Determinants of dyspnea and alveolar hypoventilation during exercise in cystic fibrosis: Impact of inspiratory muscle endurance

AbstractDyspnea is one of the main complaints of patients with cystic fibrosis (CF). Lung function at rest is not sufficient to explain dyspnea during exercise. Because inspiratory muscles are faced with an increased workload in advanced CF, we studied the impact of their strength and endurance on dyspnea and alveolar hypoventilation during exercise.MethodsEighteen stable CF patients performed a maximal exercise test on a cycloergometer. Level of exercise dyspnea was recorded by a Borg scale at exhaustion. Blood gases were analysed at rest and at maximal peak exercise. Inspiratory muscle endurance (IME), expressed as a percentage of maximal inspiratory pressure (PImax), was measured according to an incremental threshold loading technique (Martyn).ResultsFour men and fourteen women were included with a mean age of 32years (20–67). Mean FEV1 was 44% predicted (21–82%). Mean PImax was 78% predicted (24–148%). No significant correlation was found between dyspnea and age, body mass index, pulmonary function at rest, blood gases, inspiratory muscle strength (PImax) or exercise capacity. Dyspnea was correlated with IME (r=−0.72, p=0.0029) and plethysmographic airway resistance (r=0.64, p=0.009). When patients were grouped according to degree of exercise dyspnea, half expressed a dyspnea more than “severe” (above level 5 on Borg scale) and half reported a lower dyspnea (Borg score≤5). Significant differences were observed between these two groups in inspiratory muscle endurance (46.8 versus 76.4% of PImax; p