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Biomedical subjects

R B Thomas

Publications and source records attributed to R B Thomas.

At least 19 recordsLinked to original sources
PubMed1996

Growth and carbon accumulation in root systems of Pinus taeda and Pinus ponderosa seedlings as affected by varying CO(2), temperature and nitrogen.

It has been hypothesized that increasing atmospheric CO(2) concentration enhances accumulation of carbon in fine roots, thereby altering soil carbon dynamics and nutrient cycling. To evaluate possible changes to belowground pools of carbon and nitrogen in response to elevated CO(2), an early and a late successional species of pine (Pinus taeda L. and Pinus ponderosa Dougl. ex Laws, respectively) were grown from seed for 160 days in a 35 or 70 Pa CO(2) partial pressure at low or high temperature (30-year weekly mean and 30-year weekly mean + 5 degrees C) and a soil solution nitrogen concentration of 1 or 5 mM NH(4)NO(3) at the Duke University Phytotron. Seedlings were harvested at monthly intervals and growth parameters of the primary root, secondary root and tap root fractions evaluated. Total root biomass of P. ponderosa showed a positive CO(2) response (105% increase) (P = 0.0001) as a result of significant increases in all root fractions in the elevated CO(2) treatment, but all other main effects and interactions were insignificant. In P. taeda, there were significant interactions between CO(2) and temperature (P = 0.04) and CO(2) and nitrogen (P = 0.04) for total root biomass. An allometric analysis indicated that modulation of the secondary root fraction was the main response of the trees to altered environmental conditions. In P. ponderosa, there was an increase in the secondary root fraction relative to the primary and tap root fractions under conditions of low temperature. In P. taeda, there was a shift in carbon accumulation to the secondary roots relative to the primary roots under low temperature and low nitrogen. Neither species exhibited shifts in carbon accumulation in response to elevated CO(2). We conclude that both species have the potential to increase belowground biomass substantially in response to rising atmospheric CO(2) concentration, and this response is sensitive to temperature and nitrogen in P. taeda. Both species displayed small shifts in belowground carbon accumulation in response to altered temperature and nitrogen that may have substantial ecosystem consequences over time.

Journal Article↗
PubMed1995

Socioeconomic change and patterns of growth in the Andes.

Changes in the pattern of growth over a 20-year period are described for a combined rural and semi-urban population in the District of Nuñoa (Puno) in southern Peruvian Andes. Over the past two decades, Andean regions have experienced many socioeconomic changes, including the implementation of agrarian reform policies and increased integration into a market economy. Local changes in Nuñoa have included improved transportation networks, new markets, an expanded public school system, and improved health care facilities. Secular trends in stature and weight have been found to be associated with social and economic development throughout the developing world, including Peru. The purpose of this paper is to present the findings from a re-study of growth in the Nuñoan population, and to assess whether changing conditions in Nuñoa have resulted in secular increases in growth. A cross-sectional sample of 1,466 children and adults and mixed-longitudinal sample of 404 children (age 3-22), measured between 1983 and 1984, are compared to similar samples collected from the same location between 1964 and 1966. Adolescents are taller, heavier, and somewhat fatter in the present population, although these differences diminish or disappear in adulthood. Age of maturation, peak growth velocities, and cessation of growth may come 1 to 2 years earlier than in the 1960s. As was found in earlier studies, growth velocities are low, the adolescent growth spurt is small, and sexual dimorphism is delayed. No secular trends in adult stature were found. Thus, the effects of social and economic change on nutrition, health, and growth in the population are uneven and generally unclear. This points to inequalities in access to the benefits of change throughout the region.

Adolescent↗
PubMed1994

Phosphorus supply affects the photosynthetic capacity of loblolly pine grown in elevated carbon dioxide.

