Increased respiratory neural drive and work of breathing in exercise-induced laryngeal obstruction

Rationale: Exercise induced laryngeal obstruction (EILO), a phenomenon in which the larynx closes inappropriately during physical activity, is a prevalent cause of exertional dyspnea in young individuals. The physiological ventilatory impact of EILO and its relationship to dyspnea are poorly understood. Objectives: To evaluate exercise related changes in laryngeal aperture on ventilation, pulmonary mechanics and respiratory neural drive. Methods: We prospectively evaluated 12 subjects (six with EILO and six healthy age- and gender-matched controls). Subjects underwent baseline spirometry and a symptom-limited incremental exercise test with simultaneous and synchronized recording of endoscopic video, gastric-, esophageal- and transdiaphragmatic pressures, diaphragm electromyography and respiratory airflow. Results: The EILO and control groups had similar peak work rates and minute ventilation (V̇E) (work rate: 227±35 vs. 237±35W; V̇E: 103±20 vs. 98±23 L/min; p>0.05). At submaximal work rates (140-240W) subjects with EILO demonstrated increased work of breathing (p<0.05) and respiratory neural drive (p<0.05), developing in close temporal association with onset of endoscopic evidence of laryngeal closure (p<0.05). Unexpectedly, a ventilatory increase (p<0.05), driven by augmented tidal volume (p<0.05), was seen in subjects with EILO, before the onset of laryngeal closure; there were however no differences in dyspnea intensity between groups. Conclusion: Using simultaneous measurements of respiratory mechanics and diaphragm electromyography with endoscopic video we demonstrate, for the first time, increased work of breathing and respiratory neural drive in association with the development of EILO. Future detailed investigations are now needed to understand the role of upper airway closure in causing exertional dyspnea and exercise limitation.