Uterine Pressure Research Articles

Fibromyomas and uterine contractions.

Women with uterine fibromyomas may suffer from dysmenorrhea, menorrhagia or infertility, which all may be due to an effect of the fibroids on uterine activity. The effect of myomectomy on uterine contractility is unknown. In women undergoing myomectomy because of dysmenorrhea, menorrhagia or infertility, intrauterine pressure was recorded before and three months after the operation on corresponding days of the menstrual cycle. Records were obtained during spontaneous uterine activity as well as after oxytocin and vasopressin challenge by intravenous bolus injections of 10 pmol/kg body weight. The area under the recording curve (AUC), maximal amplitude of uterine contractions and deformation index of uterine pressure recordings were measured. In six women, in whom recordings could be obtained before and after operation on corresponding days of late follicular phase of the menstrual cycle, the AUC and maximal amplitude of contractions increased after myomectomy. The effect of oxytocin injection also varied, whereas no difference was seen in effect of vasopressin. It is suggested that women with uterine fibromyomas may have disturbed uterine spontaneous contractions and responsiveness, which may be regulated by myomectomy.

Effect of antenatal thyrotropin-releasing hormone on uterine contractility, blood pressure, and maternal heart rate

Objective: The goal was to study the effects on uterine contractility, blood pressure, and heart rate of thyrotropin-releasing hormone given antenatally in combination with glucocorticoids to accelerate fetal maturation. Study design: A placebo-controlled, randomized, double-blind study was performed involving 30 women whose pregnancies were followed up at the University Hospital Gasthuisberg in 1994 and 1995. Results: Thyrotropin-releasing hormone induced a significant mean increase of nearly 6 mm Hg in systolic blood pressure and approximately 5 mm Hg in diastolic blood pressure. The duration of this raise was <20 minutes. Thyrotropin-releasing hormone had no significant effect on maternal heart rate or uterine contractility: 4.2 ± 1.6 contractions per hour before versus 4.7 ± 1.7 contractions per hour after treatment. Conclusions: Thyrotropin-releasing hormone induces a small (mean <6 mm Hg) and brief mean (<20 minutes) increase in blood pressure but appears to have no clinically detectable effect on uterine contractility. (Am J Obstet Gynecol 1997;177:431-3.)

Transvaginal sonographic imaging of early second-trimester fetal anatomy assisted by uterine fundal pressure

To assess the advantage of applying uterine fundal pressure to assist transvaginal sonographic imaging of early second-trimester fetal anatomy. One hundred consecutive patients with singleton fetuses underwent routine transvaginal sonographic assessment of fetal anatomy between 13 and 17 weeks' gestation. If the entire fetal anatomy including cardiac outflow tracts was not depicted, uterine fundal pressure was applied with the operator's nonscanning hand in a bimanual fashion, to facilitate transvaginal imaging. Transabdominal sonography was performed when visualization of the entire fetal anatomy was not obtainable with transvaginal or uterine fundal pressure-assisted transvaginal sonography. Observed fetal structures with and without fundal pressure were compared. Factors assessed that may have modified the value of fundal pressure included patient weight, gestational age, fetal presentation, previous abdominal surgery, and the presence of uterine fibroids. Statistical analysis included McNemar test, chi 2, Fisher exact test, and t test, with P < .05 considered significant. Visualization of lower limbs, head (including intracranial structures), upper limbs, kidneys, spine, gender, feet, hands (digits), face, four-chamber view, and cardiac outflow tracts was significantly enhanced by uterine fundal pressure-assisted versus nonassisted transvaginal sonography. Uterine fundal pressure improved transvaginal sonographic imaging in 91% of subjects, and in 51% of all subjects, a complete examination was thus obtained. In 20% of all subjects, transabdominal sonography was required to complete the examination. Complete fetal anatomic scanning was unobtainable despite uterine fundal pressure supplemented by transabdominal sonography in 29% of cases. Completion of the transvaginal sonographic fetal anatomic survey with uterine fundal pressure was related to gestational age (P < .02) and maternal weight (P < .05) yet not related to fetal presentation (P = .13), previous abdominal surgery (P = .06), or uterine fibroids (P = .26). Uterine fundal pressure applied during early second-trimester transvaginal sonographic evaluation of fetal anatomy significantly improves visualization of fetal structures otherwise located beyond the effective range of the transvaginal transducer.

