[Evaluation of clinical reasoning in urology: contribution of the Script Concordance Test]

OBJECTIVE

The Script Concordance test is designed to measure knowledge organization, to allow interpretation of data in clinical decision making. The objective of this study was to assess the value of this new written evaluation instrument to evaluate clinical reasoning in urology.

MATERIAL AND METHOD

An 80-item examination was completed by a group of medical students (n = 15), a group of urology interns (n = 11), a group of registrars-assistants (n = 7), and a group of experienced urologists (n = 10). The scores obtained were compared by analysis of variance. The reliability of the test was studied by calculating Cronbach's coefficient alpha.

RESULTS

The mean score was 46.95 +/- 6.80 for students, 56.18 +/- 1.73 for interns, 66.27 +/- 4.92 for registrars and 63.38 +/- 2.19 for urologists. The differences observed between the scores for students, interns and urologists were significant. The reliability coefficient was 0.79 for the entire examination.

CONCLUSIONS

This test is able to discriminate various levels of experience in urology. It proposes a simple and direct approach to evaluation of knowledge organization. Further studies are necessary to confirm the contribution of this test to the strategy of evaluation of the clinical skills in urology.

Fetal umbilical cord oxygen values and birth to placental weight ratio in relation to size at birth

OBJECTIVE

Our purpose was to examine regulatory linkages between fetal oxygenation and fetal and placental growth. We determined umbilical cord PO (2) and oxygen saturation, fractional oxygen extraction, and birth to placental weight ratio values in relation to size at birth for a large tertiary hospital population delivering at term.

STUDY DESIGN

The computerized perinatal database of St Joseph's Health Care London, London, Ontario, was used to obtain the umbilical cord gases, pH, birth weight, placental weight, and other selected information for all term, singleton, liveborn infants between January 1990 and December 1999 (N = 27,043). Oxygen saturation values were calculated from the umbilical cord PO(2) and pH data with a previously derived empirical equation; fractional oxygen extraction values were calculated from the umbilical cord oxygen saturation data. Size at birth was divided into the following 5 birth weight categories using neonatal growth standards: fetal growth restriction, <3%; borderline fetal growth restriction, >or=3% and <10%; appropriate for gestational age, >or=10% and <or=90%; borderline large for gestational age, >90% and <or=97%; large for gestational age, >97%.

RESULTS

Infants in the borderline fetal growth restriction and fetal growth restriction groups had umbilical vein and artery PO(2) and oxygen saturation values that were stepwise lower than respective values for infants in the appropriate for gestational age group. Conversely, infants in the borderline large for gestational age and large for gestational age groups had umbilical vein PO(2) and oxygen saturation values that were stepwise higher than respective appropriate for gestational age group values; infants in these groups showed no change in arterial PO (2) and oxygen saturation values. Therefore infants in the borderline fetal growth restriction and fetal growth restriction groups had fractional oxygen extraction values that were stepwise higher than the appropriate for gestational age group value, whereas values for infants in the borderline large for gestational age and large for gestational age groups remained unchanged. Birth weight was disproportional to placental weight for infants in the borderline fetal growth restriction and fetal growth restriction groups when compared with that of the infants in the appropriate for gestational age group, with the birth to placental weight ratio values stepwise decreased. Conversely, birth weight was proportional to placental weight for infants in the borderline large for gestational age and large for gestational age groups with the birth to placental weight ratio values thus unchanged when compared with that of the infants in the appropriate for gestational age group.

CONCLUSION

We conclude that fetal oxygenation is related to size at birth across the entire range of birth weights as studied at term from macrosomic to growth-restricted infants; this conclusion supports oxygen as a primary determinant of fetal growth. However, there are differences in the linkage between fetal oxygenation and metabolic rate or growth for these cohort groups that may relate to underlying etiologic processes.

