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Biomedical subjects

R M Lewinsky

Publications and source records attributed to R M Lewinsky.

17 recordsLinked to original sources
PubMed1998

Autonomic imbalance in preeclampsia: evidence for increased sympathetic tone in response to the supine-pressor test.

OBJECTIVE: To examine whether an increase in sympathetic nervous tone contributes to the augmented response to cardiovascular reflex testing in preeclamptic women. METHODS: Maternal electrocardiograms were recorded from 11 nonpregnant women and 25 normotensive and 15 preeclamptic nulliparous women at term, during periods of quiet respiration in the left-lateral position and after shifting to the supine position. Power spectral analysis was applied to epochs of 512 consecutive beat-to-beat intervals to determine the contribution of sympathetic tone, parasympathetic tone, and respiratory sinus arrhythmia to heart rate variability. RESULTS: Both normotensive and preeclamptic pregnant women showed a significant decrease in respiratory sinus arrhythmia and an increase in sympathetic tone compared with nonpregnant women. In nonpregnant and in normotensive pregnant women, shifting from the left-lateral to the supine position did not cause any change in autonomic characteristics. In contrast, preeclamptic women demonstrated a marked increase in power within the very low-frequency range representing sympathetic tone, from 288 +/- 214 to 556 +/- 322 second2/Hz, in response to the same challenge (P < .05). CONCLUSION: Third-trimester pregnancy is characterized by sympathetic overactivity. When complicated by preeclampsia, sympathetic overreactivity to cardiovascular reflex testing is observed. Our data support the notion that the pathophysiologic phenomena that characterize preeclampsia are mediated not only by circulating or locally acting vasoactive substances, but also, at least in part, by an increase in sympathetic nervous tone.

Adult↗
PubMed1997

Antepartum fetal pulse oximetry.

OBJECTIVE: To examine the feasibility of antepartum fetal pulse oximetry by using a specially designed probe. STUDY DESIGN: Twenty multiparous patients at term planned for induction of labor. The probe was passed through the cervix and held against the fetal scalp. Two laser diodes provided light in the near-infrared spectral region. Only reflected signals of both wavelengths which were consistent in pulse frequency and phase and with an AC/DC ratio of > 0.02% were considered usable. RESULTS: Usable measurements were obtained in 16 out of 20 cases. Overall usable signal time was 45% (range 30.2-61.5%). There was no accidental rupture of membranes. Mean fetal oxygen saturation was 76.1 +/- 6.2%. CONCLUSIONS: This study has shown that antepartum fetal pulse oximetry is feasible once a specially designed probe and signal analysis system are used.

Female↗
PubMed1996

The effect of maternal prostaglandin administration on fetal ductus venosus blood flow velocity.

Our objective was to investigate whether maternal administration of prostaglandins PGE2 and PGF2(alpha) is associated with changes in fetal ductus venosus flow velocity waveforms. Second-trimester termination of pregnancy was induced in 11 women (group A) by intra-amniotic instillation of 40 mg PGF2(alpha). In group B, 19 patients received 0.5 mg PGE2 intracervically for preinduction cervical ripening. Doppler flow velocity waveforms were recorded from the fetal ductus venosus immediately before and 40-60 min after prostaglandin administration. The paired t-test was used for statistical analysis of the ductus venosus index (DVI). The mean DVI decreased after PGF2(alpha) administration from 0.62 +/- 0.12 to 0.52 +/- 0.13 (p < 0.01); and from 0.62 +/- 0.10 to 0.58 +/- 0.12 (p < 0.05) after PGE2 administration. Atrial peak velocities were significantly increased after the procedures. No significant changes were found for systolic peak velocity values. The data indicate that major changes in ductus venosus hemodynamics are induced by PGF2(alpha) and PGE2.

Abortion, Therapeutic↗
PubMed1995

Sonographic estimation of umbilical coiling index and correlation with Doppler flow characteristics.

