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J W Ritchie

Publications and source records attributed to J W Ritchie.

At least 37 records · Page 2Linked to original sources
PubMed1993

Absent end-diastolic flow velocity waveforms in the umbilical artery--the subsequent pregnancy.

OBJECTIVE: Our purpose was to assess the recurrence risk, course, and outcome of subsequent pregnancies in women with absent umbilical end-diastolic velocity. STUDY DESIGN: Absent umbilical end-diastolic velocity was detected in 88 women. Sixteen of them were prospectively followed up in their 19 subsequent pregnancies. These pregnancies were compared with their index pregnancies. RESULTS: The index pregnancy was invariably complicated with a perinatal mortality of 56%, growth restriction in 94% (15/16), and prematurity in 100% (75% < 32 weeks' gestation). In contrast, the outcome of the subsequent pregnancies was much better, and 74% (14/19) were uncomplicated. No perinatal deaths occurred, and none were delivered before 32 weeks' gestation. Absent umbilical end-diastolic velocity recurred in only two pregnancies, both of which were complicated. Six women had autoantibodies; these accounted for 80% (4/5) of subsequent complicated pregnancies. CONCLUSION: After an index pregnancy with absent umbilical end-diastolic velocity, subsequent pregnancies had favorable outcomes. Recurrence of absent umbilical end-diastolic velocity was low. The absence of autoantibodies and normal Doppler studies were associated with improved outcome.

Adult↗
PubMed1993

The effects of hypoxic acidemia on left ventricular end-systolic elastance in fetal sheep.

Using the conductance catheter technique, we measured the effects of hypoxic acidemia on left ventricular end-systolic elastance in anesthetized, 133-d gestation, in utero fetal sheep (n = 7). Conductance and Millar catheters were introduced into the left ventricle through a carotid artery cutdown. Fetuses were rendered progressively hypoxic and acidemic by placental embolization with repeated injections of 5 x 10(5) 50-microns plastic spheres every 15 min via a catheter placed in the fetal abdominal aorta. We recorded pressure-volume data and arterial blood gases at 15-min intervals. End-systolic elastance was computed using a single-beat method of extrapolating maximum isovolumic pressure. A mean of five boluses was required to cause fetal death. Placental embolization caused progressive fetal acidemia. Mean baseline fetal arterial pH was 7.32 +/- 0.06 (mean +/- SD) and gradually decreased with embolization (p < 0.0001). A linear relationship was found to exist between elastance and pH with a mean decrease of 0.46 kPa/mL per 0.1-unit drop in pH (r = 0.96; p < 0.0001). Despite the decrease in end-systolic elastance, stroke volume and left-ventricular output were maintained due to a parallel decrease in afterload. The decrease in end-systolic elastance was gradual and extended over the entire clinically important range of pH, rather than being a terminal event. This study, which, to our knowledge, is the first to use the conductance catheter to measure fetal left ventricular function demonstrates that hypoxic acidemia adversely affects myocardial contractility assessed by end-systolic elastance.

Acidosis↗
PubMed1992

Cardiac electromechanical dissociation in the hypoxic fetal sheep may have clinical implications.

OBJECTIVES: Our purpose was to determine the sequence of fetal cardiac electrical and mechanical events associated with acute hypoxic acidemia and to correlate those events with terminal fetal heart rate patterns preceding fetal death. STUDY DESIGN: Eight acutely catheterized fetal sheep were rendered hypoxic by placental embolization with microspheres until fetal death occurred. The fetal electrocardiogram, Doppler cardiogram, left ventricular and aortic pressures, and fetal heart rate were continuously recorded. RESULTS: All eight fetuses showed a terminal bradycardia consisting of two phases: an initial phase of falling ventricular pressures, culminating in mechanical asystole, and a subsequent phase after asystole during which the electrocardiographic signal persisted for an average duration of 15.2 +/- 8.7 minutes (range 3.1 to 32.4) and triggered a Hewlett-Packard 8040A monitor to show a heart rate pattern. CONCLUSIONS: The phenomenon of cardiac electromechanical dissociation may be occurring during similar terminal bradycardias that are observed in human labor and explains the delivery of a fresh stillbirth in spite of the recording of an electrocardiographic signal from a scalp electrode.

