893506.fig.006a
893506.fig.006b
Figure 6: (a) The coincidence of the lactate threshold and hyperventilation (falling PaCO2) in normal subjects. Mean lactate ( ), bicarbonate (—), lactate/pyruvate ratio, pHa, and PaCO2 levels during 1 min () and 4 min (∘) incremental work tests at external work rates indicated. (b) The coincidence of the lactate threshold and hyperventilation in normal subjects. Mean ( ), CO2 production ( ), metabolic rate ( ), gas exchange ratio ( ), PetCO2, and change in PetO2 at external work rates indicated in the same subjects as (a). (a) and (b) reproduced with permission from Wasserman et al. [89]. (c) The correlation between breathing ( ) and [ ]a or PaCO2 during exercise averaged over 16 subjects. is scaled for each study to a VCP at 70 L/min (the mean at the VCP for all subjects). The lowest point for each study is scaled to 17 L/min (the mean unloaded pedalling for all subjects). The diagonal dashed line is the regression line of the averaged data in the below VCP region. The labelled horizontal dashed lines indicate the mean values at the VCP (the point when begins to accelerate out of proportion to the increase in and the LAT (lactic acidosis threshold)). The other labelled horizontal dashed line indicates the mean at the LAT for the 16 subjects. The average is linearly related to [ ] up to the VCP, as indicated by . The individual points are the transformed data points used in calculating the average curve up to the VCP. The data for all 16 subjects are used in this calculation. Above the VCP, subjects drop out because of differences in exercise tolerance. The remaining studies are shifted along the [ ] axis to provide an accurate representation of the remaining data. The number of subjects determining the average curve decreases to 15, 15, 8, 5, and 4 at [ ] values of 45, 46, 48, 49, and 50 nmol/L, respectively. (d) Zigzags in the correlation between [ ]a and breathing during exercise in 16 individual subjects. The points on the respective curves identify the blood sample points. Each plot starts at the beginning of linearly increasing work rate and ends at the cessation of exercise after the highest [ ]a and are reached. The at the ventilatory compensation point (VCP), defined as the disproportionate increase in relative to as work rate increases (start of hyperventilation with respect to CO2), statistically determined, is indicated by the horizontal line. (c) and (d) reprinted from [74] with permission from Elsevier.