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Biomedical subjects

E S Genevier

Publications and source records attributed to E S Genevier.

10 recordsLinked to original sources
PubMed1997

Simultaneous monitoring of head-to-cervix forces, intrauterine pressure and cervical dilatation during labour.

In many westernized countries, the caesarean section role has now reached 15% or more, most commonly because of slow progress in labour. In order for labour to result in a vaginal delivery, the uterine cervix must dilate to allow the foetus to travel through the birth canal. This process is driven by uterine contractions, but the mechanisms by which the contractions result in cervical dilatation are still far from clear. The force exerted by the presenting part (foetal head) on the cervical tissue during contractions (head-to-cervix force, HCF) has been shown to be the variable with the best correlation with cervical dilatation. Unfortunately, the mechanism by which these two variables are related is still poorly understood. In order to investigate the relationship between head-to-cervix force, intrauterine pressure (IUP) and cervical dilatation, we have developed a system for their simultaneous and continuous monitoring during labour. The HCF is measured by using a novel intrauterine probe which is slipped alongside the foetal head so as to lie sandwiched between the latter and the cervix. The probe is fitted with six specially designed miniature force sensors, spaced 1.8 cm apart, which respond linearly and approximate the behaviour of load cells. They are interfaced with a PC by circuitry that allows auto-zeroing and drift compensation. The system enables simultaneous acquisition of intrauterine pressure and foetal heart rate (measured using a Sonicaid Meridian foetal monitor) via a serial link, together with continuous cervical dilatation measured by a caliper-like device applied to the cervix. Some preliminary data are presented, which suggest that the system can be used to investigate the role played by head-to-cervix force and intrauterine pressure in the cervix dilatation process.

Analog-Digital Conversion↗
PubMed1996

Head-to-cervix force: an important physiological variable in labour. 1. The temporal relation between head-to-cervix force and intrauterine pressure during labour.

OBJECTIVE: To investigate the relation between the rise in intrauterine pressure and rise in fetal head to cervix force in normal, slow and induced labour. DESIGN: Prospective observational study. SETTING: The labour ward of a London teaching hospital. PARTICIPANTS: Forty patients were recruited from the antenatal clinic and labour ward of a West London Hospital. Five had normal onset and progression of labour, 14 had slow progression of labour and 21 had induced onset of labour. METHOD: Intrauterine pressure and head-to-cervix force was measured simultaneously using an intrauterine pressure catheter and a specially designed four sensor head-to-cervix force probe. RESULTS: For each contraction of each labour, scattergrams of force by pressure were plotted. Three patterns were observed. When the rise in pressure preceded the rise in force, a positive 'loop' was generated. When the rise in pressure and force occurred simultaneously a linear pattern was generated (a neutral 'loop'). When the rise in pressure lags the rise in force, a negative 'loop' was generated. In normally progressive labour the distribution of loops was 29.1%, 22.6% and 48.3%, respectively, in slow labour the distribution was 26.1%, 14.1% and 59.8% and in induced labour the distribution was 33.8%, 14.4% and 51.8%. These distributions were not statistically different. However, a higher proportion of negative loops was observed in labours augmented with oxytocin compared to those receiving no oxytocin (MW-U = 87, P = 0.036). No differences were observed comparing parity, use of PGE2, epidural analgesia, or mode of delivery. Contraction frequency (number/10 minutes) was inversely correlated to the percentage of negative loops (rs = -0.34, P = 0.033) and positively correlated with percentage of positive loops (rs = 0.36, P = 0.027). CONCLUSIONS: This is the first report of the temporal relation between intrauterine pressure and head-to-cervix force in labour. The most common pattern is that the rise in pressure lags the rise in force, suggesting that a seal has to be created between the fetal head and cervix before a rise in pressure can occur. When oxytocin is given in labour, a higher proportion of loops are negative indicating that there is poor application of the fetal head and cervix in a greater proportion of contractions.

Adult↗
PubMed1996

Head-to-cervix force: an important physiological variable in labour. 2. Peak active force, peak active pressure and mode of delivery.