Animals↗
PubMed1991

What is a low-lying placenta?

Transvaginal ultrasonography was performed in 127 women thought to have placenta previa. In all cases of complete previa, placental location was confirmed at cesarean section. Where the placenta was situated in the lower segment of the uterus but did not cover the cervical os the distance from the placental edge to the internal cervical os was measured. This distance was analyzed in relation to the route of delivery. No patient with a placental edge greater than 2 cm from the internal cervical os required cesarean section for the indication of placenta previa, whereas seven of eight patients with a distance of less than or equal to 2 cm underwent cesarean section because of bleeding characteristic of a placenta previa. These preliminary results suggest that transvaginal ultrasonography measurement may indicate the optimal delivery route and make the traditional classification of placenta previa obsolete.

Cesarean Section↗
PubMed1991

Use of Doppler technology in assessing fetal health.

Doppler technology has provided new information about the fetus during intrauterine life. Changes in red cell velocity in the umbilical artery relate well to changes in downstream resistance in the placenta. Resistance (or more correctly impedance) appears to be closely linked to the number of small fetal arterioles in the tertiary stem villus. Placental pathology leading to a reduction in these arterioles is often associated with severe intrauterine growth restriction and poor perinatal outcome. Whilst there is no good evidence that screening women with low risk pregnancies is clinically useful, umbilical artery Doppler information would appear to be useful in the management of pregnancies already identified as at risk. Here abnormal Doppler findings suggest the need for maternal rest, increased fetal surveillance and early delivery when indicated.

Female↗
PubMed1991

Transvaginal Doppler assessment of the fetal cerebral circulation.

Blood flow velocity waveforms were recorded by pulsed Doppler examination of the fetal internal carotid and middle cerebral arteries using the established transabdominal route as well as a new transvaginal approach. Fourteen normal controls and 11 pregnancies complicated by intrauterine growth retardation were studied. Satisfactory recordings were obtained in all 25 cases. There was a good correlation (R2 = 0.98) between pulsatility index (PI) values obtained transabdominally and transvaginally. The PI in the middle cerebral artery was significantly higher than in the internal carotid artery in both normal and growth-retarded fetuses. Pulsatility in both cerebral vessels was significantly decreased in growth-retarded fetuses when compared with normal controls. The transvaginal route, which produces a coronal section of the fetal brain, allows better distinction between the internal carotid and middle cerebral arteries. Furthermore, signals of equal quality are obtained from vessels in both cerebral hemispheres. Transvaginal scanning of the fetal cerebral arteries is a feasible technique offering an alternative to transabdominal scanning when the latter is hampered by technical difficulties.

Abdomen↗
PubMed1991

Epidural anesthesia, episiotomy, and obstetric laceration.

The relationships among epidural anesthesia, forceps use, parity, episiotomy, and laceration were studied in 9493 uncomplicated vertex deliveries of spontaneous onset and normal course. The use of epidural anesthesia was not associated with an increased incidence or severity of birth-canal trauma. Episiotomy was associated with a decreased rate of perineal laceration, but an overall increase in the rate of perineal trauma. The trauma that did occur with episiotomies was four times more likely to be major than that when no episiotomy was performed.

Anesthesia, Epidural↗
PubMed1990

Hypoxic acidemia, hyperviscosity, and maternal hypertension do not affect the umbilical arterial velocity waveform in fetal sheep.

