Comparison of gas exchange, lactate, and lactic acidosis thresholds in patients with chronic obstructive pulmonary disease

Am Rev Respir Dis. 1993 Sep;148(3):622-6. doi: 10.1164/ajrccm/148.3.622.


During an incremental exercise test, three consequences of the onset of anaerobic metabolism can be observed: rise in blood lactate (lactate threshold, LT); fall in standard bicarbonate (lactic acidosis threshold, LAT); nonlinear increase in CO2 output (V-slope gas exchange threshold, GET). We compared these thresholds in 31 patients with COPD. We found that the GET and LAT overestimated the LT. A better relationship was found between LAT and GET, even though GET was significantly higher than LAT (by 124 ml/min; p < 0.0001). However, since the bias is appreciably greater at lower LAT values (likely because VCO2 kinetics are slower than VO2 kinetics), we separated the studies into two groups: (A) tests where LAT occurred within the first 2 min of the increasing work rate period, and (B) tests where LAT occurred after 2 min. For Group A, there was a substantial bias between LAT and GET (323 ml/min, p < 0.0001), whereas the bias was much smaller (only 5.4%, though statistically significant) for Group B (57 ml/min, p < 0.01). We conclude that when lactic acidosis occurs after the first 2 min of incremental exercise, the GET closely approximates the point at which blood bicarbonate begins to fall.

Publication types

  • Comparative Study

MeSH terms

  • Acidosis, Lactic / blood
  • Acidosis, Lactic / physiopathology*
  • Acidosis, Lactic / rehabilitation
  • Anaerobic Threshold
  • Bicarbonates / blood
  • Carbon Dioxide / physiology
  • Exercise Test
  • Humans
  • Lactates / blood*
  • Lactic Acid
  • Lung Diseases, Obstructive / blood
  • Lung Diseases, Obstructive / physiopathology*
  • Lung Diseases, Obstructive / rehabilitation
  • Male
  • Middle Aged
  • Pulmonary Gas Exchange*
  • Spirometry
  • Time Factors


  • Bicarbonates
  • Lactates
  • Carbon Dioxide
  • Lactic Acid