The Cause of Exercise Intolerance in Patients with Heart Failure and COPD: A Search for the Best Discriminator

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Cardiopulmonary exercise testing (CPET) is recommended by the AHA for the identification of the key-limiting organ in patients with exercise intolerance or dyspnea. Most CPET diagnostic algorithms are similar: using peak oxygen uptake (VO2p) to define the extent of limitation, and combination of anaerobic threshold (AT) and breathing reserve (BR) for the search of the cause of the specific limitation. A breathing reserve cutoff of 30%, and an AT cutoff of 40% of predicted VO₂p are typically used to separate between pulmonary and cardiac limitations, respectively. However, the specific limitation can be difficult to trace in the presence of coexisting cardiac and respiratory diseases.

This presentation demonstrates the CPET variables with the best ability to discriminate between respiratory and cardiac limitations in patients with COPD, Heart failure with reduced ejection fraction (HFrEF) and coexisting state of COPD and HFrEF. Based on current available physiological literature, we will show that:

1. VO₂p tend to be similar between patients with COPD and HFrEF.
2. VO₂ at AT also did not discriminate between patients with COPD and HFrEF.
3. VO₂/WR slope showed poor to moderate discriminant ability of these clinical populations.
4. On the other hand, BR and % of predicted O₂ uptake efficiency slope (OUES) had the greatest ability to discriminate between COPD & HFrEF.

Therefore, we can conclude that OUES and BR are the best discriminators between COPD and HFrEF, and can assist in establishing the key limiting factor of exercise intolerance in these typical patients. In order to enhance this knowledge, case reports of CPET in these common clinical populations will be presented to show the applicability of these two discriminators.