In cystic fibrosis (CF), peak oxygen uptake (V’O2,peak), maximal work rate (Work max) and ventilatory equivalents for oxygen uptake (V’E/V’O2) measured during incremental cardiopulmonary exercise testing (CPET) are significant predictors of mortality. Recently, data obtained in children with CF suggest that aerobic fitness is also associated with lower risk of hospitalization. Although peak exercise tolerance is reduced in CF, some studies have shown that aerobic exercise capacity increases with physical training programs.
The best clinical practice to investigate aerobic fitness includes measurements obtained during CPET, however there are still many difficulties associated with its use in clinical practice. To date, the relationship between formal CPET parameters at sub-maximal workloads and daily activity levels in CF has not been well established.
In the study titled “Relationship between daily physical activity and aerobic fitness in adults with cystic fibrosis,” Daniela Savi from the Department of Pediatrics and Pediatric Neurology, Cystic Fibrosis Center, Sapienza University of Rome in Italy, aimed to examine the relationship between daily PA and aerobic fitness both at sub maximal and maximal levels in clinically stable adults with CF. The researchers measured PA as a surrogate of CPET in the assessment of exercise capacity in CF. In addition to this primary aim, the team compared both daily PA levels and responses to CPET of adult CF patients and healthy controls.
A total of 30 adult CF patients (33 ± 8SD years) with mild to moderate lung disease (FEV1 50%-90% predicted) took part in the study. The researchers also included a total of 15 healthy control subjects matched for age, and needed to have normal baseline spirometry (FEV1 ≥ 80%predicted, FEV1/FVC ≥0.7) and free of any health problems, including cardiovascular, neuromuscular, musculoskeletal, or respiratory diseases.
All participants then undertook an incremental CPET on a cycle ergometer. CPET-related measurements included: oxygen uptake (V’O2), carbon dioxide production (V’CO2), ventilatory profile, heart rate (HR) and oxygen pulse (V’O2/HR) throughout exercise and at lactic threshold (LT) and peak. LT measures represent sub-maximal exercise related data. PA was assessed using the accelerometer SenseWear Pro3 Armband.
Results revealed that moderate and moderate + vigorous PA was related to V’O2, and work rate at LT. Moderate PA or greater was positively related to peak V’O2. The results also showed that daily PA levels were similar in CF and healthy controls. Except for peak values, V’O2 profile and the V’O2 at LT were comparable between CF and healthy controls.
Based on these results, the researchers concluded that daily PA is associated with aerobic capacity in adults with CF and mild to moderate lung function impairment and was similar to healthy controls. The V’O2 profile and the V’O2 at LT were comparable between healthy controls and patients with CF, which indicates that daily PA could be considered a valuable tool in the assessment of aerobic fitness in adult CF population. According to the researchers measuring PA is straightforward and could easily be integrated into interventional exercise trials. However, further studies are required to determine if PA measurements are sensitive enough to detect early pathophysiological changes in CF exercise capacity, in order to consider them as a simple and practical method for monitoring the disease status.