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Biomedical subjects

R Yip

Publications and source records attributed to R Yip.

At least 55 records · Page 3Linked to original sources
PubMed1995

Increasing trends in plural births in the United States.

OBJECTIVE: To determine the nature and possible reasons for the increasing trend in plural births in the United States during the 1980s. METHODS: We performed a descriptive analysis of births in the United States for five racial and ethnic groups from 1980-1989, using the United States vital records natality files. RESULTS: The rates of twin and triplet births rose 19 and 100%, respectively, during the 1980s. Approximately one-fourth of the observed increases can be attributed to rising maternal age. The increases in twin and triplet births occurred mainly among more educated and older white women. CONCLUSION: The association of high education status with rising rates of plural births, independent of maternal age, suggests that the observed increase is the result of increasing use of fertility-stimulating therapy among a subset of the childbearing population.

Adult↗
PubMed1995

The influence of fetal and maternal factors on the distribution of birthweight.

This review of common risk factors for low birthweight emphasizes the usefulness of examining the entire distribution of birthweight. Of the factors we examined, only short gestational age seemed to affect the low end of the birthweight distribution in the form of skewness. Most factors, such as maternal race, infant sex, plurality, altitude, education, and smoking seem to affect the entire birthweight distribution, indicating a generalized effect. With the exceptions of race, infant sex, parity, and altitude, these factors seemed to have similar associations with both low birthweight and infant mortality. However, only the effects of race and sex on mortality have been repeatedly studied in detail for different combinations of gestational age and birthweight. A few of the factors examined, notably infant sex and parity, have opposite associations with birthweight and infant mortality. Female infants and firstborn infants have lower birthweights than their counterparts, but are more likely to survive. For factors that significantly affect the birthweight distribution, but do not affect mortality equally across the birthweight distribution, the development and use of population-based standards may result in less misclassification of IUGR. Separate standards by infant sex, altitude, and perhaps race may lead to more accurate classification of intrauterine growth. Last, the majority of risk factors have differential effects on birthweight depending on the level of the associated factors. For example, low maternal age and low prepregnancy BMI are associated with both increased risk of low birthweight and poor infant survival. Older maternal age and high prepregnancy BMI are associated with reduced risk of low birthweight, but with increased risk of infant mortality. One possible explanation is that young maternal age and low prepregnancy BMI are associated with adverse behavioral risk factors such as cigarette smoking, whereas increased age and high prepregnancy BMI are associated with gestational diabetes, multiparity, and genetic defects. It is possible that the greater variation in birthweight at the high end of the scale is indicative of increased risk of mortality. Thus, higher birthweight does not always equal better birth outcomes.

Birth Weight↗
PubMed1994

Growth hormone stimulates tyrosine phosphorylation of insulin receptor substrate-1.

Growth hormone (GH) produces insulin-like effects in rat adipocytes that have been deprived of GH for at least 3 h. The effect of a saturating concentration of GH is qualitatively and quantitatively similar to that produced by 2-4 ng/ml insulin but differs from that of insulin in the respect that adipocytes become refractory to prolonged or repeated stimulation with GH. Since activation of tyrosine kinase is an early event in the action of both hormones, we investigated the possibility that GH stimulation of tyrosine phosphorylation of some protein in the insulin transduction cascade might result in the similar effect of the two hormones. Adipocytes were preincubated for 3 h in the absence of hormones and then reincubated without or with 500 ng/ml GH or 4-400 ng/ml insulin for 10 min. The cells were lysed with an equal volume of buffer containing 1% SDS and preheated to 100 degrees C. Proteins were separated by electrophoresis on 7.5% polyacrylamide gels and transferred to nitrocellulose membranes, and tyrosine-phosphorylated proteins were detected using anti-phosphotyrosine antiserum coupled to horseradish peroxidase and reagents to produce chemiluminescence. The faint band seen at 185 kDa in control lanes was increased by GH treatment in five independent experiments. Insulin produced a similar effect at a concentration of 4 ng/ml, and phosphorylation increased in a dose-related manner in cells treated with higher concentrations of insulin. A prominent approximately 95-kDa band that is probably not the beta subunit of the insulin receptor was also seen in GH-treated cells. The beta subunit of the insulin receptor has similar electrophoretic mobility to the 95-kDa protein, but was not phosphorylated to an extent that allowed detection when insulin was added at concentrations below 400 ng/ml. Phosphorylation of the 185- and 95-kDa bands was evident within 1 min after addition of GH, persisted for at least 30 min, and was equally prominent in sensitive and refractory cells. Antiserum to IRS-1 immunoprecipitated the tyrosine-phosphorylated 185-kDa protein. The data suggest that IRS-1 is a substrate for a GH-activated tyrosine kinase, possibly JAK-2, which may account for the insulin-like effects of GH. The data further suggest that refractoriness to insulin-like stimulation by GH may result from an additional GH-dependent action that is distinct from phosphorylation of IRS-1.

Adipocytes↗
PubMed1994

Assessments of mortality, morbidity, and nutritional status in Somalia during the 1991-1992 famine. Recommendations for standardization of methods.