The health impact of undiagnosed airflow obstruction in a national sample of United States adults

To determine the health and functional impact of undiagnosed airflow obstruction for subjects in the general population, we used data obtained as part of the Third National Health and Nutrition Examination Survey (NHANES III). Categories of diagnosed and undiagnosed airflow obstruction were defined using questionnaire responses and spirometric results. Health and functional impact of airflow obstruction was assessed from responses to questions about general health status, walking 1/4 mile, lifting or carrying something as heavy as 10 lb, or needing help with personal care. Undiagnosed airflow obstruction (12.0%) was more common than doctor-diagnosed chronic obstructive pulmonary disease (COPD) (3.1%) or asthma (2.7%). Although undiagnosed airflow obstruction was usually very mild, approximately 5% of the entire sample had an FEV(1) less than 75% predicted. After adjusting for smoking, obesity, and comorbid conditions, the risk of impaired health and functional status with undiagnosed airflow obstruction was independently associated with severity of FEV(1) impairment. For males and females, ever smoking was strongly associated with all types of airflow obstruction, diagnosed or not. However, among females with airflow obstruction, 12.2% to 35.2% never smoked. Undiagnosed airflow obstruction is common in the general population of the United States and is associated with impaired health and functional status.

KEYWORDS

airflow obstruction; spirometry; health impact; screening

History effects and phase diagram near the lower critical point in YBa2Cu3O7 single crystals

Using a sensitive torque magnetometer we have studied magnetization curves for untwinned overdoped YBa2Cu3O7 single crystals in fields of up to 28 T. We demonstrate the existence of history effects below the lower critical point and provide a full demarcation of the Bragg-glass phase. A pronounced symmetry is observed in the behavior of the phase lines, irreversible magnetization, and value of the magnetization jump near both critical points.

The risks of spontaneous preterm delivery and perinatal mortality in relation to size at birth according to fetal versus neonatal growth standards

OBJECTIVE

The aim of this study was to test the null hypothesis that size at birth relative to fetal or neonatal growth standards is not a significant variable related to the risk of spontaneous preterm delivery.

STUDY DESIGN

This was a hospital-based cohort study of consecutive births at a tertiary care perinatal center from January 1, 1985, to December 31, 1996. A total of 37,377 pregnancies met the following inclusion criteria: (1) singleton gestation, (2) 25 to 40 weeks' gestation, and (3) no anomalies. Neonates were divided into 5 birth weight categories according to either fetal (uncorrected for sex) or neonatal (corrected for sex) growth standards, as follows: (1) intrauterine growth restriction, birth weight <3rd percentile; (2) borderline intrauterine growth restriction, birth weight > or = 3rd percentile and <10th percentile; (3) appropriate for gestational age, birth weight from 10th percentile through 90th percentile; (4) borderline large for gestational age, birth weight >90th percentile but < or = 97th percentile, and (5) large for gestational age, birth weight >97th percentile. Logistic regression analysis was used to estimate the independent effect of birth weight category on the risk of preterm delivery after spontaneous onset of labor, with the appropriate-for-gestational-age group serving as a reference.

RESULTS

When fetal growth standards were applied, there was a significant increase in the risk of spontaneous preterm delivery when birth weight was outside the appropriate-for-gestational-age range (odds ratios of 2.5, 1.4, 1.2, and 1.9 for intrauterine growth restriction, borderline intrauterine growth restriction, borderline large-for-gestational age, and large-for-gestational-age groups, respectively). In contrast, when neonatal growth standards were applied, the risks of spontaneous preterm delivery in intrauterine growth restriction, borderline intrauterine growth restriction, and large-for-gestational-age groups were significantly lower (odds ratios of 0.5, 0.7, and 0.7 for intrauterine growth restriction, borderline intrauterine growth restriction, and large-for-gestational-age groups, respectively) because of an underestimation in the number of fetuses with abnormal size at birth delivered prematurely. With both fetal and neonatal growth standards there was a 5-to 6-fold greater risk of perinatal death for both preterm and term fetuses with intrauterine growth restriction.

CONCLUSION

Fetal growth standards are more appropriate in predicting the impact of birth weight category on the risk of spontaneous preterm delivery than are neonatal growth standards. When fetal standards are applied, the risks of preterm birth in both extreme abnormal birth weight categories (intrauterine growth restriction and large for gestational age) are 2- to 3-fold greater than the risk among appropriate-for-gestational-age infants.

The longitudinal case study: from Schön's model to self-directed learning

BACKGROUND

Rapid changes observed in information technologies, medical practice, and learning methods encourage physicians to develop new updating strategies. To test its feasibility and to help physicians devise new learning and updating strategies, the knowing-in-action model developed by Schön was applied in planning and evaluating an interactive workshop. Acquisition of knowledge was tested.

