Lactate Breakpoint during Slowly Increasing Work Rates and Irregular Breathing

Abstract

The breakpoint (BP) in lactate (La) was determined using the noninvasive V-slope and VE/VO2 methods. Eight normal male subjects performed three maximal graded exercise tests (GXT) with 3-min work stages during normal breathing (NB) and during irregular breathing with hypoventilation (IB-HV). The IB-HV resulted in mild but significantly increased arterialized-venous PCO2, PETCO2 and irregular VE/VO2 and irregular breathing frequency. The correlation coefficients for linear regressions of the La BP with the V-slope and VE/VO2 BPs during NB were: 0.77 (p < 0.05) and 0.79 (p < 0.05), respectively, and during IB-HV the correlations coefficients were: 0.82 (p < 0.05) and -0.02 (p > 0.05) for V-slope and VE/VO2 BPs, respectively. The differences were more apparent from the regression coefficients with the La BP; the slopes with NB for V-slope and VE/VO2 BPs were 1.06 +/- 0.40 SEM and 1.38 +/- 0.43; the intercepts with NB were -0.22 +/- 0.24 and -0.67 +/- 0.33, respectively. During IB-HV the slopes for the V-slope and VE/VO2 were 1.02 +/- 0.29 and -0.02 +/- 0.47, and the intercepts were -0.11 +/- 0.40 and 1.57 +/- 0.64, respectively. The VE/VO2 slope and intercept with IB-HV were notably different. It was concluded that the V-slope and VE/VO2 methods determine the La BP with 3-min stages during NB, whereas only the V-slope method determined the La BP with IB-HV.