Electromyographical Studies on the Human Perineal Muscles Part 1. The Functional Differentiation and the Adjustment of Contraction of the Human Perineal Muscles

With the purpose to investigate the functional changes of the perineal muscles brought about by pregnancy and delivery, the author determined the -S relationship in the electromyograph of the bulbo-cavernous muscle and levator ani muscle in women married but not pregnant, multipara, multigravida (but without normal delivery), and in women with uterovaginal prolapse at the time when the perineal muscles had been variously made to contract intensely either at rest or intentionally all the while maintaining such a contraction in each case as constantly as possible, and studied the -S relatinnship. The following are the results: 1. In the perineal muscles like in other skeletal muscles there are two kinds of the functional differentiation in NMU, namely, kinetic NMU and tonic NMU. 2. The ratio of the discharge groups between tonic NMU and kinetic NMU in the bulbocavernous muscles and levator ani muscles in any of the four goups of women mentioned above lies between 1.86 and 2.00 in the case of bulbo-cavernous muscles while between 2.14 and 2.22 in the levator ani muscles, showing no marked changes in either case. 3. In the -S relationship of the bulbo-cavernous muscles and levator ani muscles both K and T curves tend to show a shift to right in the bulbo-cavernous muscles; and therefore, the levator ani muscles seem to be the muscle more adapted for mainataining a sustained movement than the bulbo-cavernous muscles. 4. That both K and T curves, especially the T curve, tend to show the shift to right in pregnancy seems to indicate that the contracting mechanism of the perineal muscles is functioning smoothly in unison with abdominal distention, the perineal muscles playing a role of barotaxic muscle. 5. In the cases with uterovaginal prolapas T curve in both the bulbo-cavernous and levator ani muscles tends to show a shift to left, and in addition, S is increased in both K and T curves. This phenomenon is due to the shortened range of smoothly-working adjustment mechanism at the intentional contraction of muscles with consequent diminution in barotaxic action. Part 2. Clinical Application of the Electromyograph of the Contration of the Perineal Muscles As for the intensity of the muscular contraction, it is determined by the amplitude of the discharge of an individual NMU, and it is also determined by numbers of NMU acting at the same time. Therefore, there is as yet no conclusive evidence proving any clear-cut quantitative relationship between the frequency of spike discharge appearing in mucslce fibers and the intensity of the muscle contraction. However, the author has been able to clarify that the intensity of the muscle contraction, as determined even by such a simple method as to determine numbers of discharge at a given unit of time with the use of a concentric type of elctrodes, coincides with clinical findings and that the determination of the degree of perineal muscle contraction and the observation on the action of hormoues (especially progesterone) on the perineal muscle are clinically valuble. Namely: 1. In pregnancy the frequency of discharge in the perineal muscles is decreesed, and it is still further decreased with advance in the pregnant month. The abortion, however, brings this lowered frequency gradually back to the normal level. 2. Even in the cases of uterovaginal prolapse, the frequency of discharge is diminished, and such a diminution is proportional to the degree of uterovaginal prolapse. 3. Progesterone acts as to relax the perineal muscle while estradiol has no marked effect on the myogenic tonus of the muscles. 4. In the case of functional hemorrhage, the tonus of the perineal muscles is either slightly or moderately accelerated. 5. The tonus of the perineal muscles in uterine hypoplasia is also accelerated. 6. It seems that there is no causal realtion between hormones and the perineal muscle tonus in uterine cancer, uterine myoma, and ovarian cystom