title: Skeletal muscle VO₂ kinetics from cardio-pulmonary measurements: assessing distortions through O₂ transport by means of stochastic work-rate signals and circulatory modelling.
abstract: During non-steady-state exercise, dynamic changes in pulmonary oxygen uptake (VO₂pulm) are dissociated from skeletal muscle VO₂ (VO₂musc) by changes in lung and venous O₂ concentrations (CvO₂), and the dynamics and distribution of cardiac output (CO) between active muscle and remaining tissues (Qrem). Algorithms can compensate for fluctuations in lung O₂ stores, but the influences of CO and CvO₂ kinetics complicate estimation of VO₂musc from cardio-pulmonary measurements. We developed an algorithm to estimate VO₂musc kinetics from VO₂pulm and heart rate (HR) during exercise. 17 healthy volunteers (28 ± 7 years; 71 ± 12 kg; 7 females) performed incremental exercise using recumbent cycle ergometry (VO₂peak 52 ± 8 ml min(-1) kg(-1)). Participants completed a pseudo-random binary sequence (PRBS) test between 30 and 80 W. VO₂pulm and HR were measured, and CO was estimated from HR changes and steady-state stroke volume. VO₂musc was derived from a circulatory model and time series analyses, by solving for the unique combination of venous volume and the perfusion of non-exercising tissues that provided close to mono-exponential VO₂musc kinetics. Independent simulations showed that this approach recovered the VO₂musc time constant (τ) to within 7% (R(2) = 0.976). Estimates during PRBS were venous volume 2.96 ± 0.54 L; Qrem 3.63 ± 1.61 L min(-1); τHR 27 ± 11 s; τVO₂musc 33 ± 8 s; τVO₂pulm 43 ± 14 s; VO₂pulm time delay 19 ± 8 s. The combination of stochastic test signals, time series analyses, and a circulatory model permitted non-invasive estimates of VO₂musc kinetics. Large kinetic dissociations exist between muscular and pulmonary VO₂ during rapid exercise transients.
authors: Institute of Physiology and Anatomy, German Sport University, Am Sportpark Müngersdorf 6, 50933 Cologne, Germany. u.hoffmann@dshs-koeln.de
authors: U
authors: U
authors: Hoffmann
authors: U
authors: U
authors: Drescher
authors: A P
authors: AP
authors: Benson
authors: H B
authors: HB
authors: Rossiter
authors: D
authors: D
authors: Essfeld
mesh_terms: D000328:Adult; D000465:Algorithms; D002302:Cardiac Output; D015444:Exercise; D005260:Female; D006339:Heart Rate; D006801:Humans; D007700:Kinetics; D008168:Lung / Q000098:blood supply / Q000378:metabolism / Q000502:physiology; D008297:Male; D008955:Models, Cardiovascular; D018482:Muscle, Skeletal / Q000098:blood supply / Q000378:metabolism / Q000502:physiology*; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption; D011659:Pulmonary Gas Exchange; D012123:Pulmonary Ventilation; D013269:Stochastic Processes
chemical_list: D010100:Oxygen