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P J Wickham

Publications and source records attributed to P J Wickham.

10 recordsLinked to original sources
PubMed1988

Continuous measurement of biparietal distance in the intact and hypophysectomized fetal sheep using ultrasound.

Piezoelectric transducers were implanted into the parietal bones of intact (n = 4) and hypophysectomized (n = 8) fetal sheep of approximately 110-120 days gestational age (term 145-150 days). Intertransducer distance was determined by measuring the time taken for an ultrasonic pulse, generated by one transducer, to elicit a piezoelectric response in an opposing transducer. The limit of sensitivity of the timer was +/- 0.033 microsec. The ultrasonic velocity through fetal sheep brain tissue was 1549.6 +/- 2.2 m.s-1 (SEM; n = 33). This velocity remained constant throughout the entire period studied in both intact and hypophysectomized fetuses. At this velocity, the sensitivity of the measuring device was +/- 0.05mm. The ultrasonic transit time was measured daily between 0900 and 1100h until term in all fetuses. Three hypophysectomized fetuses were allowed to remain in utero until day 163 of gestation. The mean biparietal distance growth rate prior to day 135 for the intact and hypophysectomized fetuses was 0.25 +/- 0.03 and 0.27 +/- 0.025 mm/day respectively. These values were not significantly different (P greater than 0.05). A significant decrease (P less than 0.05) in growth rate was detected in both experimental groups between days 135 and 147 and was more pronounced in the sham (0.05 +/- 0.04 mm/day) than in the hypophysectomized (0.14 +/- 0.03 mm/day) group. However, the growth rate of the sham animals after day 135 was not significantly different from that of the hypophysectomized animals. In the three hypophysectomized fetuses killed at day 163 the biparietal distance growth was maintained at 0.12 +/- 0.005 mm/day. We conclude that fetal biparietal distance growth is pituitary independent from day 110 of gestation and that this technique for measuring distance is a valid and extremely accurate method for the continuous measurement of this parameter of fetal growth and may have further applications in other areas of growth research.

Animals↗
PubMed1987

Analysis of fetal breathing in real time using a microprocessor.

A system has been designed using an inexpensive microprocessor to analyze fetal breathing movements on a breath-by-breath basis in real time. An algorithm was developed which would recognize fetal breathing from the changes in tracheal pressure and which was capable of rejecting the artifactual changes caused by fetal or maternal movements. The tracheal pressure signal was digitized (at 51 samples/s), differentiated, and the start and peak of each breath was recognized from the zero-crossing points of the differentiated signal. Each breath was validated for size and shape according to a set of criteria incorporated into the breath recognition algorithm. On acceptance of the pressure change as a valid breath, the inspiratory time, breath amplitude, breath-to-breath interval, and inspiratory effort were calculated and stored in memory. The program was structured so that the microprocessor was able to accept new data and output summarizes of previous data concurrently. More than 95% of breaths in records contaminated with movement artifacts were recognized.

Computers↗
PubMed1986

Effects of reduced uterine blood flow on accelerations and decelerations in heart rate of fetal sheep.

Experiments were conducted in unanesthetized fetal sheep during the last third of gestation to examine the effects of prolonged reversible reductions in uterine blood flow on mean fetal heart rate, accelerations and decelerations in fetal heart rate, and fetal arterial pressure. With use of a Teflon vascular clamp placed around the maternal common internal iliac artery, uterine blood flow was reduced, leading to a reduction in fetal arterial oxygen saturation from 60% to 30% for 2 hours. This was associated with an initial transient fetal bradycardia and hypertension followed by tachycardia. Mean fetal heart rate remained significantly elevated for 2 hours following the release of the vascular clamp. There was no change in the number, amplitude, or duration of accelerations, but there was a significant increase in both the number and amplitude of decelerations during the period of reduced uterine blood flow.

Animals↗
PubMed1985

Relationship between accelerations and decelerations in heart rate and skeletal muscle activity in fetal sheep.

Accelerations in fetal heart rate have been shown to be closely related to fetal body movements and are indicative of well-being in the human fetus. We have examined the association of accelerations and decelerations in heart rate with skeletal muscle activity in 8 fetal sheep between 125 and 145 days' gestation. Accelerations/decelerations were defined as transient increases/decreases in fetal heart rate of greater than or equal to 10 beats/min. lasting for 5 s or longer. For accelerations (n = 1180), the mean duration was 18.8 +/- 1.5 s (SEM) and the mean amplitude was 25.3 +/- 1.2 beats/min; for decelerations (n = 237), the mean duration was 17.4 +/- 1.6 s and the mean amplitude was 18.7 +/- 1.0 beats/min. Electromyograms were recorded from the nuchal muscles and antagonistic muscle groups of the fetal forelimb and hindlimb. Electromyogram activity occurred during 88.4 +/- 2.8% of accelerations and 60.6 +/- 7.7% of decelerations. There was a 36.6% reduction in the number of accelerations following fetal paralysis with gallamine, but no change in their amplitude or duration. It is concluded that accelerations in heart rate are highly associated with skeletal muscle activity in fetal sheep. The majority of these occur as a result of central neuronal output rather than as a consequence of fetal movement.

