title: Time courses of cardiac output and oxygen uptake following stepwise increases in exercise intensity.
abstract: 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.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Physiology, German Sport University Cologne, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Leyk
authors.forename: U
authors.initials: U
authors.lastname: Hoffmann
authors.forename: K
authors.initials: K
authors.lastname: Baum
authors.forename: D
authors.initials: D
authors.lastname: Essfeld
mesh_terms: D000328:Adult; D001158:Arteries; D001794:Blood Pressure; D002302:Cardiac Output; D018619:Echocardiography, Doppler, Pulsed; D005080:Exercise Test; D005260:Female; D006339:Heart Rate; D006801:Humans; D007773:Lactates / Q000097:blood; D008168:Lung / Q000378:metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption; D005082:Physical Exertion / Q000502:physiology*; D011187:Posture; D011659:Pulmonary Gas Exchange; D013318:Stroke Volume; D016683:Supine Position; D013997:Time Factors; D014680:Veins; D014937:Work
chemical_list: D007773:Lactates; D010100:Oxygen