The relationship between cardiac hemodynamics and exercise tolerance in cystic fibrosis

Background: Individuals with cystic fibrosis (CF) have reduced pulmonary function and exercise tolerance. Additionally, these individuals may develop abnormal cardiac function. The implications of abnormal cardiac function on exercise tolerance are unclear in CF. Objective: Study relationships between exercise cardiac hemodynamics and exercise tolerance in CF. Methods: 17 CF and 25 controls participated in cardiopulmonary exercise testing to measure exercise duration and peak workload (PW). Cardiac index (Q_I) was measured using acetylene rebreathe and oxygen uptake (VO₂) breath-by-breath. Forced expiratory volume in 1-second (FEV₁) was performed at rest. Results: Peak Q_I was 6.7 ± 0.5 vs. 9.1 ± 0.3 mL/min/m², CF vs. controls, respectively (P < 0.05). Linear regressions between Q_I (R² = 0.63 and 0.51) and exercise duration or PW were stronger than VO₂ (R² = 0.35 and 0.37) or FEV₁ (R² = 0.34 and 0.36) in CF, respectively (P < 0.05). Conclusion: These data are clinically relevant suggesting attenuated cardiac function in addition to low airway function relate to exercise tolerance in CF.