OBJECTIVE: To quantitate umbilical vascular coiling antenatally, and to correlate the coiling index with Doppler flow characteristics in umbilical vessels. METHODS: We studied 45 normal term fetuses within 24 hours before delivery. The umbilical coiling index was calculated using sonographic longitudinal views of cord vessels from several segments antenatally, and by dividing the total number of helices by the cord length (in centimeters) postnatally. Doppler flow velocities were obtained from umbilical arteries and vein in each cord. Flow characteristics were correlated with the umbilical coiling index. RESULTS: The mean (+/- standard deviation) umbilical coiling index was 0.44 +/- 0.11 in the antepartum period and 0.28 +/- 0.08 after birth. Regression analysis showed a significant linear trend (r = 0.71, P < .001). The correlations between sonographic coiling index and umbilical arterial Doppler flow characteristics (mean velocity, pulsatility index, resistance index, and systolic-diastolic ratio) were not significant. The sonographic coiling index was related to time-averaged velocity and flow in the umbilical vein. A good correlation was found between umbilical vein flow and the coiling index, with a significant linear trend (r = 0.59, P < .001). CONCLUSION: An intrauterine umbilical coiling index can be determined by ultrasound and correlates well with the actual index at birth. The sonographic umbilical coiling index is related to Doppler flow characteristics in the umbilical vein.

Female↗
PubMed1994

Doppler studies of fetal cerebral blood flow.

Doppler flow velocity waveforms from fetal cerebral vessels can be reliably obtained by a transabdominal or transvaginal scanning route. Changes in pulsatility imply alterations in cerebral impedance and reflect the physiological regulatory mechanisms underlying pathological processes during pregnancy. In fetuses severely distressed due to failure of placental function, the ratios reflecting the redistribution of fetal circulation (e.g. the 'brain-sparing effect') help to identify fetuses at risk for fetal hypoxia. Apart from providing an increase in medical knowledge, this non-invasive technique is proving to be clinically useful.

Journal Article↗
PubMed1994

Power spectral analysis of fetal heart rate.

This chapter examines the role of power spectral analysis (PSA) in elucidation of the physiological control mechanisms of fetal heart rate and as a potential indicator of fetal well-being. The importance of fetal heart rate variability (FHRV) as an indicator of fetal oxygenation is discussed, and the limitations in the current methods of measurement of FHRV are highlighted. Evidence is presented for the paramount influence of the autonomic nervous system in the control of heart rate variability. The basic proposition underlying spectral analysis is that the two autonomic branches influence heart rate in a frequency-dependent way, and their differential effects can be determined by PSA which breaks down the heart rate trace into its component frequencies. The application of PSA to heart rate variability data is an established tool in cardiology, and the published literature related to its use in the adult, neonate and fetus is reviewed. The power spectrum is sensitive to the activity state of the fetus, particularly fetal breathing movements, which have a variable effect on short- and long-term FHRV. There are a variety of mathematical approaches to the construction of power spectra, and a particular method of data acquisition and analysis is presented together with some theoretical background. Recent experimental evidence indicates a role for PSA as an indicator of fetal activity state, and the effect of hypoxia on the spectrum of the fetus in labour is discussed. There are some problems with the technique of PSA, particularly in regard to accepted definitions and methods of analysis. It is a powerful non-invasive tool in the elucidation of fetal cardiac control, but its value in the detection of the compromised fetus has yet to be tested in a clinical trial.

Adult↗
PubMed1994

Cardiac systolic time intervals and other parameters of myocardial contractility as indices of fetal acid-base status.

Electronic fetal heart rate monitoring has become the standard method for the assessment of fetal status during labour. Unfortunately, the hoped-for benefit from implementation of this technique has not been realized. The non-specific nature of FHR changes has led to undesirable side-effects, especially an increase in inappropriate operative interventions. Thus, there is an obvious need for methods which will improve upon the accuracy of FHR monitoring. There is substantial evidence for a tight coupling of fetal acid-base balance and myocardial contractility. This relationship has been established in experimental animal studies where fetuses were gradually rendered hypoxic and acidaemic while myocardial contractility was assessed by dP/dtmax and end-systolic elastance (Ees). Furthermore, the correlation between pH and indices of contractility extends over the entire range of clinical importance rather than being a terminal event. Systolic time intervals have long been recognized as good indicators of myocardial contractility. Recent advances in technology, have made their measurement in the human fetus by non-invasive means feasible. Substantial evidence has been accumulated, from both animal and human studies, to indicate that fetal STIs and especially the PEP and PEP/VET ratio are good predictors of fetal acid-base status. Other indices of fetal myocardial function, such as Doppler-derived aortic acceleration time and peak acceleration, have also emerged as having a potential benefit in monitoring the fetus before and during labour. Fetal STIs and other indices of myocardial contractility may be valuable adjuncts to FHR monitoring. During labour, STIs may prove to be of value both to elucidate equivocal FHR patterns and to detect fetal hypoxaemia and acidaemia. For this to occur, the sensitivity and specificity have to be determined by large-scale prospective clinical trials comparing STIs to current monitoring methods.

