Ventilatory Thresholds (VT1 & VT2)

Ventilatory thresholds are determined from breath-by-breath gas-exchange during an incremental cardiopulmonary exercise test (CPET).

• VT1 (FeO₂) (1) – first ventilatory threshold: the workload at which expired O₂ fraction (FeO₂) and VE/VO₂ start to rise systematically while VE/VCO₂ and end-tidal CO₂ remain stable, indicating the transition from purely aerobic to mixed aerobic–anaerobic metabolism.
• VT2 (Ve) (1) – second ventilatory threshold (respiratory compensation point): the workload at which minute ventilation (VE) shows a clear second, non-linear increase relative to workload or VCO₂ because of respiratory compensation for metabolic acidosis.
• VT2_DVE (2) – VE-curve method: derived from the VE–time (or VE–workload) curve alone and defined as the workload where VE leaves its previous near-linear trend and enters the main "bend" of the curve—the onset of the sharp upswing in VE, rather than the exact mathematical intersection of the two surrounding slopes.
• VT2_CO₂ (3) – CO₂-based method: the workload where end-tidal CO₂ (PETCO₂) reaches a peak and then falls while VE/VCO₂ begins to rise, indicating the onset of respiratory compensation for metabolic acidosis.

References

1. Wasserman K, Whipp BJ, Koyal SN, Beaver WL. Anaerobic threshold and respiratory gas exchange during exercise. Journal of Applied Physiology. 1973;35(2):236–243.
2. Neder JA, Stein R. A simplified strategy for the estimation of the exercise ventilatory thresholds. Medicine and Science in Sports & Exercise. 2006;38(5):1007–1013.
3. Mezzani A. Cardiopulmonary Exercise Testing: Basics of Methodology and Measurements. Annals of the American Thoracic Society. 2017;14(Supplement_1):S3–S11.