OBJECTIVE: To assess the relation between peak active (above baseline) head-to-cervix force (paHCF) and peak active (above baseline) intrauterine pressure (paIUP) in labour, and to compare the relation between labours progressing well and ending in vaginal delivery and those labours progressing slowly and ending in caesarean section. DESIGN: Prospective observational study. SETTING: The labour ward of a London teaching hospital. PARTICIPANTS: Forty women in labour who agreed to have an experimental head-to-cervix force probe and an intrauterine pressure catheter inserted. RESULTS: The relation was linear, with a correlation coefficient which ranged from 0.012 to 0.885 (mean value 0.438). The closeness of the relation did not correlate with the rate of cervical dilatation (r = 0.0192, P = 0.574) or the mode of delivery (r = 0.215, P = 0.183). However, in women who progressed well to a vaginal delivery, the mean slope of the paHCF to paIUP regression line was 0.72, significantly steeper than in women who progressed slowly and required delivery by caesarean section (mean slope = 0.45, t = 2.31, P = 0.02). Mean paIUPs were significantly higher in women progressing well and achieving a vaginal delivery than in those progressing slowly and requiring caesarean section (45.3 mmHg SD 7.5 vs 38.4 mmHg SD 11.4, t = 2.31, P = 0.02), but the overlap between the two groups was considerable. However, in keeping with their steeper paHCF/paIUP slope, women progressing well to a vaginal delivery had substantially higher head-to-cervix forces (46.4 gWt SD 11.8 vs 28.3 gWt SD 8.2, t = 5.22, P < 0.00001) than those progressing slowly and requiring caesarean section, and there was much less overlap between paHCF than paIUP. This resulted in paHCF being a much better discriminating variable than paIUP for mode of delivery. CONCLUSIONS: The relation between paHCF and paIUP is linear, but there is a wide variation in the degree of correlation between one woman and another. Women with a steep slope of paHCF relative to paIUP are more likely to achieve a high mean paHCF, progress rapidly in labour and achieve a vaginal delivery than women with a flap slope, although mean paIUPs do not differ substantially between the two groups. The level of paHCF was substantially better than cervical dilatation rate at predicting mode of delivery. These results suggest that head-to-cervix force is sensitive to factors determining mode of delivery which are not reflected in either the level of uterine activity as measured by intrauterine pressure, or cervical compliance as measured by cervical dilatation rates.

Adult↗
PubMed1995

Separation of fetal and maternal ECG complexes from a mixed signal using an algorithm based on linear regression.

Fetal scalp ECG and Doppler ultrasound are the two methods universally used to derive the fetal heart rate (FHR) for cardiotocography. Other fetal signal sources have not been used successfully because of the complexity of the signal and the need for an additional maternal ECG input. In this paper, we present an algorithm for separating the fetal and maternal ECG signals obtained from intrauterine electrodes during labour. The algorithm detects all occurrences of ECG complexes and uses linear regression functions to compare each complex with a set templates. Sets of templates are identified as either maternal or fetal in origin and two signals are output for heart rate measurement. The outputs are also processed to eliminate artefacts that may occur when the maternal and fetal complexes are coincident. The algorithm processes 10 seconds of data at a time (in about 200 ms on a standard PC) while a further 10 s of data is being acquired. It has the advantage that no extra input is required, such as maternal ECG obtained from chest leads, and only assumes that two different populations of complexes of two different shapes are present in the input signal. The algorithm could also be used for the separation of fetal and maternal signals obtained from abdominal electrodes.

Algorithms↗
PubMed1995

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.

Cardiotocography↗
PubMed1993

A method for continuous monitoring of meconium in the amniotic fluid during labour.

