Determinants of daily physical activity limitation in patients with idiopathic pulmonary fibrosis

The purpose of the study was to determine the level of physical fitness assessed based on the physiological parameters and intensity of daily physical activity (PA) of patients with idiopathic pulmonary fibrosis (IPF). Additionally, we aimed to determine the intensity and duration of exercise that would bring beneficial modifications in the cardio-respiratory system of the patients with IPF. Eighteen patients with IPF (61.7 ± 4.3 years) and fifteen healthy volunteers performed a graded exercise test to exhaustion on a treadmill (Bruce protocol). Spirometry, dyspnea (mMRC, Borg scale) and fatigue (FAS) were measured. Total daily PA (kcal/day, MET) was monitored for seven days. The linear regression of PA (kcal/day) vs. peak oxygen uptake (%pred. peakVO₂) was used to determine the intensity of daily PA that should be used in the rehabilitation of the patients with IPF. The average energy expenditure of daily PA of patients with IPF was 147.9 ± 86.4 kcal/day and it was significantly lower compared to healthy individuals. The linear regression indicated that the predicted energy expenditure of daily PA (PAEE) is 280.0 kcal/day, estimated based on VO2peak 100%pred. Therefore, the patients should add about 30 min of exercise of the intensity of 4.5 ± 0.2 kcal (calculated at the anaerobic threshold) or about 3700 steps/day to their daily PA. Diffusion for carbon monoxide and physiological variables of aerobic capacity seem to be the most important determinants of PA limitation in patients with IPF. The method of estimating PAEE should be used to plan training loads in IPF rehabilitation.