Electrohysterogram: Study of the electromechanical activity of the uterus in humans

The electromechanical activity of the uterus was studied in 18 healthy women (mean age 38.3±14.2 SD years: 8 were nulliparous, 10 multiparous) aiming at characterizing a normal electrohysterogram. Two monopolar silver-silver chloride electrodes were applied to the uterine and one to the cervical mucosa. The uterine pressure was measured by a water-perfused tube connected to a pressure transducer. Monophasic, negatively deflected slow waves or pacesetter potentials (PPs) were recorded from the 2 uterine electrodes. They had regular rhythm and exhibited the same frequency, amplitude and velocity of conduction by the 2 electrodes. The PPs were followed randomly by bursts of action potentials (APs). The APs and not the PPs were associated with uterine pressure rise. PPs from the cervix were registered only occasionally. The occurrence of the electric activity is believed to depend on the smooth muscle fibers content which is high in the uterine body and meagre in the cervix. The APs seem to have contractile activity which might act to sweep away the uterine secretions. According to the uterocervical reflex, the cervix dilates upon uterine contractions. A normal electrohysterogram could be characterized. It might show a different pattern in the various uterine pathologic conditions and may thus represent an investigative tool in the diagnosis of such disorders.

Lung liquid production rates and volumes do not decrease before labor in healthy fetal sheep.

Previous studies have suggested that the volume and production rate of fetal lung liquid decrease late in gestation, before the onset of labor, in preparation for the clearance of lung liquid at birth. In contrast, our earlier studies have not shown a decrease in lung liquid volume near term, although these studies were not continued to the onset of labor. Our aim was to determine the changes in lung liquid volume and production rate in fetal sheep during the last 2 wk of gestation up to the onset of labor at term (approximately 147 days). In eight chronically catheterized fetal sheep, the volume and production rate of fetal lung liquid were measured at 130, 135, and 140 days of gestation and then on every 2nd day until the onset of labor. Labor was detected by monitoring uterine muscle activity and intrauterine pressure changes. On the day of labor onset, which occurred at 147 +/- 1 days of gestation, fetuses weighted 5.0 +/- 0.2 kg. The volume of fetal lung liquid was 40.4 +/- 2.7 ml/kg at 19 +/- 1 days before labor onset and had not significantly changed by 0.7 +/- 0.2 days (44.8 +/- 5.1 ml/kg) before labor. Similarly, lung liquid production rates at 19 +/- 1 days before labor (5.1 +/- 1.8 ml.h-1.kg-1) were not significantly different from those at 0.7 +/- 0.2 days before labor (3.4 +/- 0.7 ml.h-1.kg-1). We conclude that, in healthy ovine fetuses, lung liquid volumes and production rates do not decrease before the onset of labor. Our results indicate that the entire volume of fetal lung liquid (approximately 222.5 +/- 36.6 ml) must be cleared after the onset of labor.

Study of the uterine response to vaginal distension: the 'vagino-uterine reflex'.

