of cervical impedance measurements

“…Previous works published in the literature (Avis et al, 1997;Etemadi et al, 2013;Gandhi et al 2006a;2006b;Hoe et al, 2004;O'Connell et al, 2000) produced results in line with those reported here. However, none of them include an equivalent circuit for the cervical tissue, as it is done here.…”

“…The former is based on the auto fluorescent properties of the collagen cross-links; and the latter is based on the electrical impedance characteristics of the cervical tissue. The use of electrical impedance to assess cervical ripening has been reported in the literature, e.g., Avis et al (1997), Etemadi et al (2013), Gandhi et al (2006a;2006b), Hoe et al (2004) andO'Connell et al (2000). Avis et al (1997) presented in-vitro measurements of the electrical impedance of cervical tissue from samples taken at caesarean sections, and reported differences between term and preterm samples.…”

“…In O'Connell et al (2000) the authors performed measurements of electrical impedance of pregnant and nonpregnant women, and indicated that the results might be as good as those obtained by BS. Hoe et al (2004) proposed a bioimpedance probe that might be used to detect preterm labor. Laboratory in-vitro tests were conducted on various collagen concentrations with success.…”