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Biomedical subjects

D E Fixler

Publications and source records attributed to D E Fixler.

At least 19 recordsLinked to original sources
PubMed2005

Relation between ambient air quality and selected birth defects, seven county study, Texas, 1997-2000.

A population-based case-control study investigated the association between maternal exposure to air pollutants, carbon monoxide, nitrogen dioxide, ozone, sulfur dioxide, and particulate matter <10 microm in aerodynamic diameter during weeks 3-8 of pregnancy and the risk of selected cardiac birth defects and oral clefts in livebirths and fetal deaths between 1997 and 2000 in seven Texas counties. Controls were frequency matched to cases on year of birth, vital status, and maternal county of residence at delivery. Stationary monitoring data were used to estimate air pollution exposure. Logistic regression models adjusted for covariates available in the vital record. When the highest quartile of exposure was compared with the lowest, the authors observed positive associations between carbon monoxide and tetralogy of Fallot (odds ratio = 2.04, 95% confidence interval: 1.26, 3.29), particulate matter <10 microm in aerodynamic diameter and isolated atrial septal defects (odds ratio = 2.27, 95% confidence interval: 1.43, 3.60), and sulfur dioxide and isolated ventricular septal defects (odds ratio = 2.16, 95% confidence interval: 1.51, 3.09). There were inverse associations between carbon monoxide and isolated atrial septal defects and between ozone and isolated ventricular septal defects. Evidence that air pollution exposure influences the risk of oral clefts was limited. Suggestive results support a previously reported finding of an association between ozone exposure and pulmonary artery and valve defects.

Air Pollutants↗
PubMed2001

Effect of center volume on outcome of ventricular septal defect closure and arterial switch operation.

This study evaluates the effects of surgical volume and preoperative patient characteristics on length of stay following ventricular septal defect (VSD) repair and arterial switch operation (ASO). Twenty-four centers contributed data on 16,795 consecutive surgical procedures from January 1, 1992 to December 31, 1996 to the Pediatric Cardiac Care Consortium Registry. The following variables were used in the analysis: center, center volume, age, weight, date of operation, preoperative hospital days, presence of trisomy 21, and significant coexisting heart defects (risk). For VSD, all variables were associated with length of stay in the univariate analyses; however, in the multivariate model, center volume did not retain significance. Length of stay for ASO was associated with center, center volume, and preoperative days in the univariate analysis. In the multivariate analysis for ASO, center and center volume were significant variables for predicting length of stay. These findings suggest that length of stay for uncomplicated surgical procedures is not related to surgical volume; however, for technically demanding procedures, length of stay tends to be shorter in centers with more experience.

Adolescent↗
PubMed1999

The role of the right ventricle during hypobaric hypoxic exercise: insights from patients after the Fontan operation.

OBJECTIVES: The principal objective of this study was to examine the importance of the right ventricle for maximal systemic oxygen transport during exercise at high altitude by studying patients after the Fontan operation. BACKGROUND: High-altitude-induced hypoxia causes a reduction in maximal oxygen uptake. Normal right ventricular pump function may be critical to sustain cardiac output in the face of hypoxic pulmonary vasoconstriction. We hypothesized that patients after the Fontan operation, who lack a functional subpulmonary ventricle, would have a limited exercise capacity at altitude, with an inability to increase cardiac output. METHODS: We measured oxygen uptake (VO2, Douglas bag), cardiac output (Qc, C2H2 rebreathing), heart rate (HR) (ECG), blood pressure (BP) (cuff), and O2 Sat (pulse oximetry) in 11 patients aged 14.5+/-5.2 yr (mean +/- SD) at 4.7+/-1.6 yr after surgery. Data were obtained at rest, at three submaximal steady state workrates, and at peak exercise on a cycle ergometer. All tests were performed at sea level (SL) and at simulated altitude (ALT) of 3048 m (10,000 ft, 522 torr) in a hypobaric chamber. RESULTS: At SL, resting O2 sat was 92.6+/-4%. At ALT, O2 sat decreased to 88.2+/-4.6% (P < 0.05) at rest and decreased further to 80+/-6.3% (P < 0.05) with peak exercise. At SL, VO2 increased from 5.1+/-0.9 mL x kg(-1) x min(-1) at rest to 23.5+/-5.3 mL x kg(-1) x min(-1) at peak exercise and CI (Qc x m(-2)) increased from 3.3+/-0.7 L x m(-2) to 6.2+/-1.2 L x m(-2). VO2 peak, 17.8+/-4 mL x kg(-1) x min(-1) (P < 0.05), and CI peak, 5.0+/-1.5 L x m(-2) (P < 0.05), were both decreased at ALT. Remarkably, the relationship between Qc and VO2 was normal during submaximal exercise at both SL and ALT. However at ALT, stroke volume index (SVI, SV x m(-2)) decreased from 37.7+/-8.6 mL x min(-1) x m2 at rest, to 31.3+/-8.6 mL x min(-1) x m2 at peak exercise (P < 0.05), whereas it did not fall during sea level exercise. CONCLUSIONS: During submaximal exercise at altitude, right ventricular contractile function is not necessary to increase cardiac output appropriately for oxygen uptake. However, normal right ventricular pump function may be necessary to achieve maximal cardiac output during exercise with acute high altitude exposure.

