* Co–first authors.

The National Cohort Study of Idiopathic and Heritable Pulmonary Arterial Hypertension is funded by the British Heart Foundation, the Medical Research Council, and the National Institute for Health and Care Research. J.N. is in receipt of British Heart Foundation Clinical Research Training Fellowship FS/CRTF/22/24390. The views expressed are those of the authors and not necessarily those of the funders. The funders did not have a role in the design, collection, analysis, or interpretation of data in this substudy. The researchers acted independently and take responsibility for the integrity of the substudy.

Author Contributions: L.R., J.N., and M.T. conceived and designed the study. L.R. and J.N. acquired, analyzed, and curated the data. L.R. and J.N. drafted the initial manuscript and produced the figures. S.C., M.F., and I.A. assisted with the codesign of this research with patient input. E.F.M. and E.H.D. oversaw the development of the digitalization of the 1-minute-walk test and 6-minute-walk test on Aparito’s Atom5 platform. All authors reviewed and edited the manuscript.

Originally Published in Press as DOI: 10.1164/rccm.202310-1855LE on January 4, 2024

Author disclosures are available with the text of this letter at www.atsjournals.org.