Abstract

We measured blood lactate in normal subjects after 10 minutes of sustained maximum voluntary ventilation (SMVV) with end-tidal Pco₂ kept constant and after breathing against a big added respiratory load for 200 breaths. With SMVV subjects sustained on average 68% of the predicted maximum breathing capacity and achieved final lactate concentrations of 1·9 mmol/l (17·1 mg/100 ml), representing an average increase of about 1·0 mmol/l (9·0 mg/100 ml) over resting values. There was a wide range between individuals, from no increase at all to 2·7 mmol/l, despite similar levels of ventilation. Breathing against added loads produced much smaller changes in blood lactate.