Adolescent↗
PubMed1998

Prenatal exposures and congenital heart defects in Down syndrome infants.

The purpose of this study was to determine whether there are important differences in maternal and environmental prenatal risk factors between liveborn Down syndrome infants with congenital heart defects and Down syndrome infants without heart defects. Using a case control study design, we evaluated the risk associated with maternal illness, drug ingestion, substance usage, and chemical exposures in the home or workplace. The period of risk selected was 3 months before and 3 months after the last menstrual period, because cardiac development occurs early, before the mother may become aware of her pregnancy. Because fetal survival in Down syndrome may be more vulnerable to various exposures, controls were selected who also had trisomy 21. Of 171 infants studied, 89 were cases with congenital heart disease, and 82 were controls without heart disease. All interviews were performed by one nurse practitioner using a structured standardized questionnaire. Cases and controls had similar maternal ages, family incomes, parental education levels, and contraceptive practices before pregnancy. No differences were found between case and control mothers for maternal illness, medication use, or consumption of caffeinated beverages, cigarettes, or alcohol. Reporting of recreational drug usage was infrequent, may reflect underreporting, and did not differ between cases and controls. Maternal exposures were commonly reported for pesticides (50%), hair dyes (22%), craft paints (8%), varnishes (7%), and solvents (3.5%). However, in none of the categories was maternal exposure significantly more prevalent among case mothers than among control mothers. The failure of this study to identify risk factors for cardiac malformations may be attributable to the small differences in reported frequencies reducing statistical power or to the possibility that cardiac malformation in Down syndrome is a direct result of chromosomal duplication.

Case-Control Studies↗
PubMed1993

Ethnicity and socioeconomic status: impact on the diagnosis of congenital heart disease.

OBJECTIVES: The purpose of this study was to estimate the prevalence rates of specific cardiac defects for three ethnic groups and to determine the effects of ethnicity, family income and household education level on the timing of referral for pediatric cardiac care. BACKGROUND: Previous studies examining ethnic differences in rates of congenital heart disease were based on hospital referrals or were limited to diagnoses made in the 1st year of life. These limitations may lead to potential biases in the ascertainment of cases. The present study is population based and includes patients diagnosed after the 1st year of life. METHODS: Cases of congenital heart disease were enumerated among 379,561 liveborn infants to black, white and Mexican-American residents in Dallas County, Texas. Diagnosis was made on the basis of examination by a pediatric cardiologist, two-dimensional echocardiographic studies, cardiac catheterization or observations at operation or at autopsy. Ethnicity, median family income and household educational level were determined from birth certificate information. RESULTS: White children had higher prevalence rates for aortic stenosis, endocardial cushion defect and ventricular septal defect. Mexican-American children had the lowest rate for hypoplastic left heart syndrome. The median age at referral to a pediatric cardiologist was 1.9 months for blacks, 2.1 months for whites and 2.2 months for Mexican-Americans. Stratifying the cases by median family income and household educational level failed to show any significant relation to age at referral. CONCLUSIONS: Prevalence rates of specific cardiac defects vary among black, white and Mexican-American children, probably reflecting different genetic and environmental backgrounds. The timing of referral for pediatric cardiac care, however, was not related to ethnicity, median family income or household educational level.

