Ultra-low-noise instrumentation and computer-based data acquisition and processing system for obtaining a noninvasive and intrauterine catheter fetal electrocardiogram.
A fetal electrocardiogram (FECG) from the abdominal surface will be from 20 microVpp to unmeasurable. The intrauterine catheter signal will be from 50 microVpp to unmeasureable and will be corrupted with a significant direct current component of 10 to 200 microV. For electrophysiological information to be obtained from the abdominal and intrauterine catheter signals, the signals must be in a 0.05 to 100.0 Hz bandwidth. Because typical adult electrocardiogram systems have a noise specification of 5 to 10 microVpp from instrumentation, these systems are unacceptable for obtaining a FECG via the intrauterine catheter or noninvasively. Therefore, custom instrumentation has been developed with a noise specification of approximately 1.5 microVpp in a 0.05 to 100.0 Hz bandwidth. Design details of the custom instrumentation will be presented along with a laptop computer based data acquisition and signal processing system using LabVIEW. In addition, clinical data from the intrauterine catheter and noninvasive abdominal wall are presented to determine the feasibility of obtaining a FECG via the custom instrumentation. Clinical data obtained and documented indicates that after maternal electrocardiogram cancellation, a FECG with a good signal-to-noise ratio can be obtained in a diagnostic bandwidth of 0.05 to 100.0 Hz. Because the diagnostic bandwidth is preserved, electrophysiological information can be determined along with heart rate.