title: Oxygen uptake kinetics at work onset: role of cardiac output and of phosphocreatine breakdown.
abstract: The hypothesis that variability in individual's cardiac output response affects the kinetics of pulmonary O₂ uptake (VO₂) was tested by investigating the time constants of cardiac output (Q) adjustment (τ(Q)), of PCr splitting (τ(PCr)), and of phase II pulmonary O₂ uptake (τ(VO₂)) in eight volunteers. VO₂, Q, and gastrocnemius [PCr] (by (31)P-MRS) were measured at rest and during low intensity two-legged exercise. Steady state VO₂ and Q increased (ΔVO₂(s) = 182 ± 58 mL min⁻¹; ΔQ = 1.3 ± 0.4 L min⁻¹), whereas [PCr] decreased significantly (21 ± 8%). τ(VO₂), τ(PCr) and τ(Q) were significantly different from each other (38.3 ± 4.0, 23.9 ± 2.5, 11.6 ± 4.6 s, respectively; p<0.001). τ(PCr) assumed to be equal to the time constant of VO₂ at the muscle level (τ(mVO₂)), was not related to τ(Q), whereas τ(VO₂) and τ(Q) were significantly related (p<0.05) as were τ(VO₂) and τ(PCr) (p<0.05). Venous blood O₂ stores changes, as determined from arterio-to-mixed-venous O₂ content, were essentially equal to those estimated as (τ(VO₂)-τ(PCr))·ΔVO₂(s). This suggests that cardiac output responses affect O₂ stores utilization and hence τ(VO₂) : thus τ(VO₂) is not necessarily a good estimate of τ(mVO₂).
authors.affiliation: Department of Medical and Biological Sciences, University of Udine, 33100 Udine, Italy. maria.francescato@uniud.it
authors.forename: M P
authors.initials: MP
authors.lastname: Francescato
authors.forename: V
authors.initials: V
authors.lastname: Cettolo
authors.forename: P E
authors.initials: PE
authors.lastname: di Prampero
mesh_terms: D000328:Adult; D002302:Cardiac Output / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005260:Female; D006339:Heart Rate; D006801:Humans; D007700:Kinetics; D008297:Male; D015999:Multivariate Analysis; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption; D010725:Phosphocreatine / Q000378:metabolism*; D011659:Pulmonary Gas Exchange; D013223:Statistics as Topic; D055815:Young Adult
chemical_list: D010725:Phosphocreatine; D010100:Oxygen