To study the effect of vaginal distension on the uterus, the uterine pressure was measured in 20 healthy female volunteers (mean age 34.3 +/- 7.8 years; 7 nulli-, 13 multiparous) by means of a manometric tube perfused by a pneumohydraulic system. Vaginal distension was induced by a 12 F condom-ended catheter. The condom was inflated in increments of 10 ml of air. The test was repeated after anesthetizing the vagina and uterus, respectively. The uterine pressure increased upon vaginal distension; it showed more rise as the distension increased (p < 0.01). The response was momentary and the pressure returned to basal values although vaginal distension continued. It disappeared upon sustained or successive inflations of 5-7 times and was restored after a resting period of 3-5 min. There was no uterine pressure response when the vagina or uterus were anesthetized and it returned when the anesthetic effect had worn off. No significant difference was found in the pressure response between nulli- and multiparous women (p > 0.05). The aforementioned results were reproducible when repeated in the same woman with no significant difference (p > 0.05). The inflated condom looks like the erect penis, and the uterine response to the inflated condom seems to simulate that of the erect penis distending the vagina during coitus. The constant rise of uterine pressure to vaginal distension postulates a reflex relation which we call 'vagino-uterine' reflex. Uterine contractions during coitus are suggested to have a 'suction-pumping' action on the semen deposited in the vaginal fornices.

Uterine fundal pressure—Enhanced transvaginal sonographic imaging of early second-trimester fetal anatomy

Uterine fundal pressure—Enhanced transvaginal sonographic imaging of early second-trimester fetal anatomy

Breast suckling or nipple stimulation: prevention of postpartum haemorrhage?

There are well known and effective ways of reducing the frequency of postpartum haemorrhage (PPH) and of treating it. However, many women in developing countries do not have these technologies available to them. In other countries some women choose not to use them, because they prefer more natural methods. An appropriate technology which would serve the needs of both groups of women is needed. Breast suckling by the newborn induces uterine contractions. This effect is probably mediated by the high plasma oxytocin levels that occur during preparations for breast feeding and again within 3 min of the start of suckling. But would this occur in the first few minutes after childbirth and if so does it reduce postpartum blood loss ? An attempt to find out was made by testing the effect of an educational programme for traditional birth attendants (TBAs), which encouraged immediate suckling at birth. This was a controlled trial with randomisation by TBA and not by mother. There was no difference in the frequency of clinically significant PPH, the mean blood loss at delivery and the frequency of retained placenta. Assuming that the research was valid with respect to the measurement of blood loss the conclusions which can be drawn include the following : - breast suckling does not reduce the frequency of PPH ; - breast suckling may have been found to be ineffective only because the TBAs did not effectively implement the policy ; - breast suckling would be effective if only the newborn suckled earlier and more vigorously. This latter hypothesis suggested that nipple stimulation, which is known to cause uterine contractions during the antenatal period but does not depend on the baby's ability to suck, was the next technique which should be tested. Basic physiological research was carried out first. A randomised controlled trial was performed to study the effect of nipple stimulation on uterine activity in the third stage of labour. Compared with controls uterine pressure was higher during nipple stimulation. Another similar study obtained the same result with both nipple stimulation and breast suckling. It is suggested that a randomised controlled trial of breast suckling or nipple stimulation if breast suckling cannot be established is now indicated, preferably in a setting where trained midwives can conduct the research.

Uterine balloon therapy for the treatment of menorrhagia

From June 1994 to December 1995, 116 women (mean age 39 yrs, range 27-50 yrs) who met inclusion and exclusion criteria underwent endometrial ablation with a thermal balloon system. Forty-one (35%) were treated under general and 71 (61%) under neuroleptic anesthesia. Four (3%) treatments were performed under paracervical block only. A 16-cm long, 3-mm diameter catheter with a latex balloon at its tip housing a heating element was inserted into the uterus and filled with sterile 5% dextrose in water solution (mean 10.4 ml, range 2-55 ml). The catheter was connected to a control unit that maintained the temperature at 87 &plusmn; 5&deg; C, monitored the pressure, and terminated the treatment after 8 minutes. The starting uterine pressure was 80 to 140 mm Hg in the first 13 women and greater than 140 mm Hg in the rest. Nineteen women were treated for 12 minutes and all others for 8 minutes. Complications were endometritis (3), hematometra (2), and cystitis (1). At 6-month follow-up, after 8 minutes of treatment, persistent menorrhagia was reported by 38% and 12% of patients at less than and greater than 140 mm Hg pressure, respectively. At greater than 140 mm Hg pressure, menorrhagia was reported by 13% of women after 8 and 12 minutes of treatment. In 38 women, amenorrhea or spotting occurred in 29%, hypomenorrhea in 45%, eumenorrhea in 21%, and menorrhagia in 5%. Uterine balloon therapy is a safe and effective treatment for menorrhagia at uterine pressures of 150 to 180 mm Hg and of 8 minutes' duration.

