Utero-cervical inhibitory reflex. The description of a reflex and its clinical significance.

The functional relationship of the uterine corpus to the cervix was studied in 14 healthy women. The uterus was stimulated by an electro-myographic (EMG) needle electrode and the cervical pressure recorded by a balloon-tipped catheter. The test was repeated in seven women after the uterus had been anaesthetized. In the other seven patients, the response of both the uterine EMG and pressure to cervical dilatation was registered. The EMG needle electrode was then inserted into the cervix and the uterine pressure response to both stimulation and dilatation of the non-anaesthetized and anaesthetized cervix was recorded. Uterine muscle stimulation led to a cervical pressure drop from a mean of 15.8 +/- 6.6 to 5.3 +/- 2.2 cm H2O (P < 0.01). The cervical pressure did not respond to stimulation of the anaesthetized uterus. Cervical dilatation caused increase of the uterine pressure from a mean of 16.2 +/- 5.2 to 42.8 +/- 10.5 cm H2O (P < 0.01), whereas cervical stimulation effected a uterine pressure drop to a mean of 3.6 +/- 1.8 cm H2O (P < 0.01). Stimulation or dilatation of the anaesthetized cervix did not cause uterine pressure changes. The invariable cervical dilatation upon uterine stimulation suggests a reflex relationship which we have named 'utero-cervical inhibitory reflex' (UCIR). It seems that the reflex comes into action during labour and in conditions of uterine retention of blood or a dead ovum. Its impairment may interfere with cervical dilatation or lead to cervical incompetence. The UCIR could be included as an investigative tool in utero-cervical disorders.