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Biomedical subjects

J Hellemans

Publications and source records attributed to J Hellemans.

At least 19 recordsLinked to original sources
PubMed2005

Sea-level performance in runners using altitude tents: a field study.

In this study of effects of simulated altitude exposure on sea-level performance, 10 competitive runners slept in a hypoxic environment achieved with tents for 9.8+/-1.3 h.d(-1) (mean+/-standard deviation) for 24 days-30 days at 2500-3500 m (PIO2=117-103 mmHg) above sea level. The altitude group and a control group of 10 runners performed usual training (PIO2=149 mmHg). At approximately 4-wk intervals before and after exposure both groups performed an incremental test for lactate threshold. The altitude group performed an additional test, a treadmill run to exhaustion lasting approximately 5 min. One week following exposure lactate threshold speed of the altitude group relative to the control group increased by 1.2% (90% likely limits +/-3.1%), but the effect became slightly negative after controlling for baseline differences in running speed between the groups. A 16% increase in time to exhaustion was observed in the altitude group, equivalent to a 1.9% (+/-1.4%) increase in speed in a time trial. Change in performance had an unclear relationship to total altitude exposure, genotype for angiotensin converting enzyme, and change in haemoglobin concentration. Our findings are consistent with little or no effect of use of altitude tents on sea-level performance.

Adult↗
PubMed1998

The effect of glycerol and desmopressin on exercise performance and hydration in triathletes.

BACKGROUND: Hydration is an important determinant of athletic performance, and glycerol-containing solutions have been demonstrated to produce a state of hyperhydration. Secretions of arginine vasopressin (AVP) and/or other renal mechanisms may account for reduced urine output following glycerol ingestion. This study examined the effect of glycerol and the AVP analog desmopressin (DDAVP) on hydration and exercise performance in triathletes ingesting routine volumes of prerace fluids. METHODS: Eight male triathletes ages 19 to 43 participated. After determination of their VO(2peak), each athlete completed a strenuous exercise protocol three times involving 60 min of exercise at 70% VO(2peak) followed immediately by an incremental increase in workload every 2 min until exhaustion. RESULTS: Pretreatment with 1 gxkg(-1) glycerol or 20 microgram of DDAVP intranasally failed to produce hyperhydration or any enhancement of athletic performance. There was a significant difference in reduction in body mass between DDAVP and control (P < 0.05) but no change in sweat volume. No physiologically relevant differences in plasma sodium, renin, or hemoglobin were seen with either active agent. Plasma osmolality did have a different time course in response to exercise following glycerol (P < 0.03) owing to a smaller incremental increase. Urine osmolality was also raised at baseline following glycerol (P < 0.05). Responses to exercise of plasma AVP, cortisol, and indices of carbohydrate metabolism were similar, although AVP was elevated following DDAVP administration (P < 0.01) owing to assay cross-reactivity. CONCLUSION: Although maintaining adequate hydration remains important for the endurance athlete, the routine use of either glycerol of DDAVP before athletic training or competition in a thermoneutral environment does not seem to confer any advantage over conventional fluid replacement.

Adult↗
PubMed1998

Prolonged exercise increases peripheral plasma ACTH, CRH, and AVP in male athletes.

We wished to determine whether the increased ACTH during prolonged exercise was associated with changes in peripheral corticotropin-releasing hormone (CRH) and/or arginine vasopressin (AVP). Six male triathletes were studied during exercise: 1 h at 70% maximal oxygen consumption, followed by progressively increasing work rates until exhaustion. Data obtained during the exercise session were compared with a nonexercise control session. Venous blood was sampled over a 2-h period for cortisol, ACTH, CRH, AVP, renin, glucose, and plasma osmolality. There were significant increases by ANOVA on log-transformed data in plasma cortisol (P = 0.002), ACTH (P < 0.001), CRH (P < 0.001), and AVP (P < 0.03) during exercise compared with the control day. A variable increase in AVP was observed after the period of high-intensity exercise. Plasma osmolality rose with exercise (P < 0.001) and was related to plasma AVP during submaximal exercise (P < 0.03) but not with the inclusion of data that followed the high-intensity exercise. This indicated an additional stimulus to the secretion of AVP. The mechanism by which ACTH secretion occurs during exercise involves both CRH and AVP. We hypothesize that high-intensity exercise favors AVP release and that prolonged duration favors CRH release.

Adrenocorticotropic Hormone↗
PubMed1997

Locus of control, latent inhibition and reaction times in a semantic (left-hemisphere) and visuospatial (right-hemisphere) stimulus discrimination task.

Rank correlations on latent inhibition learning among internal scorers versus external scorers on Rotter's I-E locus of control scale were compared between trial numbers and speed of correct reactions in a left- and in a right-hemispheric discrimination task. On the basis of previous research and theorizing reviewed by De Brabander, Boone, and Gerits (1992) we expected latent inhibition effects to show mainly on the left-hemisphere task and more clearly among internal scorers on Rotter's I-E locus of control scale. The findings seem to confirm our expectations.

