Automated analysis of the FHR: evaluation?
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Automation↗
Biomedical subjects
G S Dawes
Publications and source records attributed to G S Dawes.
Computerized measurement of heart rate variation in fetal anemia caused by rhesus alloimmunization.
OBJECTIVE: The purpose of this study was to examine the relationship between fetal heart rate variation and fetal hematocrit. STUDY DESIGN: In 36 red-cell alloimmunized pregnancies (mean gestational age 30, range 25 to 36 weeks) 65 computerized fetal heart rate recordings were obtained before ultrasonographically guided fetal blood sampling for the measurement of fetal hematocrit. The recordings were captured and analyzed by a microcomputer on-line. Fetal heart rate variation in anemic fetuses was accurately measured. RESULTS: Significant positive correlations between short-term or long-term heart rate variation and fetal hematocrit have been demonstrated even after adjusting for the effect of gestation (r = 0.60, n = 65, p less than 0.01, y = 19.264 + 0.913x - 0.003x2; r = 0.52, n = 65, p less than 0.01, y = 21.13 + 0.858x - 0.003x2, respectively). The relationship was best described by a quadratic model. When short-term variation was less than 5 milliseconds or long-term variation was less than 30 milliseconds, the positive predictive values for fetal hematocrit of less than 30 were 85% and 90%, and the negative predictive values 56% and 57%, respectively. CONCLUSION: Computerized recording and analysis of fetal heart rate variation may prove to be a useful noninvasive tool for assessing fetal anemia in red-cell alloimmunization.
Anemia↗
Antenatal cardiotocogram quality and interpretation using computers.
OBJECTIVE: To test the application in practice of computerized fetal heart rate (FHR) analysis in pregnancy. DESIGN: Randomized distribution of subjects with computerized analysis automatically revealed or concealed. SETTING: A district general hospital and a teaching hospital outside London. SUBJECTS: 2869 pregnant women studied within a year. OUTCOME MEASURES: Quality and duration of the cardiotocogram; quantitative measurement of FHR variation; number of stillbirths. RESULTS: With interactive advice to the operator, records were of improved quality (up to 28% without signal loss) with potentially much reduced recording time. The short-term FHR variation measured in the last records before intervention is reported for the first time. CONCLUSION: The benefits of using the computers include improvement in record quality and saving of time. In addition, where interpretation depended on estimation of FHR variation there was prima facie evidence of observer misinterpretation; visual analysis was unreliable. A larger trial is now required with more rigorous constraints on intervention.
Cardiotocography↗
Short-term fetal heart rate variation, decelerations, and umbilical flow velocity waveforms before labor.
OBJECTIVE: To determine the value of computerized antepartum measurements of short-term fetal heart rate (FHR) variation and decelerations as a predictor of outcome, and to compare these with measurements of the umbilical artery flow velocity waveform. METHODS: Data were collected from 3563 high-risk patients for measurements of FHR variables (15,702 records) and outcome (intrauterine death or metabolic acidemia on delivery). Detailed analyses were made on 89 patients with one or more records in which short-term FHR variation was 3 milliseconds or less. Umbilical artery flow velocity waveforms were measured concurrently on 2441 occasions in 991 patients. RESULTS: More than half of the patients with FHR variation of 3 milliseconds or less were identified before 31 weeks. When short-term FHR variation exceeded 3 milliseconds, there were no intrauterine deaths and only one instance of metabolic acidemia on cesarean delivery. When FHR variation fell below 2.6 milliseconds, 34% of the subjects had metabolic acidemia on cesarean or intrauterine death. The appearance or absence of decelerations was an unreliable guide to outcome. The correlation between FHR variation and the umbilical artery flow velocity waveform was low (r = 0.32). The population studied contained some patients without placental vascular disease or, in five with pre-eclampsia, without abnormal umbilical artery velocity waveforms but with grossly reduced FHR variation. CONCLUSION: Reduction in short-term FHR variation, as measured by computer, reliably predicts fetal outcome and is a more general measure of fetal well-being than are umbilical artery flow velocities.
Blood Flow Velocity↗
Approximate entropy, a statistic of regularity, applied to fetal heart rate data before and during labor.
