Search PubMed⌕ Search

Biomedical subjects

J W Ritchie

Publications and source records attributed to J W Ritchie.

At least 19 recordsLinked to original sources
PubMed1995

Impact of increasing carbohydrate intolerance on maternal-fetal outcomes in 3637 women without gestational diabetes. The Toronto Tri-Hospital Gestational Diabetes Project.

OBJECTIVE: Our purpose was to assess maternal-fetal outcomes in patients with increasing carbohydrate intolerance not meeting the current criteria for the diagnosis of gestational diabetes. STUDY DESIGN: We conducted a prospective analytic cohort study in which nondiabetic women aged > or = 24 years, receiving prenatal care in three Toronto teaching hospitals, were eligible for enrollment. A glucose challenge test and an oral glucose tolerance test were administered at 26 and 28 weeks' gestation, respectively; risk factors for unfavorable maternal-fetal outcomes were recorded. Caregivers and patients were blinded to glucose values except when test results met the current criteria for gestational diabetes. RESULTS: Of 4274 patients screened, 3836 (90%) continued to the diagnostic oral glucose tolerance test. The study cohort was formed by the 3637 (95%) patients without gestational diabetes, carrying singleton fetuses. Increasing carbohydrate intolerance in women without overt gestational diabetes was associated with a significantly increased incidence of cesarean sections, preeclampsia, macrosomia, and need for phototherapy, as well as an increased length of maternal and neonatal hospital stay. Multivariate analysis showed that increasing carbohydrate intolerance is an independent predictor for various unfavorable outcomes. CONCLUSION: Increasing maternal carbohydrate intolerance in pregnant women without gestational diabetes is associated with a graded increase in adverse maternal-fetal outcomes.

Adult↗
PubMed1995

Reduced placental villous tree elaboration in small-for-gestational-age pregnancies: relationship with umbilical artery Doppler waveforms.

OBJECTIVE: Our purpose was to investigate the three-dimensional architecture of placental villi from normal and growth-restricted fetuses and relate findings to umbilical artery blood flow velocity waveforms. STUDY DESIGN: Placentas from term (n = 15) and preterm (n = 5) appropriately grown and term (n = 9) and preterm (n = 7) growth-restricted fetuses (birth weight < 10th percentile) were examined to determine the number of arteries per stem villus and the three-dimensional configuration of the villous trees and their vessels. Umbilical blood flow before delivery was assessed by Doppler ultrasonography. The effects of age and growth restriction were determined by two-way analyses of variance. RESULTS: Growth restriction was associated with reduced large vessel wall thickness (p < or = 0.05) but no reduction in the number of these vessels per stem villus. The volumes and surface areas of intermediate and terminal villi were reduced (p < or = 0.001), especially in preterm growth-restricted cases, where a marked reduction in diastolic blood flow velocity was observed in the umbilical artery. CONCLUSIONS: Reduced villous development may contribute to abnormal umbilical artery blood flood flow, as assessed by Doppler ultrasonography, in some cases of intrauterine growth restriction.

Blood Flow Velocity↗
PubMed1995

The effects of maternal aerobic exercise on human placental development: placental volumetric composition and surface areas.

The histomorphometry of term placentae from women who exercised regularly throughout either the first half or all of pregnancy was compared to that of placentae from matched controls to determine if regular exercise during pregnancy produced histomorphometric evidence of altered development and transport capacity. Conventional stereological techniques were used to estimate placental volumetric composition, surface areas, and villous and vascular configurations in the three groups. Exercise confined to early pregnancy increased the parenchymal component of the placenta, total vascular volume and site-specific capillary volume and surface area. Exercise throughout pregnancy increased these and multiple other histomorphometric parameters associated with the rate of placental perfusion and transfer function. However, significant changes were confined to villi > 80 microns in diameter. The localization of both the timing of the stimulus and the anatomical sites affected indicates that regular, sustained exercise modifies placental development primarily in early and mid-pregnancy. We speculate that the lack of significant changes in the structure and configuration of the smaller villi indicates that other adaptive mechanisms, such as increased rates of placental blood flow, must be well developed by the latter portion of the mid-trimester and adequately maintain fetal oxygenation and substrate delivery throughout the third trimester.

Adult↗
PubMed1994

Impact of time since last meal on the gestational glucose challenge test. The Toronto Tri-Hospital Gestational Diabetes Project.