Effects of phosphorus supply and mycorrhizal status on the response of photosynthetic capacity to elevated CO(2) were investigated in loblolly pine (Pinus taeda L.) seedlings. Seedlings were grown in greenhouses maintained at either 35.5 or 71.0 Pa CO(2) in a full factorial experiment with or without mycorrhizal inoculum (Pisolithus tinctorius (Pers.) Coker & Couch) and with an adequate or a limiting supply of phosphorus. Assimilation versus internal CO(2) partial pressure (C(i)) curves were used to estimate maximum Rubisco activity (V(c,max)), electron transport mediated ribulose 1,5-bisphosphate regeneration capacity (J(max)), phosphate regeneration capacity (PiRC) and daytime respiration rates (R(d)). Nonmycorrhizal seedlings grown with limiting phosphorus had significantly reduced V(c,max) and PiRC compared to seedlings in other treatments. Elevated CO(2) increased photosynthetic capacity in nonmycorrhizal seedlings in the low phosphorus treatment by increasing PiRC, whereas it induced phosphorus limitation in mycorrhizal seedlings in the low phosphorus treatment and did not affect the photosynthetic capacity of seedlings in the high phosphorus treatment. Despite the variety of effects on photosynthetic capacity, seedlings in the elevated CO(2) treatments had higher net assimilation rates than seedlings in the ambient CO(2) treatments. We conclude that phosphorus supply affects photosynthetic capacity during long-term exposure to elevated CO(2) through effects on Rubisco activity and ribulose 1,5-bisphosphate regeneration rates.

Journal Article↗
PubMed1994

The Quechua manta pouch: a caretaking practice for buffering the Peruvian infant against the multiple stressors of high altitude.

The manta pouch--a caretaking practice of tightly swaddling and enclosing the infant in a set of cloths and blankets--and other caretaking practices are described for high-altitude resident (> 4,000 m) Quechua mother-infant pairs (N = 14). The manta pouch modifies the microenvironment inside the pouch so that, compared to the ambient environment, the temperature is higher and more stable, the humidity is higher, the partial pressure of O2 is lower, and stimulation levels are reduced. As the infant gets older, the characteristics of the pouch are modified such that the infant is increasingly exposed to ambient conditions. These caretaking practices may benefit the infant by buffering the infant from the multiple ecological stressors of high altitude, but they may also incur costs by exposing the infant to additional microenvironmental stressors (e.g., higher CO2 levels) and by reducing stimulation and limiting infant movement.

Adaptation, Physiological↗
PubMed1992

Cutaneous fistulas to the vas deferens.

Cutaneous fistulas to the vas deferens are a rare occurrence. A careful review of the literature revealed only 16 cases reported within the last 70 years. We present a case of such a fistula occurring after inguinal orchiectomy for suppurative epididymo-orchitis and review the etiologies of all reported cases to provide recommendations for management.

Aged↗
PubMed1992

Urine leukotriene E4 levels are elevated in patients with active systemic lupus erythematosus.

The peptidoleukotrienes, leukotriene (LT) C4 and its metabolites LTD4 and LTE4, cause diverse physiologic effects and have been implicated in several disease processes. A potential role for enhanced peptidoleukotriene synthesis in the pathogenesis of autoimmune disease in general and systemic lupus erythematosus (SLE) in particular has been suggested by animal studies. Therefore, we measured the urinary levels of LTE4 in patients with active and inactive SLE as well as in patients with rheumatoid arthritis (RA), scleroderma (Scl), and in healthy controls. Comparisons were made to other standard clinical tests in assessing individual patient disease activity. A marked increase in urinary LTE4 levels in patients with active SLE was noted (319 +/- 49 pg/mg creatinine, n = 20) relative to patients with inactive SLE (80 +/- 8 pg/mg creatinine, n = 7 [p less than 0.02]), patients with RA (86 +/- 8 pg/mg creatinine [p less than 0.01]), and healthy controls (68 +/- 4.3 pg/mg creatinine, n = 6 [p less than 0.01]). Patients with Scl also had elevated urinary LTE4 levels (188 +/- 33 pg/mg creatinine, n = 7) relative to controls (p less than 0.02), while values from patients with RA were not significantly different from controls. Using the Systemic Lupus Activity Measurement as a gauge of clinical activity, a rise in urinary LTE4 levels was noted during stages of active disease with a subsequent decline following the resolution of these symptoms. Our data indicate that increased synthesis of leukotrienes is associated with active SLE and Scl and suggest that these leukotrienes may mediate certain symptoms associated with these diseases.

