MAXIMAL OXYGEN-UPTAKE RELATIVE TO PLASMA-VOLUME EXPANSION

Controversy exists as to whether plasma volume (PV) expansion has the potential to increase maximal oxygen uptake (VO2 max). In the present study, VO2 (max) and exercise time to fatigue were measured in nine untrained men when plasma volum (PV) was normal and then again on the next day following two levels of PV expansion. Resting PV was expanded (via intravenous infusion of a 6% dextran solution) by 282 ± 16 ml (i.e., PVX-1) and then by 624 ± 26 ml (i.e., PVX-2). PVX-1 increased stroke volume (CO2 rebreathing) during submaximal exercise by 15% (P < 0.05) above normal levels. VO2 (max) following PVX-1 was increased 4% (P < 0.05; 3.78 to 3.92 1/min) despite a 4% reduction in hemoglobin concentration. Exercise time to fatigue was also increased (P < 0.05). PVX-2 resulted in an 11% (P < 0.05) reduction in hemoglobin concentration during maximal exercise and a return of VO2 (max) and exercise time to normal levels. In summary, we have observed in untrained men that 200-300 ml of PV expansion increases SV, measured during submaximal exercise, yet causes only a small amount of hemodilution. As a result, VO2 (max) is increased slightly and performance is improved. Further Pv expansion to levels 500-600 ml above normal results in an excessive hemodilution and a subsequent decline in VO2 (max) and performance to normal levels. There is an optimal PV for eliciting VO2 (max) in untrained men which appears to be approximately 200-300 ml above their normal levels.