Low Aerobic Capacity Linked to Higher Risk of Exacerbations

Cystic fibrosis (CF) patients with lower aerobic exercise capacity — assessed with a non-invasive cardiopulmonary exercise test — have a 4.5 times higher risk of future pulmonary exacerbations, according to a small 10-year study in Greece.

Aerobic capacity, or VO2peak, is the maximal amount of oxygen a person’s lungs absorb during an exercise test. It’s a measure of an individual’s level of cardiovascular health.

These findings add to those of previous studies showing that low aerobic capacity is associated with a higher risk of death in CF patients. Together, these results suggest that maintaining a higher level of fitness may help to prevent exacerbations and improve quality of life among people with CF, according to the researchers.

“The less fit a patient seems to be, the more prone to exacerbations he is,” the investigators wrote.

The study, “The Fitter the Better? Cardiopulmonary Exercise Testing Can Predict Pulmonary Exacerbations in Cystic Fibrosis,” was published in the journal Children.

Cardiopulmonary exercise testing, called CPET, is a non-invasive assessment of the cardiopulmonary system at rest and during exercise. Several of CPET’s parameters — such as VO2peak and ventilatory efficiency indexes VE/VO2 and VE/VCO2 — are predictors of death in people with CF, previous studies have shown.

Pulmonary exacerbations are bouts of increased respiratory symptoms and diminished lung function. Given that such bouts are a main cause of death in CF, it seems likely that changes in the parameters of a person’s ability to absorb oxygen also may predict future exacerbations.

To investigate if this was the case, researchers in Greece analyzed CPET and pulmonary exacerbation data from 78 CF patients with a mean age of 14.9. These patients, who were followed at a CF unit in Greece for 10 years, had not been treated with any CFTR modulator — therapies targeting specific protein defects in CF. Each participant underwent CPET one to three times a year between 2009 and 2019.

Pulmonary exacerbation was defined as the need for additional treatment when there was a change in sputum color or quantity, an increase in cough, a loss of appetite or a feeling of being ill, or shortness of breath. Exacerbations also were counted when patients had a greater than 10% drop in lung function or an alteration in radiographic findings. Of note, sputum is the mucus that is coughed up from the lower airways.

After adjusting for potential influencing factors, the researchers found that three CPTE-related parameters — aerobic capacity (VO2peak), VE/VO2, and PetCO2 (carbon dioxide released at peak exercise) — significantly predicted the occurrence of pulmonary exacerbations in the short term after the CPET.

In addition, CF patients with less than 60% of predicted VO2peak had a 4.5 times increased risk of having a pulmonary exacerbation during the following months than those with higher exercise capacity.

Notably, a VO2peak lower than 60% predicted had previously been associated with poor survival in a global study.

These findings suggest that low aerobic capacity is not only “associated with worse prognosis but it can lead to more frequent exacerbations as well,” the researchers wrote, noting that CF patients who are less fit are “more prone to exacerbations.”

“Hence, regular estimation of a patient’s exercise capacity helps identify those in danger of exacerbations,” the investigators wrote.

Such regular monitoring also can help in initiating appropriate therapeutic interventions, such as exercise training — which has been shown to improve aerobic capacity in those with CF.

“Even if CPET equipment is not available, other methods too can allow for a rough assessment of a [patient’s] fitness levels,” the team wrote.

The data also suggest that “motivating CF patients to maintain high fitness levels can lead to fewer pulmonary exacerbations and better quality of life,” the researchers concluded.