Adult↗
PubMed1991

Elevated urinary leukotriene E4 excretion in patients with ARDS and severe burns.

Increased synthesis of peptidoleukotrienes may occur in a variety of inflammatory diseases. To test this theory, hospitalized patients with a variety of diseases were studied and urine LTE4 quantitated as an index of total body peptidoleukotriene synthesis. 10 patients with ARDS, 7 of which had additional organ involvement, and 5 patients suffering from severe burn injuries were studied. Patients with uncomplicated ARDS excreted approximately 6-fold higher amounts of LTE4 in urine compared to healthy subjects. When ARDS was complicated by multiple organ failure (MOF), urine LTE4 levels were 2- to 150-fold higher than in healthy volunteers. Patients with severe burn injuries had peak urine LTE4 levels which were approximately 20-fold higher than in healthy volunteers. As additional controls, patients with cardiac arrhythmias (absence of inflammatory disease) and patients with uncomplicated pneumonia (localized inflammation) showed normal or mildly elevated urinary LTE4 levels. The urinary LTE4 levels in ARDS patients did not correlate with serum creatinine, bilirubin, or LDH levels, or with the WBC, nor did renal or liver failure by itself predict extremely elevated urinary LTE4 levels. In conclusion, patients with ARDS or ARDS/MOF and patients with severe injuries and sepsis syndrome excrete higher levels of urinary LTE4 than patients healthy volunteers or patients with limited inflammatory disease. In certain situations, urinary LTE4 levels may be useful as a marker of the degree of inflammation.

Burns↗
PubMed1991

Root restriction as a factor in photosynthetic acclimation of cotton seedlings grown in elevated carbon dioxide.

Interactive effects of root restriction and atmospheric CO(2) enrichment on plant growth, photosynthetic capacity, and carbohydrate partitioning were studied in cotton seedlings (Gossypium hirsutum L.) grown for 28 days in three atmospheric CO(2) partial pressures (270, 350, and 650 microbars) and two pot sizes (0.38 and 1.75 liters). Some plants were transplanted from small pots into large pots after 20 days. Reduction of root biomass resulting from growth in small pots was accompanied by decreased shoot biomass and leaf area. When root growth was less restricted, plants exposed to higher CO(2) partial pressures produced more shoot and root biomass than plants exposed to lower levels of CO(2). In small pots, whole plant biomass and leaf area of plants grown in 270 and 350 microbars of CO(2) were not significantly different. Plants grown in small pots in 650 microbars of CO(2) produced greater total biomass than plants grown in 350 microbars, but the dry weight gain was found to be primarily an accumulation of leaf starch. Reduced photosynthetic capacity of plants grown at elevated levels of CO(2) was clearly associated with inadequate rooting volume. Reductions in net photosynthesis were not associated with decreased stomatal conductance. Reduced carboxylation efficiency in response to CO(2) enrichment occurred only when root growth was restricted suggesting that ribulose-1,5-bisphosphate carboxylase/oxygenase activity may be responsive to plant source-sink balance rather than to CO(2) concentration as a single factor. When root-restricted plants were transplanted into large pots, carboxylation efficiency and ribulose-1,5-bisphosphate regeneration capacity increased indicating that acclimation of photosynthesis was reversible. Reductions in photosynthetic capacity as root growth was progressively restricted suggest sink-limited feedback inhibition as a possible mechanism for regulating net photosynthesis of plants grown in elevated CO(2).

Journal Article↗
PubMed1991

Adenocarcinoma in a female urethral diverticulum.

Carcinoma occurring within a diverticulum of the female urethra is an exceedingly rare disease for which the treatment is ill-defined. We present here the first reported case of this condition from Australasia and review some of the recommendations for treatment.

Adenocarcinoma↗
PubMed1991

Urinary leukotriene E4 in patients with asthma. Effect of airways reactivity and sodium cromoglycate.