METHODS

The office and hospital charts of a family physician were reviewed. They were used to prepare a longitudinal case study, based on the real-life story of a hypertensive patient followed by her doctor over a period of 15 years. The clinician's approach to solving clinical problems was triangulated for credibility with general practitioners, specialists, and the information available in the literature. This longitudinal case study was used to develop an interactive educational workshop. The workshop was presented to physicians who had registered in an accredited continuing medical education event. Changes in pre- and postevent knowledge among the participants were assessed using touch pad technology to evaluate the effectiveness of this approach on the acquisition of knowledge related to management of arterial hypertension and associated clinical problems.

RESULTS

A comparison of pre- and post-test data showed a significant improvement in knowledge for participants who answered all questions on both questionnaires (n = 8/37). The average score of these participants increased from 5.5 of 10 before the workshop to 8.3 of 10 after the workshop (p < .05). Participants reported a high satisfaction rate for the event.

FINDINGS

A workshop using the longitudinal case study enables physicians to perceive their daily practice through a continuing education activity in which they experience the processes of reflection in action and reflection on action described by Schön. It also increases awareness of the gap between current practice and experts' recommendations and provides an opportunity to evaluate the means for bridging or closing this gap. It sensitizes the physician to patients' changing needs and prompts the clinician to reflect on the who, what, when, where, and how of learning.

Oscillatory melting temperature of the vortex smectic phase in layered superconductors

We report on transport measurements of YBa 2Cu 3O (7-delta) single crystals with different oxygen contents in the geometry B, J ||ab (J perpendicularB). Our data show that the vortices become confined between the Cu-O planes below a well-defined temperature at which the effective size 2xi of the vortex core is approximately equal to the period of the Cu-O layers. This confinement strongly increases the vortex liquid freezing temperature. A new melting line is found separating a vortex liquid and a smectic phase, which shows an oscillatory field dependence reflecting differences between commensurate and incommensurate smectic states.

Effects of propofol on cerebral oxygenation during cardiopulmonary bypass in children

PURPOSE

Neurologic complications occur following cardiopulmonary bypass surgery. We conducted a randomized, controlled, single-blind study to determine the effect of propofol on the redox status of cytaa3, and to evaluate its potential for decreasing neurologic complications.

METHODS AND MATERIALS

Twenty-four children (median age: 3.3 yr; median weight: 14.4 kg) scheduled for elective cardiopulmonary bypass surgery were assigned to either the experimental group (Group P, given sufficient propofol to eliminate brain electrical activity as measured on EEG (i.e. burst suppression)) or the control group (Group C, no propofol). Near infrared spectroscopy data were collected at one-second intervals throughout the surgical procedures. Pre- and postoperative neurologic examinations were completed by a physician blinded to the group to which the patient was assigned. Change in cytochrome aa3 data at 10-min intervals (10, 20, 30, 40 min) following start of bypass were compared between groups by repeated measures analysis of variance.

RESULTS

The patterns of change in redox state of cytochrome were different between the two groups (P < 0.002). The pattern of change within Group P was similar to that in hypothermic patients in Group C. There were correlations between change in cytaa3 redox status and temperature in the control subjects. There were no gross neurologic complications in either group.

CONCLUSIONS

Propofol appears to stabilize the energy supply/demand equilibrium of the brain during cardiopulmonary bypass surgery and thus theoretically could reduce the incidence or severity of neurologic complications.

Application of in vivo and ex vivo magnetic resonance imaging for evaluation of tranilast on neointima formation following balloon angioplasty of the rat carotid artery

OBJECTIVE

Recent studies suggest that tranilast inhibits a variety of agents implicated in neointimal growth and restenosis in experimental animal models and humans. We report here a study evaluating the efficacy of tranilast in the rat carotid artery balloon angioplasty model, a model that mimics many aspects of the percutaneous transluminal angioplasty procedure in humans. Efficacy was determined based on in vivo and ex vivo magnetic resonance imaging (MRI) as well as by histomorphometry. The utility of this study, using a reverse paradigm, is to investigate if agents successful in the clinic can demonstrate efficacy in this animal model primary screen as measured by MRI and histomorphometry.

