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J D Haas

Publications and source records attributed to J D Haas.

At least 55 records · Page 3Linked to original sources
PubMed1984

Structure-function correlation in the human placenta: the morphometric diffusing capacity for oxygen at full term.

A combination of stereology and physiology is used to estimate the morphometric diffusing capacity for oxygen of the normal human placenta at term. The morphometric diffusing capacity is found to be higher than published values determined by physiological methods. The most likely explanation for this discrepancy is that physiological values are too low because of the effects of shunts, placental oxygen consumption and uneven diffusion:perfusion ratios. Despite the discrepancy, morphometry of histological sections offers a valuable and practicable alternative for comparing the functional potential of the placenta in different species, during normal gestation, disease, experimental treatment and environmental hypoxic stress.

Diffusion↗
PubMed1983

Effects of exercise on riboflavin requirements of young women.

The riboflavin requirement of young women during periods of sedentary living and exercise was determined during a 12-wk metabolic study. The study was divided into a 6-wk no exercise period followed by a 6-wk exercise period in which subjects jogged around a track for 20 to 50 min/day. Twelve subjects, aged 19 to 27 yr, were fed a basic diet containing 0.6 mg riboflavin/1000 kcal of intake. Riboflavin intake was increased by 0.2 mg/1000 kcal increments by provision of riboflavin in a glucose polymer mixture. Linear regression analysis was used to estimate the riboflavin intake required for an erythrocyte glutathione reductase activity coefficient of 1.25 during both the no exercise and exercise periods. Individual riboflavin requirements ranged from 0.62 to 1.21 mg/1000 kcal before exercise and 0.63 to 1.4 mg/1000 kcal during the exercise periods. Riboflavin requirement could not be related to the kilocalorie intake or lean body mass of the subjects. It is concluded that healthy young women require more riboflavin to achieve biochemical normality than the 1980 Recommended Dietary Allowances and that exercise increases riboflavin requirements.

Adult↗
PubMed1982

Altitude and infant growth in Bolivia: a longitudinal study.

The growth of 79 healthy, well-nourished lowland (400 M) and highland (3600 M) Bolivian infants was analyzed in a longitudinal study through the first postnatal year. Compared to low altitude infants, the high altitude infants were found, by analysis of covariance controlling for size at the previous exam, to be significantly shorter at birth, 1 and 6 months, while they were significantly lighter only at birth and 1 year. Recumbent length gain was slower in the high altitude infants in the early months of life, while weight gain did not differ between altitudes. The observed lower weights at high altitude throughout the first year appear to be due to a persistence of lower weights seen at birth and not to postnatal growth retardation. Significantly greater triceps and subscapular skinfold thickness measurements were found in the highland group, despite their smaller length and weight. The possible causes and implications of the greater fat accumulation in the highland infants are discussed.

Altitude↗
PubMed1981

Human adaptability approach to nutritional assessment: a Bolivian example.

Recent interest in the functional correlates of mild to moderate malnutrition has provided an opportunity for anthropologists to collaborate in research with nutritional scientists. Physical anthropological studies of human adaptability have developed the methodology and theory to examine the importance of general and specific functional areas of individual and population adaptations. This anthropological approach to human adaptability corresponds well with the functional approach to nutritional sciences. Examples are presented from recent physical anthropological research on high-altitude adaptation to demonstrate how this integration of disciplinary methodology can contribute to a better understanding of human nutritional status. The functional areas of child growth and female reproductive performance are examined in relation to the multistress environment of the Peruvian-Bolivian high Andes. Knowledge of how nutritional variation affects the adaptability of high-altitude populations provides a better basis for the identification of protein-energy malnutrition during childhood and iron deficiency anemia during pregnancy.

Adaptation, Physiological↗
PubMedDate not supplied

Morphometric studies on villi in human term placentae and the effects of altitude, ethnic grouping and sex of newborn.

Stereological methods were used to test whether or not altitudinal, ethnic and sex differences in birthweight in Bolivia are associated with differences in placental morphology. Estimates of the volumes, surface areas, lengths and diameters of villi and of fetal capillaries were obtained by analysing paraffin sections of tissue. The average highland placenta contains villi of smaller overall volume, surface area and length. These villi possess a less voluminous fetal vascular space, and the capillaries are smaller in mean diameter. The average Amerindian placenta has longer but thinner capillaries than the average placenta delivered by non-indigenous women. Altitude and ethnic grouping interact to have an effect on total villous length, whilst ethnic grouping and sex interact to influence fetal capillary length. These structural differences are discussed in the context of their likely impact on placental functioning, notably on exchange by passive diffusion.

Acclimatization↗
PubMedDate not supplied

On the factors which contribute to thinning of the villous membrane in human placentae at high altitude. I. Thinning and regional variation in thickness of trophoblast.

Sections of human term placentae delivered at low and high altitude to indigenous and non-indigenous populations in Bolivia were analysed by stereological methods. Estimates were obtained of the arithmetic and harmonic mean thicknesses of villous membrane and of trophoblast. These values were then used to derive indices of thickness variation. No significant ethnic, sex or interaction effects were found. At high altitude, the villous membrane was significantly more variable in thickness owing to a lower harmonic mean but the same arithmetic mean thickness. Alterations in the arithmetic and harmonic mean thicknesses of the trophoblast contributed to the thinning of the villous membrane. The trophoblast was thinner and more irregular in thickness at high altitude. These findings are discussed in the context of placental diffusing capacity and the possible mechanisms for formation of vasculosyncytial membranes.

