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Biomedical subjects

J D Haas

Publications and source records attributed to J D Haas.

At least 19 recordsLinked to original sources
PubMed1992

Predicting body composition from anthropometry and bioimpedance in marginally undernourished adolescents and young adults.

Body-composition prediction equations were developed using data from a sample of 201 female and male Guatemalan ladinos (ie, people of Amerindian-European descent) aged 11-25 y. Fat-free mass (FFM) values were estimated from body density by using the two-component model and age- and sex-specific values for the density of FFM. The root-mean-square error (RMSE) of the best model predicting FFM from a set of simple anthropometric variables was 1.59 kg for females and 1.90 kg for males. The addition of more extensive anthropometry to the set of candidate predictors reduced the RMSE to 1.42 kg for females and 1.88 kg for males. The subsequent addition of a bioelectrical impedance measure (Ht2/R) further reduced the RMSE to 1.32 kg for females and 1.82 kg for males. These results suggest that for a marginally undernourished population with relatively little body fat, simple anthropometrics are as useful as more sophisticated measures for the prediction of body composition.

Adolescent↗
PubMed1991

Differences in early postnatal morbidity risk by pattern of fetal growth in Argentina.

Information on a cohort of 5539 singleton births delivered at term in two hospitals in Rosario, Argentina, was used to examine differences in early postnatal morbidity between small for gestational age (SGA) infants classified by their ponderal index (PI). SGA infants with low PI (SGA-LPI) were 4.35 (90% CI: 1.50, 12.61) times more likely to have asphyxia, 13.75 (2.48, 76.31) times more likely to have hypoglycaemia and 2.32 (1.03, 5.26) times more likely to have respiratory distress (RD) than SGA infants with adequate PI (SGA-API). The increased risks of asphyxia and hypoglycaemia observed for SGA-LPI infants diminished, but remained statistically significant after controlling for the infant's gender, birthweight, gestational age and hospital of birth. There was no difference in risk of hyperbilirubinaemia between SGA-API and SGA-LPI infants. With the exception of risk of hyperbilirubinaemia, SGA-API infants carried the same risks of morbidity as non-SGA infants. The results of the study show that SGA infants do not constitute a homogeneous group with respect to their prospects for early postnatal health and survival. Furthermore, the pattern of differences in morbidity risk between SGA-API and SGA-LPI infants observed in this study is consistent with the timing hypothesis for the aetiology of variation in PI among SGA infants.

Argentina↗
PubMed1991

Retarded fetal growth patterns and early neonatal mortality in a Mexico City population.

The study reported here classified 9,660 newborn infants delivered at a maternal and child health center in Mexico City by length of gestation, presence or absence of growth retardation, and (in the case of growth-retarded infants) proportionate or disproportionate growth retardation in terms of the infants' weight and length. It was found that preterm infants (delivered before 38 weeks of gestation) had nine times the early neonatal mortality of term infants, irrespective of growth retardation patterns. Also, the type of fetal growth retardation involved (proportionate or disproportionate) in those cases where such retardation was present was found to have an impact on early neonatal mortality. That is, preterm and term infants classified as having proportionate growth retardation respectively exhibited 1.5 and 9.5 times the early neonatal mortality of preterm and term infants with disproportionate growth retardation. Among other things, these findings suggest a need for assessing types of growth retardation as well as etiologic factors when evaluating mortality risk in newborns.

Classification↗
PubMed1990

Consequences for maternal nutrition of reproductive stress across consecutive pregnancies.

Frequent cycles of reproduction increase the risk that lactation will overlap with pregnancy and shorten the duration of the recuperative interval (nonpregnant and nonlactating portion) within the reproductive cycle, thereby increasing the risk of maternal nutritional depletion. Nutritional responses to these stresses have been demonstrated by contrasting groups of women with different experiences; however, these relationships may be spurious and the result of third factors. In this study, responses to changing stress over consecutive pregnancies were studied and contrasted within individual Guatemalan women; biases caused by factors constant to women were eliminated. Stress was assessed by examining responses in maternal supplement intake, maternal fat stores, and birth weight. Overlap and short recuperative intervals were found to be stressful (in that order) for mothers as shown by increased supplement intake and reduced fat stores. Birth weight in term gestations was not affected, indicating that fetal growth is being protected at the cost of maternal nutritional status.

Adipose Tissue↗
PubMed1989

Accuracy of heart-rate monitoring and activity diaries for estimating energy expenditure.

The accuracy of heart-rate monitoring and activity diaries for measuring energy expenditure in free-living individuals was studied in 12 women. Estimates of energy expenditure were calculated from heart-rate monitoring by use of four different prediction equations to describe the relationship between heart rate and energy expenditure. Estimates of energy expenditure from activity diaries were calculated using both individually measured and published values for the energy cost of activities. Energy intake adjusted for changes in body-energy stores was used as a reference. Heart-rate monitoring overestimated group energy expenditure from 2 to 9% and the errors in estimating individual energy expenditure ranged from -53 to 67%. Activity diaries underestimated group energy expenditure by 2-6% and the errors in estimating individual energy expenditure ranged from -39 to 56%. Heart-rate monitoring and activity diaries may prove useful for estimating the energy expenditure of groups but not individuals.

