What is a cardiopulmonary metabolic stress test?

A cardiopulmonary metabolic exercise stress test is also referred to as a CPX test or a VO2-Max test. This is a special type of exercise test that measures your combined heart and lung function and your body’s ability to use oxygen at rest and with exercise. You walk on a treadmill while attached to a special breathing monitor/ apparatus. Sometimes a bicycle is used.

This special breathing apparatus is called a “metabolic cart,” and it uses sophisticated technology that precisely quantifies your oxygen intake, carbon dioxide exhalation, your metabolic rate (your body’s baseline energy expenditure without exercise), as well as your heart’s and lung’s ability to properly process and use oxygen while exercising.

Cardiopulmonary exercise testing provides important information in a patient who has heart failure. The “maximal oxygen consumption” is known as the “VO2- Max” or the “MVO2.” The VO2-Max is regulated by your heart function, and it reflects the maximum amount of oxygen that your heart can provide to your muscles during sustained activity. The VO2-Max is the point at which your body cannot increase its intake of oxygen despite an increase in exercise intensity. This is quantified as a number.

Under normal circumstances a healthy body continues to increase oxygen intake and uptake as it increases its exercise intensity. Patients who have heart failure have decreased exercise capacity and a diminished ability to properly augment oxygen intake to meet increasing body demands. They have a lower VO2-Max; a lower VO2-Max number correlates with worse heart failure symptoms as well as a worsened overall prognosis. Studies have shown that the VO2-Max is one of the strongest predictors of survival in patients with heart failure.

Because of this established correlation in heart failure patients, your maximal oxygen consumption number is considered as a part of your transplant evaluation. A healthy person should have a VO2-Max of well over 25 mL/kg/min. In most transplant centers, a VO2-Max score of less than 14 mL/kg/min qualifies you for a transplant. Of course, as with all of your pretransplant testing, your case is considered individually, but this is still an important component of your evaluation.