Breathing by double-lung recipients during exercise: Response to expiratory threshold loading

Ventilation during exercise is near-normal in double-lung transplant recipients despite lung denervation. We tested the hypothesis that denervation effects might be unmasked during exercise by exposing these patients to an expiratory load. Eight double-lung recipients and nine intact control subjects were exercised to exhaustion. Ergometer work increased 20 Watt every 2 min; expiratory threshold loading (4 cm H₂O) was imposed for five to six breaths at each exercise level; ventilation and O₂ consumption were measured. Transplant recipients and control subjects increased ventilation similarly for comparable fractions of maximal work. At maximal exercise, transplant recipients achieved lower work (62 versus 155 W; p < 0.001) and O₂ consumption (0.88 versus 2.26 L/min; p < 0.001) than control subjects, with proportional reductions in tidal volume (1.6 versus 2.6 L; p < 0.05) and ventilation (38 versus 79 L/min; p < 0.01). Threshold loading decreased expiratory flow, breathing frequency, and minute ventilation in both groups (p < 0.05). Unlike control subjects, transplant recipients also slowed inspiratory flow (p < 0.05) and prolonged inspiration (p < 0.01), exaggerating the fall in breathing frequency and ventilation (p < 0.01). We conclude that afferent information from pulmonary receptors modulates inspiration during expiratory loading; bilateral denervation disrupts these pathways, causing double-lung recipients to inspire more slowly.