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Biomedical subjects

E R Poore

Publications and source records attributed to E R Poore.

At least 19 recordsLinked to original sources
PubMed1989

The effect of continuous or pulsatile administration of oxytocin to ewes at 126 to 136 days' gestation on myometrial activity and fetal oxygenation.

Oxytocin was infused either continuously or in pulses to pregnant ewes to compare the responses of myometrial activity (contractures) and changes in fetal arterial PO2. Group 1 (n = 5) was infused with saline solution throughout the experiment. In group 2 (n = 5) oxytocin was infused continuously (160 microU.kg-1.min-1) for 7 days whereas group 3 (n = 5) ewes received 960 microU.kg-1.min-1 for 5 minutes every 30 minutes for 7 days. Contracture frequency increased in both oxytocin-infused groups. With continuous infusion contracture frequency returned to preinfusion levels during the last 4 days of infusion, whereas the pulsatile infusion contracture frequency remained increased throughout the infusion period. Fetal arterial PO2 was decreased throughout the 7 days of infusion in both oxytocin-infused groups. Pulsatile group fetal arterial PO2 levels remained decreased after the oxytocin infusion was stopped. These findings show: (1) Myometrial response to oxytocin in late pregnant ewes is influenced by the mode of administration; (2) administration of oxytocin to pregnant ewes resulted in a decrease in fetal PO2, and thus fetal hypoxemia cannot be attributed exclusively to increased contracture frequency.

Animals↗
PubMed1986

Modification of maternal and fetal oxygenation with the use of tracheal gas infusion.

A new technique is described for producing changes in fetal blood gases in the chronically instrumented pregnant sheep. Gas mixtures were infused directly into the maternal trachea. Maternal and fetal carotid arterial blood gases and pH were measured. Air infusion at 16 L X min-1 produced no change. Oxygen infusion caused significant increases in maternal PaO2 at 2 L X min-1 and in fetal PaO2 at 4 L X min-1. Nitrogen infusion significantly decreased maternal anf fetal PaO2 at 4 L X min-1. During 4 L X min-1 oxygen infusion, maternal PaO2 rose rapidly to plateau at 314 +/- 47 mm Hg at 4 minutes and fetal PaO2 rose to plateau at 28.7 +/- 2.8 mm Hg after 7 to 8 minutes. Maternal PaO2 fell to 56.4 +/- 4.3 mm Hg during nitrogen infusion (4 L X min-1) while fetal PaO2 fell to 15.9 +/- 1.8 mm Hg. Continuous infusion for 5- to 6-hour periods produced a consistent rise in maternal PaO2 during oxygen infusion and a consistent decrease during nitrogen infusion. Tracheal infusion of gases can be used to change maternal and fetal PaO2 rapidly and predictably.

Animals↗
PubMed1985

Characteristics and analysis of uterine electromyographic activity in the pregnant sheep.

Myometrial electromyographic activity was recorded with electrodes placed on the uterus in seven pregnant sheep. Electromyographic recordings were made continuously in two groups of animals. One group of four animals was studied for the first 8 days after operation at 60 to 132 days' gestation. The second group of three animals was studied at least 8 days after operation. Myometrial electromyographic activity could be divided into epochs of varying duration. With the use of microprocessor-based data acquisition systems and computerized analysis it was demonstrated that (1) on the basis of an analysis of duration of electromyographic activity there were at least two populations of electromyographic epoch, (2) myometrial electromyographic activity increased in the first 3 to 4 days after operation, and (3) by 6 to 7 days after operation a relatively stable level of activity had been achieved. The separation of electromyographic activity into two populations was most marked in the animals observed in the immediate postsurgical period. In these animals the population of epochs with the longer-lasting activity had a median duration of 5.9 minutes in eight pairs of electromyographic electrodes from four animals. Curve-fitting techniques demonstrated that no more than 14% of uterine electromyographic activity had a duration less than 3 minutes. The longer-lasting group of myometrial electromyographic events corresponds to uterine contractures we have described previously; the other group of epochs of activity was of shorter duration.

Animals↗
PubMed1984

Effect of fetal intravascular 4-aminoantipyrine infusions on myometrial activity (contractures) at 125 to 143 days' gestation in the pregnant sheep.

Myometrial activity of low amplitude and long duration--contractures--is present throughout gestation in the pregnant ewe and other species. This activity differs from the contractions of labor and delivery. Between 125 and 143 days' gestation, 4-aminoantipyrine infused into the fetus at rates that produced maternal uterine vein plasma concentrations of 4-aminoantipyrine of 5.95 +/- 1.23 (mean +/- SEM, n = 5) mg X 100 ml-1 markedly depressed both total myometrial electromyographic activity to 28.6% and frequency of contractures to 30.5% of preinfusion values. By 60 minutes of infusion, maternal uterine vein plasma 13,14-dihydro-15-keto prostaglandin F2 alpha concentration was reduced to 14% of the resting level. Two conclusions were drawn from this study. First, prostaglandins are involved in the regulation of contractures. Second, when infusions of 4-aminoantipyrine are used to quantify uterine or umbilical blood flow, the possibility exists that changes will occur in physiologic systems that are modified by prostaglandins.