A group of 17 patients with allergic asthma was challenged with aerosolized antigen, and the excretion of the peptidoleukotriene metabolite leukotriene (LT) E4 in the urine was determined as an index of leukotriene synthesis. The allergen challenge caused a drop in FEV1 of 25 to 59% within the first 2 h in all patients. This was associated with an increase in urine LTE4 excretion during the subsequent 12 h. The amount of urinary LTE4 excreted increased from a 12-h baseline level of 46 +/- 6.8 ng to a postallergen challenge level of 92 +/- 13 ng. In a similar experimental protocol methacholine challenge alone did not significantly increase urinary LTE4 excretion. In comparing all individuals as a group, there was no significant positive correlation between the magnitude of the drop in FEV1 during the immediate asthmatic response (IAR) and the increased amount of LTE4 excreted in the urine (p = 0.08). These parameters were still not significantly correlated when airways reactivity (log PC20) was also considered (p = 0.057). However, when each individual was compared to self in the presence and absence of cromoglycate, a significant correlation was found to exist between the drop in FEV1 during the IAR, the excretion of urinary LTE4, and the airways reactivity. No correlation was found between the increase in urine LTE4 excreted during the 12 h following allergen challenge and the severity of late (3 to 12 h) responses to allergen, but there was a significant prolonged (12 to 36 h) elevated urine LTE4 excretion in those patients with the most severe late asthmatic response.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Household coping strategies and contradictions in response to seasonal food shortage.

Uncertainty is a primary consideration in adjusting to seasonal environments as attempts are made to synchronize productive inputs with critical periods in the annual cycle. Coping responses of small scale producers therefore rely on the coordination and control of diverse resources, and on flexibility in choosing between multiple options. Generalizations concerning seasonal coping responses to food shortage of households, and of women within households, are reviewed. Particular attention is given to how socio-economic differentiation affects the capacity to use such strategies, and how these differ with regard to the degree of resource commitment and reversibility once initiated. Our primary concern is in exploring the process whereby seasonal strategies become eroded. Thus, as seasonal uncertainties are exacerbated by unpredictable fluctuations in commercial economies, and as productive resources become less accessible to households, adaptive conflicts and contradictions are introduced. Uncertainty is further intensified by illness and unequal access to adaptive options based on class and gender. The increasing inability of small scale producers to cope with seasonal uncertainty emphasizes the need to understand this erosive process.

Adaptation, Physiological↗
PubMed1989

Biosocial responses to seasonal food stress in highland Peru.

This paper examines patterns of seasonal variation in food consumption and responses to food stress in the highland community of Nuñoa, Peru. Dietary and anthropometric data collected from January through August of 1985 on a sample of 26 households (127 individuals) are analyzed. This study finds sharp seasonal differences in energy intake (pre-harvest = 1150 calories/day; post-harvest = 1519/day; p less than 0.01) associated with variation in the availability of locally-produced products (e.g., tubers and cereals). Seasonal energy reduction, however, does not uniformly affect all sectors of this population. Children experience little seasonal change in energy intake and have a more adequate pre-harvest diet and better nutritional status than adults. The responses used to "protect" children from energy stress and minimize the overall impact of seasonal food scarcity on this community include: 1) reduction of pre-harvest household caloric needs through emigration of adolescent and adult males, 2) preferential allocation of food to children during the pre-harvest period, 3) seasonal reduction of activity levels and the year-round use of children for many productive activities, and 4) seasonal changes in meal patterns that minimize post-prandial energy loss during periods of stress. Evaluation of similar data from other anthropological populations underscores the diversity of responses to seasonal change in food availability. Moreover, these data indicate that the protection of children from seasonal energy stress is more common than previously thought. Variation in adaptive responses to food stress appears to be dependent upon 1) the nature of the subsistence economy, 2) the relative contributions of children and adults to household production, and 3) the demographic structure of the population.

Adolescent↗
PubMed1986

The effect of acute discontinuation of total parenteral nutrition.

