Summary Ninety‐seven recordings of the fetal heart rate, lasting for one hour, were made from 59 normal patients between 21 and 41 weeks of gestation. The heart rate was measured from beat to beat using the R‐wave of the fetal electrocardiogram (ECG) as the indicator of each heart cycle. The recordings showed a significant decrease in the baseline heart rate as gestation advanced. Significant departures from the baseline took the form of short episodes of bradycardia in the earlier recordings and short episodes of tachycardia in the later recordings. The undulatory pattern of variability was most common (46 per cent of the recording time); the proportion of narrowed undulatory variability decreased significantly and the proportion of saltatory variability increased significantly as gestation advanced. From 34 weeks of gestation, long‐term changes in the pattern of the fetal heart rate, related to periods of fetal rest and activity, were observed in the recordings. The periods of rest lasted for an average of 15 minutes and were characterized by a reduction in heart rate variability to the narrowed undulatory and silent types. Analysis of the cardiac beat‐to‐beat variation showed an arrhythmia, not previously described in the human fetus, that may be related to fetal breathing.

A forced periodic variation in blood pressure produces a similar variation in cerebral blood velocity. The amplitudes and phases of the pressure and velocity waveforms are indicative of the dynamic response of the cerebral autoregulation. The phase of the velocity leads the pressure; the greater the phase difference the faster the autoregulation response. Various techniques have been employed to oscillate arterial blood pressure but measurement reproducibility has been poor. The purpose of this study was to assess the reproducibility of phase measurements when sinusoidal lower body negative pressure is used to vary blood pressure. Five healthy volunteers were assessed at two vacuum levels on each of eight visits. For each measurement a 12 s sinusoidal cycle was maintained for 5 min. The Fourier components of blood pressure and the middle cerebral artery velocity were determined at the oscillation frequency. The phase of velocity consistently led the pressure. The mean phase difference was 42+/-13 degrees for the stronger vacuum and 36+/-42 degrees for the weaker vacuum. The variation given is the within-subjects standard deviation estimated from a one-way analysis of variance. Sinusoidal lower body negative pressure is a useful stimulus for investigating autoregulation; it has advantages over other methods. High vacuums show good reproducibility but are too uncomfortable for patient use.

Ninety-seven one-hour recordings of the abdominal fetal electrocardiogram (ECG) were made from 59 normal patients between 21 and 41 weeks of gestation. The heart intervals, measured between successive R-waves, were analysed by computer. The signal-to-noise ratio of the fetal ECG limited the precision of the interval measurements to approximately one millisecond. The characteristics of the baseline heart rate changed significantly as gestation advanced, the mean R-R interval, the standard deviation of the intervals and the standard deviation of the interval differences all increasing with gestation (p <0*001). In later gestation the baseline heart rate during periods of fetal rest differed significantly from that during periods of fetal activity; during rest the mean R-R interval was greater (p <0.001) and the standard deviations of the intervals and interval differences were smaller (p < 0.001). Examination of the coefficient of variation of the heart intervals gave a result which contradicted the significance of this measurement as an index of fetal welfare as proposed by Curran and MacGregor (1970).COMPUTER analysis of the fetal heart rate (FHR) can provide an objective means of condensing the large quantity of information which results from continuous monitoring of the fetus. In particular, a more accurate analysis of cardiac beat-to-beat variation can be obtained com-* Present address: Department of Obstetrics and Gynaecology, John Radcliffe Hospital, Headington, Oxford OX3 9DU. pared with that provided by conventional FHR monitors. The relatively slow recording speeds of the latter, combined with the small scales allowed for the display of the heart rate, make it difficult to distinguish the changes in rate from beat to beat. Furthermore the scales, being linear to frequency, compress the changes in heart interval at the lower rates and expand them at higher rates.Reliable observations of heart interval can 186

This paper describes a study to assess the clinical value of bilateral femoral neck bone mineral density (BMD) measurements. Although a range of factors will determine clinical decisions, the classification of the site with the lowest T-score is likely to have significant bearing on the management of a patient. While it is common practice to measure BMD at the lumbar spine and a single neck of femur, knowledge of the BMD of the second femur may also be of diagnostic value. Using dual-energy X-ray absorptiometry, BMD of the lumbar spine and right and left femoral neck was measured in a group of 2372 white, Caucasian women (mean age +/- SD, 56.6 +/- 13.9 years) routinely referred for bone densitometry. Analysis of the measurements showed a significant (p = 0.02) but small difference between the mean BMD of the right (0.840 +/- 0.152 g/cm2) and left (0.837 +/- 0.150 g/cm2) femoral neck. Further investigation of femur scans revealed 79 (3.3%) patients in whom one side was osteoporotic while the other side and spine were normal or osteopenic using the World Health Organization diagnostic criteria in combination with manufacturer's reference data. Patients in whom the femoral neck BMD measurements differed by less than the precision error of the system were then excluded. This left only 51 (2.2%) patients, that is 29 (1.2%) for right femur and spine scan and 22 (0.9%) for left femur and spine scan, in whom knowledge of both femoral neck BMD measurements could have altered the classification of the lowest site assessed to osteoporotic. These data suggest that there is only a small benefit from performing bilateral femoral neck BMD measurements. Since BMD measurements are only one of a range of factors considered as part of a patient's management, it is suggested that the extra time, cost and radiation dose associated with measurement of the second femur may not be justified.