Biomedical subjects
M W Carpenter
Publications and source records attributed to M W Carpenter.
Rationale and performance of tests for gestational diabetes.
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Cardiovascular response to maximal cycle exercise during pregnancy and at two and seven months post partum.
We examined the cardiovascular response at rest and during upright cycle exercise in nine women during pregnancy (25.6 +/- 3.0 weeks' gestation) and at 2 months (8.8 +/- 1.8 weeks) and 7 months (30.0 +/- 2.5 weeks) post partum. Antepartum resting cardiac output, heart rate, and stroke volume were higher, whereas the arterial-venous oxygen difference was lower than both postpartum values. The antepartum resting oxygen uptake did not differ from 2 months post partum but was higher than at 7 months post partum. Cardiac output during submaximal exercise was greater antepartum than at both postpartum tests. Submaximal antepartum oxygen uptake, heart rate, and stroke volume were generally higher, and the arterial-venous oxygen difference was lower than at 7 months post partum. The slope of the antepartum cardiac output versus oxygen uptake relationship did not differ from the value at 2 months post partum, (6.16 +/- 1.38 and 5.84 +/- 1.34, p greater than 0.05) but was higher than at 7 months post partum (5.22 +/- 0.78, p less than 0.05). There were no significant differences in maximal oxygen uptake or heart rate among the three testing periods. Maximal cardiac output and stroke volume were higher antepartum than at 2 and 7 months post partum, whereas the arterial-venous oxygen difference was lower than at 7 months post partum. There were few significant differences in resting, submaximal, or maximal measurements between the two postpartum conditions. These data suggest that the augmented cardiac response to exercise during pregnancy is reduced by 2 months post partum but that additional time may be required for a complete resolution of the cardiovascular changes induced by pregnancy.
Effect of maternal weight gain during pregnancy on exercise performance.
We examined the effect of maternal weight gain during pregnancy on exercise performance. Ten women performed submaximal cycle (up to 60 W) and treadmill (4 km/h, up to 10% grade) exercise tests at 34 +/- 1.5 (SD) wk gestation and 7.6 +/- 1.7 wk postpartum. Postpartum subjects wearing weighted belts designed to equal their body weight during the antepartum tests performed two additional treadmill tests. Absolute O2 uptake (VO2) at the same work load was higher during pregnancy than postpartum during cycle (1.04 +/- 0.08 vs. 0.95 +/- 0.09 l/min, P = 0.014), treadmill (1.45 +/- 0.19 vs. 1.27 +/- 0.20 l/min, P = 0.0002), and weighted treadmill (1.45 +/ 0.19 vs. 1.36 +/- 0.20 l/min, P = 0.04) exercise. None of these differences remained, however, when VO2 was expressed per kilogram of body weight. Maximal VO2 (VO2max) estimated from the individual heart rate-VO2 curves was the same during and after pregnancy during cycling (1.96 +/- 0.37 to 1.98 +/- 0.39 l/min), whereas estimated VO2max increased postpartum during treadmill (2.04 +/- 0.38 to 2.21 +/- 0.36 l/min, P = 0.03) and weighted treadmill (2.04 +/- 0.38 to 2.19 +/- 0.38 l/min, P = 0.03) exercise. We conclude that increased body weight during pregnancy compared with the postpartum period accounts for 75% of the increased VO2 during submaximal weight-bearing exertion in pregnancy and contributes to reduced exercise capacity. The postpartum increase in estimated VO2max during weight-bearing exercise is the result of consistently higher antepartum heart rates during all submaximal work loads.
Cardiovascular response to cycle exercise during and after pregnancy.
Our purpose was to determine if pregnancy alters the cardiovascular response to exercise. Thirty-nine women [29 +/- 4 (SD) yr], performed submaximal and maximal exercise cycle ergometry during pregnancy (antepartum, AP, 26 +/- 3 wk of gestation) and postpartum (PP, 8 +/- 2 wk). Neither maximal O2 uptake (VO2max) nor maximal heart rate (HR) was different AP and PP (VO2 = 1.91 +/- 0.32 and 1.83 +/- 0.31 l/min; HR = 182 +/- 8 and 184 +/- 7 beats/min, P greater than 0.05 for both). Cardiac output (Q, acetylene rebreathing technique) averaged 2.2 to 2.8 l/min higher AP (P less than 0.01) at rest and at each exercise work load. Increases in both HR and stroke volume (SV) contributed to the elevated Q at the lower exercise work loads, whereas an increased SV was primarily responsible for the higher Q at higher levels. The slope of the Q vs. VO2 relationship was not different AP and PP (6.15 +/- 1.32 and 6.18 +/- 1.34 l/min Q/l/min VO2, P greater than 0.05). In contrast, the arteriovenous O2 difference (a-vO2 difference) was lower at each exercise work load AP, suggesting that the higher Q AP was distributed to nonexercising vascular beds. We conclude that Q is greater and a-vO2 difference is less at all levels of exercise in pregnant subjects than in the same women postpartum but that the coupling of the increase in Q to the increase in systemic O2 demand (VO2) is not different.(ABSTRACT TRUNCATED AT 250 WORDS)
Aerobic exercise during pregnancy. Special considerations.
