title: Cardiac output during exercise: a comparison of four methods.
abstract: Several techniques assessing cardiac output (Q) during exercise are available. The extent to which the measurements obtained from each respective technique compares to one another, however, is unclear. We quantified Q simultaneously using four methods: the Fick method with blood obtained from the right atrium (Q(Fick-M)), Innocor (inert gas rebreathing; Q(Inn)), Physioflow (impedance cardiography; Q(Phys)), and Nexfin (pulse contour analysis; Q(Pulse)) in 12 male subjects during incremental cycling exercise to exhaustion in normoxia and hypoxia (FiO2  = 12%). While all four methods reported a progressive increase in Q with exercise intensity, the slopes of the Q/oxygen uptake (VO2) relationship differed by up to 50% between methods in both normoxia [4.9 ± 0.3, 3.9 ± 0.2, 6.0 ± 0.4, 4.8 ± 0.2 L/min per L/min (mean ± SE) for Q(Fick-M), Q(Inn), QP hys and Q(Pulse), respectively; P = 0.001] and hypoxia (7.2 ± 0.7, 4.9 ± 0.5, 6.4 ± 0.8 and 5.1 ± 0.4 L/min per L/min; P = 0.04). In hypoxia, the increase in the Q/VO2 slope was not detected by Nexfin. In normoxia, Q increases by 5-6 L/min per L/min increase in VO2, which is within the 95% confidence interval of the Q/VO2 slopes determined by the modified Fick method, Physioflow, and Nexfin apparatus while Innocor provided a lower value, potentially reflecting recirculation of the test gas into the pulmonary circulation. Thus, determination of Q during exercise depends significantly on the applied method.
authors.affiliation: Center for Integrative Human Physiology, Institute of Physiology, University of Zürich, Zürich, Switzerland.
authors.forename: C
authors.initials: C
authors.lastname: Siebenmann
authors.forename: P
authors.initials: P
authors.lastname: Rasmussen
authors.forename: H
authors.initials: H
authors.lastname: Sørensen
authors.forename: M
authors.initials: M
authors.lastname: Zaar
authors.forename: M
authors.initials: M
authors.lastname: Hvidtfeldt
authors.forename: A
authors.initials: A
authors.lastname: Pichon
authors.forename: N H
authors.initials: NH
authors.lastname: Secher
authors.forename: C
authors.initials: C
authors.lastname: Lundby
mesh_terms: D000328:Adult; D006328:Cardiac Catheterization / Q000379:methods; D002302:Cardiac Output / Q000502:physiology*; D002307:Cardiography, Impedance / Q000379:methods; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test / Q000379:methods*; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D009609:Nitrous Oxide / Q000032:analysis; D010101:Oxygen Consumption / Q000502:physiology*; D063177:Pulse Wave Analysis / Q000379:methods; D055815:Young Adult
chemical_list: D009609:Nitrous Oxide
keywords: Inert gas rebreathing; hypoxia; impedance cardiography; maximal oxygen uptake; pulse contour analysis