METHODS

Tranilast (300 mg/kg/day, p.o.) was administered to Sprague-Dawley rats 3 days prior to balloon injury and continued for 14 days after injury. Three methods of measuring the vascular injury that occurs in this model were employed: (1) in vivo MRI, used to measure in vivo lumen volumes for the carotid artery once at baseline (pre-surgery) and again at 14 days post angioplasty; (2) ex vivo MRI (and histomorphometry), used to evaluate the total arterial wall thickness and the intima-to-media ratio; and (3) analysis of collagen density, used to evaluate the efficacy of tranilast to abrogate collagen synthesis and deposition following vascular injury.

RESULTS

Tranilast provided 33% protection (P<0.05) from angioplasty-induced lumen narrowing as measured by MRI in vivo. The results of the ex vivo MR analysis of total wall thickness showed a 14% protection of angioplasty-induced narrowing (P<0.05), and the mean intima-to-media ratio showed a 39% (P<0.006) protection for the tranilast-treated rats. Histological analysis of the mean intima-to-media ratio demonstrated that tranilast provided 36% (P<0. 01) protection in the intima-to-media ratio. Further, treatment with tranilast showed a 52% reduction in collagen density of the intimal layer and a 70% reduction in collagen density of the medial layer of the injured arteries.

CONCLUSION

The data obtained by in vivo MRI, ex vivo MRI, histology and collagen analysis demonstrate that tranilast provided significant beneficial effects in inhibiting neointimal formation in the rat carotid artery model. Also this study, to the best of our knowledge, is the first to harness complimentary information from various technologies, including lumen patency by in vivo MRI, neointimal formation by ex vivo MRI and conventional histomorphometry, and histological analysis for collagen density, to provide a comprehensive understanding of the pathology in this disease model.

Determining the Wiedemann-Franz ratio from the thermal hall conductivity: application to Cu and YBa2Cu3O6.95

The Wiedemann-Franz (WF) ratio compares the thermal and electrical conductivities in a metal. We describe a new way to determine its value, based on the thermal Hall conductivity. The technique is applied to copper and to untwinned YBaCuO. In the latter, we uncover a T-linear dependence and suppression of the Hall-channel WF ratio. We discuss the implications of this suppression. The general suppression of the WF ratio in systems with predominant electron-electron scattering is discussed.

Changes in surfactant-associated protein mRNA profile in growth-restricted fetal sheep

To test the hypothesis that chronic placental insufficiency resulting in fetal growth restriction causes an increase in fetal lung surfactant-associated protein (SP) gene expression, we embolized chronically catheterized fetal sheep (n = 6) daily using nonradioactive microspheres in the abdominal aorta for 21 days (between 0.74 and 0.88 of gestation) until fetal arterial oxygen content was reduced by approximately 40-50%. Control animals (n = 7) received saline only. Basal fetal plasma cortisol concentration was monitored. At the end of the experiment, fetal lung tissues were collected, and ratios of tissue levels of SP-A, SP-B, and SP-C mRNA to 18S rRNA were determined by standard Northern blot analysis. Total DNA content of fetal lungs was reduced by 30% in the embolized group compared with control group (P = 0.01). There was a 2.7-fold increase in fetal lung SP-A mRNA (P < 0.05) and a 3.2-fold increase in SP-B mRNA (P < 0.01) in the chronically embolized group compared with those in the control group. SP-A and SP-B mRNA tissue levels were highly correlated with the mean fetal plasma cortisol levels on days 20-21 (r = 0.90, P < 0.01 for SP-A mRNA and r = 0.94, P < 0.01 for SP-B mRNA). SP-C mRNA tissue levels were not significantly affected by placental insufficiency. We conclude that fetal growth restriction due to placental insufficiency is associated with alterations in fetal lung SP, suggesting enhanced lung maturation that was highly dependent on the degree of increase in fetal plasma cortisol levels.