OBJECTIVE: To determine whether approximate entropy (ApEn), a new statistic of regularity, when applied to fetal heart rate (FHR) data antepartum or in labor, would offer an advantage over standard statistics of variation in predicting outcome. METHODS: A large data base of antepartum FHR records collected in clinical practice over 10 years was available. Two data sets in labor were stored on disk in small computers interfaced to fetal monitors on-line. Outcomes were assessed using blood gas values on delivery and Apgar scores. RESULTS: Antepartum, when the most favorable form of ApEn was used on 769 good-quality FHR records, the correlation with measurement of short-term variation was high. This was especially true when the fetal pulse interval variation fell below the normal range (less than 6 milliseconds short-term; r = 0.93) and in 20 other records with sinusoidal variation (r = 0.96). Approximate entropy varied with fetal sleep cycles and took longer to calculate than FHR variation. During the last hour of labor, in 319 records, there was no significant correlation between umbilical artery base deficit values on delivery and ApEn measurement. In 871 additional good-quality records of fetuses with normal outcome, the mean (+/- standard error [SE]) ApEn (0.95 +/- 0.005) was significantly greater than in 22 records (0.88 +/- 0.028) from fetuses with abnormal outcome (umbilical artery base deficit more than 12 mmol/L and Apgar score of 3 or less at 1 minute). However, consideration of the frequency distributions of these measurements showed that ApEn did not discriminate between normal and abnormal outcomes. The SD of fetal pulse intervals rose in labor whereas ApEn values fell, confirming that this new statistic of regularity differs from standard statistics of variation. CONCLUSION: Approximate entropy offered no advantage over measurement of short-term FHR variation antepartum, and neither measurement predicted outcome in labor.
Adult↗
Short-term variation in abnormal antenatal fetal heart rate records.
In a retrospective study the relation of reduced fetal heart rate variation to fetal acidemia was analyzed with a computerized system for numeric analysis. Between 1983 and 1987, 78 pregnancies were identified in which at least one record of the fetal heart rate had very low long-term variation. The outcome was analyzed to determine the numeric criteria of fetal heart rate variation that most efficiently detect a fetus that will die (preterminal) or is dying (terminal). Because fetal compromise was found on occasion to be associated with a slow sinusoidal fetal heart rate rhythm that increased measures of long-term variation. It was necessary to define a new index of short-term fetal heart rate variation (the 1/16 minute epoch-epoch variation). This was closely related to long-term variation (r = 0.9) but provided better detection of preterminal records as judged by metabolic acidemia at delivery or intrauterine death.
Adult↗
Computerized analysis of episodic changes in fetal heart rate variation in early labor.
Fetal heart rate variation in early labor was measured by computerized analysis in cyclic episodes of low or high variation in 136 women at 37 to 42 weeks' gestation. The amplitude (mean +/- SE) in episodes of low variation was 20.6 +/- 0.4 milliseconds; in high variation it was 57.3 +/- 1.1 milliseconds. The duration (mean +/- SE) of low episodes (24.3 +/- 1.3 minutes) was less than that of high episodes (45.1 +/- 2.7 minutes) but was sometimes greater than 1 hour. In episodes of low variation the amplitude was less than 5 beats/min long term in 11% and less than 2.5 milliseconds (pulse intervals) short term in 8%; these measures would be predictive of intrauterine death if persistent before birth. We conclude that the use of decreased fetal heart rate variation as a diagnostic sign of acute fetal hypoxemia in labor is incorrect, because changes of this size occur randomly as a consequence of fetal sleep states. There was no significant correlation between fetal heart rate variation over the last hour of labor and umbilical arterial base deficit on delivery.
Adult↗
The advantages of computerized fetal heart rate analysis.
A brief account is given of the advantages of computerized analysis of human fetal heart rate (FHR) traces antenatally, based on clinical use over 8 years. Accuracy is greater. Results are presented quantitatively and consistently. The numerical measures of the FHR pattern are related to other objective measures of fetal health, e.g. initial compensated hypoxaemia or terminal acidaemia. Computerized analysis has shown that changes in FHR variation are a better guide than the presence or absence of large decelerations. Recording time is used better. Synoptic displays of data over 4 weeks show significant trends in fetal heart rate variation and movements with time. And the problems generated by the limitations of fetal heart rate monitors are identified to exclude spurious information.
Cardiotocography↗
System 8000: computerized antenatal FHR analysis.
