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Biomedical subjects

G R Leon

Publications and source records attributed to G R Leon.

At least 19 recordsLinked to original sources
PubMed2002

Individual thermal profiles as a basis for comfort improvement in space and other environments.

BACKGROUND: The development of individualized countermeasures to address problems in thermoregulation is of considerable importance for humans in space and other extreme environments. A methodology is presented for evaluating minimal/maximal heat flux from the total human body and specific body zones, and for assessing individual differences in the efficiency of heat exchange from these body areas. The goal is to apply this information to the design of individualized protective equipment. METHODS: A multi-compartment conductive plastic tubing liquid cooling/warming garment (LCWG) was developed. Inlet water temperatures of 8-45 degrees C were imposed sequentially to specific body areas while the remainder of the garment was maintained at 33 degrees C. RESULTS: There were significant differences in heat exchange level among body zones in both the 8 degrees and 45 degrees C temperature conditions (p < 0.001). The greatest amount of heat was absorbed/released by the following areas: thighs (8 degrees C: -2.12 +/- 0.14 kcal min(-1); 45 degrees C: +1.58 +/- 0.23); torso (8 degrees C: -2.12 +/- 0.13 kcal min(-1); 45 degrees C: +1.31 +/- 0.27); calves (8 degrees C: -1.59 +/- 0.26 kcal min(-1); 45 degrees C: +1.53 +/- 0.24); and forearms (8 degrees C: -1.67 +/- 0.29 kcal x min(-1); 45 degrees C: +1.45 +/- 0.20). These are primarily zones with relatively large muscle mass and adipose tissue. Calculation of absorption/release heat rates standardized per unit tube length and flow rate instead of zonal surface area covered showed that there was significantly greater heat transfer in the head, hands, and feet (p < 0.001). The areas in which there was considerable between-subject variability in rates of heat transfer and thus most informative for individual profile design were the torso, thighs, shoulders, and calves or forearms. CONCLUSIONS: The methodology developed is sensitive to individual differences in the process of heat exchange and variations in different body areas, depending on their size and tissue mass content. The design of individual thermal profiles is feasible for better comfort of astronauts on long-duration missions and personnel in other extreme environments.

Adult↗
PubMed2001

Efficacy of wrist/palm warming as an EVA countermeasure to maintain finger comfort in cold conditions.

INTRODUCTION: This study explored the effectiveness of local wrist/palm warming as a potential countermeasure for providing finger comfort during extended duration EVA. METHODS: There were six subjects (five males and one female) who were evaluated in a liquid cooling/warming garment (LCWG) wearing modified liquid cooling/warming (LCW) gloves in three different experimental conditions: Condition 1: Stage 1--no LCWG, LCW glove inlet water temperature 33 degrees C; Stage 2--no LCWG, LCW glove inlet water temperature cooled to 8 degrees C; Stage 3--no LCWG, LCW glove inlet water temperature warmed to 45 degrees C; Condition 2: Stage 1--LCWG and LCW glove inlet water temperature 33 degrees C; Stage 2--LCWG inlet temperature cooled to 31 degrees C, LCW gloves, 8 degrees C; Stage 3--LCWG inlet water temperature remains at 31 degrees C, LCW glove inlet water temperature warmed to 45 degrees C; Condition 3: Stage 1--LCWG and LCW gloves 33 degrees C; Stage 2--LCWG inlet water temperature cooled to 28 degrees C, LCW gloves, 8 degrees C; Stage 3--LCWG remains at 28 degrees C, LCW glove water temperature warmed to 45 degrees C. RESULTS: Wrist/palm area warming showed a statistically significant increase in finger temperature (Tfing) in Stage 3 compared with Stage 2. Blood perfusion showed a trend toward a significantly greater value in Stage 3 compared with Stage 2. The LCW gloves were significantly more effective in increasing Stage 3 Tfing in Condition 1 (33 degrees C) compared with Condition 3 (28 degrees C). Across conditions, subjective perception of heat in the hands was significantly greater at Stage 3 than Stage 2; perception of overall body heat showed a trend for higher heat ratings in Stage 3 than Stage 2. CONCLUSIONS: Local wrist/palm warming was effective in increasing blood circulation to the distal upper extremities, suggesting the potential usefulness of this technique for enhancing astronaut comfort during EVA while decreasing power requirements.

Adult↗
PubMed2000

Augmentation of blood circulation to the fingers by warming distant body areas.

