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. Author manuscript; available in PMC: 2021 Feb 1.
Published in final edited form as: J Physiol. 2020 Jan 19;598(3):599–610. doi: 10.1113/JP279135

Figure 4. Convective and diffusive components of peripheral O2 transport at peak small muscle mass exercise.

Figure 4.

An illustration of the peripheral O2 transport determinants of muscle peak O2 uptake (V̇MO2peak) in both patients with chronic obstructive pulmonary disease (COPD) (n = 8) and control subjects (n = 8) during single leg knee-extension exercise. The Fick principle (convective O2 transport, sigmoidal lines) and Fick’s law of diffusion (diffusive O2 transport, linear lines) are integrated in a model linking V̇MO2peak and venous O2 partial pressure (PvO2). It is the intersection of the convective and diffusive O2 transport components that dictates the V̇MO2peak for each group. This model clearly depicts that the ≈36% lower V̇MO2peak in the patients with COPD compared to the control subjects was the result of both a ≈36% lower muscle O2 delivery (Q̇MO2) and ≈36% diffusional conductance (ḊMO2). Importantly, this model emphasizes the integrated nature of V̇MO2peak, as it is evident that an independent change in either Q̇MO2 or ḊMO2 would have resulted in a substantially smaller alteration (≈25%) in V̇MO2peak in the patients with COPD.