Black or African American↗
PubMed1993

Limitations of an oscillometric ambulatory blood pressure monitor in physically active children.

OBJECTIVE: To determine the limitations of an oscillometric device for measuring ambulatory blood pressure in physically active children. DESIGN: Observational descriptive. SUBJECTS: Sixty-one children 4.3 to 18.7 years of age. INTERVENTIONS: Twenty-two high school students wore an ambulatory blood pressure monitor (SpaceLabs model 90202) for 24 hours. A subject-kept activity diary facilitated data interpretation. In 39 additional subjects, measurements were recorded during strenuous exercise, at rest, and after ambulation. Before and after the students wore the unit, oscillometric and auscultatory blood pressure measurements were simultaneously taken to calibrate the ambulatory blood pressure monitor, evaluate its accuracy, and assess deterioration in the calibration of the unit with use. RESULTS: During 24-hour ambulatory monitoring, 29% of the readings were edited because of error codes, primarily because of vibratory interference. At the end of the 24-hour monitoring period, simultaneous pressures by oscillometric and auscultatory techniques agreed within 6 mm Hg in 17 of 18 cases for both systolic and diastolic blood pressures. During exercise, 88.4% of the systolic and diastolic blood pressure readings agreed within 8 mm Hg. In 20 other ambulatory subjects with 80 simultaneous oscillometric and auscultatory measurements, all systolic and 88.5% of the diastolic values agreed within 10%. CONCLUSIONS: These results indicate that the SpaceLabs model 90202 unit provides a reasonably accurate assessment of ambulatory blood pressures in mildly active and inactive children and that blood pressure can be monitored with time.

Adolescent↗
PubMed1990

Ambulatory blood pressure monitoring in hypertensive adolescents.

The purpose of this study was to determine the ability of ambulatory blood pressure monitoring to identify youths with chronic blood pressure elevation. Nineteen adolescent boys were studied, ten had 5-year average systolic or diastolic pressures above the 95th percentile, nine had normal pressure. A Del Mar Avionics Pressurometer III system recorded an average of 121 readings on each subject. The coefficients of variation for pressure were similar for hypertensive and normotensive individuals. During classes, eight of the ten hypertensive youths had elevated pressures in over half of the measurements. Also during these classes eight of ten hypertensive boys had average systolic or diastolic pressure above the 95th percentile, whereas only one of nine normotensive boys had average pressures above this level. We suggest that schooltime ambulatory pressures may be most useful in classifying the blood pressure trend in a youth.

Adolescent↗
PubMed1990

Trends in congenital heart disease in Dallas County births. 1971-1984.

To examine the changes in birth cohort prevalence rates and severity of congenital heart disease, we studied children with congenital heart disease born to blacks, whites, and Mexican-Americans in Dallas County from 1971 through 1984. Diagnoses were made by pediatric cardiologists' clinical evaluations, echocardiography, catheterization, surgery, or autopsy. During this study period, 2,509 of 379,561 liveborn infants were diagnosed, a prevalence rate of 6.6/1000. The rates for whites was significantly higher than for blacks or Mexican-Americans--7.2/1,000, 5.6/1,000, and 5.9/1,000, respectively. The rate for severe cases requiring cardiac catheterization or surgery or undergoing autopsy was 3.1/1,000 and did not differ among the three groups. The time trend for rates of congenital heart disease suggested an apparent increase in prevalence rate during the 1970s; however, the prevalence rate of severe forms remained relatively stable. This indicates that the apparent rise in prevalence could be accounted for by an increase in detection of mild cases. These findings were interpreted as reflecting a greater tendency for pediatricians to refer asymptomatic children with significant heart murmurs to a pediatric cardiologist.

Black People↗
PubMed1988

Left ventricular dysfunction due to chronic right ventricular pressure overload. Resolution following percutaneous balloon valvuloplasty for pulmonic stenosis.

Left ventricular dysfunction due to chronic right ventricular pressure overload is well documented in experimental animals, but is controversial in humans. Whether left ventricular dysfunction resolves following the relief of chronic right ventricular pressure overload has not been studied. In this report, rapid improvement in both right and left ventricular function following successful percutaneous balloon valvuloplasty is described in a patient with severe isolated valvular pulmonic stenosis and biventricular dysfunction. It appears that: (1) geometric distortion played a major role in his reversible left ventricular dysfunction, and (2) severe biventricular dysfunction should not be a contraindication to valvuloplasty for valvular pulmonic stenosis.