The effect of hypoxic acidemia, hyperviscosity, and maternal hypertension on the umbilical arterial velocity waveform was studied in 23 chronically catheterized fetal sheep. Fetal hypoxic acidemia induced by lowering the maternal inspired oxygen concentration (n = 7) caused no change in the ratio of systolic/diastolic blood velocity even when fetal arterial pH was as low as 6.8. Fetal blood hyperviscosity (n = 7) induced by exchange transfusion with packed maternal blood cells increased placental vascular resistance by greater than or equal to 50% but had no significant effect on the systolic/diastolic ratio. Similarly, maternal hypertension induced by intravenous infusion of angiotensin II to the ewe (n = 9) did not affect the systolic/diastolic ratio despite a 50% increase in maternal arterial blood pressure. We conclude that umbilical arterial velocity waveform abnormalities observed in growth-restricted human fetuses are probably not a direct result of fetal hypoxemia or hyperviscosity or maternal hypertension.

Acids↗
PubMed1990

Site-dependent effects of increases in placental vascular resistance on the umbilical arterial velocity waveform in fetal sheep.

Placental vascular resistance was increased by embolization or by arterial vasoconstriction with angiotensin II and the effect on the flow and velocity waveforms in the umbilical artery was examined. Fetal sheep (n = 6) were studied under halothane anesthesia following the implantation of vascular catheters and an umbilical arterial electromagnetic flow probe. Blood flow and velocity (measured using Doppler ultrasound) gradually decreased during diastole and ultimately reversed in direction as cotyledon resistance was increased up to 14 fold. Cotyledon resistance was significantly correlated with the ratio of diastolic to systolic values (D/S ratio) of blood flow (r = -0.94) and velocity (r = -0.79). In contrast, increasing placental resistance up to 16 fold by constricting the umbilical arteries caused no significant change in the shape of the flow or velocity waveform.

Angiotensin II↗
PubMed1990

Acute hypoxemia does not affect the umbilical artery flow velocity waveform in fetal sheep.

The present study in sheep was undertaken to test whether acute fetal hypoxemia causes abnormalities in the umbilical artery velocity waveform. A 1-hour period of hypoxemia was induced in six chronically catheterized fetal sheep by reducing the inspired oxygen content of the ewe. During hypoxemia, the ratio of the systolic to diastolic velocity did not change significantly compared with controls. From this experimental evidence, we conclude that normal Doppler waveforms in the umbilical artery do not necessarily imply fetal normoxemia in sheep and that, because a direct cause-effect relationship has not been established, fetuses that have abnormal waveforms are not necessarily hypoxemic. Whether this is also true in humans remains to be shown.

Acute Disease↗
PubMed1989

Epidural anaesthesia and blood flow velocity in mother and fetus.

Doppler ultrasound has recently been used to assess changes in blood velocity in the uterine and umbilical arteries. Alterations in the ratio of systolic to diastolic velocity (S/D ratio) are believed to reflect changes in placental vascular resistance. We have used this technique to assess potential beneficial or detrimental effects of epidural anaesthesia on blood flow to the placenta. Continuous wave Doppler ultrasound was used to measure the S/D ratio in the uterine and umbilical arteries of 12 patients undergoing epidural anaesthesia prior to elective caesarean section. Anaesthesia was achieved using lidocaine and epinephrine. The S/D ratio in both the uterine and umbilical arteries remained unaltered either by the fluid preload or by the epidural anaesthesia. It is concluded that epidural anaesthesia using this technique has neither a beneficial nor detrimental effect on uterine or umbilical blood velocity in the uncomplicated pregnancy.

Anesthesia, Epidural↗
PubMed1989

Fetal and maternal hemodynamic responses to exercise in pregnancy assessed by Doppler ultrasonography.