Alterations in maternal physiology during pregnancy affect the physiological respect to aerobic exercise. Maternal resting oxygen consumption (VO2) and cardiac output increase during pregnancy. Heart rate (HR) becomes progressively elevated through gestation, whereas stroke volume (SV) increases until the third trimester and then declines until term, probably because of diminished venous return. Plasma volume increases earlier and to a greater magnitude than red cell volume, resulting in the 'haemodilutional anaemia' of pregnancy and a decline in the oxygen-carrying capacity. Ventilation is greater during pregnancy because of elevated tidal volume and unchanged rate of breathing. The acute and chronic (training) responses to aerobic exercise during pregnancy have not been thoroughly investigated. Specifically, the effect of gestational age, maternal activity status, and type, duration and intensity of exercise on maternal cardiovascular response have only recently begun to be explored. During pregnancy cardiac output during submaximal exertion increases above values in non-pregnant women, except perhaps late in gestation. Both heart rate and stroke volume contribute to the elevated cardiac output. Changes in submaximal exercise VO2 during pregnancy are dependent on the mode of exercise. At the same workload, VO2 increases during weight-bearing exercise, but usually does not differ from postpartum values during weight-supported exercise. One study found no change in VO2max during pregnancy compared to postpartum values. Some recent evidence indicates that the cardiac output vs VO2 relationship for pregnant women is within the range of average values reported for non-pregnant individuals. Exercise arterial-venous oxygen difference is lower during pregnancy, suggesting that the higher cardiac output is distributed to non-exercising vascular beds. The data are limited but suggest that the perfusion of exercising muscle is unchanged during pregnancy and that the major haemodynamic change is an augmented cardiac output so that blood flow to the uterus and fetus is not compromised. Only one study has measured blood flow during exercise in pregnant women. The reported 25% decrease in uterine blood flow during supine cycle exercise in women late in gestation must be interpreted cautiously because the uterus may obstruct the vena cava in the supine position. Studies of exercising pregnant animals usually indicate a decreased uterine blood flow but an enhanced oxygen extraction; the lower blood flow may be limited to non-placental areas. The applicability of these results to humans is unknown.(ABSTRACT TRUNCATED AT 400 WORDS)
Maternal age and screening for gestational diabetes: a population-based study.
The American College of Obstetricians and Gynecologists (ACOG) has recommended screening for gestational diabetes, using a 50-g, 1-hour glucose challenge (threshold for further testing 140 mg/dL or higher), for all pregnant women aged 30 or older and for younger women with risk factors. In order to assess these recommendations, we collected demographic and historic data on 6214 pregnant women representing a population of universally screened individuals. Of 125 cases of gestational diabetes diagnosed (ACOG criteria), 70 patients (56%) were under the age of 30. In addition, 44% of gestational diabetics had no risk factors. The cost per case diagnosed would be $190 with the ACOG recommendations, $192 if the age for routine screening were lowered to 25 years or more, and $222 if universal screening were practiced. Using the ACOG recommendations, 35% of gestational diabetes would go undiagnosed, with little cost savings.
Fetal heart rate response to maternal exertion.
Doppler monitoring of fetal heart rates during maternal exertion has suggested that fetal bradycardia occurs frequently during vigorous exercise, causing concern for fetal safety. Doppler determination of fetal heart rate during vigorous maternal effort is difficult. To avoid motion artifact, we observed fetal heart rate using two-dimensional ultrasound and determined the incidence of fetal bradycardia in 45 pregnant women (age, 29.0 +/- 3.7 years [mean +/- SD]; gestational age, 25.2 +/- 3.0 weeks) during 85 submaximal and 79 maximal cycle ergometer tests. Average fetal heart rate did not change during exercise. A single episode of fetal bradycardia (heart rate less than 110 beats per minute for greater than or equal to 10 s) occurred during submaximal exertion during a maternal vasovagal episode. Sixteen episodes of fetal bradycardia were noted within three minutes after cessation of exercise, 15 of which followed maximal maternal effort. We conclude that brief submaximal maternal exercise up to approximately 70% of maximal aerobic power (maternal heart rate less than or equal to 148 beats per minute) does not affect fetal heart rate. In contrast to submaximal maternal exertion, maximal exertion is commonly followed by fetal bradycardia. This may indicate inadequate fetal gas exchange.
