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Beyond VO2: the complex cardiopulmonary exercise test
Irene Mattavelli1, Carlo Vignati1,2, Stefania Farina1,3
1Centro Cardiologico Monzino, IRCCS, Via Parea, 4, Milan 20138, Italy.
Insights
Cardiopulmonary exercise testing (CPET) provides key insights into heart failure (HF). Advanced CPET methods can now distinguish between impaired oxygen delivery and extraction, offering a more precise diagnosis.
Area of Science:
- Cardiology
- Exercise Physiology
- Diagnostic Technologies
Background:
- Cardiopulmonary exercise test (CPET) is crucial for diagnosing heart failure (HF).
- Peak oxygen uptake (peak VO2) is a key prognostic parameter in HF.
- Standard CPET cannot differentiate between impaired oxygen delivery and extraction.
Purpose of the Study:
- To explore advanced CPET technologies for differentiating causes of reduced VO2 in heart failure.
- To highlight methods for assessing cardiac output and peripheral oxygenation during exercise.
Main Methods:
- Utilizing non-invasive techniques like inert gas rebreathing and thoracic impedance cardiography to measure cardiac output (Qc) during CPET.
- Employing near-infrared spectroscopy for non-invasive assessment of peripheral muscle oxygenation.
- Integrating these measurements with Fick principle calculations.
Main Results:
- Advanced CPET can distinguish between impaired oxygen delivery (Qc) and impaired oxygen extraction (C(a-v)O2).
- Non-invasive methods for Qc and tissue oxygenation are validated in HF patients.
- Combined measurements allow for precise attribution of VO2 deficits to cardiac, muscular, or anemia-related factors.
Conclusions:
- Complex CPET provides a more detailed understanding of exercise limitation in heart failure.
- These advanced techniques enhance diagnostic accuracy and prognostic assessment in HF patients.
- Differentiating the causes of VO2 impairment can guide targeted therapeutic strategies.
Abstract:
Cardiopulmonary exercise test (CPET) is a valuable diagnostic tool with a specific application in heart failure (HF) thanks to the strong prognostic value of its parameters. The most important value provided by CPET is the peak oxygen uptake (peak VO2), the maximum rate of oxygen consumption attainable during physical exertion. According to the Fick principle, VO2 equals cardiac output (Qc) times the arteriovenous content difference [C(a-v)O2], where Ca is the arterial oxygen and Cv is the mixed venous oxygen content, respectively; therefore, VO2 can be reduced both by impaired O2 delivery (reduced Qc) or extraction (reduced arteriovenous O2 content). However, standard CPET is not capable of discriminating between these different impairments, leading to the need for 'complex' CPET technologies. Among non-invasive methods for Qc measurement during CPET, inert gas rebreathing and thoracic impedance cardiography are the most used techniques, both validated in healthy subjects and patients with HF, at rest and during exercise. On the other hand, the non-invasive assessment of peripheral muscle perfusion is possible with the application of near-infrared spectroscopy, capable of measuring tissue oxygenation. Measuring Qc allows, by having haemoglobin values available, to discriminate how much any VO2 deficit depends on the muscle, anaemia or heart.
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