Association Learning↗
PubMed1997

Corroborative evidence for difference in arousability between internal and external scorers on Rotter's I-E Locus of Control Scale.

Here we report data about the answers on the Hopkins Symptom Check List for 68 students who participated in an experiment. About random half of the subjects were submitted to sham physiological measurements, the others not. Scores on Rotter's I-E Locus of Control Scale were also available. Analysis indicated that sham physiological measurement treatment is associated with more health complaints and more among external scorers on the Locus of Control Scale. These findings are interpreted as the result of increased arousal by the treatment and higher arousability among external scorers.

Analysis of Variance↗
PubMed1997

Self-reported locus of control is based on feelings of depression as well as on asymmetry in activation of cerebral hemispheres.

In a sample of 50 patients with primary breast cancer we obtained interviews, answers to questionnaires, blood samples, and reaction times on two stimulus discrimination tests on the day of admission to the hospital for a biopsy. Locus of control scores on Rotter's I-E Locus of Control Scale seemed to be directly associated with an indicator of depressed mood and one of relative activation of the right cerebral hemisphere. Other variables of which one might have expected a mediating role did not show significant partial relationships with the dependent variable.

Adult↗
PubMed1996

Locus of control, sensation seeking, and stress.

We explored the relations among locus of control, sensation seeking, and stress (N = 68 students). Corroborating evidence was found that subjects with an external locus of control are more vulnerable to stress. Subjects scoring higher on the thrill and adventure seeking-dimension of sensation seeking reported less severe physical and psychological complaints thought to be associated with stress. These results suggest that high sensation seeking is associated with protective mechanisms against life-stress. Some possible intervening mechanisms are further discussed.

Adult↗
PubMed1995

Elevated basal adrenocorticotropin and evidence for increased central opioid tone in highly trained male athletes.

Basal cortisol and ACTH levels have previously been shown to be elevated in highly trained athletes, whereas the ACTH response to ovine CRH has been reported to be diminished compared to that in nonathletic controls. Naloxone, a nonselective opioid receptor antagonist, is known to stimulate ACTH and cortisol secretion. The mechanism of this response is thought to be via increased hypothalamic CRH secretion. The aim of this study was to examine basal and naloxone-stimulated levels of hypothalamic-pituitary-adrenal axis hormones in male athletes. Ten highly trained male athletes and 10 nonathletic controls took part in the study. Peripheral venous blood was sampled for cortisol, ACTH, CRH, and arginine vasopressin (AVP) for 2 h before the administration of 20 mg naloxone, i.v., and 15, 30, 45, 60, 90, and 120 min after naloxone treatment. Body mass index was significantly lower in the athletes (P < 0.001). Basal (prenaloxone) ACTH levels were higher in the athletes (P < 0.05), whereas levels of cortisol, CRH, and AVP were similar in both groups. After naloxone treatment, there was a significantly greater rise in ACTH in the athletes (P < 0.02). There was also a trend for the cortisol response to be greater, which was not statistically significant (P < 0.07). Although in both groups, peripheral CRH rose after naloxone treatment (P < 0.005), a rise of similar magnitude occurred over the 2-h period before naloxone (P < 0.0001). Plasma AVP did not change significantly after naloxone treatment. Neither the plasma cortisol level at baseline nor the body mass index correlated significantly with the ACTH or cortisol response to naloxone. The presence of an enhanced ACTH response to naloxone is evidence that central opioid tone may be increased in highly trained athletes. However, there is no associated suppression of the hypothalamic-pituitary-adrenal axis, and basal ACTH levels are raised, without any detectable change in peripheral plasma CRH or AVP. An additional factor (other than CRH) that stimulates ACTH secretion may be released after naloxone administration.

Adrenocorticotropic Hormone↗
PubMed1993

Stone geometry and structure dependence on extracorporeal shock wave lithotripsy.

The in vitro fragmentation effects of electromagnetic-induced shock wave lithotripsy (Siemens Lithostar) were studied on parallel laminated schists in relation to the incoming shock wave energy and the incoming angle of the incident shock wave. Well above the threshold energy, the total amount of acoustic energy required for fragmentation remained unchanged regardless of the power setting of the high-tension supply. The amount of energy transmitted to the stone was limited by a total reflection angle, restricting the available transmission surface. These observations determine the effect of shock waves on calculi with an irregular shape such as staghorn stones. Lithotripsy-induced cavitation has been recognized, but no immediate influence on disintegration has become apparent until now.

Animals↗
PubMed1984

Positive 14CO2 bile acid breath test in elderly people.

