Time courses of cardiac output and oxygen uptake following stepwise increases in exercise intensity
Deutscher übersetzter Titel: | Zeitliche Verlaeufe der Herzfoerderleistung und der Sauerstoffaufnahme im Verlauf stufenweiser Erhoehung der Belastungsintensitaet |
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Autor: | Leyk, D.; Hoffmann, Uwe; Baum, K.; Essfeld, D. |
Erschienen in: | International journal of sports medicine |
Veröffentlicht: | 16 (1995), 6, S. 357-363, Lit. |
Format: | Literatur (SPOLIT) |
Publikationstyp: | Zeitschriftenartikel |
Medienart: | Gedruckte Ressource Elektronische Ressource (online) |
Sprache: | Englisch |
ISSN: | 0172-4622, 1439-3964 |
DOI: | 10.1055/s-2007-973020 |
Schlagworte: | |
Online Zugang: | |
Erfassungsnummer: | PU199510103353 |
Quelle: | BISp |
Abstract des Autors
The adjustment of pulmonary oxygen uptake (VO2) following a step increase in work rate has been characterized as consisting of an early "cardiodynamic" component with unchanged mixed-venous O2-content ("phase 1") and a subsequent "metabolic" component ("phase 2") starting when venous blood from the muscle arrives at the lungs. The aim of the present study was to investigate whether the onset of phase 2 actually indicates the arrival of blood influenced by the altered muscle metabolism. Parallel measurements of cardiac output (Doppler technique) and VO2 (breath-by-breath measurements at the mouth) were performed in eight subjects during step increases in exercise intensity (from a 20 W baseline to either 80 W, 120 W, 160 W or 200 W). To vary the absolute cardiac output values for given muscle VO2 the subjects exercised both in upright and supine position. Individual time-courses of the arterio-venous O2 difference (a-v delta O2) were computed from cardiac output and VO2 data. Independent of body position two clear-cut phases of similar duration were seen both in VO2 and in the computed a-v delta O2. The duration of the first component with unchanged a-v delta O2 was about 20 s at the lowest step amplitudes (20-80 W and 20-120 W). It decreased to about 15 s for the 20-160 W and 20-200 W steps. At the lower exercise intensities the duration of phase 1 appears too long to be entirely due to the transit time of venous blood from the exercising muscles to the lungs. The present data rather suggest that, a lower exercise intensities, there is no abrupt decrease in venous O2-content in the muscle so that the arrival of muscle blood at the lungs cannot simply be discerned by means of the respiratory VO2 measurements or computed a-v delta O2 time courses. Verf.-Referat