Postpartum testing for antecedent gestational diabetes.
Gestational diabetes is a predictor of glucose intolerance in subsequent pregnancies and in the nongravid state. Many pregnant women are not tested for gestational diabetes, although they or their offspring may show signs suggestive of antecedent hyperglycemia. We examined the diagnostic utility of a postpartum (within 48 hours), 100 gm, oral glucose tolerance test and cord plasma glucose, cord plasma C-peptide, and 2-hour neonatal plasma glucose tests to detect antecedent gestational diabetes in women with documented gestational diabetes (n = 37) or with normal glucose tolerance test results late in the third trimester (n = 28). The 1-hour, 2-hour, and incremental 1-hour + 2-hour [( 1-hour - fasting] + [2-hour - fasting]) [2-hour - fasting]) glucose values of the postpartum glucose tolerance test showed significant differences between study participants with and without gestational diabetes (164 +/- 30 versus 115 +/- 22, 145 +/- 31 versus 101 +/- 21, and 153 +/- 51 versus 67 +/- 33 mg/dl, respectively, p less than 0.025). Maternal fasting and 3-hour postpartum glucose tolerance test glucose, cord plasma glucose, cord plasma C-peptide, and 2-hour neonatal plasma glucose values showed no significant between-group differences. Receiver operating characteristic curve analyses for these tests indicated that the incremental 1-hour + 2-hour postpartum glucose tolerance test glucose values best sustain test specificity at the low test threshold values necessary for high test sensitivity. A threshold of 110 mg/dl for this test yielded a predicted specificity of 90% and sensitivity of 80% with regard to antecedent gestational diabetes.
Prediction of VO2max during cycle exercise in pregnant women.
We measured maximal O2 uptake (VO2max) during stationary cycling in 40 pregnant women [aged 29.2 +/- 3.9 (SD) yr, gestational age 25.9 +/- 3.3 wk]. Data from 30 of these women were used to develop an equation to predict the percent VO2max from submaximal heart rates. This equation and the submaximal VO2 were used to predict VO2max in the remaining 10 women. The accuracy of VO2max values estimated by this procedure was compared with values predicted by two popular methods: the Astrand nomogram and the VO2 vs. heart rate (VO2-HR) curve. VO2max values estimated by the derived equation method in the 10 validation subjects were only 3.7 +/- 12.2% higher than actual values (P greater than 0.05). The Astrand method overestimated VO2max by 9.0 +/- 19.4% (P greater than 0.05), whereas the VO2-HR curve method underestimated VO2max by only 1.6 +/- 10.3% in the same 10 subjects (P greater than 0.05). Both the Astrand and the VO2-HR curve methods correlated well with the actual values when all 40 subjects were considered (r = 0.77 and 0.85, respectively), but the VO2-HR curve method had a lower SE of prediction than the Astrand method (8.7 vs. 10.4%). In a comparison group of 10 nonpregnant sedentary women (29.9 +/- 4.5 yr), an equation relating %VO2max to HR nearly identical to that obtained in the pregnant women was found, suggesting that pregnancy does not alter this relationship. We conclude that extrapolating the VO2-HR curve to an estimated maximal HR is the most accurate method of predicting VO2max in pregnant women.
The "breakfast tolerance test": screening for gestational diabetes with a standardized mixed nutrient meal.
In a group of 50 presumed normal pregnant women and 20 known gestational diabetic women, all in the early third trimester, the function of a standard 50 gm, 1-hour screening test for gestational diabetes was compared with that of a plasma glucose level determined 1 hour after the ingestion of a standard 600 kcal mixed nutrient breakfast (breakfast tolerance test). The mean plus 2 SD for the breakfast tolerance test was 120 mg/dl. If this were used as the threshold for a screening test, 75% of cases of gestational diabetes would be identified (sensitivity), while 94% of normal pregnant women would be excluded (specificity). A threshold of 100 mg/dl yields a sensitivity of 96% and a specificity of 74%. These results are compared with those for the standard 50 gm glucose challenge.
Practice environment is associated with obstetric decision making regarding abnormal labor.
Nonmedical factors affecting obstetric decisions regarding abnormal labor were investigated in Maine, a rural state. Obstetricians were questioned about practice structure, hospital services, anesthesia support, and legal liability. Cesarean section rates specific for abnormal labor, based on hospital discharge summaries in the previous two years, correlated inversely with improved night coverage support, 24-hour blood bank availability, and more adequate anesthesia services. Neither the payment differential between vaginal and cesarean delivery nor previous legal liability were associated with increased cesarean rates for abnormal labor. We conclude that improved ancillary services may lead to lower dystocia-specific cesarean section rates.