OBJECTIVE: The purpose of the study was to evaluate the impact of time since the last meal on the glucose challenge test and to find cut points that are most likely to predict the outcome of the oral glucose tolerance test in patients screened for gestational diabetes. STUDY DESIGN: This prospective analytic cohort study was carried out at the University of Toronto Perinatal Complex. A 50 gm glucose load was given at 26 weeks' gestation and the time since previous meal ingestion was recorded. At 28 weeks' gestation a 100 gm oral glucose tolerance test was administered. A total of 4274 eligible patients were screened. RESULTS: Time since the last meal had a marked effect on mean plasma glucose. Receiver-operator characteristic curve analysis with National Diabetes Data Group criteria to interpret the oral glucose tolerance allowed the selection of the most efficient cut points for the glucose challenge test on the basis of time since the last meal. These cut points were 8.2, 7.9, and 8.3 mmol/L for elapsed postprandial times of < 2, 2 to 3, and > 3 hours, respectively. With this change from the current threshold of 7.8 mmol/L the number of patients with a positive screening test dropped from 18.5% to 13.7%. There was an increase in positive predictive value from 14.4% to 18.7%. The rate of patient misclassification fell from 18.0% to 13.1%. CONCLUSION: We suggest that screening strategies for detection of gestational diabetes be reconsidered, to account for the impact of variable postprandial status on the test results.

Adult↗
PubMed1994

Localization of two angiogenic growth factors (PDECGF and VEGF) in human placentae throughout gestation.

The spatiotemporal distribution of two angiogenic growth factors, platelet-derived endothelial cell growth factor (PDECGF) and vascular endothelial growth factor (VEGF) were determined using immunohistochemistry on sections of human placentae from each trimester of pregnancy. In the first trimester PDECGF was detected in trophoblast and in a band in the centre of the villous core. During gestation staining spread throughout the stroma but began to weaken in trophoblast until, by term, it was found only in stroma and in some endothelial cells. VEGF was detected exclusively in cytotrophoblast during the first trimester and then in syncytiotrophoblast throughout the remainder of pregnancy. Western blot analysis revealed that PDECGF antisera bound to three bands approximately 27, 47 and 94 kDa. The lowest band was not detected in platelet lysate and may represent an alternatively processed form of this peptide in placenta. VEGF antisera bound strongly to bands approximately 36, 46, 54, 56 and 64 kDa. The intensity of most bands increased between the first and second trimesters, consistent with an increased level of angiogenesis as the placenta develops. The presence of both factors in trophoblast in early pregnancy may be indicative of the trophoblast playing an active role in influencing the development of the villous vascular network.

Blotting, Western↗
PubMed1994

Determinants of increased left ventricular output during in utero ventilation in fetal sheep.

A model of in utero ventilation was used to elucidate the mechanisms by which left ventricular (LV) output increases with the transition from a fetal to a neonatal circulation. Using a conductance catheter, LV volumes were measured in seven anesthetized, near-term fetal sheep. Pressure-volume data was recorded before and with oxygen ventilation and again after occlusion of the umbilical cord. Ventilation caused increases in LV end-diastolic volume measured in seven anesthetized, near-term fetal sheep. Pressure-volume data was recorded before and with oxygen ventilation and again after occlusion of the umbilical cord. Ventilation caused increases in LV end-diastolic volume (2.3 +/- 0.9 to 2.9 +/- 0.6 mL/kg; p < 0.05), stroke volume (1.2 +/- 0.3 to 1.9 +2- 0.2 mL/kg; p < 0.001), and ejection fraction (52.8 +/- 11.1 to 66.4 +/- 8.8%; p < 0.001). Contractile state, as assessed by end-systolic elastance, did not change during the transition. Heart rate also remained constant. Afterload, as assessed by effective arterial elastance, decreased from 1.80 +/- 0.37 to 1.04 +/- 0.33 kPa/mL (p < 0.01). Occlusion of the umbilical cord did not result in any further change in hemodynamic parameters. Pressure-volume analysis revealed that a decrease in effective LV afterload and an increased LV end-diastolic volume are the major determinants of, and contribute comparably to, the profound increase in LV output with in utero ventilation. Enhanced contractility is not required for the increase in LV output to occur.

Animals↗
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↗