Adult↗
PubMed1988

Milrinone effects in the isolated immature rabbit heart.

Milrinone, a new positive inotropic agent, was evaluated and compared to isoproterenol in an immature isolated isovolumic rabbit heart model. Three age groups were studied: newborns (0-6 days), juveniles (4-6 weeks old) and adults (5-7 months old). Heart rate did not change significantly with milrinone or isoproterenol in adults or juveniles, but increased in newborns from 144 +/- 1 to 162 +/- (SEM) 6 beats/min at peak milrinone effect. Milrinone had a greater effect on the contractility (maximum positive dP/dt) of the mature hearts, with newborns increasing to 134 +/- 6% of baseline, juveniles to 154 +/- 8% and adults to 216 +/- 15%. Results were similar for isoproterenol, although the positive inotropic effect occurred over a wider dosage range for this drug. No additive effects of the two drugs were noted. We conclude, that although milrinone is a positive inotropic drug in all age groups studied, the response of the newborn heart is quantitatively much weaker than that of the adult.

Aging↗
PubMed1988

Coarctation of the aorta.

This article discusses the clinical and laboratory findings of isolated coarctation of the aorta, with emphasis on the newer methods of diagnosis and treatment, as well as the long term natural history following surgical repair.

Aortic Coarctation↗
PubMed1987

Global myocardial ischemia in the newborn, juvenile, and adult isolated isovolumic rabbit heart. Age-related differences in systolic function, diastolic stiffness, coronary resistance, myocardial oxygen consumption, and extracellular pH.

Controversy persists over the relative tolerance of the immature myocardium to global ischemia. Thus, we evaluated the physiologic effects of 30, 60, and 180 minutes of global ischemia in an isolated, isovolumic rabbit heart model, at 3 different ages: newborns (less than 1 week of age) (n = 36), juveniles (4 to 6 weeks old) (n = 36), and adults (5 to 7 months old) (n = 36). Following 30 and 60 minutes of ischemia, respectively, adults recovered 87 +/- 4% (mean +/- SEM) and 90 +/- 7% of baseline systolic function, and juveniles recovered 91 +/- 10% and 85 +/- 8%. In contrast, newborns recovered only 27 +/- 6% and 28 +/- 4% of baseline systolic function (p less than 0.05 compared to adults and juveniles). During ischemia, newborn hearts became stiff more rapidly, reaching 361 +/- 46% of baseline stiffness by 60 minutes, whereas adults and juveniles were at 122 +/- 33% and 92 +/- 18% of baseline stiffness (p less than 0.05 newborns compared to adults and juveniles). With reperfusion after 60 minutes of ischemia, the work efficiency of the newborn heart deteriorated to 39 +/- 7% of baseline, compared with 95 +/- 7% and 91 +/- 7% of baseline efficiency in the adult and juvenile hearts (p less than 0.05, newborns compared to adults and juveniles). The ratio of tissue wet-to-dry weights were similar in all age groups after ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1986

Longitudinal blood pressures in blacks, whites, and Mexican Americans during adolescence and early adulthood.

This study, designed to assess the extent blood pressure distributions become divergent between blacks, whites, and Mexican Americans during adolescence and early adulthood, is a mixed cross-sectional and longitudinal survey of blood pressures of adolescents in Dallas, Texas. The initial survey was performed on 10,641 eighth grade students in 1976 comprising 92% of the eighth grade population. This population was resurveyed two and four years later. Systolic blood pressures were consistently higher in males than females; diastolic pressures were higher in males after age 15. Between 13 and 18 years, black males had systolic and diastolic pressures that were lower or the same as those of whites and Mexican Americans. At these ages, black males and white males were of similar stature and weight. Black females had systolic pressures that were slightly higher than those of whites and Mexican Americans, whereas diastolic pressures among females showed no consistent ethnic differences. Black females were significantly heavier than either the white or Mexican-American females. The distribution of blood pressure from Dallas youths were consistently lower over all age-ethnic-sex groups than that reported from the National Heart, Lung, and Blood Institute Task Force on Blood Pressure Control in Children. The results of this longitudinal study indicate that no substantial ethnic differences in blood pressures developed between blacks, whites, and Mexican Americans prior to 20 years of age.