Should the fifty-gram, one-hour plasma glucose screening test for gestational diabetes be administered in the fasting or fed state?
To determine whether the 50 gm, 1-hour plasma glucose screening test for gestational diabetes should be administered in the fasted or fed state, 50 presumed normal and 20 gestational diabetic pregnant women in the early third trimester underwent this test twice, once under each condition, within a 1-week interval. There was no difference in test results under the two conditions among the normal individuals (fasted 118.4 +/- 24.7 mg/dl; fed 115.8 +/- 23.4 mg/dl). However, when the test was administered to women with known gestational diabetes, the result was significantly (p = 0.011) higher if patients were fasted (173.9 +/- 28.8 mg/dl) than if they had been given a standard 600 kcal meal 1 hour previously (154.8 +/- 24.1 mg/dl). The effect of these two conditions on the sensitivity and specificity of the screening test is described, and it is suggested that the threshold for glucose tolerance testing be 130 mg/dl if the test is administered in the fed state.
The Apgar score revisited: influence of gestational age.
We tested the hypothesis that Apgar scores are in part related to the newborn infant's level of maturity. Seventy-three pregnant women with normal fetuses of gestational age 22 to 42 weeks were studied. Fetal well-being was documented by a prospectively designed recording of pregnancy history, labor complications, and birth outcome, including cord blood pH and base deficit measurements. The 1- and 5-minute Apgar scores were directly related to gestational age. Respiratory efforts, muscle tone, and reflex were the major determinants for a decreasing Apgar score with declining gestational age. We conclude that the 1- and 5-minute Apgar scores are influenced by the infant's level of maturity and that our data may be useful in evaluating the true value of Apgar scores in assessing the fetal and neonatal condition of low birth weight infants.
Midtrimester diagnosis of severe deforming osteogenesis imperfecta with autosomal dominant inheritance.
Sonographic examination of a fetus whose father had severe deforming osteogenesis imperfecta (OI) was performed. The father had multiple congenital rib and extremity fractures. Subsequent fracture and deformity had suggested an autosomal recessive OI syndrome. However, fetal sonography at 18 weeks gestational age showed foreshortening of long bones in both legs and a reduced thoracic circumference, recapitulating, in part, the father's phenotype. This third reported case of early fetal diagnosis of autosomal dominant OI suggests that the fetal sonographic phenotype reflects that of the affected parent. Implications of this case for the application of fetal sonography in dominant OI syndromes are discussed.
Detection and treatment of gestational diabetes.
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Neonatal morbidities in infants of mothers with glucose intolerance in pregnancy.
Of 1839 pregnant women screened prospectively, 52 were identified to have glucose intolerance. Ten additional pregnant women identified as having glucose intolerance before the universal screening were also included in the study cohort. These 62 patients were followed in a perinatal high-risk clinic with weekly plasma glucose determinations. The patients were treated with diet and, in addition, 21 of 62 were treated with insulin therapeutically. By observational cohort design, the infants and a comparable number of matched controls were evaluated for evidence of neonatal morbidities and classified into percentile for birth weight. Compared with the control group, the operative mode of delivery, the mean birth weight, the birth-weight percentile, the male/female ratio, the frequency of low Apgar score (less than or equal to 6 at 1 min), and the number of infants with congenital anomalies were significantly higher in the infants born to the glucose-intolerant mothers. Although the mean maternal blood sugar was maintained within a reasonably euglycemic range, the usual neonatal morbidities were not eliminated entirely. Further understanding and management of glucose intolerance in pregnancy is necessary to further diminish or eliminate neonatal morbidities.
Perinatal management of ventral wall defects.
Reported is the analysis of morbidity, mortality, and mode of delivery in 38 cases of ventral wall defects identified from among 128,500 consecutive live births in Maine (January 1975 to December 1982). Thirteen of the ventral wall defects were classified as gastroschisis, and only one had an additional defect not directly attributable to the ventral wall defect itself. By contrast, 16 of the 25 omphalocele cases had additional defects, including eight congenital heart lesions, four genitourinary malformations, two neural tube defects, and three trisomies. Ten cases of omphalocele and one of gastroschisis died, all as a result of independent defects or involvement of adjacent structures. Intrauterine growth retardation was prominently associated with gastroschisis. Vaginal delivery occurred in three of the six ventral wall defects diagnosed antenatally and in 28 of the 32 ventral wall defects not diagnosed until delivery. The only episode of birth trauma to ventral wall defect sac or abdominal viscera occurred during cesarean section in an undiagnosed case. The present data provide a basis for prognosis and management of antenatally diagnosed ventral wall defects and suggest that these defects are not, a priori, an indication for abdominal delivery.