Cardiopulmonary exercise testing (CPET) should be considered the gold standard for evaluating the causes of exercise intolerance in patients with pulmonary and cardiac disease. It provides a global assessment of the integrative exercise response involving the pulmonary, cardiovascular, hematopoietic, neuropsychologic, and skeletal muscle systems. In spite of the widespread clinical use of CPET in the world, in our country it has been underutilized.
CPET is increasingly being used in a wide spectrum of clinical applications for the evaluation of undiagnosed exercise intolerance and for the objective determination of functional capacity, impairment and as prognostic, invaluable tool in the evaluation of patients with cardiovascular and pulmonary diseases, specifically heart failure patients.
PHYSIOLOGY OF EXERCISE
Exercise tolerance is determined by three important factors: pulmonary gas exchange, cardiovascular performance, including peripheral vascular system, and skeletal muscle metabolism. The efficient gas exchange requires: normal lungs mechanics, adequate ventilatory control mechanisms, an effective pulmonary circulation, an effective system of blood vessels, blood with normal hemoglobin of adequate concentration, a heart with the ability to pump oxygenated blood needed to sustain energy production and appropriate intracellular structure, energy substrate and enzyme concentration to permit adequate cell metabolism, especially in muscle cells. Peak exercise capacity has been defined as “the maximum ability of the cardiovascular system to deliver oxygen to the peripheral tissue and of the muscle to extract oxygen from the blood”. Therefore, it is important understand the Fick equation to appreciate the utility of this kind of test.
The Fick equation states that the oxygen uptake (VO2) equals cardiac output times the arterial minus mixed venous oxygen content. The equation is as follows:
VO2 = (Stroke Volume x Heart Rate) x (Arterial Oxygen Content – Mixed Venous Oxygen Content).
Mixed venous oxygen content (CVO2) is determined from a catheter in pulmonary artery, and systemic arterial oxygen content (CaO2) is determined from an arterial catheter. This method is the gold standard for cardiac output measurement. In the CPET VO2 measurements are made from respired gas measured at the mouth in a breath-by-breath basis, and increase in VO2 reflects O2 utilization by the muscle cells performing the work of exercise. The measurement of VO2 is based on mass balance equation: VO2 = (VI x FIO2) – (VE x FEO2). VI and VE represent the volumes of inhaled and exhaled gas; FIO2 and FEO2 represent the oxygen concentration in the inhaled and mixed exhaled gas. VI is calculated from VE. The measurement of VCO2 is easy, because FECO2 in the inhaled gas is zero and the equation is as follow: VCO2 = VE x FECO2.
The VO2 maximum defines the functional aerobic capacity of patients. It was originally defined as the VO2 at which performance of increasing levels of constant work rate exercise failed to increase VO2 by 150 ml/min, despite increasing work rate. In healthy people, a plateau occurs at near maximal exercise, however only about one third of normal subjects making maximal effort reach a plateau in a VO2. Therefore, peak VO2 is used as an estimate of VO2 max.
INDICATIONS FOR CPET
1. Evaluation of exercise tolerance.
2. Evaluation of exercise intolerance.
3. Evaluation of patients with unexplained dyspnea
4. Evaluation of patients with cardiovascular diseases.
5. Evaluation of patients with heart failure.
6. Evaluation of patients with respiratory diseases.
7. Exercise prescription for cardiac rehabilitation.
8. Exercise prescription for pulmonary rehabilitation.
9. Evaluation for heart transplantation.
10. Evaluation for lung transplantation.
11. Preoperative evaluation for lung surgery.
Exercise tolerance. The CPET define functional capacity and impairment, and factors limiting exercise for exercise prescription in a healthy population.
Exercise Intolerance. There is no correlation between resting pulmonary and cardiac function with exercise performance and functional capacity. Although exertional dyspnea is a common symptom in patients with cardiovascular and/or respiratory disease, the cause of exercise intolerance is related with other factors like leg discomfort, fatigue and chronotropic incompetence.
Evaluation of patients with heart failure. All patients with heart failure should undergo CPET. Peak VO2 has consistently demonstrated prognostic significance in congestive heart failure and the relationship between ventilation and carbon dioxide production (VE/VCO2) is abnormal. Patients with heart failure and high VE/VCO2 (more than 34) are at greater risk of a cardiovascular event.
PRACTICAL CONSIDERATIONS
Modes of CPET. CPET is a safe procedure with low risk of potential complications. Modes of exercise testing involve either treadmill walking and cycle ergometry. Treadmill leads to higher peak oxygen uptake values and a greater hyperventilation during exercise. Cycle ergometer is generally well tolerated in patients with heart failure and a protocol wit 10 W increment has been recommended.
Anaerobic Threshold (AT). The point at which anaerobic production of high energy phosphate compounds supplements aerobic production is known like anaerobic threshold. AT value less than 11/ml/Kg/min is a good indicator of risk of early cardiac death. It has been recommended that the AT should be determined by the V-Slope method.
CONCLUSIONS
CPET provides important diagnostic and prognostic information in a non-invasive setting, for patients with cardiovascular and respiratory diseases.
REFERENCES
1. Wasserman K et al. Principles of Exercise Testing and Interpretation. Fourth edition. Lippincott Williams and Wilkins Philadelphia 2005.
2. ATS/ACCP statement on cardiopulmonary exercise testing. American Journal of Respiratory and Critical Care Medicine 2003: 167:212.
