Vaginal algometer: development and application of a device to monitor vaginal wall pressure pain threshold.

We describe a device (which we have named a vaginal algometer) which can measure the pressure pain threshold (PPT) on the lateral walls of the vagina. The device was assessed in 63 healthy women and a normal range for this measurement was established. Each woman had her vaginal wall PPT measured and was asked about the acceptability of the procedure. We demonstrate that the vaginal algometer can provide a quantitative assessment of vaginal PPT and that the procedure is acceptable to most women.

Receiver operating characteristic analysis for intelligent medical systems--a new approach for finding confidence intervals.

Intelligent systems are increasingly being deployed in medicine and healthcare, but there is a need for a robust and objective methodology for evaluating such systems. Potentially, receiver operating characteristic (ROC) analysis could form a basis for the objective evaluation of intelligent medical systems. However, it has several weaknesses when applied to the types of data used to evaluate intelligent medical systems. First, small data sets are often used, which are unsatisfactory with existing methods. Second, many existing ROC methods use parametric assumptions which may not always be valid for the test cases selected. Third, system evaluations are often more concerned with particular, clinically meaningful, points on the curve, rather than on global indexes such as the more commonly used area under the curve. A novel, robust and accurate method is proposed, derived from first principles, which calculates the probability density function (pdf) for each point on a ROC curve for any given sample size. Confidence intervals are produced as contours on the pdf. The theoretical work has been validated by Monte Carlo simulations. It has also been applied to two real-world examples of ROC analysis, taken from the literature (classification of mammograms and differential diagnosis of pancreatic diseases), to investigate the confidence surfaces produced for real cases, and to illustrate how analysis of system performance can be enhanced. We illustrate the impact of sample size on system performance from analysis of ROC pdf's and 95% confidence boundaries. This work establishes an important new method for generating pdf's, and provides an accurate and robust method of producing confidence intervals for ROC curves for the small sample sizes typical of intelligent medical systems. It is conjectured that, potentially, the method could be extended to determine risks associated with the deployment of intelligent medical systems in clinical practice.

Four channel foetal ECG data collection system.

Recently there has been an increased interest in the development of improved techniques for the diagnosis of foetal distress during labour. Many of the techniques have been based on extracting extra information from the foetal ECG obtained from a scalp electrode. To fully develop and test the prototypes of these systems requires recorded data from patients. However due to the poor level of prediction of these cases at present, it is very difficult to collect the data using simple single channel data collection systems. The system described here will automatically collect and document data from up to four deliveries at the same time and does not add to the work load of the clinical staff.

Plymouth randomized trial of cardiotocogram only versus ST waveform plus cardiotocogram for intrapartum monitoring in 2400 cases.

OBJECTIVE: The physiology of changes in the ST waveform of the fetal electrocardiogram has been elucidated in extensive animal and human observational studies. A combination of heart rate and ST waveform analysis might improve the predictive value of intrapartum monitoring. Our purpose was to compare operative intervention and neonatal outcome in labors monitored by the conventional cardiotocogram with those monitored by ST waveform plus the cardiotocogram. STUDY DESIGN: A prospective, randomized clinical trial was performed on 2434 high-risk labors in a district general hospital in Plymouth, England. Statistical analysis was performed by Student t test and chi 2 analysis. RESULTS: There was a 46% reduction (p < 0.001, odds ratio 1.85 [1.35-2.66]) in operative deliveries for "fetal distress" and a trend to less metabolic acidosis (p = 0.09, odds ratio 0.38 [0.13-1.07]) and fewer low 5-minute Apgar scores (p = 0.12, odds ratio 0.62 [0.35-1.08]) in the ST waveform plus cardiotocogram arm. CONCLUSIONS: ST waveform analysis discriminates cardiotocogram changes in labor, and the protocol for interpretation is safe. Further randomized studies are warranted.

Randomised trial of cardiotocography alone or with ST waveform analysis for intrapartum monitoring.

