Measurement and Interpretation of Exercise Ventilatory Efficiency

Abstract

Cardiopulmonary exercise testing (CPET) is a method for evaluating pulmonary and cardiocirculatory abnormalities, dyspnea, and exercise tolerance in healthy individuals and patients with chronic conditions. During exercise, ventilation (V E) increases in proportion to metabolic demand [i.e., carbon dioxide production (V CO 2)] to maintain arterial blood gas and acid-base balance. The response of V E relative to V CO 2 (V E /V CO 2) is commonly termed ventilatory efficiency and is becoming a common physiological tool, in conjunction with other key variables such as operating lung volumes, to evaluate exercise responses in patients with chronic conditions. A growing body of research has shown that the V E /V CO 2 response to exercise is elevated in conditions such as chronic heart failure (CHF), pulmonary hypertension (PH), interstitial lung disease (ILD), and chronic obstructive pulmonary disease (COPD). Importantly, this potentiated V E /V CO 2 response contributes to dyspnea and exercise intolerance. The clinical significance of ventilatory inefficiency is demonstrated by findings showing that the elevated V E /V CO 2 response to exercise is an independent predictor of mortality in patients with CHF, PH, and COPD. In this article, the underlying physiology, measurement, and interpretation of exercise ventilatory efficiency during CPET are reviewed. Additionally, exercise ventilatory efficiency in varying disease states is briefly discussed.

Importance of Cardiopulmonary Exercise Testing amongst Subjects Recovering from COVID-19

“…The cardiopulmonary exercise test (CPET) provides an objective assessment of exercise capacity, adding physiological aspects that limit the individual’s performance [ 3 ]. In particular, the exercise minute ventilation (V E ) relative to carbon dioxide output (V CO2 ) (V E /V CO2 ) shows complementary information about ventilatory limitation and ventilatory control [ 4 , 5 ]. During incremental exercise, the relationship between V E and V CO2 may be plotted on a y -axis (V E ) and x -axis (V CO2 ); the slope of this regression line (V E /V CO2 slope ) may be considered an indicator of ventilatory efficiency [ 4 , 5 ].…”

“…In particular, the exercise minute ventilation (V E ) relative to carbon dioxide output (V CO2 ) (V E /V CO2 ) shows complementary information about ventilatory limitation and ventilatory control [ 4 , 5 ]. During incremental exercise, the relationship between V E and V CO2 may be plotted on a y -axis (V E ) and x -axis (V CO2 ); the slope of this regression line (V E /V CO2 slope ) may be considered an indicator of ventilatory efficiency [ 4 , 5 ]. Lower and upper limits of normal range of V E /V CO2 slope are reported from approximately 21 to 31 [ 4 , 6 , 7 ].…”

“…During incremental exercise, the relationship between V E and V CO2 may be plotted on a y -axis (V E ) and x -axis (V CO2 ); the slope of this regression line (V E /V CO2 slope ) may be considered an indicator of ventilatory efficiency [ 4 , 5 ]. Lower and upper limits of normal range of V E /V CO2 slope are reported from approximately 21 to 31 [ 4 , 6 , 7 ]. High values of V E /V CO2 slope define an exercise ventilatory inefficiency (EV in ) [ 4 , 5 ]; this pathophysiological feature may explain the out-of-proportion breathlessness of patients with chronic obstructive pulmonary disease (COPD) [ 5 ].…”

“…Lower and upper limits of normal range of V E /V CO2 slope are reported from approximately 21 to 31 [ 4 , 6 , 7 ]. High values of V E /V CO2 slope define an exercise ventilatory inefficiency (EV in ) [ 4 , 5 ]; this pathophysiological feature may explain the out-of-proportion breathlessness of patients with chronic obstructive pulmonary disease (COPD) [ 5 ]. Smokers with normal spirometry but with low values of DL CO may have EV in [ 8 ].…”

Motor Pathophysiology Related to Dyspnea in COPD Evaluated by Cardiopulmonary Exercise Testing

“…The forced expiratory volume in one second (FEV 1 ) is an important indicator that correlates well with minute ventilation ( V’ E ), but has a weak relationship with exercise tolerance [ 12 ]. This distinction reflects the fact that the ventilatory efficiency is related to wasted ventilation [ 13 , 14 , 15 ] and to the fact that the difference between inspired and expired oxygen concentrations (measured as the difference between average inspired oxygen concentration and average expired oxygen concentration) [ 9 , 10 ], not just the ventilation amount, is related to exercise tolerance. In this context, it is worth noting that oxygen uptake ( V’ O2 ) is determined using an equation that includes the product of V’ E and the difference between inspired and expired oxygen concentrations, and that the average expired oxygen concentration is dependent on the collective cardiac, pulmonary and muscular metabolism [ 9 , 10 ].…”