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On sait depuis longtemps que l’exposition à l’altitude est associée à une réduction de l’aptitude aérobie. Différentes hypothèses ont été posées pour expliquer cette limitation à l’effort en hypoxie (une limitation ventilatoire ou diaphragmatique, une altération de la diffusion pulmonaire et une disconcordance entre de la perfusion et la diffusion tissulaire, etc.) mais généralement, la limitation de l’effort aérobie en hypoxie est attribuée à une diminution du transport sanguin de l’O2 (TO2) parc convection vers les muscles. Le TO2 dépend du débit cardiaque (Q) et du contenu artériel en O2 (CaO2). Le CaO2 est diminué en altitude à cause d’une diminution de la pression partielle inspirée en O2. Cependant, le chémoréflexe hypoxique tente de contrebalancer cet effet en élevant la ventilation et en diminuant la pression alvéolaire en CO2 afin de maintenir la pression alvéolaire en O2 constante. De plus, avec l’acclimatation, le rein produit de l’érythropoïétine permettant au taux d’hémoglobine d’augmenter. Ces deux principales adaptations à l’altitude ramènent le CaO2 à sa valeur de base du niveau de la mer en 2 à 3 semaines passées à 5000 m d’altitude mais sans amélioration de l’aptitude à l’effort aérobie. L’exposition à l’altitude est aussi associée à une diminution du Q maximal. Les mécanismes à l’origine de cette limitation du Q maximal restent, à l’heure actuelle, incompris. Les principales explications évoquées sont, une diminution de la réserve chronotrope, une diminution de la commande nerveuse centrale vers le cœur ou une diminution de la demande périphérique. Récemment, des études sur des sujets sains en hypoxie suggérèrent qu’au moins une partie de la limitation du Q maximal à l’effort est liée à une élévation de la postcharge ventriculaire droite suite à l’hypertension pulmonaire induite par l’hypoxie. C’est cette hypothèse que nous avons voulu vérifier dans une première étude. Nous avons étudié l’effet d’une inhibition de l’hypertension pulmonaire d’altitude par le sildénafil, un inhibiteur de la phosphodiestrérase-5, chez des sujets sains, en normoxie, en hypoxie aiguë et en hypoxie chronique. Les résultats de cette étude ont confirmé l’effet vasodilatateur pulmonaire du sildénafil et une augmentation de la VO2max en hypoxie aiguë. Cependant, la prise de ce dernier était couplée à une amélioration de l’oxygénation, si bien que l’élévation de la performance aérobie observée en hypoxie aiguë sous sildénafil ne pouvait être entièrement attribuée à une réduction de l’hypertension pulmonaire. Nous conclurent que cette amélioration de la performance était probablement d’avantage liée à une amélioration de l'oxygénation qu’à un effet vasodilatateur pulmonaire. Les résultats équivoques obtenus lors de cette première étude nous ont incité à tester les effets d’une amélioration de l’oxygénation sur la performance aérobie en haute altitude. Pour ce faire, quinze sujets sains ont été testés au niveau de la mer et après acclimatation à 4700 m d’altitude soit sous placebo, soit sous acétazolamide, un inhibiteur de l’anhydrase carbonique augmentant l’oxygénation par stimulation ventilatoire en réponse à une acidose métabolique. La prise d’acétazolamide n’eut aucun effet sur l’hémodynamique pulmonaire et sur la VO2max et la charge maximale. Nous avons toutefois observé qu’une amélioration de l’oxygénation durant l’effort retarde l’apparition du seuil ventilatoire améliorant ainsi la phase aérobie de l’effort. Cette étude confirme donc qu’une élévation du CaO2 permet une amélioration de l’aptitude aérobie. Finalement, la dernière étude a pour but d’étudier les effets isolés d’une vasodilatation pulmonaire sur la performance aérobie en altitude. Les résultats d’une étude préliminaire montrent que l’inhibition de la vasoconstriction hypoxique par un agent pharmacologique antagoniste des récepteurs de l’endothéline ETA et ETB, le bosentan, permet une élévation de l’aptitude aérobie en hypoxie aiguë, sans effets sur l’oxygénation, confirmant ainsi notre hypothèse initiale qu’une postcharge ventriculaire droite augmentée en hypoxie peut contribuer à une limitation de l’aptitude à l’effort aérobie en hypoxie. Conclusions : L’ensemble de nos résultats suggère que l’aptitude aérobie en altitude est déterminée par le transport d’O2 qui peut être augmenté par manipulation pharmaceutique du débit ventriculaire droit maximal après inhibition de la vasoconstriction pulmonaire hypoxique (bosentan), amélioration de l’oxémie (acétazolamide) ou des deux (sildénafil).

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Thesis (PhD) -- Auckland University of Technology, 2004. / Also held in print (175 leaves, 30 cm.) in Akoranga Theses Collection. (T 612.0144 HIN)

Thesis (MHSc--Health Science) -- Auckland University of Technology, 2003. / Also held in print (102 leaves, col. ill., 30 cm.) in North Shore Theses Collection (T 612.0144 WOO).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1952. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references ([25-27]).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1947. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 73-87).

