Dynamic Ventilatory Reserve During Incremental Exercise: Reference Values and Clinical Validation in COPD

Rationale: Ventilatory demand-capacity imbalance - as inferred by a low ventilatory reserve - is currently assessed only at peak cardiopulmonary exercise testing (CPET). Peak ventilatory reserve, however, is poorly sensitive to the submaximal, dynamic mechanical-ventilatory abnormalities which are key to dyspnea genesis and exercise intolerance.

Objectives: After establishing sex- and age-corrected norms for dynamic ventilatory reserve at progressively higher work rates, we compared peak and dynamic ventilatory reserve in their ability to expose increased exertional dyspnea and poor exercise tolerance in mild to very severe COPD.

Methods: We analyzed resting functional and incremental CPET data from 275 controls (130 men, aged 19-85) and 359 GOLD 1-4 patients (203 men) who were prospectively recruited for previous ethically-approved studies in three research centers. In addition to peak and dynamic ventilatory reserve ([1-(ventilation/estimated maximal voluntary ventilation) x 100]), operating lung volumes, and dyspnea scores (0-10 Borg scale) were obtained.

Results: Dynamic ventilatory reserve was asymmetrically distributed in controls; thus, we calculated its centile distribution at every 20 W. The lower limit of normal (<5th centile) was consistently lower in women and older subjects. Peak and dynamic ventilatory reserve disagreed significantly in indicating an abnormally-low test result in patients: whereas ~ 50% of those with normal peak ventilatory reserve showed reduced dynamic ventilatory reserve the opposite was found in ~ 15% (p<0.001). Irrespective of peak ventilatory reserve and COPD severity, patients showing dynamic ventilatory reserve<lower limit of normal at an iso-work rate of 40 W had higher ventilatory requirements, prompting earlier attainment of critically-low inspiratory reserve.

Consequently, they reported higher dyspnea scores, showing poorer exercise tolerance compared to those with preserved dynamic ventilatory reserve. Conversely, patients with preserved dynamic ventilatory reserve but reduced peak ventilatory reserve reported the lowest dyspnea scores, showing the best exercise tolerance.

Conclusion: Reduced submaximal dynamic ventilatory reserve - even in the setting of preserved peak ventilatory reserve - is a powerful predictor of exertional dyspnea and exercise intolerance in COPD. This new parameter of ventilatory demand-capacity mismatch may enhance the yield of clinical CPET in the investigation of activity-related breathlessness in individual patients with COPD and other prevalent cardiopulmonary diseases.

CITATION  Ann Am Thorac Soc. 2023 Jul 6. doi: 10.1513/AnnalsATS.202304-303OC