Acid-Base Imbalance↗
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↗
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

Factor XII deficiency and pregnancy.

A 19-year-old primigravida with known factor XII deficiency (prepregnant factor XII level of 21%) presented with placental abruption and preterm labor at 26 weeks' gestation. A healthy 925-g female infant was born by spontaneous vaginal delivery. The mother had no postpartum hemorrhage or further complications, and the infant demonstrated no intracranial or other forms of hemorrhage up to 70 days of age. The infant's factor XII level was 34% (normal for her age). There are only two previous reports of factor XII deficiency in pregnancy cited in the English literature, and both were uncomplicated. In view of the risk of thromboembolic complications in nonpregnant individuals with factor XII deficiency, pregnant women with a prolonged activated partial thromboplastin time and no lupus anticoagulant or anticardiolipin antibody syndrome should also be investigated for deficiencies of factors VIII, IX, and XII. These patients should be given the appropriate counseling and should be monitored for features of thromboembolism if factor XII deficiency is confirmed.

Abruptio Placentae↗
PubMed1991

Flow-velocity profiles of the fetal aorta and umbilical artery in pregnancies complicated by pregnancy-induced hypertension and fetal growth retardation.

Sixty-seven women undergoing ultrasonographic evaluation in the high-risk clinic were randomly recruited to be examined by a newly developed computerized method that presents flow-velocity profiles derived from pulsed Doppler-generated flow-velocity waveforms. Each woman had pulsed Doppler flow velocimetry of the fetal aorta and umbilical arteries done. Subjects were either normal controls (N = 20) or had pregnancies complicated by pregnancy-induced hypertension (N = 29), fetal growth retardation (N = 11), or both (N = 7). Distinct patterns of flow-velocity distribution across the fetal aorta and proximal umbilical arteries were identified in the pregnancies characterized by increased placental resistance. At peak systole, normal velocity was maintained only at a narrow area around the center of the vessel, whereas velocity in the rest of the vessel area was markedly reduced. These changes were present in 40 of 47 subjects (85.1%) with complicated pregnancies, whereas 27 of 47 (57.4%) had umbilical artery systolic-diastolic ratios above the 95th percentile. No significant differences between normal and complicated pregnancies were seen during diastole. Our findings suggest that increased placental resistance results in a redistribution of velocities within fetal blood vessels, often before maximal end-diastolic velocity is decreased.

Adult↗
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↗
PubMedDate not supplied

Prediction of pregnancy outcome by combined analysis of the fetal electrocardiogram and systolic time intervals.

A microcomputer-based system has been developed that continuously analyzes the fetal electrocardiogram (ECG) and Doppler cardiogram during labor by noninvasive means. Three systolic time intervals (preejection period [PEP], ventricular ejection time [VET], and isovolumetric contraction time), and four ECG parameters (P-R interval, QRS wave duration, T/QRS amplitude ratio, and S-T slope) are simultaneously measured and displayed. Normal values were derived from 126 uncomplicated pregnancies at term. A second group of 89 cases showing fetal heart rate patterns suggestive of fetal distress were subsequently studied: 64 had a good outcome (umbilical artery pH 7.20 or higher and a 5-minute Apgar score 7 or greater) and 25 were asphyxiated. Results were retrospectively analyzed. All asphyxiated fetuses had preejection period, PEP to VET ratio and T to QRS ratio values of more than 1 SD above the mean for the normal population. The PEP to VET ratio, which is an indicator of myocardial function independent of heart rate, proved to be the most sensitive predictor of fetal asphyxia. We conclude that analysis of systolic time intervals and ECG parameters of the fetal heart during labor improves the diagnostic accuracy of fetal heart rate monitoring.

Adult↗
PubMedDate not supplied

Transient ascites associated with a fetal ovarian cyst. Case report.

A case of fetal ovarian cyst associated with transient ascites is presented. The cyst showed serial changes from a fluid-debris interface to an anechoic structure. The changing ultrasonographic appearance of the cyst, disappearance of ascites and postnatal spontaneous resolution, suggests in utero torsion of the cyst.

Adult↗