Adolescent↗
PubMed1986

Maturational differences in the isolated isovolumic rabbit heart.

To determine maturational differences in myocardial pressure work, oxygen consumption, and stability, we evaluated an isolated retrogradely perfused isovolumic rabbit heart model in newborns (0-6 days of age, mean 3.3 +/- 1.9 days), immatures (4-6 wk) and adults (5-7 mo). To reduce ischemic time and cardiac trauma, the hearts were isolated and instrumented within the chest cavity. By design, there were no significant age-related differences in coronary flow per gram, heart rate, or resting pressure. Left ventricular developed pressure was similar at all ages, but myocardial oxygen consumption was much lower in newborns and immatures than in adults. Coronary resistance was lower in the younger hearts. There were no significant age-related differences in contractility, left ventricular stiffness, or myocardial pH. All hearts were stable for 120 min, but thereafter immatures and adults deteriorated more rapidly than newborns. The study demonstrates that this model is technically suitable for the study of age-related differences in cardiac physiology. Furthermore, newborn and immature hearts are able to more efficiently use oxygen to develop left ventricular pressures, possibly due to a lower wall tension.

Aging↗
PubMed1985

Aortic and mitral regurgitation in an infant with Kawasaki disease.

A fatal case of Kawasaki disease with extensive cardiac involvement in an 11-week-old boy is described. Two-dimensional echocardiography revealed enlargement of the left ventricle, left atrium, and aortic root as well as dilatation of the left main coronary artery. Cardiac catheterization revealed both aortic and mitral regurgitation and fusiform dilatation of the proximal segments of the coronary arteries. The clinical course was characterized by multisystem failure and death on day 31 of the illness. Aortic regurgitation is a very rare complication of Kawasaki disease and has been previously reported in one Japanese infant. The pathogenesis of aortic regurgitation in this disease is not known but may be due to aortitis and/or valvulitis. Kawasaki disease should be included as a cause of aortic regurgitation in infants.

Aortic Valve Insufficiency↗
PubMed1985

Usefulness of exercise stress testing for prediction of blood pressure trends.

The purpose of this study was to determine whether values of blood pressure during exercise help predict which adolescents are prone to maintain high blood pressure. Dynamic and isometric exercise stress tests were performed on 131 adolescents who had had systolic or diastolic pressures greater than the 95th percentile on three examinations the previous year. Follow-up blood pressures were measured 1 year after the stress testing, and outcomes were classified on the basis of the blood pressure status that year. Stepwise regression analysis was used to examine the association between earlier blood pressures and exercise pressures with outcome pressures. In both male and female adolescents, the average resting systolic pressure on the earlier survey was the best predictor of systolic pressure 2 years later. Blood pressures and heart rates during dynamic and isometric exercise did not significantly contribute to the models' prediction of future systolic or diastolic pressures. The data suggest that exercise stress testing is not a valid method for predicting youths whose blood pressures will remain elevated over the next 1 to 2 years.

Adolescent↗
PubMed1983

Validity of mass blood pressure screening in children.

The validity of a mass blood pressure screening program carried out on Dallas high school students who were followed for at least 3 years is reported. Blood pressure results on initial screening in the tenth grade were related to outcome blood pressure status. The frequency of initial blood pressure elevation (systolic and/or diastolic pressure above the 95th percentile) was 10%, whereas the prevalence of sustained elevation in the tenth grade was less than 2%. The initial screening correctly identified 72% of those who had sustained elevations on all three tenth grade examinations (sensitivity), and correctly identified 91% of those who did not have sustained elevations (specificity). However, the predictive value of an initial positive screening result was low, at only 17% (152/900). The high proportion of false-positive results represents a significant cost to any blood pressure screening program, both in economic terms and in its potential for creating anxiety among families with children having only transiently elevated blood pressure. Because the costs are high and the yield from mass screening of children low, case finding of childhood hypertension should remain the responsibility of the physician who sees children in the clinical setting.

Adolescent↗