Dynamic and steady-state metabolic changes in running dogs

Dynamic and steady-state changes of VO2, VE, VCO2, PaO2 and blood lactate concentration (Lab) 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 X h-1. A) Non-steady state results: The half times of the VO2 on-response (t1/2 VO2 on-) to rectangular work loads were 18.9 sec +/- 1.2 (SE) in I and 15.6 sec +/- 1.0 in T dogs (P less than 0.05), independent of work intensity and similar to those found for isolated perfused dog gastrocnemii (15-17 sec). Lab during the rest to work transient was almost unchanged. B) Steady-state results: VO2 and VE increased with increasing speed up to 8 km X h-1 (+ 10%) then levelled off both in I and T. Asymptotic VO2, and VE values were higher for I than for T (VO2 = 93 and 83 ml X kg-1 X min-1; VE = 2.6 and 1.75 l X kg-1 X min-1, respectively). Calculated delta VO2/delta VE ratios for equal external work loads indicate that the energy cost of breathing was about 12 ml O2 per liter VE. 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 VE becomes a sizeable part of the overall energy expenditure.