Estimating cardiopulmonary fitness with a new sampling technology in patients with rheumatoid arthritis-associated interstitial lung disease

Abstract

Background and objectives: Although peak oxygen uptake (VO_2peak ) is one of the most important measures in clinical practice, the high cost and time consumption have led to the search for simpler devices and the development of the estimating cardiopulmonary fitness (eCPF) equation. Since the lungs are one of the sites most affected by rheumatoid arthritis (RA), this study aimed to create a predictive equation for VO_2peak obtained by simple sampling technology in women with RA-associated interstitial lung disease (RA-ILD).

Methods: This cross-sectional study evaluated 47 women with RA-ILD. The participants underwent the following evaluations: computed tomography (CT); evaluation of disease activity through the Clinical Disease Activity Index (CDAI); measurement of physical function using the Health Assessment Questionnaire disability index (HAQ-DI); pulmonary function testing, including spirometry, diffusing capacity for carbon monoxide (Dl_CO ), nitrogen single-breath washout (N₂ SBW) test, and impulse oscillometry; and cardiopulmonary exercise testing (CPET) using FitMate™.

Results: VO_2peak was correlated with age (r = -0.550, p < 0.0001), rheumatoid factor (r = -0.443, p = 0.002), anti-cyclic citrullinated peptide antibodies (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), Dl_CO (r = 0.621, p < 0.0001), phase III slope of N₂ SBW (r = -0.647, p < 0.0001), resonance frequency (F_res , r = -0.717, p < 0.0001), integrated low-frequency reactance (r = -0.535, p = 0.0001), and the inhomogeneity of respiratory system resistance between 4 and 20 Hz (r = -0.631, p < 0.0001). In the CT examination, patients with extensive ILD had significantly lower VO_2peak than patients with limited ILD (p < 0.0001). In the stepwise forward regression analysis, F_res , Dl_CO and age explained 61% of the VO_2peak variability.

Conclusions: As assessed by CPET, women with RA-ILD show reduced cardiopulmonary fitness, 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 eCPF may be clinically important and support the use of the eCPF equation to improve patient outcomes.

Keywords: exercise; pulmonary function testing; rehabilitation; rheumatoid arthritis.