1,721,009 research outputs found
The effects of physical exercise at high altitude on adrenocortical function in humans.
No full textThe combined effects of sustained physical activity and hypoxia on adrenocortical function were investigated in 14 healthy volunteers, 8 males and 6 females (mean age 40.9 +/- 3.3 years), during a scientific expedition in the Himalayas. Plasma cortisol levels were measured in all subjects in basal conditions and after the administration of 1 mg dexamethasone (DXM) p.o. The study was performed before and after 15 days of intense trekking (Leh, altitude 3700 m). While on both occasions subjects retained their cortisol circadian fluctuations, basal and post-DXM cortisol levels at high altitude were significantly higher (p < 0.005 and p < 0.0005) than before climbing. Cortisol suppression was noted in all cases at low altitude, whereas 4 out of the 14 subjects did not show reduced hormone levels after 15 days of trekking. Moreover, nonsuppressor subjects had significantly higher (p < 0.05) baseline cortisol levels than suppressors. Basal and post-DXM hormone levels were found to be unrelated to age and sex of subjects. The present data further suggest that sustained physical activity at altitude activates adrenocortical function in normal individuals; however, in 30% of subjects DXM-induced cortisol suppression does not occur. To explain the latter observation, the concomitant role of hypoxia (and/or other environmental changes) and the subjective perception of physical stressors should be taken into account
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Respiratory and cardiovascular adaptations to progressive hypoxia; effect of interval hypoxic training.
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Gene expression in the Andes; relevance to neurology at sea level.
No full textChronic mountain sickness (CMS), a maladaptation syndrome to chronic hypoxia, occurs in the Andes. Gene expression differences in Andeans could explain adaptation and maladaptation to hypoxia, both of which are relevant to neurology at sea level.Expression of genes responsive to cellular oxygen concentration, hypoxia-inducible factor-1alpha (HIF-1alpha), three splicing variants of vascular endothelial growth factor (VEGF) and von Hippel-Lindau protein (pVHL) was measured by reverse transcription polymerase chain reaction (RT-PCR) in 12 Cerro de Pasco (CP) (altitude 4338 m) natives and 15 CMS patients in CP. Thirteen high altitude natives living in Lima and five Lima natives were sea level controls. A CMS score (CMS-sc) was assigned clinically. Expression was related to the clinical assessment.High expression of HIF-1alpha and VEGF-121 was found in CMS (P<0.001). Samples from CP had higher expression than those from Lima (P<0.001). Expression of HIF-1alpha and VEGF-121 was related to age (P<0.001); adjusting for age did not abolish the group effect. Higher CMS-sc was related to expression independent of age (P<0.001). VEGF-165 and -189 were expressed only in CMS. Birth altitude had no effect on gene expression. pVHL was not quantifiable.HIF-1alpha and VEGF-121 participate in adaptation to hypoxia. The high levels may explain blood vessel proliferation in Andeans and hold lessons for patients at sea level. VEGF-165 expression suggests that it contributes to preservation of neuronal function in human chronic hypoxia. VHL mutations may mark those destined to develop neural crest tumors which are common in the Andes
Breathing patterns and cardiovascular autonomic modulation during hypoxia induced by simulated altitude.
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