Effects of inorganic mercury on the respiration and the swimming activity of shrimp larvae, Pandalus borealis

In order to test the sensitivity of respiration (physiological and potential) to mercury (Hg) contamination, larval shrimp Pandalus borealis were exposed to inorganic Hg (0-160 ppb) for 27 h in the laboratory. Oxygen consumption rates (RO2), potential respiration (determined by respiratory electron transfer system activity, ETSA), protein content, and swimming activity for zoeae III and zoeae V stages were measured. For both zoeae stages, ETSA and protein content remained constant after 27 h exposure to 160 ppb Hg whereas RO2 and swimming activity decreased. This study revealed the impact of different Hg levels and different exposure times on RO2 of shrimp larvae. After 10 h exposure to 160 ppb Hg, the RO2 decreased by 43 and 49% in zoeae III and zoeae V stages, respectively. Exposure time of 27 h to 80 ppb Hg and higher, induced paralysis in nearly 100% larvae. Surprisingly, the paralysed larvae displayed almost 50% of the control's RO2. The results showed that Hg disturbs a part of the respiration process without modifying the maximum activity of the enzymes involved in the ETSA assay. Therefore, the ETSA assay can not be used as a sublethal bioanalytic probe to detect Hg in short-term exposures. The decline of the RO2/ETSA ratios reported here, indicates an inability of contaminated larvae to adapt their metabolism to physiological stress caused by Hg.

Effect of chronic hypoxemia on the regulation of nitric-oxide synthase in the fetal sheep brain

We tested the hypothesis that chronic hypoxemia modulates NO production of the fetal brain by altering its gene and protein expression. Chronically instrumented preterm fetal sheep were made hypoxemic by placental embolization for 21 days. Fetal oxygen content was measured to determine the level of hypoxemia. The expression of both eNOS and nNOS proteins and mRNA and enzyme activities of fetal sheep cerebrum were measured and compared between normoxic and hypoxemic animals. Our results show that in utero hypoxemia downregulates both Ca2+ dependent NOS activity and expression of eNOS protein and mRNA in the fetal sheep brain. In contrast, hypoxemia increased nNOS protein and mRNA levels in the cerebrum. This suggests that chronic hypoxemia has an opposing effect on eNOS and nNOS gene regulation. We propose that increased nNOS activity during chronic hypoxemia may excessively stimulate the neurons and contribute to fetal brain injury. On the other hand, downregulation of eNOS activity and expression may compromise the neuroprotective effect of eNOS and, therefore, further exacerbate brain injury.

Effects of the novel antimigraine agent, frovatriptan, on coronary and cardiac function in dogs

The effects of frovatriptan (VML 251/SB-209509) on coronary artery function were investigated in isolated coronary arteries from beagle dogs. Low concentrations of frovatriptan produced contraction with -logEC50 7.55 +/- 0.08 (n = 11). The maximal observed contraction attained was 56 +/- 7% of the control 5-hydroxytryptamine (5-HT; 10 microM) response. At high concentrations of frovatriptan (>6 microM), reversal of sumatriptan (10 microM)-induced contractions was noted. In arteries precontracted with the thromboxane mimetic, U46619, frovatriptan produced a bell-shaped concentration-response relation with a maximal response at 600 nM. Concentrations of frovatriptan >2 microM produced marked reversal of tone, with full relaxation of precontracted tissues at 200 microM. In anesthetized, open-chest mongrel dogs, intravenous (n = 5) or intracoronary (n = 5) artery administration of frovatriptan (0.0001-1 mg/kg) had no consistent effect on left ventricular end-diastolic pressure, left end-systolic pressure, cardiac contractility, aortic blood flow, systemic peripheral resistance, coronary blood flow, coronary vascular resistance, mean arterial blood pressure, or heart rate when compared with vehicle (n = 3). Intravenous sumatriptan produced minor effects on blood pressure and heart rate. Intracoronary artery administration of sumatriptan (0.0003 mg/kg) produced an increase in systemic peripheral resistance to 120.5 +/- 8.2% compared with vehicle (97.8 +/- 5.4%; p < 0.05). This dose of sumatriptan also produced a significant increase in coronary blood flow and decrease in coronary vascular resistance. Intravenous administration of sumatriptan produced a dose-related reduction in left ventricular diastolic pressure with a reduction to 58.3 +/- 8.3% and 41.7 +/- 25% of control values observed at 0.3 and 1 mg/kg, respectively; however, administration of sumatriptan by an intracoronary route had no effect. In a model of myocardial infarction, comparable doses of sumatriptan (1.0 mg/kg) or frovatriptan (0.1 mg/kg), in terms of their effect on carotid vascular resistance, had no significant effect on infarct size. Frovatriptan had no effect on coronary blood flow after reperfusion; however, sumatriptan produced a significant reduction in coronary blood flow for < or =3 h. These studies show that frovatriptan has the capability of relaxing coronary arteries in vitro, has no overall effect on cardiac function at rest with no effect on coronary hemodynamics after myocardial infarction, and has a profile superior to that of sumatriptan.