The present study was undertaken to assess the impact of acute discontinuation (AD) of total parenteral nutrition (TPN) on serum glucose, insulin, and glucagon levels and on the generation of symptomatic hypoglycemia. Fifty studies were performed in 48 patients. In none of the 30 studies of 1 hour duration nor in the 20 studies of 8 hours duration was there a single episode of symptomatic hypoglycemia. One patient had a glucose below normal (60 mg/dl) during the first hour after AD. Glucose and insulin concentrations were elevated at the start of TPN discontinuation but returned to normal values within 60 minutes and remained there during the successive 7 hours of study. Although glucagon levels were slightly elevated at zero time, no significant decrease occurred. There was no evidence for counter-regulation based on the patterns of glucose and hormone levels. With some restrictions, acute discontinuation is a safe, rapid method of ending a prolonged TPN infusion.

Adolescent↗
PubMed1983

Microbial growth patterns in intravenous fat emulsions.

Microbial growth patterns were studied in intravenous fat emulsions under conditions that simulated touch contamination before or during administration. Commercially available emulsions of 10% and 20% soybean oil and 10% safflower oil in 500-ml bottles were inoculated with two concentrations of each of four organisms: a coagulase-negative Staphylococcus isolated from a venipuncture site, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans. The bottles were kept at room temperature, and samples were taken by direct puncture of the i.v. port at 0, 3, 6, 12, 24, 48, and 72 hours, diluted, and plated. Emulsions were visually inspected daily. Growth of the coagulase-negative Staphylococcus was minimal for 48 hours. E. coli showed substantial growth within 12 hours in all three emulsions. Growth patterns for Ps. aeruginosa were similar in all emulsions, and growth approximated that of E. coli within 48 hours. The growth rate of C. albicans was intermediate between that of Staphylococcus and those of E. coli and Ps. aeruginosa. Growth of C. albicans was greater in 10% safflower oil emulsion than in the other emulsions. No physical changes were observed. The coagulase-negative Staphylococcus showed less growth than C. albicans, Ps. aeruginosa, and E. coli. Substantial growth within 12 hours was seen only with E. coli. C. albicans exhibited preferential growth in 10% safflower oil emulsion.

Bacteria↗
PubMed1981

Evaluation of a device for monitoring sterility of injectable fluids.

An evaluation of a sterility-testing device (Addi-Chek) that uses total-sample membrane filtration is presented. Parenteral nutrition solutions were deliberately contaminated at low levels with 16 bacterial and four fungal strains. Some contaminated solutions were stored at 20 degrees C or 4 degrees C for up to 24 hours before testing; the rest were tested immediately. Additionally, one liter of pharmacy-prepared infusion fluid was tested each day for 100 days. Broth (added to the Addi-Chek unit after filtration to permit microbial growth) was cultured when it became turbid or after a 10-day incubation. Fifty-nine deliberate-inoculation tests were done. The organism was recovered from 56 of these; the other three tests may have been negative because no organisms were present in the aliquot used for inoculation or because of experimental error. The number of organisms used for inoculation varied from 1 to 80; 86% of the tests used 25 organisms or less. Storage for up to 24 hours at 20 degrees C and 4 degrees C had no effect on the results of sterility testing. In testing 100 units of pharmacy-prepared fluid (not deliberately contaminated), one unit (1%) was found to be contaminated. Pharmacy personnel correctly identified positive and negative Addi-Chek units based on visual turbidity of the broth. It is concluded that Addi-Chek is easy to use and effective in detecting low-level contamination in intravenous fluids.

Drug Combinations↗
PubMed1981

Insulin adsorption to polyolefin infusion bottles and polyvinyl chloride administration sets.

The availability of various dosages of insulin from a new collapsible polyolefin bottle fitted with a conventional polyvinyl chloride administration set was studied. Intravenous solutions containing various dosages of insulin (20, 40, 70, and 100 units), to which 125I-labeled insulin was added, were prepared. Solutions were mixed and delivered at a maintained flow rate of 125 ml/hour. Effluents were collected at 15, 30, 45, and 60 minutes and then at hourly intervals up to seven hours. One-milliliter samples were drawn from the end of the administration set at the end of each interval, and the level of radioactivity in the sample was measured. Greater percentages of binding occurred at the lower levels of insulin added. Saturation limits of 7.8, 2.7, and 5.4 units were found for the system, administration set, and bottle, respectively. Adsorption values for this bottle were less than that found in another study for polyvinyl chloride.

Adsorption↗