OBJECTIVES: To evaluate the various survey methods used in Somalia between 1991 and early 1993 while assessing documentation of mortality and malnutrition rates and common causes of morbidity and mortality. DATA SOURCES: Twenty-three population surveys were identified from the Center for Public Health Surveillance for Somalia, the United Nations Children's Fund, and other humanitarian organizations. STUDY SELECTION: Only surveys with defined populations and apparently systematic methodology that focused on mortality, morbidity, and/or nutritional status were included. RESULTS: Extensive methodological differences were found among the 23 surveys. Target populations and sampling strategies varied widely. Twelve studies were considered not reproducible. Of the 16 studies assessing mortality, only eight assessed cause of death. Use of units of measurement and inclusion of denominators in rate calculations were inconsistent. None of the studies provided confidence intervals around the point estimates of the rates. Of the 11 studies providing information on morbidity, none provided case definitions. And in the 16 studies reporting nutritional status, a variety of measurement methods and definitions of malnutrition were used. Three studies presented information based on mid-upper-arm circumference measurements, and 10 presented weight-for-height data below 70% and 80% of the reference median; only four studies presented z scores. CONCLUSIONS: While the results of some studies may have influenced policy and program management decisions, their effects may have been limited by failure to adequately document results and by differences among studies in objectives, design, parameters measured, methods of measurement, definitions, and analysis methods. We recommend that agencies conducting population studies in emergency situations define clear study objectives, use standard sampling and data collection methods, and ensure precise written documentation of study objectives, methods, and results.

Cause of Death↗
PubMed1994

Hemoglobin difference between black and white women with comparable iron status: justification for race-specific anemia criteria.

To determine the appropriateness of race-specific criteria for anemia, we used the sample of women of child-bearing age from the Second National Health and Examination Survey to examine the relationship between hemoglobin and iron status for blacks and whites. After adjustment for major factors known to cause hemoglobin variation, including iron nutrition status, black women overall had a significantly lower mean hemoglobin value (126 +/- 12 g/L) than white women (134 +/- 11 g/L). Comparison of the probability plots of black and white hemoglobin distributions found the difference across the distributions to not be uniform, likely because a subset of black women had lower hemoglobin values rather than because of a generalized lowering. This finding suggests that it may not be appropriate to have a separate criteria for all blacks to accommodate the subset with lower hemoglobin. However, evaluation of the screening performance of hemoglobin found that race-specific anemia criteria (10 g/L difference) yielded a comparable sensitivity and specificity in detecting iron deficiency for both races. In contrast, a fixed anemia criterion did not yield comparable screening performances for the two races. This functional evaluation supports considering race-specific anemia criteria for screening iron deficiency.

Adult↗
PubMed1994

Iron deficiency: contemporary scientific issues and international programmatic approaches.

Iron deficiency is a common nutritional disorder in developing countries and contributes significantly to reduced work productivity and economic output as well as to increased morbidity and mortality. There are well established biochemical tests for assessing iron status in developed countries. However, cost and interference from infectious conditions make it difficult to assess iron status in many developing country settings. Examination of the hemoglobin distribution in the population and assessment of the hemoglobin response to supplementation are alternative approaches to defining iron status and the nature of anemia. Prevention and control of iron deficiency requires the combined approach of dietary improvement, fortification of a common staple food when feasible, and appropriate iron supplementation for infants and pregnant women. In all these intervention activities, operational research is needed to improve effectiveness. In addition, controlling iron deficiency requires coordination with other nutrition and primary health care programs as part of an integrated approach to improved health and nutrition of the population.

Adult↗
PubMed1994

Issues in the assessment of nutritional status using anthropometry.

Four issues in the use and interpretation of anthropometry are discussed at the level of the population and of the individual. The first issue is the index or indices of choice: weight-for-height versus height-for-age versus weight-for-age. The selection of an index or indices depends upon many factors, and no one index is completely adequate in all situations. Proposed criteria are provided to assess the severity of low anthropometry within populations. The second issue is the scale of the index: z-scores (or standard deviations) versus percentiles versus percent-of-median. z-Scores have several properties that make them superior to the other two scales. A third issue deals with limitations in the current growth reference; one of these is the disjunction between the growth curves at 2 years of age, resulting from the use of two different populations in the reference. It is important that this disjunction be recognized by researchers so that the anthropometric findings are interpreted correctly for this age range. Lastly, some issues to do with the collection of single versus multiple anthropometric measurements on children are discussed.

Anthropometry↗
PubMed1993

Acute malnutrition and high childhood mortality related to diarrhea. Lessons from the 1991 Kurdish refugee crisis.

