Ventilatory Threshold

Ventilatory threshold is an exercise intensity at which ventilation begins to increase disproportionately relative to oxygen uptake during progressively harder exercise. It is identified from changes in ventilation and respiratory gas exchange during a cardiopulmonary exercise test. The term often refers specifically to the first ventilatory threshold (VT1), although exercise physiology also recognizes a second ventilatory transition at a higher intensity .^1,2

At VT1, carbon dioxide production begins to rise more steeply relative to oxygen consumption. Ventilation increases in response to the accompanying changes in carbon dioxide production and acid-base regulation. VT1 can be estimated using patterns such as an increase in the ventilatory equivalent for oxygen (VE/VO₂) while the ventilatory equivalent for carbon dioxide (VE/VCO₂) remains relatively stable, or from a change in the relationship between carbon dioxide production and oxygen uptake known as the V-slope method .^1,2

A second ventilatory transition occurs at a higher exercise intensity and is commonly identified as the respiratory compensation point. At this point, ventilation rises disproportionately relative to carbon dioxide production as respiratory compensation for increasing metabolic acidosis becomes evident. The first ventilatory threshold and respiratory compensation point can therefore help characterize different exercise-intensity domains .^1,2

Ventilatory thresholds are related to, but not identical to, lactate thresholds. Lactate thresholds are identified from changes in blood lactate, whereas ventilatory thresholds are identified noninvasively from respiratory measurements. The corresponding transitions are often close, but the measurements and underlying definitions should not be treated as interchangeable .¹