Fetal oxygen saturation and fractional extraction at birth and the relationship to measures of acidosis

OBJECTIVE

We sought to determine umbilical cord oxygen saturation and fractional oxygen extraction values as measured at birth for a large tertiary hospital population and their predictive value for measures of acidosis.

STUDY DESIGN

The computerized perinatal database of St. Joseph's Health Centre, London, Ontario, was used to obtain the umbilical cord gases, pH, mode of delivery, gestational age at delivery, and nuchal cord status for all live-born infants >500 gm between January 1991 and December 1995 (n = 22,134). Oxygen saturation values were calculated from the umbilical cord PO2 and pH data with a previously derived empirical equation, the accuracy of which was rechecked with 100 consecutive cord blood samples where oxygen saturation values were both calculated and measured with a hemoximeter (r = 0.99, p = 0.001). Fractional oxygen extraction values were calculated from the umbilical cord oxygen saturation data.

RESULTS

There were 18,250 "validated" paired umbilical vein and artery blood gas and pH results available for analysis after patient case exclusions for missing, unreliable, or "unphysiologic" data. For all validated patient cases, mean umbilical vein oxygen saturation was 63% +/- 16% (SD), mean umbilical artery oxygen saturation was 24% +/- 15%, and mean fractional oxygen extraction was 0.62 +/- 0.20, with all three of these parameters significantly affected by mode of delivery, gestational age at delivery, and nuchal cord status. Umbilical vein and artery oxygen saturation and fractional oxygen extraction values showed significant relationships with umbilical artery base excess, albeit weak (r = 0.18 to 0.22), and pH (r = 0.46), which were best described using cubic regression models. Receiver-operator characteristic curve statistics for the prediction of acidosis at birth were also significant for all three of these parameters but lower when predicting metabolic versus mixed acidosis. However, all showed a poor positive predictive value for significant acidosis at birth, whether metabolic or mixed and regardless of the cutoff values used.

CONCLUSION

Umbilical cord oxygen saturation and fractional oxygen extraction values as measured at birth for a large tertiary hospital population indicate a decreased oxygen margin of safety for infants born postterm, by cesarean section after labor, and with a nuchal cord. However, these values have a limited relationship to measures of acidosis, which may have clinical implications for the usefulness of intrapartum pulse oximetry.

Chronic hypoxemia selectively down-regulates 11beta-hydroxysteroid dehydrogenase type 2 gene expression in the fetal sheep kidney

The present study was designed to examine the effects of chronic fetal placental embolization on the expression of 11beta-hydroxysteroid dehydrogenase (11beta-HSD) types 1 and 2, the intracellular enzymes responsible for the metabolism of glucocorticoids. Twelve instrumented fetal sheep were randomly allocated on Day 110 (term = 147 days) to either a control (n = 6) or embolized (n = 6) group. Embolized fetuses received daily injections of nonradioactive microspheres into the abdominal aorta for 21 days to decrease arterial oxygen content by 40-50% of the pre-embolization values. At the end of the experiment, fetal liver and kidney tissues as well as placental cotyledons were collected, and tissue levels of 11beta-HSD mRNA and activity were determined by standard Northern blot analysis and radiometric conversion assay, respectively. There was a 44% reduction (p < 0.01) in the level of renal 11beta-HSD2 mRNA in the embolized group as compared with the control group. Moreover, this reduction in mRNA was carried through to 11beta-HSD2 protein, since there was a corresponding decrease in the level of 11beta-HSD2 activity (4.5+/-0.2 vs. 2.9+/-0.1 pmol/min per milligram protein, p < 0.01). In contrast, levels of both 11beta-HSD1 mRNA and activity in the fetal liver remained unchanged. Moreover, both 11beta-HSD types 1 and 2 mRNA and activity in the placenta were not altered by the fetal placental embolization. In conclusion, chronic hypoxemia selectively inhibits renal 11beta-HSD2 mRNA expression and enzyme activity in the ovine fetus, which may contribute, at least in part, to the mechanisms leading to fetal hypertension.

