Splenic contraction, catecholamine release, and blood volume redistribution during exercise in man
Notice bibliographique
Résumé
Numerous mammals have the ability to autotransfuse oxygenated red cells from the spleen into circulation during times of stress. This enhancement of the oxygen transport system has benefited mammals capable of heavy work (such as the thoroughbred horse, fox and greyhound) in an improved endurance performance. During times of inactivity the spleen in these mammals can sequester up to 50% of the total red cell volume. This reduces the viscosity of the blood and work of the heart. In humans the spleen is capable of storing considerably less red cells and is primarily a lymphoid organ. Although significant volume reductions have been observed with physical stress, the mechanism responsible remains unidentified and represents a primary objective of this dissertation. To determine the mechanism responsible for splenic volume reduction nine male subjects participated in a two part study. Initially they undertook three cycling bouts of 5, 10, and 15 minute duration at 60% VO^max. Spleen size and volume was assessed by scintography before and immediately following each cycling bout. Although there was a significant decrease in spleen size and volume with exercise, no significant differences were observed between the three durations. In the second part of the study the same subjects undertook an incremental ride to exhaustion. The spleen size and volume were measured prior to exercise and during one hour of passive recovery. Blood samples were collected in conjunction with spleen imaging and analyzed for plasma catecholamine concentrations. The spleen was restored to its pre-exercise value 20 minutes following the completion of exercise. The volume of the spleen during this time was inversely related to plasma catecholamine levels. It is apparent that the spleen will contract in response to an intensity dependent signal and that sympathetic stimulation, as reflected in changes in plasma catecholamine concentrations, is involved in this effect. In a simultaneous study, the effect of splenic contraction during exercise on the circulating red cell volume and indirect calculations of plasma volume change (Hb/Hct) was determined. Radio nuclide measurements of red cell and plasma volume were performed, and a blood count taken, prior to and immediately following exercise. The release of 50 mls of red cells from the spleen during exercise accounted for a 2.2% increase in the total circulating red cell volume. The indirect calculations of plasma volume were unaffected by the minor increase in peripheral hematocrit and were equivalent to radio labelled measurements. In conjunction the results of this dissertation imply that the release of red cells during exercise is not a primary function of the human spleen.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,001 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».