Altitude↗
PubMedDate not supplied

On the factors which contribute to thinning of the villous membrane in human placentae at high altitude. II. An increase in the degree of peripheralization of fetal capillaries.

The contribution made by fetal capillary peripheralization to the thinning of the villous membrane seen in human placentae from high-altitude pregnancies is examined by stereological methods. Variables characterizing the shape of the villous core and the spatial relationships between trophoblast and capillaries are quantified. They shed light on the relative importance of dynamic versus mechanistic processes of villous membrane attenuation. Highland villi differ from lowland villi in several ways. On average, they possess a thinner barrier due to closer approximation of capillaries to overlying trophoblast; in consequence, the villous core is more irregular in outline and its surface (that of the inner aspect of the trophoblast) exceeds in area that of the outer aspect of the trophoblast. These results suggest that the dynamic process (protoplasmic streaming within syncytiotrophoblast) cannot alone explain thinning of the villous membrane. A mechanistic process (capillary peripheralization and obtrusion into the trophoblastic epithelium) is sufficient to account for the differences observed, although the possibility that both processes operate concurrently cannot be discounted. This report completes a study into factors contributing to villous membrane thinning at high altitude.

Altitude↗
PubMedDate not supplied

Oxygen diffusive conductances of human placentae from term pregnancies at low and high altitudes.

A morphometric model of oxygen diffusion is employed to calculate the partial, total and specific conductances of human placentae from low- and high-altitude term pregnancies. Placentae were obtained from indigenous and non-indigenous populations and the diffusion pathway dissected into six tissue compartments. Birthweights were reduced at high altitude but were greater in natives versus non-natives. The altitudinal differences were associated with changes in placental diffusive conductances. The partial conductance of the villous trophoblast was conserved but the conductance on the maternal side was increased as was the conductance of the villous stroma. Fetal conductances were conserved (plasma) or diminished (erythrocytes). We conclude that birthweights are reduced at high altitude despite the attempts to increase the total placental diffusive conductance for oxygen. The mechanisms underlying these adaptations are discussed.

Adaptation, Physiological↗
PubMedDate not supplied

Stereological studies on the true thickness of the villous membrane in human term placentae: a study of placentae from high-altitude pregnancies.

Stereological principles were used to calculate functionally significant dimensions of the human villous membrane, its arithmetic mean thickness (Ta) and its harmonic mean thickness (Th). The former is proportional to tissue mass and oxygen consumption, the latter to diffusional resistance. For a group of 15 term placentae from uncomplicated pregnancies at high altitude, the average values were Ta = 4.44 micron, Th = 3.56 micron and Ta/Th = 1.26. The latter figure provides a useful quantitative expression for the efficiency of the membrane in gas and metabolite diffusion. It implies that vasculosyncytial membranes and syncytial knots decrease resistance to diffusion by 26 per cent, compared with that of a membrane with uniform thickness throughout. The methods are simple to apply and provide better estimates of true thickness than do measurements confined to thin sections.

Altitude↗
PubMedDate not supplied

Microscopical morphology of the human placenta and its effects on oxygen diffusion: a morphometric model.

A combination of stereological and physicochemical data was used to estimate the oxygen-diffusing capacity of the human term placenta. The effects on this morphometric diffusing capacity of isolated changes in placental structure were investigated by permitting volumes, surface areas and harmonic mean diffusion distances to deviate from normal baseline (term) values. Diffusion performance could be monitored effectively by estimating only three structural quantities. The most influential variable was the harmonic mean thickness of the villous membrane followed by the surface areas of villi and of fetal capillaries. Blood space volumes and plasma diffusion distances had negligible effects on diffusing capacity. Conclusions are discussed in the context of published findings on changes in placental anatomy which occur during gestation, abnormal pregnancies and pregnancies at high altitude.

Chorionic Villi↗
PubMedDate not supplied

Maximal aerobic power in trained youths at high altitude.

The sample for this study consisted of 25 males and 19 females between the ages of 8.8 and 19.5 years. The subjects were healthy, well nourished and trained swimmers residing in La Paz, Bolivia (mean altitude 3700 m). The purpose of this study was to provide normative values for the work capacity of high-altitude youths. Mean VO2 max was 46.9 ml/kg/min in males and 39.3 ml/kg/min in females. VO2max increased significantly with age in males but not in females. Mean VO2max tended to be 10-20% lower in the swimmers than in sea-level athletes.

Adolescent↗
PubMedDate not supplied

Work performance of high-altitude Aymara males.

The sample for this study consisted of 28 Aymara males between the ages of 15 and 43 years. The subjects were rural high-altitude natives who were temporarily working as porters in La Paz, Bolivia (3700 m). Mean VO2max was 46 X 5 ml/kg/min. There was a significant negative relationship between VO2max and age in adult porters . However, there was also a significant positive relationship between maximal work output and age and a significant negative relationship between VO2 during submaximal exercise and age. Relative work intensity (VO2/VO2max) during submaximal exercise did not change significantly with age. Thus, even though VO2max decreased significantly with age, these data suggest that there may not be a substantial decrease with age in the adaptive status of these men. Minimal support was found for the hypothesis that chest size in Andean highlanders influences the effectiveness of the oxygen transport system.

Acclimatization↗