Functional exercise testing: Ventilatory gas analysis
- Frank G Yanowitz, MD
Frank G Yanowitz, MD
- Professor of Medicine
- University of Utah School of Medicine
Although exercise physiologists and pulmonary physicians have used exercise testing with respiratory gas analysis for many years, its application to cardiovascular medicine is relatively new. The purpose of this review is to discuss the physiologic basis for functional exercise testing, methodologic considerations, and clinical applications. Cardiologists have used this technique most often in the evaluation and management of patients with heart failure. (See "Exercise capacity and VO2 in heart failure".)
PHYSIOLOGIC ASPECTS OF EXERCISE
An understanding of exercise physiology and the Fick equation is a prerequisite for appreciating the utility of functional exercise testing. (See "Exercise physiology".)
Aerobic parameters — The Fick equation states that oxygen uptake equals cardiac output times the arterial-mixed venous oxygen content difference. This is usually expressed as follows:
Vo2 = (SV x HR) x (CaO2 - CvO2)
where Vo2 is the oxygen (O2) uptake, SV is the stroke volume, HR is heart rate, CaO2 is arterial oxygen content, and CvO2 is the mixed venous oxygen content. Oxygen uptake is often normalized for body weight and expressed in units of mL O2/kg per min. One metabolic equivalent (MET) is the resting oxygen uptake in a sitting position and equals 3.5 mL/kg per min.
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