Device and Instrumentation of Tokomonitor Type "MDE"

Abstract

The application of electronic methods to the study of the uterine contraction during labor pains) and of the fetus in utero have received great impetus, and there are now many equipments for this purpose. We made up a newly-designed Tokomonitor type " MDE " (Tokomonitor : monitoring of labor and fetal life, type " MDE ": MD =The Tokyo Medical and Dental University, E =electronic), consisted of an External Electrotocograph type " MDE " and a Fetal Heart Rate Computer type " MDE ". The External Electrotocograph type " MDE " The pick up of external electrotocograph type " MDE " is equipped with linear variable differential transformer (Fig. 2 and Fig. 3). Characteristics of the differential, transformer is shown in Figure 4. In the pick up, the primary winding is excited from oscillator (frequency : about 1000 cycles per second). With the core in the mid position with respect to the secondaries, equal voltages are induced in the two secondaries. The core is connected with plunger, and hence the displacement of plunger according to the uterine action is that of the core. The difference of voltages induced in two secondaries by the movable core will be amplified with electron tube system (Fig. 6, right), and this output drives one galvanometer of two-channel recorder. The block diagram is illustrated in Figure 5 (upper). The recorder which we have employed to provide a written record of the uterine action is a two-channel direct ink writer (Fig. 7) newly-designed as follows : Deflection of pen 50 mm (paper 50 mm in width). The linearity of calibration at maximum deflection within±2.5 %. Characteristics of frequency Fig. 8. Sensitivity 50 mm/5 mA (Fig. 9). Chart speeds of 10 mm/min. General characteristics of our external tocograph is shown in Figure 10, and a tocogram is illustrated in Fig. 11. The Fetal Heart Rate Computer type " MDE " The fetal heart rate computer consists of a contact type "ceramic" microphone, an electron tube system equipped with preamplifier, amplifier, bandpassfilter, trigger, chipper, multivibrator, integrator DC amplifier, and a recorder. Experience with various types of microphones led us to choose a newly-designed "ceramic " contract microphone instead of crystal microphone (Fig. 2 and Fig. 3). The block diagram of the electron tube system (Fig. 6,left) is illustrated in Figure 5 (lower). For tocography one galvanometer of the two-channel recorder which has previously mentioned in this paper was used and the other one was employed is recording fetal heart rate (Fig. 7). A few written record of fetal heart rate are shown in Fig. 14 (without labor pains) and Fig. 15 (with labor pains). Tokomonograms, that is a written record of labor pains and fetal heart rate are illustrated in Fig. 16 and Fig. 17.