Cardiopulmonary exercise testing to indicate increased ventilatory variability in subjects with dysfunctional breathing

Background

Dysfunctional breathing (DB) is a common, but largely underappreciated, cause of chronic dyspnoea. Under visual inspection, most subjects with DB present with larger sequential changes in ventilation (V̇E) and breathing pattern (tidal volume (VT) and breathing frequency (f)) before and/or during incremental cardiopulmonary exercise testing (CPET). Currently, however, there are no objective criteria to indicate increased ventilatory variability in these subjects.

Methods

Twenty chronically dyspnoeic subjects with DB and 10 age- and sex-matched controls performed CPET on a cycle ergometer. Cut-offs to indicate increased V̇E, VT, f, and f/VT ratio variability (Δ = highest-lowest 20 s arithmetic mean) over the last resting minute (_rest), the 2^sd min of unloaded exercise (_unload), and the 3rd min of loaded exercise (_load) were established by ROC curve analyses.

Results

Subjects with DB presented with increased V̇E, higher ventilatory variability, higher dyspnoea burden, and lower exercise capacity compared to controls (p < 0.05). ΔV̇E_load (>4.1 L/min), Δf_rest (>5 breaths/min; bpm), Δf_unload (>4 bpm), Δf_load (>5 bpm), Δf/VT_rest (>4.9 bpm/L), and Δf/VT_load (>1.3 bpm/L) differentiated DB from a normal pattern (areas under the curve ranging from 0.729 to 0.845). High Δf, in particular, was associated with DB across all CPET phases.

Conclusions

This study provides objective criteria to indicate increased ventilatory variability during incremental CPET in dyspnoeic subjects with DB. Large variability in breathing frequency seems particularly useful in this context, a finding that should be prospectively confirmed in larger studies.