Measurement of Anaerobic Threshold in Chronic Airflow Obstruction

Abstract

We compared determinations of anaerobic threshold (AT) made from measurements of arterial lactate concentration with AT determined from ventilatory response measurements of subjects with chronic airflow obstruction (CAO). Six untrained subjects with CAO performed incremental maximal cycle ergometer tests. Ventilation (V_E); O₂ uptake (V_O2), CO₂ output (V_co2); end-tidal CO₂ fraction (F_ETCO2); and end-tidal O₂ fraction (F_ETO2) were measured breath by breath. Arterial lactate concentration was sampled at rest and every 30 s during exercise from an indwelling arterial catheter. For three subjects with more severe airflow obstruction, plots of V_E/Vo₂ and F_ETO2 failed to detect AT. In contrast, a systematic increase of the respiratory gas exchange ratio across the lung (R) accompanied increasing arterial lactate concentrations in all 6 subjects. We conclude that progressive increases of V_E/V_O2 and F_ETO2 cannot be relied upon for the measurement of AT in patients with severe CAO. Progressive increases of R unaccompanied by decreasing F_ETCO2 detect AT in CAO