Prediction of umbilical artery base excess by intrapartum fetal oxygen saturation monitoring

OBJECTIVE

Our purpose was to evaluate the predictive value of intrapartum fetal oxygen saturation as monitored by reflectance pulse oximetry (SpO2) for metabolic acidosis at birth.

STUDY DESIGN

An observational study was carried out on intrapartum patients at > or = 35 weeks' gestation having either a nonreassuring fetal heart rate pattern, intrauterine growth restriction, or thick meconium. Fetal oxygen saturation monitoring was performed with use of the Nellcor N-400 monitor and the FS-14 fetal oxygen sensor. Mean values of SpO2 from the last 30 minutes of monitoring were correlated with umbilical artery base excess and pH at birth, with use of regression analysis, whereas the prediction of acidosis by SpO2 at different thresholds was tested with use of receiver-operator characteristic curve calculations.

RESULTS

Fifty-four patients met the criteria for data analysis, with a mean SpO2 monitoring time of 150 +/- 124 minutes (SD) and a mean signal loss of 30% +/- 20%. Mean fetal SpO2 for the last 30 minutes of monitoring averaged 42.1% +/- 9.9% and, for individual patient studies, correlated significantly with calculated oxygen saturation in the umbilical vein (r = 0.52, p < 0.001) and in the umbilical artery (r = 0.34, p = 0.02) as measured at birth. However, the correlation with umbilical artery base excess values at birth was somewhat weaker (r = 0.30, p < 0.05), as was the correlation with umbilical artery pH values (r = 0.26, p = 0.05). Receiver-operator characteristic curve calculations were all nonsignificant when SpO2 from the last 30 minutes of monitoring was used as a diagnostic test for predicting acidosis at birth.

CONCLUSIONS

Intrapartum fetal SpO2 as monitored in the current study was of limited use as a diagnostic test for predicting acidosis at birth, regardless of the SpO2 cutoff value used.

Cerebral circulatory responses of near-term ovine fetuses during sustained fetal placental embolization

To test the hypothesis that, in response to an increase in placental vascular resistance and progressive fetal asphyxia, the changes in external carotid blood flow waveforms are directly related to changes in external carotid vascular resistance, we embolized the fetal side of the placenta in pregnant sheep and measured cerebral and external carotid artery circulatory changes in relation to changes in external carotid artery flow waveforms. Chronically catheterized fetal sheep at 0.85 of gestation were embolized (n = 11) in the descending aorta for 6 h, until fetal arterial pH fell to approximately 6.90. Fetuses became rapidly hypoxemic (P < 0.0001) and developed a mixed respiratory and metabolic acidosis (P < 0.0001 for PCO2, pH, and base excess). There was a transient 40% increase in external carotid blood flow at pH approximately 7.25 and a parallel 32% increase in fetal arterial blood pressure (both (P < 0.01), whereas the external vascular resistance remained unaltered. Cerebral blood flow increased by 130% (P < 0.0001), and cerebral vascular resistance decreased by 125% (P < 0.0001) throughout the study. The external carotid resistance index (RI) decreased by 32% (P < 0.0001) at the time external carotid vascular resistance remained unchanged. This fall in external carotid RI was due almost entirely to a 110% increase in external carotid fundamental impedance (P < 0.001). We conclude that the poor relationship between the changes in external carotid vascular resistance and RI indicated that other hemodynamic factors such as vascular impedance to pulsatile flow must be measured for correct interpretation of changes in flow waveform shape under hypoxic conditions. In addition, changes in external carotid blood flow were not proportional to changes in cerebral blood flow in this model.

Fetal sheep endocrine responses to sustained hypoxemic stress after chronic fetal placental embolization

