Strategies of exercise testing in chronic lung disease
Brown, H.V.; Wasserman, K.; Whipp, B.J.
Bulletin Europeen de Physiopathologie Respiratoire 13(3): 409-423
1977
ISSN/ISBN: 0395-3890 PMID: 880402 Document Number: 112904
The mechanisms of exercise intolerance in patients with chronic obstructive pulmonary disease (COPD) are intimately related to the underlying pulmonary pathophysiology and include mechanical factors, ventilatory inefficiency and gas exchange abnormalities. Airflow obstruction causes reduction in maximal exercise ventilation and consequently limits work capacity. Ventilatory efficiency, as measured by the wasted ventilation fraction of each breath (VD/VT) [ventilatory dead space/tidal volume] may also be abnormal during exercise, requiring increased minute ventilation in order to maintain normal levels of arterial PCO2 [CO2 tension]. If alveolar ventilation is inappropriately low during exercise, secondary to inadequate minute ventilation, an abnormally high VD/VT or hypercapnia will ensue. Hypoxemia may also occur during exercise, either as a result of hypoventilation with hypercapnia (normal (A-a)PO2 [alveolar arterial O2 tension] difference), ventilation-perfusion mismatching, right-to-left shunting, or diffusion abnormalities. In the presence of an increased (A-a)PO2 difference during exercise, 100% O2 breathing will separate the contribution of right-to-left shunt from that of diffusion and ventilation-perfusion abnormalities. Testing procedures utilizing cycle ergometry and incremental exercise protocols are useful in uncovering these physiologic abnormalities in patients with COPD. The incremental work test produces highly reproducible results and may be used in patients with both mild and severe impairments. Using non-invasive techniques, measurements can be made of minute ventilation, tidal volume, breathing frequency, the expiratory air flow pattern, ECG complexes and heart rate. If CO2 and O2 analyzers are available, O2 consumption, CO2 production, the gas exchange ratio, O2 pulse and the ventilatory equivalents for O2 and CO2 can be determined. Invasive techniques such as percutaneous arterial catheterization allow sampling for arterial blood gas and acid-base analysis and direct measurement of arterial blood pressure. Pulmonary artery catheterization may be used during exercise to determine mixed venous gas tensions, pulmonary vascular resistance and cardiac output. Appropriate measurements during exercise make it possible to quantify the patient's work intolerance and identify the associated physiologic abnormalities.