Ampyrone↗
PubMed1984

The effect of myometrial contractures on uterine blood flow in the pregnant sheep at 114 to 140 days' gestation measured by the 4-aminoantipyrine equilibrium diffusion technique.

Uterine blood flow, between 114 and 140 days' gestation, measured by the 4-aminoantipyrine equilibrium diffusion technique, was significantly decreased from 1359.1 +/- 84.4 ml X min-1 (mean +/- SE) in the absence of contractures to 1147.4 +/- 71.8 ml X min-1 (mean +/- SE) during a contracture (p less than 0.01). Contractures reduced total uterine blood flow regardless of whether the ewe was standing or lying. These observations are in keeping with the suggestion that changes in total uterine blood flow may be an important mechanism responsible for the previously described temporal relationship between contractures and fetal neurophysiologic function.

Ampyrone↗
PubMed1984

Ingestion in fetal sheep and its relation to sleep states and breathing movements.

Swallowing was recorded electromyographically in unanaesthetized fetal sheep in utero during the last third of gestation. In control fetuses bouts of swallowing were, on average, 2.0 min in duration and occurred at intervals of 2.31 h. Swallowing bouts were associated with a low-voltage electrocorticogram, eye movements and, in 82% of instances, with phasic activity in the dorsal neck muscles. These data indicate that fetuses are not in quiet (non-rapid eye movement; n.r.e.m.) sleep when swallowing and also suggest that they are not in r.e.m. sleep as conventionally defined; we consider that fetuses may be in a state of heightened activity resembling wakefulness. Swallowing bouts were always accompanied by fetal breathing movements. When a swallow coincided with an inspiratory effort the diaphragm was briefly inhibited. Evidence was obtained that bouts of fetal ingestive activity were not dependent upon outpourings of fluid from the lungs and were not significantly influenced by volume information from the gastric compartments.

Animals↗
PubMed1984

Aortic wall properties and baroreceptor behaviour at normal arterial pressure and in acute hypertensive resetting in dogs.

In order to throw light on the mechanism of acute hypertensive baroreceptor resetting, we examined the relationship between aortic baroreceptor firing and aortic wall properties in anaesthetized dogs as pressure was varied in a number of ways. We recorded baroreceptor impulses from the left aortic nerve, and measured aortic pressure with a catheter-tip transducer and external aortic diameter with ultrasonic transit-time transducers. Narrow anticlockwise hysteresis loops were evident in the pressure-diameter relationship of the upper thoracic aorta, both during the rapid pulsatile pressure changes of the cardiac cycle and during the slow excursions of mean pressure imposed for construction of baroreceptor pressure--response curves. In contrast to the 'phase-lag' response of diameter to pressure, the baroreceptor response was 'phaselead' in character, decreasing when stress-induced creep occurred in the aortic wall. When the mean arterial pressure set-point was increased from 100 to 125 mmHg for 20 min, the hysteresis loops relating mean diameter to mean pressure in the range 60-200 mmHg were displaced along the diameter axis in the direction of wall creep. A reduction in the baroreceptor response to pressure (i.e. resetting) always accompanied this displacement. Administration of ouabain (25-35 micrograms/kg) had no consistent effect on baroreceptor resetting. It has been suggested that acute baroreceptor resetting is akin to adaptation. To investigate the possibility that the two processes are accompanied by similar changes in aortic wall properties, we converted the aorta into a closed sac and distended it with a square wave of pressure. Like resetting, adaptation of the baroreceptor response to maintained pressure was associated with a small degree of creep of the aortic wall. Our results are compatible with the hypothesis that acute hypertensive resetting of aortic baroreceptors is similar to adaptation, both phenomena being attributable to relaxation of viscoelastic coupling elements, leading to a reduction of strain at the receptor membrane. Whether viscoelastic processes alone can account for acute resetting, or whether changes in ionic balance are involved also, baroreceptor responsiveness is a function of the stress history of the wall, the pressure-response curve moving along the pressure axis in the direction of the prevailing set-point. Hence, in early hypertension physiological resetting of baroreceptors will precede pathological resetting, and may even promote an upward movement of set-point.

Action Potentials↗
PubMed1984

The effects of myometrial activity on fetal thoracic dimensions and uterine blood flow during late gestation in the sheep.