Pregnancy enhances cocaine-induced stimulation of uterine contractions in the chronically instrumented rat

OBJECTIVE: Our purpose was to test whether cocaine stimulates uterine activity in nonpregnant and pregnant rats. STUDY DESIGN: The carotid artery and jugular vein were chronically catheterized, and a microballoon probe was inserted into the uterine cavity of 15 pregnant and 14 nonpregnant female rats. Conscious animals received a bolus dose of either cocaine or saline solution intravenously. Cardiovascular and uterine contractile responses were studied. RESULTS: Cocaine (2.5 mg/kg) induced a marked increase in uterine activity and arterial blood pressure in both pregnant and nonpregnant animals without producing systemic toxicity. The maximum change in uterine contractions was greater in the pregnant group than in the nonpregnant group, and blood pressure responses were transient in both. CONCLUSION: This study is the first demonstration that cocaine stimulates the rat uterus in vivo, with a greater increase in contractions in pregnant compared with nonpregnant animals. These differences are not related to the hemodynamic response or pharmacokinetic profile of cocaine. (Am J Obstet Gynecol 1996;175:188-93.)

The pharmacokinetics of oxytocin as they apply to labor induction

OBJECTIVE: Our purpose was to determine the relationship among plasma oxytocin levels, metabolic clearance rate of oxytocin, and uterine activity in gravid women undergoing labor induction. STUDY DESIGN: Ten women receiving oxytocin for labor induction and agreeing to participate had blood sampled before initiation of oxytocin and at different levels of uterine pressure. Samples were analyzed with 200 μl extracts from 1 ml of plasma with an oxytocin radioimmunoassay. The intraassay coefficient of variation was <3%. Sensitivity of the assay was 1.5 pg/ml. Pharmacokinetic parameters including plasma levels and metabolic clearance rates were calculated. Data were analyzed with the paired t test and linear and logistic regression. RESULTS: Mean oxytocin levels and metabolic clearance rates were 26.6 pg/ml and 7.97 ml/min. There was no correlation between changes in oxytocin level and metabolic clearance rate. Increases in infusion rates were correlated with increases in oxytocin levels ( r = 0.71, p < 0.001). Cervical dilatation and uterine contraction pressures did not correlate with oxytocin levels. CONCLUSION: Peripheral plasma levels of oxytocin may not accurately reflect uterine activity or progress in labor. Plasma levels of oxytocin may merely reflect the rate of oxytocin infusion. (A M J O BSTET G YNECOL 1996;174:1590-3.)

Effect of epidural analgesia on fundal dominance during spontaneous active-phase nulliparous labor.

The purpose of this investigation was to determine if epidural analgesia, established during active phase labor, results in elimination or reversal of fundal dominance (lower uterine segment pressure equal to or greater than fundal pressure). Upper and lower uterine segment intrauterine pressures were prospectively evaluated for 50 min before and 50 min after epidural analgesia using 0.25% bupivacaine in 11 nulliparous women in spontaneous active labor. A total of 958 contractions were evaluated. No significant differences were found in the number of contractions in the interval before epidural analgesia compared to after epidural analgesia. Significantly greater pressure readings were recorded in the upper segment than in the lower segment (consistent with fundal dominance) both before and after epidural analgesia (P<0.01). In addition, fundal dominance increased after epidural analgesia when compared to the preanalgesia period (P<0.01). Fundal dominance is present both before and after active phase epidural analgesia and is increased during the immediate 50-min postanalgesia period.