Activities of Daily Living↗
PubMed1989

Body composition and energy intake: do overweight women overeat and underreport?

The relationship between energy consumption and body composition was evaluated in 63 women by use of energy-intake values that were precisely measured in a metabolic unit and corrected for deviations from energy balance. Energy requirement for the maintenance of body weight was not significantly correlated with adiposity expressed as percent body fat. However, energy requirement was positively associated with lean mass (p less than 0.0001) whereas fat mass added no predictive value to the same multivariate regression equation. Self-reported energy intake (before the experiments) was not correlated with lean mass and was underestimated by lean subjects at least as much as by obese subjects. Discrepant findings in the literature concerning relationships between obesity and energy intake may be explained by reporting error and by the relative lean mass of obese vs nonobese women but not by systematic underreporting unique to obese subjects.

Adult↗
PubMed1989

Iron deficiency and behavior: criteria for testing causality.

The association between iron deficiency and poor behavioral-test performance is well established. The question of causality, however, remains unanswered. This paper presents the essential criteria for a valid test of causality. Internal validity is examined in terms of positive and negative findings. Plausibility of the findings requires analyzing the congruency of the results; for example, those who respond to the iron treatment are also those who respond behaviorally. External validity describes the extent to which inferences may be made about other populations or circumstances.

Behavior↗
PubMed1988

Iron deficiency anemia and steady-state work performance at high altitude.

Thirty-seven young adult male highland residents at 3,600-4,100 m in La Paz, Bolivia, performed short-duration cycle ergometry at 60, 80, and 100% of maximal voluntary O2 consumption (VO2max). Three groups of subjects representing the high-altitude population mean hemoglobin (Hb), the 10th percentile Hb, and below the 1st percentile were examined to test the hypothesis that the relationship of exercise performance to Hb concentration is similar to those relationships established at low altitude. Anemic individuals (n = 8) had 23% lower voluntary VO2max and 28% lower maximal work loads compared with controls (n = 17) or marginally anemic subjects (n = 12) although the relationship of VO2 to work load was similar. Anemic individuals maintained significantly higher arterial O2 partial pressures and Hb saturations during heavy exercise (90 +/- 0.5 vs. 85 +/- 0.6%) in conjunction with a greater heart rate up to maximal effort. A significantly decreased erythrocyte 2,3-diphosphoglycerate (2,3-DPG)-to-Hb molar ratio (0.70 +/- 0.04 vs. 1.12 +/- 0.06), suggestive of a left-shifted dissociation curve in anemics, is in contrast to the expected right-shifted curve. Moderate anemics were similar to controls. Anemic individuals did not differ in arterial lactate concentration from controls at absolute work loads; anemics had significantly lower arterial lactate concentrations at maximal effort than controls with no differences in the work load-to-lactate relationship. In conclusion, O2 transport during exercise at high altitude seems unaffected by the Hb concentrations as low as the 10th percentile of the population mean.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Variation in early neonatal mortality for different types of fetal growth retardation.

Birth and first-48-hr death records were analyzed for 10,024 liveborn infants in Mexico City and 12,786 liveborn infants in Santa Cruz, Bolivia. The objective of the analysis was to characterize the early postnatal mortality rates for different types of fetal growth retardation and prematurity. Infants who were delivered prior to 37 weeks of gestation had 23-100 times the mortality risk of infants born at full term and normal weight. Light-for-gestational-age infants (birth weight less than 2,900 g) were further divided into proportionately growth-retarded with normal Rohrer's index (weight/height) and disproportionately growth-retarded with low Rohrer's index. The proportionately growth-retarded infant had nearly twice the mortality of the full-term, appropriate-weight infants, whereas the disproportionately growth-retarded infants had 2.9-5.7 times the mortality rate of the full-term, appropriate-weight infants. There were some differences between samples in mortality rates and prevalence of the different classes of small infants, but the pattern of mortality within samples was consistent between samples.

Bolivia↗
PubMed1987

The volumetric composition of human term placentae: altitudinal, ethnic and sex differences in Bolivia.

Point counting volumetry has been used to decide whether or not altitudinal, ethnic and sex differences in birth weight in Bolivia are accompanied by changes in placental composition. Sixty eight placentae from healthy, term pregnancies were sampled from populations of Amerindian and non-Indian women living in Santa Cruz (400 m) and La Paz (3600 m). Altitudinal reductions in birth weight were not accompanied by significant alterations in placental weight yet highland placentae were substantially different in histological composition. On average, the highland placenta had a more voluminous intervillous space but reduced volumes of villi, juxtavillous fibrin and non-parenchyma. Whilst Amerindian newborn were heavier, placental weights were similar in both ethnic groups. However, the Amerindian placenta tended to possess more trophoblast and more villous stroma than its non-Indian counterpart. No sex differences were detected save for an interaction effect on fibrin which involved altitude, ethnic group and sex. Findings are discussed in the context of known morphometric and physiological differences between placentae in different experimental groups, notably in other types of pregnancy associated with reduced fetal growth.

