Ventilation/carbon dioxide output relationships during exercise in health

"Ventilatory efficiency" is widely used in cardiopulmonary exercise testing to make inferences regarding the normality (or otherwise) of the arterial CO2 tension (PaCO2) and physiological dead-space fraction of the breath (VD/VT) responses to rapid-incremental (or ramp) exercise. It is quantified as: 1) the slope of the linear region of the relationship between ventilation (V'E) and pulmonary CO2 output (V'CO2); and/or 2) the ventilatory equivalent for CO2 at the lactate threshold (V'E/V'CO2 ) or its minimum value (V'E/V'CO2min), which occurs soon after but before respiratory compensation. Although these indices are normally numerically similar, they are not equally robust. That is, high values for V'E/V'CO2 and V'E/V'CO2min provide a rigorous index of an elevated VD/VT when PaCO2 is known (or can be assumed) to be regulated. In contrast, a high V'E–V'CO2 slope on its own does not, as account has also to be taken of the associated normally positive and small V'E intercept. Interpretation is complicated by factors such as: the extent to which PaCO2 is actually regulated during rapid-incremental exercise (as is the case for steady-state moderate exercise); and whether V'E/V'CO2 or V'E/V'CO2min provide accurate reflections of the true asymptotic value of V'E/V'CO2, to which the V'E–V'CO2 slope approximates at very high work rates.
Source: European Respiratory Review - Category: Respiratory Medicine Authors: Tags: Mechanisms of lung disease Ventilatory efficiency and its clinical prognostic value in cardiorespiratory disorders Source Type: research