Rationale

Dysfunctional breathing (DB) is diagnosed using various approaches. Recent guidelines suggested cardiopulmonary exercise testing (CPET)-based diagnostic criteria based on hyperventilation and measurement of the irregularity of the tidal volume (VT)-/ breathing frequency (BF)-response to exercise. The aim was to develop a statistical methodology for the diagnosis of DB based on the quantification of the irregularity of the respiratory response and compare its performance to standard clinical evaluations.

Methods

The study population consisted of 212 consecutive patients who underwent a CPET at our institution (Jan-Jul 2022). Breath-by-breath data were extracted, including VT, BF and minute ventilation (VE). Nonlinear regression models were fitted to the ventilation slopes and the proportional tidal volume variation (PTVV) was calculated using normalized root mean squared errors. The validity of our approach was compared to independent assessments of 2 CPET-experts using receiver operating characteristics (ROC).

Results

Patients underwent CPET in context including post-COVID-19 infections (40%), COPD, disproportional dyspnea due to sleep apnea, asthma, preoperative assessments before lung cancer resections. In 122/212 (59%) of CPETs, moderate or severe DB was diagnosed by the experts. The prediction accuracy of PTVV compared to expert consensus was 78% (sensitivity: 78% and specificity: 77%), and was comparable with the inter-expert concordance (81%). The prevalence of DB varied depending on the CPET context.

Conclusion

DB is very prevalent in patients undergoing CPET. PTVV provides an objective and accurate diagnostic tool for DB.