Dynamic and steady-state metabolic changes in running dogs

Dynamic and steady-state changes of V̇_O2, V̇E, V̇_CO2, Pa_O2 and blood lactate concentration (La_b) were studied in 4 intact (I) and in the same tracheostomized (T) dogs walking or running uphill (+ 10%) on a treadmill at speeds up to 12 km · h^-1. A) Non-steady state results: The half times of the V̇_O2 on-response (t _{1 2} V ̇_O2on-) to rectangular work loads were 18.9 sec ± 1.2 (SE) in I and 15.6 sec ± 1.0 in T dogs (P < 0.05), independent of work intensity and similar to those found for isolated perfused dog gastrocnemii (15-17 sec). La_b during the rest to work transient was almost unchanged. B) Steady-state results: V̇_O2 and V̇E increased with increasing speed up to 8 km · h^-1 (+ 10%) then levelled off both in I and T. Asymptotic V̇_O2 and V̇E values were higher for I than for T ( V ̇_O2 = 93 and 83 ml · kg^-1 · min^-1; V ̇E = 2.6 and 1.75 1 · kg^-1 · min^-1, respectively). Calculated ΔV_O2/ΔVE ratios for equal external work loads indicate that the energy cost of breathing was about 12 ml O₂ per liter V̇E. From (A) it is concluded that the adjustment of oxidative reactions upon work onset is as fast for the whole animal as for isolated gastrocnemius and can be assessed from gas exchange in the upper airways. From (B) it appears that, in the absence of glycolysis, the cost of running per unit distance decreases with increasing speed while the cost of V̇E becomes a sizeable part of the overall energy expenditure.