The ‘clitoromotor’ reflex

The effect of glans clitoris (GC) stimulation on the vagina, uterus and pelvic floor muscles (levator ani (LA) or pubococcygeus, puborectalis (PR)) was studied in 16 healthy volunteers (mean age 34.9 years). The GC was stimulated mechanically and electrically while recording the vaginal and uterine pressures and the electromyographic activity of PR and LA. Stimulation caused a drop in the uterine (P<0.001) and upper vaginal (P<0.05) pressures (1.6 and 2.9 cmH2O, respectively) and an increase in the middle (P<0.001) and lower (P<0.001) vaginal pressures (58.6 and 89.2 cmH2O, respectively). It also effected an increase of EMG activity in the PR (P<0.01) and LA (P<0.01). Response was greater with electrical than with mechanical stimulation (P<0.05). No response occurred upon stimulation of the anesthetized GC or the anesthetized PR or LA. The reproducibility of the PR and LA contraction on GC stimulation postulates a reflex relationship which we call the ‘clitoromotor reflex’. This induces uterovaginal changes that enhance the sexual response of both partners, and also prepares the uterus and vagina for the reproductive process. LA contraction pulls open and reduces the pressure in the upper vagina as well as elevating the cervix uteri. PR contraction constricts the middle and lower vagina and increases their pressure.

An assessment of the intrauterine sound intensity level during obstetric echo-planar magnetic resonance imaging.

In order to assess the sound level experienced by the fetal ear during obstetric magnetic resonance imaging, a fluid filled stomach was used as an experimental model of the gravid uterus. A better than 30 dB attenuation in intensity was recorded across the frequency band of interest for all patient orientations. This was enough to reduce acoustic sound pressure from a level close to the instantaneous damage threshold (120 dB), to an acceptable level (< 90 dB). Direct mechanical coupling through the patient table was also shown to increase uterine sound pressure levels by as much as 10 dB. Much higher peak pressures could be obtained by tapping of abdomen with the fingers.

An Experimental Model for Long-Term Examinations of Urethral and Uterine Pressures in Conscious Dogs: Effect of a Highly Selective Compound Contracting Urethral Smooth Muscles

An experiment model was designed for studies of urethral and uterine pressures in a conscious animal, thereby avoiding the interference of anesthesia on these responses. Dogs were trained to stand in cradles for an experimental period of 3 hours, during which urethral and uterine pressures and ECG were recorded. Substances were administered either orally or intravenously. Intravenously given phenylpropanolamine (PPA; 0.3 mg./kg.) and a newly synthetized compound S113 (0.5 mg./kg. intravenously) increased the urethral pressure by about 30 and 100%, respectively. Oral administration of PPA (3.5 mg./kg.) and S113 (6 mg./kg.) increased it by about 60 and 85%, respectively. In contrast to PPA, S113 evoked no cardiac effects. Whereas PPA had pronounced effects on uterine contractility, S113 had only minor effects. Furthermore, the responses in the experiments were stable and reproducible. This dog model seems to be useful for long-term recordings of urethral and uterine pressures.

A Microsoft ® Windows ™ based application for acquisition and replay of cardiotocograph data

The electronic fetal monitor or cardiotocograph is an integral part of all modern labour wards. It records fetal heart and uterine contractions and charts this data as a cardiotocogram (CTG). The CTG is used to assess fetal well-being by the labour attendants and in some circumstances for research. A means to acquire and display the CTG by microcomputer as an aid to archiving and to obstetric research is presented. A Microsoft Windows-based application was written using Microsoft C version 7.0 to acquire and replay the CTG data. The application acquires the CTG data by using the RS232 serial link fitted on most modern fetal monitors. Additionally, comments and events can be entered by the user throughout recording. The data are saved to disk files which can be replayed on screen in the manner of a CTG. The data replay functions of the application calculates the uterine activity integral and active pressure for each contraction and for 15 min intervals. This calculated data is not available from many fetal monitors but is widely used for research into the mechanics of labour. This application provides an easy, reliable and accurate means of acquiring the CTG data, for archiving and research. It also provides a framework for further CTG analysis.

