Explain the concept of the ventilation threshold and how it is determined

Answer 1

As the work rate increases during an incremental load exercise test, there is a rapid increase in VO2, VCO2, and ventilation. This continues until the ventilation threshold—or the appearance of lactate in the venous blood, indicating a greater production of lactate than the clearance of lactate—is reached, at which time the CO2 expired is greater than the VO2 because the CO2 generated from the buffering reaction of the bicarbonate with the lactic acid is added to the metabolically produced CO2 . At this workload, the increase in Ve is equivalent to the increase in VeCO2 and results in a constant ventilatory equivalent for CO2 . However, at this same ventilation-threshold workload, the Ve-VO2 ratio, or ventilatory equivalent for O2 (VEO2), is increased. Since the chemoreceptor drive to ventilation is primarily a result of CO2, the workload at which the increase in the VEO2 occurs without a change in VECO2 is the workload at which the ventilation threshold begins. These measures provide a sensitive, noninvasive method of identifying the ventilation threshold without having to actually measure arterial or venous lactate concentrations.