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Cardiopulmonary Exercise Testing: How Do We Differentiate the Cause of Dyspnea?

Case report: A 54-year-old man is referred for dyspnea on exertion. He has a history of type II diabetes and 35 pack-years of smoking. He suffered an anterior myocardial infarction 14 months ago, and on recent echocardiography was found to have an ejection fraction of 25%. Since his myocardial infarction, he has quit smoking and has gained an additional 27 pounds. He admits to a sedentary lifestyle and has recently tried to initiate an exercise program in an effort to lose weight. His current body mass index is 33.4 kg/m2. He denies orthopnea but does have progressive lower-extremity edema.

What is the primary cause of his dyspnea? Is it ventilatory or circulatory? Obesity or deconditioning? What is the prognosis for his ischemic cardiomyopathy? What would be the appropriate diagnostic study to obtain these answers?

Exercise stress testing is commonly used in clinical practice to evaluate the presence and severity of coronary ischemia. A significant enhancement of clinical information available during exercise can be obtained by concurrent measurement of respiratory gas exchange via use of a metabolic cart. This modality of stress testing has been called cardiopulmonary stress testing (CPX). This article will update the cardiovascular clinician on the utility of CPX in the modern cardiovascular practice.

A major function of the cardiovascular system is gas exchange, supplying O2 and other fuels to working muscles, as well as removal of CO2 and other metabolites. The heart, lungs, and pulmonary and systemic circulations form a single circuit for exchange of respiratory gases between the environment and the cells of the body.1,2 Under steady-state conditions, respiratory oxygen uptake (Vo2) and carbon dioxide outflow (Vco2) measured at the mouth are equivalent to oxygen utilization (![Graphic][1] o2) and carbon dioxide production (![Graphic][2] co2) occurring in the …

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