It is possible to record the fetal electrocardiographic waveform (ECG) from the scalp electrode used in labour for detection of fetal heart rate. Animal and observational studies of changes in the ST waveform of the ECG during hypoxia suggest that a combination of heart rate and ST waveform analysis might improve the predictive value of intrapartum monitoring. In a randomised trial, we have studied intervention rates and neonatal outcome for high-risk labours monitored either by conventional cardiotocography (CTG) or by ST waveform analysis plus CTG. 1200 women with pregnancy of at least 34 weeks' gestation were assigned to the groups when the decision to apply a fetal scalp electrode was made. Neonatal outcome was assessed by umbilical-cord blood gas analysis, Apgar scores, resuscitation needed, and postnatal course. All recordings were retrospectively viewed by an observer unaware of clinical details to check adherence to the trial protocol. The addition of ST waveform monitoring to CTG substantially reduced the proportion of deliveries for fetal distress (ST + CTG 27/615 vs CTG 58/606; p less than 0.001). The groups did not differ in rate of operative delivery for other reasons, incidence of asphyxia at birth, or neonatal outcome. Metabolic acidosis and low 5 min Apgar scores were less common in the ST + CTG than the CTG group, but not significantly so. The only case of birth asphyxia in the ST + CTG group was identified by both heart rate and ST changes. The review of recordings showed that the reduction in intervention rate was among cases with CTG patterns classified as normal or intermediate, whereas there was no difference in intervention rates among cases with abnormal recordings. Our findings confirm that ST waveform analysis discriminates CTG changes in labour and that our protocol for interpretation is safe. Further randomised studies are warranted.

Suitability of fetal scalp electrodes for monitoring the fetal electrocardiogram during labour.

As the limitations of heart-rate based intrapartum monitoring have become apparent, there is renewed interest in analysis of the fetal electrocardiographic waveform as obtained from a fetal scalp electrode. A high quality ECG signal is necessary for waveform analysis. This study examined the suitability of five commonly available scalp electrodes for collecting this signal by examining their physical and electrical characteristics, together with a randomised clinical trial in which the ECG trace quality was assessed in 50 patients. The frequency response of Copeland electrodes was such that they attenuate the ECG signal more than the baseline noise. Difficulties were experienced in obtaining optimum attachment and the long, semi-rigid design increased movement artefact resulting in significantly poorer quality ECG signals. Whilst the Hewlett-Packard double spiral electrode had a near ideal frequency response, certain design features made it difficult to apply and remain secure so the clinical signals were of intermediate quality. The Corometrics and Cetro single spirals had the most stable attachment to the scalp and a near ideal frequency response, so produced significantly better signal quality in the clinical trial. Currently, single spiral electrodes are the most suitable for electrocardiographic data collection.

The ventilatory response to carbon dioxide. An analysis of data obtained by the rebreathing method.

The ventilatory response to carbon dioxide using the rebreathing method was studied repeatedly in four healthy volunteers. The data were collected and processed in different ways using a microcomputer. Least squares linear regression analysis described the responses almost as accurately as a non-linear second-order polynomial regression. Linear regression analysis was undertaken on VI/PE'CO2 points, first breath-by-breath and then on three different groupings of breaths. The gradients and intercepts obtained by grouping agreed with those from breath-by-breath analysis both for a single response and for the mean result of a number of responses. Grouping tended to increase the correlation coefficient of a response, but widened the statistical confidence limits of the calculated gradient. The performance variability between repeated responses, the same no matter which data points were used, produced a range of gradients for each subject which was larger than the confidence limits on the gradient of a single response.

Effect of rebreathing on psychomotor skills when wearing integral crash helmets.

Nine volunteer subjects underwent psychomotor testing when wearing an integral crash helmet in a variety of conditions which lead to rebreathing. There was a wide individual variation in the extent of rebreathing. In the worst conditions the minimum inspired carbon dioxide tension (PICO2) increased to 2.6 kPa. The psychomotor test was a tracking test based on a microcomputer. There was a significant deterioration in the ability to perform the test when the helmet was worn with the visor down and restricted airflow into the helmet (P = less than 0.05). In those tests when the minimum PICO2 exceeded 0.5 kPa the decrease in performance was more highly statistically significant (p = less than 0.005). Rebreathing wearing integral crash helmets results in a variable impairment in the subjects' ability to perform a tracking test. We recommend that the maximum level of CO2 retention inside integral crash helmets should not exceed 0.5 kPa minimum PICO2.

Infusions of minaxolone to supplement nitrous oxide-oxygen anaesthesia. A comparison with althesin.

In 19 patients, minaxolone citrate, a water-soluble steroid anaesthetic agent, has been used as a continuous infusion to supplement nitrous oxide anaesthesia. The minimum infusion rate (MIR) was found to be 11.3 micrograms kg-1 min-1 for patients premedicated with morphine 10 mg i.m. and breathing spontaneously 66% nitrous oxide in oxygen. The cardiovascular and respiratory effects were similar to those described in a previous study for Althesin administered under comparable conditions. Recovery from minaxolone was prolonged compared with Althesin, and this may be related both to the water-solubility of the drug, and to its greater apparent volume of distribution.