Future activities in space will require greater periods of time in extreme environments in which the body periphery will be vulnerable to chilling. Maintaining the hands and fingers in comfortable conditions enhances finger flexibility and dexterity, and thus effects better work performance. We have evaluated the efficacy of promoting heat transfer and release by the extremities by increasing the blood flow to the periphery from more distant parts of the body. The experimental garment paradigm developed by the investigators was used to manipulate the temperature of different body areas. Six subjects, two females and four males, were evaluated in a stage-1 baseline condition, with the inlet temperature of the circulating water in the liquid cooling/warming garment (LCWG) at 33 degrees C. At stage 2 the total LCWG water inlet temperature was cooled to 8 degrees C, and at stage 3 the inlet water temperature in specific segments of the LCWG was warmed (according to protocol) to 45 degrees C, while the inlet temperature in the rest of the LCWG was maintained at 8 degrees C. The following four body-area-warming conditions were studied in separate sessions: (1) head, (2) upper torso/arm, (3) upper torso/arm/head, and (4) legs/feet. Skin temperature, heat flux and blood perfusion of the fingers, and subjective perception of thermal sensations and overall physical comfort were assessed. Finger temperature (T(fing)) analyses showed a statistically significant condition x stage interaction. Post-hoc comparisons (T(fing)) indicated that at stage 3, the upper torso/arm/head warming condition was significantly different from the head, upper torso/arm and legs/feet conditions, showing an increase in T(fing). There was a significant increase in blood perfusion in the fingers at stage 3 in all conditions. Subjective perception of hand warmth, and overall physical comfort level significantly increased in the stage 3 upper torso/arm/head condition. The findings indicate that physiological methods to enhance heat transfer by the blood to the periphery within protective clothing provide an additional tool for increasing total and local human comfort in extreme environments.

Adult↗
PubMed2000

Thermoregulation and heat exchange in a nonuniform thermal environment during simulated extended EVA. Extravehicular activities.

BACKGROUND: Nonuniform heating and cooling of the body, a possibility during extended duration extravehicular activities (EVA), was studied by means of a specially designed water circulating garment that independently heated or cooled the right and left sides of the body. The purpose was to assess whether there was a generalized reaction on the finger in extreme contradictory temperatures on the body surface, as a potential heat status controller. METHOD: Eight subjects, six men and two women, were studied while wearing a sagittally divided experimental garment with hands exposed in the following conditions: Stage 1 baseline--total body garment inlet water temperature at 33 degrees C; Stage 2--left side inlet water temperature heated to 45 degrees C; right side cooled to 8 degrees C; Stage 3--left side inlet water temperature cooled to 8 degrees C, right side heated to 45 degrees C. RESULTS: Temperatures on each side of the body surface as well as ear canal temperature (Tec) showed statistically significant Stage x Side interactions, demonstrating responsiveness to the thermal manipulations. Right and left finger temperatures (Tfing) were not significantly different across stages; their dynamic across time was similar. Rectal temperature (Tre) was not reactive to prevailing cold on the body surface, and therefore not informative. Subjective perception of heat and cold on the left and right sides of the body was consistent with actual temperature manipulations. CONCLUSIONS: Tec and Tre estimates of internal temperature do not provide accurate data for evaluating overall thermal status in nonuniform thermal conditions on the body surface. The use of Tfing has significant potential in providing more accurate information on thermal status and as a feedback method for more precise thermal regulation of the astronaut within the EVA space suit.

Adult↗
PubMed1999

Eating-disordered behaviors and personality characteristics of high school athletes and nonathletes.

OBJECTIVE: To assess whether high school athletes are at risk for an eating disorder, whether personality characteristics differentiate athletes from nonathletes, and whether high levels of perfectionism put athletes at risk. METHOD: 318 high school athletes were randomly matched to 360 nonathletes. Comparisons were made by means of the Eating Disorders Inventory (EDI), Restraint Scale, Risk Symptom Checklist, Multidimensional Personality Questionnaire (MPQ), and body mass index (BMI). RESULTS: Athletes did not have higher levels of disordered eating behaviors and attitudes than their nonathletic counterparts. Athletes had less negative views of life than nonathletes. However, perfectionistic tendencies may put some athletes at risk. DISCUSSION: High school athletes are not at greater risk for the development of an eating disorder than other students. Athlete's positive outlook on life and high self-efficacy may serve as protective factors. Alternatively, athletes may not be at risk until they train for one particular sport in a highly competitive environment.

Adolescent↗
PubMed1998

Disordered eating in adolescent males from a school-based sample.