We wished to investigate mechanisms by which non-labour contractions of the uterus influence fetal sleep states and respiratory activity during late pregnancy. The relationship between the dimensions of the fetal chest and uterine contractions was examined in 5 pregnant sheep. The dorso-ventral dimension at the level of the xiphisternum (3 fetuses) decreased, on average by 4.4-9.4% while increases of 16.6-18.7% were seen in the transverse dimension (4 fetuses). Blood flow in a middle uterine artery was monitored using a Doppler technique in 5 pregnant sheep. Non-labour uterine contractions were accompanied by mean reductions of 6.5-12.7% in blood flow. Postural adjustments by the ewe also influenced uterine blood flow. A mean increase in blood flow of 5.9-12.0% followed a change from standing to lying; standing caused a mean reduction of 5.9-11.8%. We conclude that the influence of uterine contractions on the fetus is likely to be complex, involving distortion of the body and alterations in utero-placental haemodynamics.

Animals↗
PubMed1982

Electromyographic activity of the nonpregnant and pregnant sheep uterus.

Myometrial electromyograms were studied in nonpregnant ewes, pregnant ewes throughout the second half of gestation, and during labor and delivery in normal spontaneous vaginal delivery and premature delivery induced by the continuous infusion of synthetic adrenocorticotropin 1-24, 1 microgram x h-1, to the fetus at 120 and 130 days' gestation. The bursts of electromyographic (EMG) activity during estrus were very similar to those seen in the pregnant ewe in the second half of gestation. In the second half of gestation, the bursts of EMG activity lasted a mean of 6.7 minutes and occurred at intervals of 54.7 minutes in utero, without an incision for fetal instrumentation, and were 7.2 minutes in duration, occurring every 46.6 minutes when the uterus had been incised. EMG activity occurred simultaneously at most recording sites within the uterus. There was no evidence to support the view that a uterine pacemaker exists with a fixed location. As delivery approached, the mean duration of each EMG burst began decreasing more than 24 hours before delivery, and the frequency of the bursts increased, demonstrating that the recording of uterine electromyograms provides a precise and sensitive method for the study of the early changes that lead to labor and delivery.

Animals↗
PubMed1981

The effect of brief episodes of diminished uterine blood flow on breathing movements, sleep states and heart rate in fetal sheep.

Responses to brief episodes of occlusion of the middle uterine artery were examined in six fetal sheep in utero between 122 and 140 days of gestation. Continuous recordings were made of fetal breathing movements, electro-cortical (ECoG) and electro-ocular (EOG) activity, arterial pressure and heart rate. Five minutes of unilateral or bilateral arterial occlusion caused fetal hypoxaemia while changes in mean arterial PCO2 and pH were not statistically significant. Occlusions usually led to a cessation of rapid eye movements (REM) and respiratory activity (86% of trials), to the appearance of high-voltage slow waves in the ECoG (84% of trials) and to a fall in heat rate of more than 10% (81% of trials). With the exception of the changes in heart rate, these responses resemble those which frequently occur during non-labour contractions of the uterus. We conclude that the cessation of fetal breathing movements and rapid eye movements and the onset of slow waves in the ECoG seen in association with uterine contractions may be due to the mild hypoxaemia which accompanies them.

Animals↗
PubMed1980

THe relationship between myometrial activity and sleep state and breathing in fetal sheep throughout the last third of gestation.

Between 106 and 144 days' gestation, periods of uterine electromyographic (EMG) activity and associated increases in uterine tone (contractures) were accompanied by a change in fetal ocular activity in 294 (63%) of 467 cases. In 260 (88.4%) of the changes, there was a switch fromm the active to nonactive state. The incidence of this change was significantly greater (p < 0.01) than the switch from the nonactive to the active state. The fetal electrocorticogram changed state in 34 (74%) of 46 contractures, the change being from low-amplitude to high-amplitude activity in 28 (82%) of the cases. This difference was significant (p < 0.01). Fetal breathing movements (FBM), as indicated by activity of the posterior cricoarytenoid muscle, changed in 134 (55%) of 243 contractures, the change being from active to the quiescent state in 115 (85%) of contractures. Diaphragmatic activity changed in 11 (61%) of 183 contractures, with a change from activity to quiescence occurring in 100 instances (90%). Changes in tracheal pressure were associated with an altered state of FBM in 190 (61%) of 314 contractures, and the change was from the presence of FBM to absence of them in 178 (94%) of the changes. In all three of these indicators of FBM, the change from breathing activity to quiescence was statistically significant (p < 0.01).

Animals↗
PubMed1980

Chest wall movements during fetal breathing in the sheep.

1. Movement of the chest wall and abdomen during episodes of breathing has been measured by an ultrasound technique in ten fetal lambs. 2. The fetal thoracic and abdominal walls move inwards and outwards respectively during inspiration. The position where this transition occurs is variable. 3. Movement of the lateral thoracic walls is reduced or reversed during breathing stimulated by hypercapnia while inward dorso-ventral movement increases. 4. Deep inspiratory efforts were associated with large inward then outward movements of the lateral and large inward movements of the dorso-ventral thoracic walls. 5. No relationship was found between the amplitude of the tracheal pressure deflexions and the extent of thoracic wall movements during fetal breathing.

Abdominal Muscles↗