Medroxyprogesterone acetate (Depo-Provera) use in adolescents: Uterine bleeding and blood pressure patterns, patient satisfaction, and continuation rates

Study Objective: This study examined the utilization of medroxyprogesterone acetate (Depo-Provera) in adolescent patients to determine selected side effects, degree of satisfaction, and continuation rates.Design: The design was a retrospective chart review of 50 adolescent patients totaling 384 clinic visits and accumulating 1007 woman-months of experience on DepoProvera.Setting: The Teenage Clinic at Children's Hospital, Columbus, Ohio, was the setting for this study.Participants: The mean age was 15.6 (±2.5); racial distribution was 52% African-American and 48% white. The mean number of visits per patient was 7.4 (±7.9), ranging from 2 to 39 visits.Interventions: Each patient was given Depo-Provera for either a pre-existing medical indication or for contraception.Main Outcome Measures: Uterine bleeding patterns, blood pressure readings, patient satisfaction, and continuation rates. Results: A strong correlation was found between length of time on Depo-Provera and amenorrhea and spotting (p < 0.01). No new recordings of hypertension occurred. The majority of patients expressed overall satisfaction with Depo-Provera, and most found amenorrhea to be a positive aspect of the drug. Continuation rates exceeded 50% after 2 years and generally fell within ranges reported for adult women. No pregnancies were recorded during the course of the study.Conclusions: This study indicates that Depo-Provera can be used in an adolescent population with a high degree of acceptability and does not increase patient risk for hypertension. The likelihood of amenorrhea increases greatly with duration of treatment and does not seem to deter the continuation of its use.

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.

A simple alternative to parenteral oxytocics for the third stage of labor

Objective: To determine the effect of nipple stimulation on uterine activity during the third stage of labor. Methods: Randomized controlled study comparing; (i) 15 min of nipple stimulation ( n = 6), (ii) routine syntometrine injection ( n = 3), (iii) no action/control ( N = 5). Uterine activity was continuously measured using the placenta as an in-situ hydrostatic bag connected to a pressure transducer. Results: Compared to controls uterine pressure was higher during nipple stimulation (103 mmHg vs. 70.8 mmHg, P = 0.04). The duration of the third stage and blood loss tended to be reduced with nipple stimulation compared to controls (20.3 vs. 12.3 min) and (257 vs. 166 ml) respectively but was not significant. Similar differences were observed between syntometrine and control groups. Conclusion: For women in developing countries where parenteral oxytocics are not available, nipple stimulation might reduce the incidence of postpartum hemorrhage. A larger trial now seems warranted.

Uterocervical reflex: description of the reflex and its clinical significance.

The effect of uterine distension on the cervix was studied in 16 women (mean age 38.4 years). Carbon dioxide was infused, in increments up to 50 ml, into a condom-ended catheter introduced into the uterus. The response of uterine and cervical pressures to uterine distension was determined before and after anesthetizing the uterine body and the cervix, respectively. Upon slow uterine distension, the cervical pressure increased (p < 0.01), while the uterine pressure showed insignificant changes (p > 0.05). Rapid distension led to cervical pressure decrease (p < 0.01) and increase of uterine pressure (p < 0.01). The cervical pressure did not respond to slow or rapid inflation of the anesthetized uterus, neither did the anesthetized cervix respond to uterine inflation. A reflex relationship seems to exist between the uterine body when distended and the cervix, which we call 'uterocervical reflex'. The study demonstrates that the uterus behaves differently under physiologic and pathologic conditions. Upon slow uterine distension as in pregnancy, the uterus adapts by uterine dilatation and cervical tightening. In pathologic conditions which distend the uterus rapidly, the latter reacts with uterine contraction and cervical dilatation, discharging the uterine contents. Dysfunction of the uterocervical reflex may result in uterine and cervical disorders. The reflex may thus be included as a diagnostic tool in such disorders.