SYSTEM 8000 is a computerized system for antenatal fetal heart rate (FHR) analysis, with interaction online to ensure good quality recording and to minimize the time required to obtain the necessary information (based on fetal movements and tocodynamometer readings as well as FHR). The equipment consists of a Personal Computer with hard disk, interfaced to a fetal monitor. Software is written in C. An extensive definition is given on most of the functions and parameters as calculated by the system, e.g. record quality, uterine contraction peaks, basal heart rate, variation, decelerations and accelerations. System 8000 is designed to take account of the episodic changes in FHR and fetal movements characteristic of sleep states. Their presence naturally affects the mean FHR variation calculated over, say 20-30 mins. But, as the amplitude of these episodes is attenuated in association with growth retardation and hypoxaemia, the measurements of variation decline. In practice inter- and intra-observer variation is greatest in assessing FHR variation. Yet a decrease in variation is the most reliable index of fetal deterioration. The system measures FHR variation accurately and reproducibly, as well as fetal movements. In the synoptic display these two equally important fetal variables are given their rightful prominence. It has been interesting to observe how rarely the basal FHR changes in fetuses suffering progressive respiratory insufficiency, and how extreme tachycardia (a basal rate greater than 170/min) tends to reflect other fetal problems such as infection or maternal pyrexia.
Cardiotocography↗
Computerised analysis of the fetal heart rate.
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Computers↗
Computerized fetal heart rate analysis in labor.
Observer variation in visual analysis of fetal heart rate (FHR) records is reportedly high, but can be avoided by computerized numerical analysis. The FHRs of 394 women in labor at 37 or more weeks' gestation were recorded on-line and analyzed to examine how different patterns related to outcome, as judged by umbilical arterial base deficit or Apgar score on delivery. The range of normality and the diversity of patterns of those delivered without acidemia were great. Late decelerations were of poor prognostic value. There was an increase in FHR variation during labor averaging 40%. In this preliminary study, conventional attributes of the FHR, alone or in combination, did not predict metabolic acidemia. Epidural analgesia in 240 women was identified as a confounding variable that significantly affected FHR patterns without influencing the condition of the infant at birth. It was associated with a higher FHR, less FHR variation and fewer decelerations, primiparity, longer labors, more operative deliveries, and a threefold greater cesarean rate. The rise in basal FHR, perhaps due to a rise in maternal temperature, may partly explain the high intervention rate in those without fetal acidemia.
Acid-Base Imbalance↗
Limitations of antenatal fetal heart rate monitors.
Erroneous or doubtful decelerations in fetal heart traces were present in 111 of 1000 consecutive antenatal clinical records obtained by monitors with autocorrelation. The incidence was 20% in fetuses less than 30 weeks of gestational age. Their elimination reduced the number of "decelerative" records by 42%. Erroneous or doubtful accelerations were also present in 11% of records. These errors are caused by the fetal heart rate monitor and may contribute to the high intraobserver and interobserver variation on visual analysis. They can be detected by computer analysis.
Equipment Failure↗
Criteria for the design of fetal heart rate analysis systems.
Criteria are described for the automated analysis of fetal pulse intervals, fetal movements and of uterine contractions measured externally, antenatally and interactively on-line, for implementation on a personal computer interfaced to an appropriate fetal monitor, and tested on 10,000 records. Measurements of short and longer term fetal heart rate variation are compared; both are required to identify sinister records. Recall and display of records acquired on the same patient over several weeks has proved a useful diagnostic aid.
Computer Graphics↗
Hypoxia and electrocortical activity in the fetal lamb: effects of brainstem transection and chemoreceptor denervation.
In order to investigate possible mechanisms for the effect of hypoxia on fetal electrocortical (ECoG) activity, the effects of 30 min of isocapnic hypoxia on ECoG were studied in three groups of unanaesthetized late-gestation fetal lambs in utero. One group was intact, in the second the brainstem was transected between the colliculi, and in the third the carotid sinus nerves and cervical vagosympathetic trunks were cut bilaterally to denervate the systemic arterial chemoreceptors. The incidence of high voltage (HV) ECoG activity was lower in brainstem-transected fetuses than in the other groups. All three groups showed an increased number of changes from low to high voltage and an increase in the incidence of HV activity at the onset of hypoxia, but the increases reached statistical significance only in the brainstem-transected group. It is concluded that the onset of hypoxia is often associated with an increase in HV ECoG activity, with the most consistent changes occurring after brainstem transection and similar but smaller increases in intact and denervated fetuses. Thus the response of fetal electrocortical activity to the onset of hypoxia does not depend on intact connections with the lower brainstem. However, the effect of hypoxia on fetal ECoG is minor and inconsistent and may be physiologically unimportant.
Animals↗
Antenatal fetal heart rate variation in relation to the respiratory and metabolic status of the compromised human fetus.
