Physiological Underpinnings of Exertional Dyspnoea in Mild Fibrosing Interstitial Lung Disease.

Smyth RM; Neder JA; James MD; Vincent SG; Milne KM; Marillier M; de-Torres JP; Moran-Mendoza O; O’Donnell DE; Phillips DB

Respiratory physiology & neurobiology [Respir Physiol Neurobiol] 2023 Feb 27, pp. 104041.
Date of Electronic Publication: 2023 Feb 27.

The functional disturbances driving “out-of-proportion” dyspnoea in patients with fibrosing interstitial lung disease (f-ILD) showing only mild restrictive abnormalities remain poorly understood. Eighteen patients (10 with idiopathic pulmonary fibrosis) showing preserved spirometry and mildly reduced total lung capacity (≥70% predicted) and 18 controls underwent an incremental cardiopulmonary exercise test with measurements of operating lung volumes and Borg dyspnoea scores. Patients’ lower exercise tolerance was associated with higher ventilation (V̇ E )/carbon dioxide (V̇CO 2 ) compared with controls (V̇ E /V̇CO 2 nadir=35±3 versus 29±2; p<0.001). Patients showed higher tidal volume/inspiratory capacity and lower inspiratory reserve volume at a given exercise intensity, reporting higher dyspnoea scores as a function of both work rate and V̇ E . Steeper dyspnoea-work rate slopes were associated with lower lung diffusing capacity, higher V̇ E /V̇CO 2 , and lower peak O 2 uptake (p<0.05). Heightened ventilatory demands in the setting of progressively lower capacity for tidal volume expansion on exertion largely explain higher-than-expected dyspnoea in f-ILD patients with largely preserved dynamic and “static” lung volumes at rest.