OBJECTIVE: To determine the extent, major causes, and contributory factors of high rates of morbidity and mortality among children at mountain camps along the Turkey-Iraq border during the 1991 Kurdish refugee crisis. DESIGN: A cross-sectional rapid nutrition survey among children and a retrospective mortality survey covering a 2-month period from the onset of the crisis. POPULATION STUDIED: Households of Kurdish refugees at resettlement camp 1 near Zakho in northern Iraq. MAIN OUTCOME MEASURES: Prevalence of wasting (low weight-for-height) and mean weight-for-height status, prevalence of diarrhea, and crude and age-specific mortality rates. RESULTS: Weight-for-height measurements indicated that children under 2 years of age had suffered significant (P < .001) recent malnutrition. The elevated prevalence of wasting and the reduced mean weight-for-height status in this group indicated generalized weight loss. This weight loss was likely the result of the high rates of diarrhea, which still affected 50% of the younger children at the time of survey. The crude mortality rate for all ages was 8.9 per 1000 per month (expected rate, 0.6 per 1000); two thirds of the deaths occurred among children aged 5 years or younger, and half among infants younger than 1 year. An estimated 12% of all infants died during the first 2 months of the crisis. Most deaths were due to diarrhea, dehydration, and resulting malnutrition. CONCLUSIONS: The high rates of malnutrition and mortality related to diarrhea in infants and younger children of Kurdish refugees took place rapidly despite prompt relief efforts and a previously healthy population. This experience underscores the need for early and aggressive public health management of sanitation, water sources, and diarrhea control programs to augment the traditional focus on food and medical relief during the emergency phase of a refugee crisis.

Acute Disease↗
PubMed1993

Acute mountain sickness in a general tourist population at moderate altitudes.

OBJECTIVE: To determine the incidence of acute mountain sickness in a general population of visitors to moderate elevations, the characteristics associated with it, and its effect on physical activity. DESIGN: A cross-sectional study. SETTING: Resort communities located at 6300 to 9700 feet elevation in the Rocky Mountains of Colorado. PARTICIPANTS: Convenience sample of 3158 adult travelers, 16 to 87 years old (mean age [+/- SD], 43.8 +/- 11.8 years). RESULTS: Twenty-five percent of the travelers to moderate elevations developed acute mountain sickness, which occurred in 65% of travelers within the first 12 hours of arrival. Fifty-six percent of those with symptoms reduced their physical activity. The odds favoring acute mountain sickness were 3.5 times as large for visitors whose permanent residence was below 3000 feet elevation as for those whose residence was above 3000 feet; 2.8 times as large for visitors with previous symptoms of acute mountain sickness; and twice as large in travelers younger than 60 years. Women, obese persons, those in poor or average physical condition, and those with underlying lung disease also had a higher occurrence of acute mountain sickness (P < 0.05). CONCLUSIONS: Acute mountain sickness occurs in 25% of visitors to moderate altitudes and affects activity in most symptomatic visitors. Persons who are younger, less physically fit, live at sea level, have a history of acute mountain sickness, or have underlying lung problems more often develop these symptoms.

Acute Disease↗
PubMed1993

Acute mountain sickness in children at 2835 meters.

OBJECTIVE: Acute mountain sickness has been described in adults but little is known concerning its occurrence in children. Our objective was to determine the incidence of acute mountain sickness in children. METHODS: A survey questionnaire was completed by 558 children (aged 9 to 14 years) after they ascended from 1600 to 2835 m and from 405 similarly aged children after travel at sea level. RESULTS: Three or more of the following symptoms in the high-altitude setting were considered as the case definition of acute mountain sickness: headache, loss of appetite, vomiting, fatigue, insomnia, shortness of breath, and dizziness. One hundred fifty-six (28%) of the children at 2835 m developed acute mountain sickness. Three or more symptoms developed in a smaller, but nonetheless considerable, number (86 [21%]) of children at sea level. Headache, shortness of breath, and dizziness were reported more frequently at high altitude than at low altitude, whereas the other symptoms occurred with equal frequency at the two locations. CONCLUSIONS: More than one fourth of the children visiting high altitude developed acute mountain sickness. A high proportion (21%) of children at sea level developed similar symptoms, suggesting that an appreciable portion of the symptoms present were due to factors other than altitude, such as travel, anxiety, or disruption of daily routine.

Adolescent↗
PubMed1993

Trends and patterns in height and weight status of low-income U.S. children.

To better define the trends and patterns of growth for low-income children, we studied the anthropometry data collected by the second National Health and Nutrition Examination Survey (NHANES II) and the CDC Pediatric Nutrition Surveillance System (PNSS). Based on NHANES II, we found that low-income children appear to have a greater prevalence of shortness (low height-for-age), but do not have a greater prevalence of overweight (high weight-for-height) when compared with children from higher income families. Based on 12 states that were monitored continuously by the PNSS from 1980 to 1989, low-income children under 5 years of age appear to have a stable trend of height and weight status, with the exception of Asian children, most of whom were from Southeast Asian refugee background, showed a dramatic improvement in height status. However, based on PNSS data for the years 1977 to 1990 from Louisiana and Michigan, school-aged children and adolescents appear to have become slightly taller as well as having significant increases in body weight in relation to height. An additional investigation is needed to verify this trend of increasing excess weight among older, low-income children.

Adolescent↗