[Common and current measurement parameters]

Abstract

The different parameters used in cardiopneumologic exercise tests allow an assessment of exercise tolerance on the basis of the subject's ventilatory response, cardiac and metabolic adaptation and gas exchanges during exercise. VO2max and dyspnea are indicators of good or poor exercise tolerance. Normal values established for adults in three reference articles depend on age, body weight and height. In a 20-year-old non sedentary subject, VO2max is approximately 45 ml/mn/kg and decreases to 25 ml/mn/kg at 65 years of age. Dyspnea is measured on two types of scales, categorical and visual analogue scales. "Minimal dyspnea" at maximal effort is normal in a healthy subject but becomes "very severe" in diseased subjects. A dyspnea threshold can be determined from the evolution of dyspnea during the test and is useful for retraining in patients with chronic obstructive lung disease. The normal ventilatory response always leaves a ventilatory reserve equal to 30% of the theoretical maximal ventilatory output. If the reserve is diminished, exercise is limited by ventilatory capacity. Gas exchanges reflect muscle adaptation to exercise and the homogeneous nature of alveolar ventilation compared with pulmonary perfusion (VA/Q). This depends on the physiological dead space (VD/VT) which is approximately 1/3 at rest decreasing to 1/4 or 1/5 at maximal exercise. VD/VT is high at rest and stays high during exercise in interstitial lung disease and vascular lung disease. VA/Q also depends on the alveo-arterial oxygen differential (P(A-a)O2) which increases two-fold during exercise. Expired gas and arterial gas must be measured simultaneously for the calculation. To measure cardiac adaptation, the ECG, heart rate and oxygen pulse (VO2/HR) must be recorded. The kinetics of oxygen pulse is more important than its maximal value, a decrease with unchanged heart rate suggests early-stage cardiomyopathy. Finally, blood lactate, the metabolic response to exercise, is used to determine the lactate threshold or the anaerobic threshold. Measurement of the ventilatory threshold is less invasive, ventilatory outflow increasing with increasing lactate level as described by the Beaver or Wassermann model. These thresholds indicate the subject's aerobic capacity. The exercise test has diagnostic value but can also be useful for individual patient management, particularly cardiorespiratory rehabilitation.