The 14CO2- glycylcholate breath test (also called the bile acid breath test) was performed in a group of 42 normal young volunteers (group A), a group of 25 elderly subjects in apparently good health (group B) and a group of 22 hospitalized geriatric patients presenting with weight loss (group C). The 95 percentile value of the cumulative 14CO2 excretion at the third and the sixth hour in group A was taken as the limit for normal values for 14CO2 excretion. Using these criteria 56% of group B subjects and 50% of group C patients were considered abnormal at the third hour, whereas at the sixth hour these percentages were 56% and 54%, respectively. Repetition of the bile acid breath test after antibiotic treatment in the hospitalized group suggested that bacterial overgrowth in the small intestine was responsible for the abnormal 14CO2 breath test in the elderly persons. However, the large number of abnormal tests in healthy elderly people, not complaining of any gastro-intestinal discomfort, indicates that bacterial overgrowth may remain asymptomatic and that an abnormal test does not necessarily mean that the symptoms of a patient are to be ascribed to this finding.

Adult↗
PubMed1982

Pancreatic polypeptide is not involved in the regulation of the migrating motor complex in man.

The role of pancreatic polypeptide (PP) and motilin in the regulation of the migrating motor complex (MMC) was studied in normal subjects. Both plasma motilin and PP levels changed cyclically in the fasted state and were highest in the late phase II period preceding the activity front in the duodenum. A continental breakfast invariably disrupted the MMC and induced a fed pattern of motility. After the meal plasma motilin levels decreased whereas PP levels rose significantly. Infusion of pure porcine motilin during the fasted state induced an activity front and a rise in plasma PP levels. Infusion of bovine PP in doses producing plasma PP levels above the postprandial values neither induced an activity front nor prevented its occurrence. During PP infusion, however, plasma motilin levels were low, although the activity front was not inhibited. PP seems to have no clear role in the regulation of the motor component of the MMC of man. The role of motilin in the production of the activity front of the MMC is discussed.

Duodenum↗
PubMed1982

Antihypertensive therapy in patients above age 60 with systolic hypertension. A progress report of the European Working Party on High Blood Pressure in the Elderly (EWPHE).

1. Although systolic blood pressure elevation is responsible for increased incidence of cardiovascular accidents in old people, the preventive benefit of lowering systolic hypertension in elderly has not been confirmed. 2. A double blind study comparing the effects of a placebo and of an active regimen (hydrochlorothiazide-triamterene with or without methyldopa) in people over 60 years with isolated systolic hypertension has been undertaken by the European Working Party on High blood pressure in the Elderly (EWPHE). 3. The actively treated group shows a lowered sitting blood pressure (-15/6 mm Hg), a mild increase of serum creatine, serum uric acid and blood glucose and a mild decrease of serum potassium after two years of treatment when compared to the spontaneous changes observed in the placebo treated group. 4. The study is continuing to evaluate if the blood pressure reduction prevents or reduces the incidence of cardiovascular accidents, although some biochemical changes were provoked by the treatment.

Aged↗
PubMed1982

[Problems and future perspectives in the treatment of Parkinson's disease].

The most prominent neuropathological lesions in Parkinson's disease have been found in the substantia nigra. The neurochemical alterations are numerous; the most prominent one is the imbalance between acetylcholine and dopamine, the latter transmitter being deficient. Up to now the striato-nigral dopaminergic receptor is the best investigated and the most useful target for an effective therapy. However, a more specific modulation, stimulation or blockade of these receptors, could strongly reduce the occurrence of the side-effects and the drug resistance that are to be seen after a dopamine substitution started too early or too vigorously.

Acetylcholine↗
PubMed1982

[Specialism in geriatrics and training as a geriatrician. The development of geriatrics as a medical specialty].

Two geriatricians--Belgian and Dutch--have attempted to define their ideas and principles regarding clinical geriatrics based on their work. They strongly recommend the establishment of geriatric hospital departments which are in level and prestige equal to other hospital departments. As attending specialist the geriatrician is responsible for the overall-management of elderly patients with multiple pathology, delicate balances, specific clinical syndromes, mutual involvement of somatic and mental disorders, loss of functions, etc. The execution of this task is based on clinical expertise, knowledge of specific provisions for the elderly in the community and on teamwork with the nursing and paramedical staff of the geriatric department who know how to deal with geriatric patients. Close co-operation with other specialists is necessary to guarantee the quality of the care. Geriatricians and other specialists need to complement each other. In addition it is necessary that the geriatrician select one or more areas of special interest in the extensive professional field in order to carry out clinical research. It is important that geriatric patients are not admitted in hospital departments where they happen to be referred to, but where they have the best chance of recovery. As the geriatric department offers a specific approach, it is recommended that the very old will be admitted there in the first place unless they urgently need other specialist treatment. The elderly who are in serious distress as far as general care is concerned, but do not need hospital expertise, have to be taken care of in other ways.

Education, Medical, Graduate↗