3. ERS Task Force. Recommendations on the use of exercise testing in clinical practice. Eur Respir J 2007; 29: 185–209
4. Ingle L. Prognostic value and diagnostic potential of cardiopulmonary exercise testing in patients with chronic heart failure. Eur J Heart Failure 2008; 10: 112-118.
CPET is increasingly being used in a wide spectrum of clinical applications for the evaluation of undiagnosed exercise intolerance and for the objective determination of functional capacity, impairment and as prognostic, invaluable tool in the evaluation of patients with cardiovascular and pulmonary diseases, specifically heart failure patients.
PHYSIOLOGY OF EXERCISE
Exercise tolerance is determined by three important factors: pulmonary gas exchange, cardiovascular performance, including peripheral vascular system, and skeletal muscle metabolism. The efficient gas exchange requires: normal lungs mechanics, adequate ventilatory control mechanisms, an effective pulmonary circulation, an effective system of blood vessels, blood with normal hemoglobin of adequate concentration, a heart with the ability to pump oxygenated blood needed to sustain energy production and appropriate intracellular structure, energy substrate and enzyme concentration to permit adequate cell metabolism, especially in muscle cells. Peak exercise capacity has been defined as “the maximum ability of the cardiovascular system to deliver oxygen to the peripheral tissue and of the muscle to extract oxygen from the blood”. Therefore, it is important understand the Fick equation to appreciate the utility of this kind of test.
The Fick equation states that the oxygen uptake (VO2) equals cardiac output times the arterial minus mixed venous oxygen content. The equation is as follows:
VO2 = (Stroke Volume x Heart Rate) x (Arterial Oxygen Content – Mixed Venous Oxygen Content).
Mixed venous oxygen content (CVO2) is determined from a catheter in pulmonary artery, and systemic arterial oxygen content (CaO2) is determined from an arterial catheter. This method is the gold standard for cardiac output measurement. In the CPET VO2 measurements are made from respired gas measured at the mouth in a breath-by-breath basis, and increase in VO2 reflects O2 utilization by the muscle cells performing the work of exercise. The measurement of VO2 is based on mass balance equation: VO2 = (VI x FIO2) – (VE x FEO2). VI and VE represent the volumes of inhaled and exhaled gas; FIO2 and FEO2 represent the oxygen concentration in the inhaled and mixed exhaled gas. VI is calculated from VE. The measurement of VCO2 is easy, because FECO2 in the inhaled gas is zero and the equation is as follow: VCO2 = VE x FECO2.
The VO2 maximum defines the functional aerobic capacity of patients. It was originally defined as the VO2 at which performance of increasing levels of constant work rate exercise failed to increase VO2 by 150 ml/min, despite increasing work rate. In healthy people, a plateau occurs at near maximal exercise, however only about one third of normal subjects making maximal effort reach a plateau in a VO2. Therefore, peak VO2 is used as an estimate of VO2 max.
INDICATIONS FOR CPET
1. Evaluation of exercise tolerance.
2. Evaluation of exercise intolerance.
3. Evaluation of patients with unexplained dyspnea
4. Evaluation of patients with cardiovascular diseases.
5. Evaluation of patients with heart failure.
6. Evaluation of patients with respiratory diseases.
7. Exercise prescription for cardiac rehabilitation.
8. Exercise prescription for pulmonary rehabilitation.
9. Evaluation for heart transplantation.
10. Evaluation for lung transplantation.
11. Preoperative evaluation for lung surgery.
Exercise tolerance. The CPET define functional capacity and impairment, and factors limiting exercise for exercise prescription in a healthy population.
Exercise Intolerance. There is no correlation between resting pulmonary and cardiac function with exercise performance and functional capacity. Although exertional dyspnea is a common symptom in patients with cardiovascular and/or respiratory disease, the cause of exercise intolerance is related with other factors like leg discomfort, fatigue and chronotropic incompetence.
Evaluation of patients with heart failure. All patients with heart failure should undergo CPET. Peak VO2 has consistently demonstrated prognostic significance in congestive heart failure and the relationship between ventilation and carbon dioxide production (VE/VCO2) is abnormal. Patients with heart failure and high VE/VCO2 (more than 34) are at greater risk of a cardiovascular event.
PRACTICAL CONSIDERATIONS
Modes of CPET. CPET is a safe procedure with low risk of potential complications. Modes of exercise testing involve either treadmill walking and cycle ergometry. Treadmill leads to higher peak oxygen uptake values and a greater hyperventilation during exercise. Cycle ergometer is generally well tolerated in patients with heart failure and a protocol wit 10 W increment has been recommended.
Anaerobic Threshold (AT). The point at which anaerobic production of high energy phosphate compounds supplements aerobic production is known like anaerobic threshold. AT value less than 11/ml/Kg/min is a good indicator of risk of early cardiac death. It has been recommended that the AT should be determined by the V-Slope method.
CONCLUSIONS
CPET provides important diagnostic and prognostic information in a non-invasive setting, for patients with cardiovascular and respiratory diseases.
REFERENCES
1. Wasserman K et al. Principles of Exercise Testing and Interpretation. Fourth edition. Lippincott Williams and Wilkins Philadelphia 2005.
2. ATS/ACCP statement on cardiopulmonary exercise testing. American Journal of Respiratory and Critical Care Medicine 2003: 167:212.
3. ERS Task Force. Recommendations on the use of exercise testing in clinical practice. Eur Respir J 2007; 29: 185–209
4. Ingle L. Prognostic value and diagnostic potential of cardiopulmonary exercise testing in patients with chronic heart failure. Eur J Heart Failure 2008; 10: 112-118.
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