In about 10% of pregnancies overall, the fetus discharges meconium (its bowel contents) into the amniotic fluid during labour. In about 10% of cases where meconium is passed, the fetus gasps, inhaling the sticky meconium into the upper respiratory tract. After birth, the meconium blocks the air passages in the lungs, impairing gas exchange--meconium aspiration syndrome (MAS). Up to 20% of infants suffering from MAS die and recently published studies have shown a long-term effect of MAS in causing cough and wheeze. The risk of meconium aspiration is thought to be increased by intrauterine hypoxia. At present, meconium is only noticed at birth or occasionally when amniotic fluid leaks past the presenting part of the fetus. A method has been developed which measures absolute meconium concentration with a 99% prediction interval of +/- 30 g l-1; allows monitoring of the rate of appearance of meconium linearly with a nonlinearity of 5%, and differentiates between meconium and blood. The method uses the ratio of the intensity of back-scattered light from the amniotic fluid at 700 and 415 nm, the latter being near the peak of light absorption by meconium and the former a reference value. The ratio is also affected by the presence of blood. However, blood has specific absorption peaks at 540 and 575 nm from which it can be detected (the presence of blood is also a significant abnormality, and is relatively uncommon). The measurement method could easily be integrated into an optical sensor mounted onto an intrauterine probe.(ABSTRACT TRUNCATED AT 250 WORDS)

Amniotic Fluid↗
PubMed1993

Continuous meconium monitoring during labour using an intrauterine probe.

The fetus discharges meconium (its bowel contents) into the amniotic fluid during labour in approximately 10% of pregnancies. In about 10% of cases where meconium is passed, the fetus gasps, inhaling the sticky meconium into the upper respiratory tract. After birth, the meconium blocks the air passages in the lungs, impairing gas exchange (meconium aspiration syndrome, MAS). Up to 20% of infants suffering from MAS die and recently published studies have shown a long-term effect of MAS in causing cough and wheeze. At present, meconium is only noticed at birth or occasionally when amniotic fluid leaks past the presenting part of the fetus. We have developed a system to monitor meconium continuously during labour, using a flexible intrauterine probe. The system provides a measurement of the meconium concentration of amniotic fluid during labour every 2 min, with a 60% prediction interval of +/- 10 g l-1, and a 99% prediction interval of +/- 30 g l-1 (clinically 'thick meconium' contains around 100 g l-1). The noise of the measurement is of the order of +/- 10 g l-1, and the response to changes in the meconium concentration is from 40 to 120 s, depending on its configuration. The system also provides other obstetric variables such as fetal heart rate and uterine activity measurement, obtained from a fetal monitor. Preliminary clinical results indicate that this system can measure meconium not apparent to the attending staff; the system can detect changes in the meconium concentration of amniotic fluid; the measurements are confirmed by visual observation at delivery; and changes of meconium concentration seem to correlate with known stressful stimuli. The system therefore provides a new tool from which new variables are obtained, which can greatly enhance clinical research into the pathophysiology of meconium passage and aspiration.

Female↗
PubMed1990

Assessment of cardiotocographs.

In recent years advances in medical electronic equipment for monitoring, diagnosis and treatment of patients have led to a large increase in the number and variety of instrumentation available to the medical profession. There is a considerable amount of duplication of equipment and in the absence of readily available information buyers are unlikely to make informed decisions about the ideal instrument for their particular circumstances. One method of increasing the users' awareness is a comparative, independent assessment of equipment, with the results disseminated to the interested parties. This paper describes the essential qualities of cardiotocographs: how they are assessed as part of the UK Department of Health's evaluation programme and the measures to inform users of the latest evaluation information.

Cardiotocography↗
PubMed1990

Head-to-cervix forces and their relationship to the outcome of labor.

The force (as distinct from pressure) between the fetal head and the maternal cervix during labor was measured for the first time in an attempt to improve the intrapartum prediction of progress in labor. The 50th percentile of the variables active pressure and active force and the mean uterine activity integral were compared with the cervical dilatation rate and delivery mode in 31 women. The 50th percentile of active force had the highest correlation with the cervical dilatation rate (r = 0.54) (50th percentile of active pressure, r = 0.43; mean uterine activity integral, r = 0.40). The 50th percentile of active force was significantly higher in women who achieved a vaginal delivery (mean +/- SD 45 +/- 21.2 g wt) than in those who underwent cesarean delivery for failure to progress (16.5 +/- 9 g wt). The 50th percentile of active force discriminated among modes of delivery as effectively as did the cervical dilatation rate. These results support the hypothesis that head-to-cervix force measurements may have clinical value in the management of labor.

Biomechanical Phenomena↗