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Figure 4


Fig. 4. Estimating D by fitting simple equations to complicated biological situations. When O2 is consumed by metabolic processes, estimating D in biological structures is non-trivial, as metabolism draws down interior O2 levels and alters the time course of change after external step changes. Here we simulated step change traces under both first-order and Michaelis–Menten reaction kinetics and then fitted a simple equation (Eqn. 9) to the simulated traces. Under first-order kinetics (A), estimated D was good when initial drawdown (or Formula 9) was small. At higher k, giving greater initial drawdown, fitted D increasingly overestimated the known D used in the simulations (3x10–6). Under Michaelis–Menten kinetics (B), estimated D was again good when initial drawdown was small. At higher Vmax, giving greater initial drawdown, the down- and up-traces were highly asymmetrical. In this case, fitted D from the up-trace always gave values closer to the known, simulated value.





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