Exercise ventilatory limitation may be present despite normal breathing reserve in CF

For individuals with mild to moderate-severe cystic fibrosis, relying solely on reduced breathing reserve may underestimate ventilatory limitation during exercise, according to new research published in Respiratory Medicine.

“Cardiopulmonary exercise test (CPET) offers a functional assessment of lung performance and efficiency in a dynamic setting. Despite this, assessing the degree of exercise ventilatory limitation by CPET is rarely used in the follow-up of lung function decline in cystic fibrosis,” Ronen Reuveny, MD, from the Pulmonary Institute at Sheba Medical Center, Tel Hashomer, Ramat Gan, and the Sackler School of Medicine at Tel Aviv University and the department of physical therapy and Faculty of Social Welfare and Health Sciences at the University of Haifa, Israel, and colleagues wrote. “Assessing the degree of exercise ventilatory limitation is traditionally based on measurement of the breathing reserve, that is — how closely the minute ventilation achieved at peak exercise approaches the maximal voluntary ventilation.”

Researchers enrolled 20 adults with cystic fibrosis and a wide range of pulmonary obstruction severity. All participants completed a symptom-limited incremental exercise test using a cycle ergometer and were categorized by mild to moderate-severe airway obstruction with an FEV₁ of 46% to 103% predicted and a normal breathing reserve of 12 L/min to 62 L/min (n = 14; mean age, 35 years; 35.7% women) or an FEV₁ of less than 45% predicted and a breathing reserve lower than 15% (n = 6; mean age, 33 years; 50% women).

Those with cystic fibrosis and mild to moderate-severe lung disease showed clear evidence of ventilatory limitation during exercise with dynamic respiratory mechanics, the researchers wrote.

Inspiratory capacity decreased by a median of 580 mL during exercise, which indicated dynamic hyperinflation, according to the researchers. At peak exercise, inspiratory reserve volume was 445 mL, which indicated mechanical constraint on the individuals’ respiratory system, they wrote. Exercise tidal flow met or exceeded the expiratory boundary of the maximal flow volume loop over 72% of the expiratory volume, which indicated expiratory flow limitation.

Researchers noted that FEV₁ percent predicted correlated with percent of breathing reserve (P = .01). In addition, in a multiple linear regression analysis, peak oxygen consumption was correlated with resting inspiratory capacity percent predicted (P = .0001), FEV₁ percent predicted (P = .03), inspiratory capacity/total lung capacity (P = .002) and FVC percent predicted (P = .027).

“Our results therefore contribute to a better understanding of exercise limitation in individual patients with cystic fibrosis,” the researchers wrote. “The assessment of the dynamic respiratory response to exercise, instead of relying exclusively on the traditional breathing reserve, adds clinically important information, guiding the management of dyspnea in cystic fibrosis.”