As the impairment due to elevated pulmonary pressure is primarily seen with exercise, there is a strong rationale to measure the capacity of the patient to accomplish some sort of standardized effort.
- 6 minute walking test (6 MWT)
The free and unopposed distance walked during 6 minutes has been used in most clinical studies on PAH for medication approval. The test has been precisely standardized (ATS reference) and the practical aspects can be seen here. The absolute value, and not the change between visits, has been shown to correlate with prognosis. The threshold has been defined, according to studies between 320-380 m (Sitbon c.f. Table 15 from ESC).
Although widely used, the 6 MWT has some limitations:
- It has not been validated for PH except for PAH Dana Point group 1.
- Patients with orthopaedical disability cannot be assessed.
- Normal values for both extremes of the life span (children – adults > 80 years) are lacking.
- Finally, although correlated to mortality, the 6 MWT is far from having a perfect positive and negative predictive value, especially for NYHA < II, and should therefore not be seen as the unique goal in PH treatment.
- Cardiopulmonary exercise testing (CPET)
Peak oxygen consumption as measured by CPET is of high prognostic value in both PAH and PH. However, due probably to the complexity of the test, it is not assessed systematically in every centre outside in research protocols. CPET could be of added value when there is a discordance between hemodynamic data and functional class. It should not be performed, unless with extreme caution, in patients NYHA class IV.