It is common for women to undertake vigorous exercise in the late phase of pregnancy. This may have detrimental effects on the blood flow to the uterus and placenta or from the fetus to the placenta. Fifteen pregnant women with no obstetric or medical complications were subjected to a 5-minute exercise period. The maternal heart rate and blood pressure were elevated after exercise. The uteroplacental and umbilical circulations were assessed with Doppler ultrasonography. The ratio of the systolic/diastolic velocity in the uterine artery was elevated, which suggests that uteroplacental vascular resistance increased. The fetal heart rate was elevated after exercise, whereas the systolic/diastolic velocity ratio in the umbilical artery was unaltered. We conclude that moderate maternal exercise causes increased resistance to blood flow in the uterine circulation, whereas the umbilical circulation remains unaltered.

Blood Flow Velocity↗
PubMed1989

The influence of spontaneous accelerations of fetal heart rate on umbilical artery velocity waveforms.

For clinical interpretation of Doppler waveforms, it is important to establish the extent to which fetal heart rate changes affect the umbilical artery velocity waveform. Umbilical artery waveforms were measured with continuous wave ultrasonography during spontaneous accelerations of the fetal heart rate in 20 uncomplicated, near-term pregnancies. On average, an acceleration of 20 beats/min of fetal heart rate within an individual was associated with a reduction in the systolic/diastolic velocity ratio of 0.25. There was, however, considerable variability in the response, and in six patients the systolic/diastolic ratio actually increased with heart rate. We conclude that fetal heart accelerations within the normal range cause only small and variable changes in the systolic/diastolic ratio.

Blood Flow Velocity↗
PubMed1989

Effect of placental embolization on the umbilical arterial velocity waveform in fetal sheep.

Absent diastolic velocity and reversed diastolic velocity have been observed in the umbilical artery of growth-retarded human fetuses by means of Doppler ultrasonography. Because the physiologic mechanism is unknown, the purpose of this study was to determine whether such waveform changes could be induced in sheep fetuses by embolization of the resistance vessels of the placenta. Seven chronically catheterized sheep fetuses were instrumented with Doppler crystals mounted on one umbilical artery. The placenta was progressively embolized from the fetal side with plastic microspheres. In all cases the umbilical arterial waveform showed a progression from normal to zero diastolic velocity with embolization. In six of seven animals diastolic velocity eventually reversed in direction before fetal death. We conclude that occlusion of placental arteries and arterioles in fetal sheep recreates the waveform changes observed in severely growth-retarded human fetuses.

Animals↗
PubMed1989

Effect of placental resistance, arterial diameter, and blood pressure on the uterine arterial velocity waveform: a computer modeling approach.

A computer model was used to simulate velocity waveforms that can be visualized in the human uterine artery using Doppler ultrasound. It was found that increasing uteroplacental vascular resistance from normal caused an increase in the systolic/diastolic velocity ratio (S/D) and pulsatility index (PI) of the waveform. Increasing uteroplacental resistance also caused the appearance of a dicrotic notch. Reducing the uterine artery radius increased the S/D and PI and this effect was accentuated at high placental resistance. In contrast, increasing mean arterial pressure in the uterine artery had little effect on S/D and PI. Results suggest that waveform shape abnormalities observed in obstetric patients with pregnancy-induced hypertension are primarily caused by high uteroplacental vascular resistance and a reduced uterine arterial diameter.

Arteries↗
PubMed1988

Maternal cigarette smoking: the effects on umbilical and uterine blood flow velocity.

Maternal and fetal effects of smoking one cigarette were assessed in 15 healthy women at 36 to 41 weeks' gestation with no obstetric complications. It was found that smoking was associated with increases in maternal heart rate and blood pressure, but there was no significant change in the uterine artery vascular resistance as measured by means of the systolic/diastolic velocity ratio. There also was an increase in the fetal heart rate as well as a highly significant rise in the systolic/diastolic velocity ratio of the umbilical artery. The responses suggest that smoking causes a direct increase in the vascular resistance of the placenta from the fetal side. This resistance may impair oxygen exchange across the placenta and contribute to the increased perinatal morbidity associated with smoking.

Blood Pressure↗