Orientadores: Luiza Sumiko Kinoshita, George John Shepherd / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-03T21:40:19Z (GMT). No. of bitstreams: 1 Meireles_LeonardoDias_M.pdf: 6951328 bytes, checksum: 62f64c68379b88fe3ed70beefd07367b (MD5) Previous issue date: 2003 / Resumo: A Floresta Atlântica lato sensu apresenta um conjunto de formações florestais e campestres com fisionomia, estrutura e composição florística diferenciadas. O sudeste brasileiro representa um dos centros de diversidade deste bioma. Apesar disso, ainda existem fisionomias pouco conhecidas floristicamente. São exemplos as fisionomias alto-montanas da Serra da Mantiqueira e da Serra do Mar. Este estudo foi realizado no distrito de Monte Verde, Serra da Mantiqueira, MG, onde ocorrem diferentes fisionomias vegetacionais como: Floresta Alto-Montana, Floresta de Araucária, Campos de Altitude e Afloramentos Rochosos. Realizou-se o levantamento florístico dessas fisionomias e a estrutura fitossociológica da Floresta Alto-Montana. Um número representativo de espécies foi coletado. Foram 444 espécies, distribuídas entre 97 famílias e 246 gêneros. As famílias mais ricas neste levantamento foram Asteraceae (64 espécies), Melastomataceae (24 espécies), Cyperaceae (23 espécies), Myrtaceae (23 espécies), Orchidaceae (23 espécies) e Solanaceae (21 espécies). No levantamento fitossociológico foram amostrados 1191 indivíduos, pertencentes a 64 espécies arbóreas e dois bambus, distribuídos entre 42 gêneros e 26 famílias. A biomassa morta se destacou pelo alto VI (42,06), seguida de Pimenta pseudocaryophy/lus (24,59), Roupala rhombifolia (19,98) e Drimys brasiliensis (18,57). Houve uma forte substituição f1orística ao longo do curto gradiente altitudinal amostrado, cerca de 120m. Novos registros de ocorrência foram observados, com espécies apresentando distribuição disjunta com o sul do país e com outras áreas elevadas do sudeste. A maioria das espécies coletadas são típicas de ambientes alto-montanos, apresentando distribuição restrita. A abundância de espécies com distribuição restrita, formando uma ligação f1orística com o sul do Brasil, representando um conjunto florístico bastante distinto das f1oretas em altitudes menores e contribuindo para o aumento da riqueza da Floresta Atlântica, faz desses tipos de vegetação fortes candidatos à medidas urgentes para sua conservação / Abstract: The Atlantic Forest biome in the broad sense consists of a group of forest and grassland formations with different physiognomies, structures and floristic compositions. The Southeast of Brazil is one of the centres of diversity of this biome. In spite of numerous studies in the Atlantic Forest, there are still several poorly known physiognomies, such as the upper montane forests and grasslands of the Serra da Mantiqueira and the Serra do Mar. The present study was carried out in the Monte Verde district, in the Serra da Mantiqueira, in the State of Minas Gerais, where different formations such as upper montane forest, Araucaria forest, high altitude grassland and rocky outcrops can be found. A general floristic study of these physiognomies was made, together with a phytosociological study of the upper montane forest. A total of 444 species was collected, distributed among 97 families and 246 genera. The richest families were Asteraceae (64 species), Melastomataceae (24 species), Cyperaceae (23 species), Myrtaceae (23 species), Orchidaceae (23 species) and Solanaceae (21 species). In the phytosociological study 1191 individual trees were sampled, and included 64 woody species and two bamboos, belonging to 42 genera and 26 families of plants. Dead biomass was very prominent, showing the highest importance value (42.06) followed by Pimenta pseudocaryophy/lus (24.59), Roupala rhombifolia (19.98) and Drimys brasiliensis (18.57). We observed quite a strong substitution of species along the very short (about 120 m) altitudinal gradient that was studied. A number of new occurrence records were made, with some species showing a disjunct distribution with the south of Brazil and with other high areas in the southeast of Brazil. The majority of the species collected are typical of high mountain environments and have very restricted distributions. The abundance of relatively rare species with limited distributions, forming a floristic link with the south of Brazil and representing floristic elements quite distinct from the surrounding lower-level forests adds greatly to the total floristic richness of the Atlantic Forest and make these vegetation types strong candidates for rapid and energetic conservation measures / Mestrado / Mestre em Biologia Vegetal

With the consideration of extending track competition for girls of a middle altitude community to include the sea level valley nearby, the problem for this investigation evolved. The main question to be answered was, "Is the athletic performance of young female athletes, native to middle altitude, impaired when performing at sea level?" Subsidiary problems of the relationship of partial pressure of oxygen to performance, and microhematocrit changes in the subjects were also studied. Eight females between the ages of 12 and 14 participated in this experiment having eight treatments. Four treatments were at sea level and four were at middle altitude. Each treatment included taking a fingertip blood sample for a microhematocrit reading, a 50 yard dash, a 440 yard dash, a softball throw and an 880 yard run. These events were to represent the assortment found at a track meet. Recordings were also made of temperature, humidity, barometric pressure, and air pollution. It was hypothesized that; a) the denser air and increased gravitational pull at sea level cause impairment in throwing and short runs; b) with oxygen uptake reduced at altitude, the 880 yard run is faster at sea level than at middle altitude; c) if hematocrits are in the upper portion of the normal range for sea level, the resultant increase in the oxygen carrying capacity of the blood does not improve sea level performance. The findings indicated that physical training and learning progressed markedly from the start of the experiment to the finish, The only significant altitude effect was found in the 50 yard dash with times being faster at sea level. It is doubtful that this was a result of the change in altitude, more likely, conditions other than barometric pressure were responsible for the differences found at the two testing locations. Wind disadvantage and insufficient warm-up more likely accounted for slower times at altitude. Superior performances occurred in warm weather, and when subjects were psychologically peaked indicating that warm-up and psychological climate may be more important to performance than the change of altitude that was employed. Hematocrits remained within normal ranges for middle altitude dwelling females throughout the experiment. Therefore, a coach of healthy young athletes from middle altitude should have no unusual concerns for competition at a related sea level environment. Concerns should be only those normally attended to at all competitions. / Education, Faculty of / Curriculum and Pedagogy (EDCP), Department of / Graduate