Influence of acute plasma volume expansion on V̇O ₂ kinetics, V̇O _{2 peak}, and performance during high-intensity cycle exercise

The purpose of this study was to examine the influence of acute plasma volume expansion (APVE) on oxygen uptake (V̇O ₂) kinetics, V̇O _{2 peak}, and time to exhaustion during severe-intensity exercise. Eight recreationally active men performed "step" cycle ergometer exercise tests at a work rate requiring 70% of the difference between the gas-exchange threshold and V̇O ₂ max on three occasions: twice as a "control" (Con) and once after intravenous infusion of a plasma volume expander (Gelofusine; 7 ml/kg body mass). Pulmonary gas exchange was measured breath by breath. APVE resulted in a significant reduction in hemoglobin concentration (preinfusion: 16.0 ± 1.0 vs. postinfusion: 14.7 ± 0.8 g/dl; P < 0.001) and hematocrit (preinfusion: 44 ± 2 vs. postinfusion: 41 ± 3%; P < 0.01). Despite this reduction in arterial O ₂ content, APVE had no effect on V̇O ₂ kinetics (phase II time constant, Con: 33 ± 15 vs. APVE: 34 ± 12 s; P = 0.74), and actually resulted in an increased V̇O _{2 peak} (Con: 3.90 ± 0.56 vs. APVE: 4.12 ± 0.55 l/min; P = 0.006) and time to exhaustion (Con: 365 ± 58 vs. APVE: 424 ± 64 s; P = 0.04). The maximum O ₂ pulse was also enhanced by the treatment (Con: 21.3 ± 3.4 vs. APVE: 22.7 ± 3.4 ml/beat; P = 0.04). In conclusion, APVE does not alter V̇O ₂ kinetics but enhances V̇O _{2 peak} and exercise tolerance during high-intensity cycle exercise in young recreationally active subjects.