Mechanisms Of Exertional Dyspnea In Unilateral Diaphragmatic Dysfunction

Background: Dyspnea is a commonly reported symptom during exercise in patients with unilateral diaphragmatic dysfunction (UDD) and is likely related to breathing abnormalities during exercise. Objective: To compare breathing pattern and neuromechanical coupling during exercise hyperpnea between UDD and healthy controls (CON). Methods: 10 UDD (age 61.3±7.8 yr.; FVC 74±7% pred.; sniff Pdi 50±16 cmH2O) and 10 CON (age 41.7±10.6 yr.; FVC 111±9% pred.; sniff Pdi 105±30 cmH2O) performed a maximal incremental cycling test with continuous assessments of respiratory muscle EMG, respiratory pressures, and breathing pattern. Results: VO2max was lower in UDD than CON (91±21%pred. vs. 114±17%pred.; p<0.05). Comparable activation of inspiratory muscles (Figure 1 panels A-C) was observed along with abnormal inspiratory Pga, reduced inspiratory Pdi (Figure 1 panels D-F) and lower tidal volume at peak exercise (Figure 1 panels G-H) in UDD compared to CON. Dyspnea was the main reason for stopping exercise in 90% of UDD vs 40% of CON (p=0.019). Conclusion: These data indicate that neuromechanical uncoupling contributes to exertional dyspnea in patients with unilateral diaphragmatic dysfunction.