Reply: CPET for Long COVID-19.

We appreciate the comments from Drs Naeije and Caravita and the citation of their work which was not available at the time our report was written. Drs Naeije and Caravita are correct that we performed a detailed analysis of cardiopulmonary stress tests in 41 patients with long coronavirus disease-2019 (COVID-19). Careful review of individual tests should not detract from our overall findings which showed ventilatory abnormalities in 88% of this cohort including 41% with elevated VE/VCO2, 61% with hypocapnia, and 63% with disordered breathing. Deconditioning is generally not characterized by ventilatory changes. The mechanism underlying these ventilatory abnormalities remain unclear. Anxiety or psychological stress is one potential explanation for the hyperventilation, but altered chemosensitivity, lung thrombotic, or fibrotic changes are also possible. I think we can agree that more research is needed to clarify the significance of our findings and to help find an answer for those patients afflicted with long COVID-19 syndrome.