Cardiopulmonary exercise (CPX) testing is an objective method of evaluating both cardiac and pulmonary function. Cardiac function is evaluated in terms of aerobic capacity and respiratory function is evaluated by dynamic flow volume loops and VQ measurements actually performed during exercise.
The subject is exercised preferably on a bicycle ergometer or failing that a treadmill. During exercise he breathes through a mouthpiece which is in fact a minaturised pressure differential pneumotachygraph. The inspired and expired gas is continuously sampled and both oxygen uptake and carbon dioxide elimination is computed.
Not only is maximal aerobic capacity calculated but also the point during exercise where anaerobic metabolism is used to supplement aerobic metabolism as a source of energy. That point is very accurately measured via gas exchange data and is termed the anaerobic threshold or AT. Cardiac failure may be very accurately assessed in quantified fashion by use of the AT.
As postoperative mortality following major surgery is closely related to pre-existing cardiac failure, CPX testing is used at the Western Hospital (Melbourne, Australia) to routinely evaluate all elderly patients prior to major intra-cavity surgery. We have used this system since 1988 and we now have the full cooperation of the Divisions of Surgery, Anaesthesia and Intensive Care. Elsewhere on this site you may read the articles published by our group. Bear in mind this is a totally non invasive test.