OBJECTIVE: The authors sought to describe a sample of adolescent males who reported disordered eating, to explore whether males with disordered eating are overweight or obese, and to determine if patterns displayed by females would be replicated with a male sample. METHOD: Three school-based adolescent samples were selected. (1) 27 males reporting disordered eating (2) 27 physically matched controls, and (3) 27 randomly selected controls. RESULTS: Findings indicated that boys reporting disordered eating expressed greater body dissatisfaction, depression, restraint, and poorer interoceptive awareness compared to matched and randomly selected controls. Negative Emotionality and poor Interoceptive Awareness scores showed the strongest associations with eating pathology. Body mass index and Negative Emotionality scores showed the strongest relationships to restrained eating. DISCUSSION: Previous results for female adolescents were replicated, suggesting that findings for females can be generalized to males. Disordered eating appears to exist in the absence of significant weight problems in adolescent males.

Adolescent↗
PubMed1997

Rescue worker and population protection in large-scale contamination disasters.

We discuss disaster preparedness and emergency response to large-scale disasters. Our particular focus is disaster management and protection of disaster response personnel in situations involving chemicals and radiation. We describe a unit system that protects rescuers working in the epicenter of a disaster, and we examine effective protective clothing and procedures for enhancing human performance in extreme environmental conditions. We also present on outline of patient triage in response to radiation disasters. Finally, we describe recent efforts underway in Minnesota to prepare for managing large-scale disasters.

Disaster Planning↗
PubMed1997

The future of risk factor research in understanding the etiology of eating disorders.

This article explores whether particular risk factors are best seen as precursors or as symptoms. Psychological, cultural, family, developmental, and biological risk domains that may be important in the etiology of eating disorders are briefly reviewed. We describe a 4-year prospective study assessing a wide range of risk factors for development of eating disorders in a large school-based sample of adolescents. For subjects who were relatively asymptomatic, a personality or temperamental characteristic of negative affect/esteem measured at study entrance was the only significant predictor of later risk score for both girls and boys. The significant comorbidity demonstrated in a separate group that had high risk for eating disorders suggests that negative affectivity may be a vulnerability factor for overall psychopathology rather than a predisposition specifically for eating disorders. Following subjects through the young-adult years and later may further clarify the range of influences affecting disordered eating. Primary prevention and early intervention programs in the schools are also recommended.

Feeding and Eating Disorders↗
PubMed1996

Self-esteem and change in body mass index over 3 years in a cohort of adolescents.

Self-esteem has been hypothesized to be lower in obese adolescents relative to their normal weight peers and to be an important factor in preventing or reversing obesity. The present study examined the relationship between obesity and self-esteem cross-sectionally and prospectively over three years in a cohort of 1278 adolescents in grades 7 to 9 at baseline. Cross-sectional analyses revealed an inverse association between physical appearance self-esteem and body mass index in both males and females. In females, body mass index was inversely associated with global self-esteem, close friendship, and behavioral conduct self-esteem. In males, body mass index was inversely associated with athletic and romantic appeal self-esteem. Prospectively, in females, physical appearance and social acceptance self-esteem at baseline were inversely related to body mass index three years later. Baseline self-esteem was unrelated prospectively to change in body mass index in males. All associations were modest in magnitude. These results suggest that in a middle class white sample of adolescents, self-esteem specific to physical appearance is modestly associated with body mass index. Low self-esteem does not appear to predict the development of obesity over time.

Adolescent↗
PubMed1995

Changes in psychological variables and health behaviors by dieting status over a three-year period in a cohort of adolescent females.

PURPOSE: Psychologic and behavioral changes associated with frequent dieting were examined. Compared to nondieters, frequent dieters were hypothesized to show more adverse psychologic changes and increased use of unhealthy weight control behaviors, but possibly healthier eating and exercise behavior changes, over the three-year period of observation. METHODS: A prospective study of female students, in grades 7-10 at baseline completed a health behavior survey in school once a year for a total of three years. RESULTS: Restrained eating, body dissatisfaction and drive for thinness, self-induced vomiting, laxative use, diet pill use, and alcohol use, significantly increased, and physical appearance and self-concept significantly decreased among frequent dieters, compared to non-dieters. Changes in scores on five EDI subscales, eight self-esteem subscales, weight fluctuations, dietary intake, and physical activity patterns did not significantly differ over time by dieting status. CONCLUSION: Dieting may reflect a general pattern of unhealthy behaviors adopted in adolescence, rather than act as a causal factor in promoting psychologic distress.