Animals↗
PubMed1984

The regulation of flow of pulmonary fluid in fetal sheep.

The flow of fluid within the trachea of fetal sheep (121-135 days) has been measured using a newly developed flowmeter. The flowmeter, which is basically a miniature servo-controlled peristaltic pump, is connected in series with an extra-corporeal tracheal loop. Integrated tracheal flow was measured for periods of at least 8 h in 5 control fetuses during which we determined its relationship to fetal breathing movements detected by EMG's of inspiratory muscles or tracheal pressure fluctuations. The overall flow of fluid away from the lungs was 14.4 ml/h; on average outward flow was 5.3 times greater during episodes of breathing movements than during apnea. Interruption of the motor innervation of the larynx in 5 fetuses led to a 25% reduction in mean overall flow and, compared with control fetuses, there was a reduction in net flow associated with breathing movements and an increased flow during apnea. These findings suggest that tracheal flow is normally retarded by a laryngeal mechanism during apnea, giving rise to an elevated pressure within the trachea and probably resulting in increased pulmonary distension. Paralysis of the fetus with gallamine triethiodide reduced the flow of liquid from the lungs and abolished variations in flow rate related to fetal electrocortical states.

Animals↗
PubMed1984

Composition and volume of fluid swallowed by fetal sheep.

Oesophageal cannulations were performed in seven fetal sheep between 109 and 128 d of gestation. Fluid swallowed by the fetuses was collected externally and periodically returned to the fetal stomach by a peristaltic pump. The volume of fluid swallowed daily was calculated from the movement of water in a parallel pump circuit. Samples of oesophageal fluid were removed from the collection bag at the same time as tracheal and amniotic fluid samples. Oesophageal fluid was very viscous and was usually intermediate in colour between tracheal and amniotic fluids. After reduction of viscosity by dithiothreitol, the compositions of the three fluids were analysed. Mean concentrations of Na+, Cl- and protein, and mean osmolarity of oesophageal fluid, were intermediate between values obtained in tracheal and amniotic fluids. [K+] was often greater in oesophageal fluid than would be expected by the relative contribution of tracheal and amniotic fluids as indicated by [Na+] and [Cl-] in the three fluids. It is suggested that the high viscosity of oesophageal fluid and its relatively high [K+] may result from fetal salivary secretions. Ionic concentrations in individual sets of samples show that the proportions of tracheal and amniotic fluids swallowed by the fetus are variable from day to day. The mean daily volumes of fluid swallowed by the seven fetuses ranged from 98 to 577 ml, and are in agreement with previously published data.

Amniotic Fluid↗
PubMed1983

Development of methods for quantitative analysis of the fetal heart rate.

A description is given of the development of methods for the quantitative analysis of measurements of the fetal heart rate, uterine pressure and fetal movements, with data collection, reduction and analysis via a digital cassette off-line, or on-line. The on-line system consists of a small microprocessor, which reduces and digitizes the data, and which passes it for display and analysis to a larger microprocessor (NASCOM Z80). Analysis on-line offers the opportunity of interaction to optimise record quality and to compare at once sequential records on the same patient.

Female↗
PubMed1983

Fetal and maternal influences on arterial oxygen levels in the sheep fetus.

Continuous recordings of arterial oxygen tension (PaO2) and percent oxygen saturation (SaO2) were made in 8 instrumented fetal sheep during late gestation. Fetal behavioural states were monitored from recordings of rapid eye movements, the electrocorticogram, and the nuchal electromyogram (EMG). In addition, fetal breathing and swallowing movements and uterine motility were measured using EMG techniques. Variations in PaO2 and SaO2 were related to fetal muscular activity, non-labour uterine contractions and maternal postural changes. Significant reductions in the variability of PaO2 and SaO2 were brought about in 7 of the 8 fetuses by skeletal muscle paralysis. Variation was further reduced in each fetus by paralysis of the myometrium by a beta-adrenergic agonist. Remaining variations were largely attributable to postural changes by the ewe. It is concluded that fetal skeletal muscle activity contributes to reduced amounts of oxygen in fetal arterial blood, although the mechanism by which this occurs has not yet been identified.

Animals↗