Although maximum oxygen consumption (VO2peak) is one of the most important measurements in clinical practice, the high cost, time consumption and complications associated with the test have led to the search for simpler devices and the development of equations for estimating of cardiopulmonary fitness (eACP). Since the lungs are one of the sites most affected by rheumatoid arthritis (RA).

to create a predictive equation for VO2peak obtained by simple sampling technology in women with RA-associated interstitial lung disease (RA-ILD) considering the variables related to pulmonary involvement.

This cross-sectional study evaluated 47 women with RA-IPD. The participants were submitted to the following evaluations: dosage of autoantibodies; chest computed tomography (CT); assessment of disease activity through the Clinical Disease Activity Index (CDAI); measurement of physical function through the Health Assessment Questionnaire disability index (HAQ-DI); lung function tests including spirometry, carbon monoxide diffusing capacity (DLco) measurement, single-breath nitrogen washout test (N2SBW), impulse oscillometry (IOS) and cardiopulmonary exercise testing (CPET) using the FitMateTM®.

VO2peak was significantly correlated with age (r=-0.550, p<0.0001), rheumatoid factor (r=-0.443, p=0.002), anti-cyclic citrullinated peptide antibodies (anti-CCP, r=-0.410 , p=0.004), CDAI (r=-0.462, p=0.001), HAD-DI (r=-0.486, p=0.0005), forced vital capacity (r=0.491, p=0.0004), DLco (r=0.621, p<0.0001), phase III slope of the N2SBW test (r=-0.647, p<0.0001), resonance frequency (Fres, r=-0.717, p<0.0001), respiratory system reactance (r=-0.535, p = 0.0001) , and inhomogeneity of respiratory system resistance between 4-20 Hz (r=-0.631, p<0.0001). On CT scan, patients with extensive ILD had significantly lower VO2peak than patients with limited ILD (p<0.0001). In the multivariate regression analysis, Fres, DLco and age explained 61% of the VO2peak variability.

As assessed by CPET, women with RA-ILD show reduced ACP, which can be explained at least in part by the presence of small airway disease, deterioration of pulmonary gas exchange, and advanced age.

These associations of pulmonary variables with CPET may be clinically important and support the use of the eACP equation to improve patient outcomes.