Adolescent↗
PubMed1995

Prospective analysis of personality and behavioral vulnerabilities and gender influences in the later development of disordered eating.

This article presents the 2-year findings of a prospective investigation of the precursors to the later development of an eating disorder in adolescents. The sample consisted of 852 girls and 815 boys who began to study in Grades 7-10 and participated for 3 consecutive years. For both genders, the strongest predictors of Year 3 risk status were Years 1 and 2 risk scores. When the effects of Year 1 and Year 2 risk were controlled, race (Caucasian) and poor interoceptive awareness at Year 2 were significant predictors of disordered eating at Year 3 for girls. Previous risk status was the only significant predictor of Year 3 risk for boys. Gender difference evaluations in the risk score components indicated that a significantly greater proportion of girls than boys endorsed behaviors that were similar to eating disorder diagnostic criteria. Poor interoceptive awareness may provide a vulnerability for eating disorders; possible pathways were discussed.

Child↗
PubMed1995

Dieting behaviors and weight change history in female adolescents.

The prevalence of dieting, weight change history, and specific weight loss behaviors was examined in a population-based sample of 1,015 female 9th-12th graders. Healthy weight loss behaviors were reported much more frequently than unhealthy weight loss behaviors (e.g., healthy behaviors: exercise = 32.4%, decrease fat intake = 26.0%, reduce snacks = 25.0%, reduce kilocalorie intake = 22.4%; unhealthy behaviors: fasting = 8.1%, diet pills = 5.4%, vomiting = 4.4%). Obesity status and restrained eating scores were positively related to greater history of weight loss episodes, pounds lost, and weight fluctuations and to greater use of healthy weight loss methods and weight loss programs. Implications for public health recommendations regarding dieting and its associated behaviors in female adolescents are discussed.

Adolescent↗
PubMed1994

Food preferences, eating patterns, and physical activity among adolescents: correlates of eating disorders symptoms.

PURPOSE: Food preferences, eating patterns, and physical activity patterns were examined in a cohort of adolescent females and males participating in a longitudinal study of the developmental antecedents of eating disorders. METHODS: All adolescents (n = 1494) in grades seven through ten in an entire school district completed a survey about their dieting behaviors, eating, and exercise patterns. RESULTS: Principal components analysis showed similar factor structures for food preferences and eating patterns among males and females. Gender differences were present in physical activity patterns. Sports participation was correlated with healthy food preference and was a significant predictor of eating disorders symptoms. Junk food preference was marginally inversely related to eating disorders symptoms in females. Preference for other types of foods and reported intake of foods were not related to eating disorders symptoms. The percent of variance in risk score accounted for by dietary intake and physical activity patterns was small. CONCLUSIONS: Psychological and social/environmental variables may explain a larger proportion of the variance in eating disorders risk than the dietary and physical activity variables examined in this study. Implications for understanding the etiology and behavioral expression of eating disorders are discussed.

Adolescent↗
PubMed1994

Weight concerns, dieting behavior, and smoking initiation among adolescents: a prospective study.

Students (n = 1705) in grades 7 through 10 were surveyed at baseline and 1 year later about their weight concerns, dieting behaviors, and smoking behavior. Three of six weight concerns and dieting behaviors assessed at baseline were prospectively related to smoking initiation in girls (trying to lose weight, eating disorder symptoms, constant thoughts about weight). Four of six weight concerns and dieting behaviors were cross-sectionally related to current smoking at baseline in girls (trying to lose weight, eating disorder symptoms, fear of weight gain, desire to be thin). Weight concerns and dieting behaviors were largely unrelated to current smoking in boys. Implications for smoking prevention efforts are discussed.

Adolescent↗
PubMed1993

Personality and behavioral vulnerabilities associated with risk status for eating disorders in adolescent girls.

This article presents first-year cross-sectional findings from a study of the development of eating disorders. Adolescent female (N = 937) 7th through 10th graders completed measures that included information on personality, self-concept, eating patterns, and attitudes. A risk status score was calculated on the basis of comprehensive information regarding DSM-III-R eating disorders criteria and other weight and attitudinal data. All personality measures showed significant differences according to risk, based on subject classification into high, moderate, and mild risk status and comparison groups. Early puberty was not associated with increased risk. The strongest predictor variables for risk were body dissatisfaction, negative emotionality, and lack of interoceptive awareness. The possible diathesis of personality including temperamental factors in the later development of an eating disorder is discussed.

Adolescent↗