Abstract

Blood lactate concentrations were measured in five patients with chronic airways obstruction after 10 minutes' sustained maximal voluntary ventilation (SMVV) with end-tidal carbon dioxide tension kept constant and after a 12-minute walk. No patient showed a significant rise in blood lactate after SMVV but all showed evidence of low-frequency fatigue of the sternomastoid muscle. After a 12-minute walk three patients showed a significant rise in blood lactate and two of them also had evidence of low-frequency fatigue of the sternomastoid muscle. The absence of a rise in blood lactate after SMVV may be due to the fact that in patients with chronic airways obstruction ventilation is limited by airflow obstruction to a level where only a small muscle mass is used, or where the aerobic capacity of the respiratory muscles is not exceeded.