The purpose of this study was to determine the endocrine and circulatory responses of the ovine fetus, near term, to sustained hypoxemic stress superimposed on chronic hypoxemia. Fetal sheep were chronically embolized (n = 7) for 10 days between 0.84 and 0.91 of gestation via the descending aorta until arterial oxygen content was decreased by approximately 30%. Control animals (n = 8) received saline only. On experimental day 10, both groups were embolized over a 6-h period until fetal arterial pH decreased to approximately 7.00. Regional distribution of lower body blood flows was measured on day 10, before and at the end of acute embolization. On day 10, the chronically embolized group had lower arterial oxygen content (P < 0.05), Po2 (P < 0.01), and placental blood flow (P < 0.05) than controls and higher prostaglandin E2 (PGE2) and norepinephrine plasma concentrations (both P < 0.05). In response to a superimposed sustained hypoxemic stress, there was a twofold greater increase in PGE2 in the chronically embolized group than in the control group (P < 0.05). However, the increase in fetal plasma cortisol in response to superimposed hypoxemic stress was similar in both groups, despite significantly lower adrenocorticotropic hormone and adrenal cortex blood flow responses in the chronically hypoxemic group (both P < 0.05). We conclude that PGE2 response to a sustained superimposed reduction in placental blood flow, leading to metabolic acidosis, is enhanced under conditions of chronic hypoxemia and may play an important role for the maintenance of the fetal cortisol response to an episode of superimposed acute stress.

Fetal heart rate patterns in growth-restricted fetal sheep induced by chronic fetal placental embolization

OBJECTIVE

Our purpose was to test the hypothesis that chronic placental insufficiency and intrauterine growth restriction in fetal sheep causes a decrease in the number of fetal heart rate accelerations and fetal heart rate variability.

STUDY DESIGN

Chronically catheterized fetal sheep were embolized (n = 6) daily with 15 to 50 microns latex microspheres for 21 days between 0.74 and 0.88 of gestation into the abdominal aorta, until fetal arterial oxygen content was decreased by 40% to 50% of the preembolization value. Control animals (n = 6) received saline solution only. Signals from chest electrodes were analyzed on-line with the Sonicaid System 8000 in 2-hour epochs every 6 hours starting at 8 AM over the first 48 hours of hypoxemia and for 2 hours between 8 and 10 AM every other day from day 3 to day 21 of hypoxemia. Umbilical artery Doppler-derived resistance index and fetal plasma catecholamine concentrations were also measured.

RESULTS

Embolized fetuses had asymmetric intrauterine growth restriction and became chronically hypoxemic (p < 0.001) with a progressive increase in the umbilical artery resistance index (p < 0.001). During the first 48 hours of hypoxemia the number of accelerations and decelerations and both short- and long-term fetal heart rate variability increased initially, followed by a return to control levels by 20 hours after the onset of embolization. After 21 days of hypoxemia the number of accelerations was significantly reduced by 30% compared with controls (p < 0.05). Both short- and long-term fetal heart rate variability in control fetuses gradually increased with advancing gestational age (p < 0.001 and p < 0.01, respectively), whereas in embolized fetuses the fetal heart rate variability remained unchanged and was 20% lower than that of controls on day 21 (both p < 0.01).

CONCLUSION

Intrauterine growth restriction and long-term hypoxemia in fetal sheep are associated with a decrease in short- and long-term fetal heart rate variability, possibly because of a delay in the normal maturational changes of the autonomic control of fetal heart rate.

Chronic fetal placental embolization and hypoxemia cause hypertension and myocardial hypertrophy in fetal sheep

To examine the cardiovascular effects on the fetus of an elevated umbilical vascular resistance resulting in fetal hypoxemia, we embolized the fetal side of the placenta in pregnant sheep and measured cardiovascular and hormonal changes and cellular growth in fetal heart. Chronically catheterized fetal sheep were embolized (n = 6) for 21 days between 0.74 and 0.88 of gestation into the descending aorta until arterial oxygen content was decreased by 40-50% of the preembolization value. Control animals (n = 6) received saline only. During embolization, fetuses became chronically hypoxemic (P < 0.001) and hypertensive (P < 0.001), with a progressive increase in umbilical artery resistance index (P < 0.001). There was also an increase in fetal plasma norepinephrine throughout the study period (P < 0.05). On day 21 of embolization, fetuses showed asymmetrical growth restriction, increased heart weight (P < 0.01), and increase in right and left ventricular wall thickness (P < 0.05) compared with control animals. The protein-to-DNA ratio, an index of cell size, increased in the right ventricular myocardium in the embolized group (P < 0.001), suggesting myocardial cell hypertrophy. We conclude that, during chronic placental damage leading to fetal hypoxemia with an increase in umbilical artery resistance index, fetuses developed arterial hypertension and asymmetrical growth restriction and that increases in afterload to the heart and plasma norepinephrine likely caused fetal myocardial hypertrophy.