Ventilatory response to exercise in cardiopulmonary disease: the role of chemosensitivity and dead space.

The lungs and heart are irrevocably linked in their oxygen (O) and carbon dioxide (CO) transport functions. Functional impairment of the lungs often affects heart function and The steepness with which ventilation (') rises with respect to CO production (' ) ( the '/' slope) is a measure of ventilatory efficiency and can be used to identify an abnormal ventilatory response to exercise. The '/' slope is a prognostic marker in several chronic cardiopulmonary diseases independent of other exercise-related variables such as peak O uptake (' ). The '/' slope is determined by two factors: 1) the arterial CO partial pressure ( ) during exercise and 2) the fraction of the tidal volume () that goes to dead space () ( the physiological dead space ratio (/)). An altered set-point and chemosensitivity are present in many cardiopulmonary diseases, which influence '/' by affecting Increased ventilation-perfusion heterogeneity, causing inefficient gas exchange, also contributes to the abnormal '/' observed in cardiopulmonary diseases by increasing / During cardiopulmonary exercise testing, the during exercise is often not measured and / is only estimated by taking into account the end-tidal CO partial pressure ( ); however, is not accurately estimated from in patients with cardiopulmonary disease. Measuring arterial gases ( and ) before and during exercise provides information on the real (and not "estimated") / coupled with a true measure of gas exchange efficiency such as the difference between alveolar and arterial O partial pressure and the difference between arterial and end-tidal CO partial pressure during exercise.