title: Distinguishing the effects of convective and diffusive O₂ delivery on VO₂ on-kinetics in skeletal muscle contracting at moderate intensity.
abstract: With current techniques, experimental measurements alone cannot characterize the effects of oxygen blood-tissue diffusion on muscle oxygen uptake (Vo₂) kinetics in contracting skeletal muscle. To complement experimental studies, a computational model is used to quantitatively distinguish the contributions of convective oxygen delivery, diffusion into cells, and oxygen utilization to Vo₂ kinetics. The model is validated using previously published experimental Vo₂ kinetics in response to slowed blood flow (Q) on-kinetics in canine muscle (τQ = 20 s, 46 s, and 64 s) [Goodwin ML, Hernández A, Lai N, Cabrera ME, Gladden LB. J Appl Physiol. 112:9-19, 2012]. Distinctive effects of permeability-surface area or diffusive conductance (PS) and Q on Vo₂ kinetics are investigated. Model simulations quantify the relationship between PS and Q, as well as the effects of diffusion associated with PS and Q dynamics on the mean response time of Vo₂. The model indicates that PS and Q are linearly related and that PS increases more with Q when convective delivery is limited by slower Q dynamics. Simulations predict that neither oxygen convective nor diffusive delivery are limiting Vo₂ kinetics in the isolated canine gastrocnemius preparation under normal spontaneous conditions during transitions from rest to moderate (submaximal) energy demand, although both operate close to the tipping point.
authors.affiliation: Departments of Biomedical Engineering, Case Western Reserve Univ., Cleveland, OH 44106-7207, USA.
authors.forename: Jessica
authors.initials: J
authors.lastname: Spires
authors.forename: L Bruce
authors.initials: LB
authors.lastname: Gladden
authors.forename: Bruno
authors.initials: B
authors.lastname: Grassi
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Goodwin
authors.forename: Gerald M
authors.initials: GM
authors.lastname: Saidel
authors.forename: Nicola
authors.initials: N
authors.lastname: Lai
mesh_terms: D000818:Animals; D003198:Computer Simulation; D004285:Dogs; D007700:Kinetics; D008657:Metabolic Clearance Rate; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D010100:Oxygen / Q000008:administration & dosage / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*
chemical_list: D010100:Oxygen
keywords: diffusion; modeling; permeability-surface area; tipping point; transport