Electrical uterine activity recorded from the rat abdominal surface during tocolysis

OBJECTIVE: To test if the electromyographic (EMG) recording of uterine activity obtained from the abdominal surface can be used as a non-invasive measure of uterine contractility during tocolysis in rats. STUDY DESIGN: EMG activity was acquired by use of unipolar electrodes attached simultaneously to the uterine wall (UT) and abdominal surface (AS). EMG activity was recorded in the 0.3-50 Hz range and digitied at 200 sampless. Intrauterine pressure (IUP) was measured continuously using an Intrauterine catheter. Rats on day 18 of gestation were given 40 mg onapristone, a specific progesterone antagonist. On day 19, the animals were in preterm labor and the effect of additive doses of terbutaline on the electrical power density spectrum (PDS) and integrated IUP was recorded in anesthetized rats. RESULTS: Bursts of EMG activity recorded from AS mirrored those from the UT, albeit at a lower amplitude. Terbutaline inhibited uterine contractility by decreasing the IUP. This was accompanied by a decrease in PDS as measured from UT and AS. (Figure Presented) [Terbutaline], log M CONCLUSIONS: Uterine electrical activity can be reliably recorded from the abdominal surface. This tool can replace invasive intrauterine measuring devices, which may themselves interfere with studies of myometrial function and pharmacology in-vivo. Since uterine contractions are the result of myometrial electrical activity, analysis of electrical energy may add useful information to measurement of IUP alone. Clinical studies comparing this technology to traditional tocodynamometry are warranted.