Three groups of women were delivered by caesarean section before labour: for an abnormal fetal heart rate (FHR) trace (21 cases, group 1), or for maternal deterioration in severe pre-eclampsia without gross fetal heart rate abnormalities (20 cases, group 2), or to avoid mechanical difficulties in labour at term (30 cases, group 3). The mean gestational ages of the first two groups were 32 weeks with a high proportion of infants small-for-gestational-age. In group 1, FHR variation (mean range of pulse intervals) was less than half (20.6 SE 1.2 ms) of the normal value at the same age (44.4 SE 1.5 ms). This was associated with hypoxaemia (mean umbilical artery PO2 of 6 mmHg at delivery), with evidence of compensation shown by an elevated amniotic fluid erythropoietin. The fetuses were hypoglycaemic and had greater umbilical artery blood alanine concentrations, but no large changes in adenine nucleotide or endorphin plasma concentrations. Although there was a minor degree of respiratory acidaemia at birth, there was not significant metabolic acidaemia. The results demonstrate that the reduced variation of 'suboptimal' and 'decelerative' fetal heart rate records is associated with fetal hypoxaemia and evidence of nutritional deprivation, but not with asphyxia.
Cesarean Section↗
Screening of the fetal heart rate in early labour.
The fetal heart rates (FHR) of 588 women admitted in labour, or in early labour after induction, were screened for up to 60 min (average 17 min) using computerized numerical analysis. Decelerative records with normal FHR variation occurred in eight (1.4%) and were not associated with acidaemia or depression at birth. Forty women (6.8%) had fetuses with a reduced FHR variation. They were more likely to be in spontaneous labour, to be at an earlier gestational age, and to be delivered operatively for fetal distress of babies that were more hypoxaemic and acidaemic. However, none of the fetuses with the least variable FHR patterns required resuscitation at birth or special care. The results of the screening procedure were not fully concealed and could have influenced clinical management. This is unlikely to have caused the associations that were observed, but could have reduced an association between low FHR variation and poor outcome. We conclude that there is a basis for a randomized controlled trial of FHR screening in early labour, but that this would need to be large (more than 10,000 patients) to test the benefit of detecting the most sinister pattern (decelerations with reduced variation) of which only one example was found in this study.
Female↗
The 1987 James A. F. Stevenson memorial lecture. The development of fetal behavioural patterns.
The development of fetal behaviour is reviewed. Fetal cutaneous and muscle sensory receptors are developed by the time movements are first seen. Human infants certainly respond to painful stimuli at 28 weeks. There is no clear evidence that prenatal "stress," e.g., maternal exposure to random noise and bright lights, impairs fetal development in the rat, on the contrary. Fetal diurnal rhythms appear in man and sheep before the development of sleep states; they are dependent on maternal corticosteroids, but the fetal mechanism is uncertain. With the development of sleep states (in late gestation in man and sheep, postnatally in the rat), the complex central control of behaviour is gradually established, but wakefulness is still of low incidence. The location of the sleep cycle generator is uncertain; the results of experimental lesions of the brainstem in fetal lambs appear incompatible with studies in adult rats and cats.
Animals↗
Carotid baroreceptors in fetal and newborn sheep.
The responses of single carotid baroreceptor afferents were determined in anaesthetized fetal lambs at 88-113 and 131-144 days gestation, and in newborn lambs 1-8 and 30-40 days old. The baroreceptors discharged in synchrony with the arterial pressure pulse and increased their discharge rate as pressure was raised by compression of the abdominal aorta. When step increases in pressure were applied to the vascularly isolated carotid sinus, baroreceptor discharge increased abruptly and then showed adaptation to a steady state level. Basal mean arterial pressure increased from 49.1 in the young fetuses to 87.5 mm Hg in the 30- to 40-day-old lambs without an accompanying increase in basal baroreceptor discharge expressed absolutely or as a function of maximum discharge for each unit. The slope of the steep portion of the stimulus-response curve decreased with gestational age from 7.89 +/- 1.57 (mean +/- SE) at 88-113 days gestation to 1.82 +/- 0.37% nerve activity.mm Hg-1 in the 30- to 49-day-old lambs. Dynamic and steady state response curves were determined using step increases in carotid sinus pressure in two fetal lambs of 135 days gestation and two lambs 8 days old. Both the dynamic and the steady state curves were less steep in the older lambs. We conclude that the sensitivity of the carotid baroreceptors is reset as arterial pressure increases throughout the last third of gestation and the first postnatal month. This resetting is seen as a shift to the right of the response curve and a decrease in its slope.(ABSTRACT TRUNCATED AT 250 WORDS)
Aging↗