Altitude↗
PubMed1986

Hematologic evidence of fetal hypoxia among newborn infants at high altitude in Bolivia.

The reduced birth weight widely reported for high-altitude infants has been attributed to intrauterine hypoxia. This assertion may be tested by comparing hematologic values of high-altitude and low-altitude newborn infants, since the human fetus can respond to intrauterine hypoxia with enhanced erythropoiesis. This report presents cord blood values of term Bolivian infants classified by altitude, ethnic group, and parity: 105 from La Paz (3600 m) and 46 from Santa Cruz (400 m). Hematocrit, hemoglobin concentration, and the proportion of hemoglobin F are higher among newborn infants at high altitude. Ethnic group and parity interact with altitude in effect on hematocrit and hemoglobin concentration. Gestational age, birth weight, maternal hematologic variables, and socioeconomic indicators are not significantly associated with cord blood values. The high-altitude newborn infant displays evidence of enhanced erythropoiesis, which supports the suggestion that the high-altitude fetus experiences a greater degree of hypoxia in utero than does the low-altitude fetus.

Altitude↗
PubMed1986

Functional anemia of complicated protein-energy malnutrition at high altitude.

The effect of severe protein-energy malnutrition (PEM) on erythropoiesis in children living in the highlands of Bolivia, altitude 3700 m, was studied. Forty percent reduced hemoglobin concentrations, significantly lower arterial oxygen tensions, and a right-shifted, oxygen-dissociation curve were observed compared to high-altitude controls. Serum and erythrocyte folate concentrations were 44% and 82%, respectively, of control values. Low initial transferrin saturation decreased significantly during the 10-wk refeeding period. Thus, iron and folate deficiency contributed significantly to the poor red cell response. Results suggest that the anemia associated with severe PEM has a more significant impact on oxygen transport at high altitude than at sea level and requires an adaptive response in the oxygen-dissociation curve to satisfy tissue-oxygen demands. Furthermore, marginal iron and folate status and an inflammatory block of iron supply may limit the reestablishment of a normal tissue mass during refeeding.

Altitude↗
PubMed1986

The effects of exposure misclassification on estimates of relative risk.

In epidemiologic studies, individuals may be misclassified with respect to exposure to a risk factor for disease. Such misclassification causes the relative risk of disease associated with the exposure in the population to be biased toward the null value. Here, a formula is derived for the apparent relative risk under misclassification (R) as a function of the sensitivity (U) and specificity (V) of the test for exposure and of the true relative risk (R) and true prevalence of exposure (P(E] in the population. The relative influence of U and V on the bias in R depends both on R and on P(E), with U tending to be more influential at higher values of P(E). When there is misclassification of exposure, variation in P(E) may bias comparisons of relative risk between groups or exposures, either by producing spurious differences or by masking true differences, and may generate spurious trends associated with a third variable such as age. Because the possible effects of misclassification of exposure on relative risk are complex and not easily generalized, the potential degree of bias should be evaluated individually in each situation.

Diagnostic Errors↗
PubMed1986

Combined effects of exercise and restriction of energy intake on moderately obese women.

The current study was designed to assess the contribution of dietary-induced weight reduction on improvements in functional capacity in moderate obesity. Twelve females (means age = 29 yr, means fat percentage = 37%) served as subjects for the study. Subjects trained on a cycle ergometer 30 min.day-1, six day.wk-1 for three or six weeks at 75 to 85 per cent of maximum heart rate (HR max). Improvements in maximal oxygen uptake (delta VO2 max I.min-1) and functional capacity (delta VO2 max ml.kg-1 min-1) were compared in an attempt to separate out training and dietary effects respectively. Measurements were also taken on both the cycle ergometer and treadmill to test for any specificity of training effects. Changes in body composition were assessed by densitometry. Following three weeks of training, there was an average increase in VO2 max ml.kg-1 min-1 on the cycle ergometer and the treadmill of 14 and 19 per cent respectively. By six weeks, this had increased to 18 and 26 per cent respectively. The contribution of weight reduction to the improvements in functional capacity was calculated to range from 20 to 33 per cent. Thus, both energy restriction and exercise training appear to be effective means of improving functional capacity in moderately obese women.

Adult↗
PubMed1985

Distribution of hemoglobin and functional consequences of anemia in adult males at high altitude.

In order to assess better the normal hemoglobin (Hb) range among adult males at high altitude, a hematological survey was completed in La Paz, Bolivia (3700 m). Two statistical methodologies were utilized to identify the anemic and polycythemic contributions to the Hb distribution of normal healthy men (n = 526). The Hb of normal men has a Gaussian distribution with mean and SD of 18.8 +/- 1.4 g/dl. Cutoff levels of 15.8 and 22.0 g/dl Hb were selected to identify the anemic and polycythemic subpopulations. Iron status in this high altitude population is similar to that of low altitude populations, and iron deficiency is the cause of most anemia found. An exercise test on a subsample of 56 men was utilized to validate the anemia cutoff level. Anemics as identified by the 15.8 g/dl Hb level showed a significant reduction in aerobic capacity as measured by PWC150 and estimated VO2max.

Adolescent↗