Effects of dead space loading on neuro-muscular and neuro-ventilatory coupling of the respiratory system during exercise in healthy adults: Implications for dyspnea and exercise tolerance

• Published in: Respiratory physiology & neurobiology Vol. 179; no. 2-3; pp. 219 - 226
• Main Authors: Jensen, Dennis, O’Donnell, Denis E., Li, Ruifa, Luo, Yuan-Ming
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.12.2011; Elsevier
• Subjects: Aged; Biological and medical sciences; Cross-Over Studies; Dead space; Diaphragm; Dyspnea; Dyspnea - physiopathology; Electromyography; Exercise; Exercise - physiology; Exercise Tolerance - physiology; Female; Fundamental and applied biological sciences. Psychology; Humans; Male; Medical Education; Middle Aged; Oxygen Consumption - physiology; Pulmonary Ventilation - physiology; Pulmonary/Respiratory; Respiratory Dead Space - physiology; Respiratory Function Tests; Respiratory Muscles - physiology; Vertebrates: respiratory system; Electromyography; Dyspnea; Exercise; Diaphragm; Dead space; Human; Physical exercise; Electrophysiology; Tolerance; Respiratory system; Vertebrata; Mammalia; Loading; Adult
• ISSN: 1569-9048; 1878-1519; 1878-1519
• DOI: 10.1016/j.resp.2011.08.009

► Dead space loading decreased exercise tolerance by 20–25% in healthy adults. ► Neuro-muscular and neuro-ventilatory coupling was preserved during exercise in the setting of increased dead space. ► Exertional dyspnea reflects the awareness of increased neural respiratory drive, respiratory effort and ventilatory output. ► Healthy adults possess large ventilatory reserve during exercise. We examined the effects of dead space loading (DSL) on ventilation (V˙E), neural respiratory drive (EMGdi%max, diaphragm EMG expressed as a % of maximal EMGdi), contractile respiratory muscle effort (Pes,tidal%PImax, tidal esophageal pressure swing expressed as a % of maximal inspiratory Pes) and exertional dyspnea intensity ratings in 11 healthy adults with normal spirometry. Subjects completed, in random order, symptom-limited incremental cycle exercise tests under control (CTRL) and DSL (500ml) conditions. Compared with CTRL, DSL decreased exercise tolerance by 20–25%; increased exertional dyspnea intensity ratings in direct proportion to concurrent increases in EMGdi%max, Pes,tidal%PImax and V˙E; and had little/no effect on the inter-relationships between EMGdi%max, Pes,tidal%PImax and V˙E during exercise. In conclusion, DSL was associated with an earlier onset of intolerable dyspnea; however, neuro-muscular and neuro-ventilatory coupling of the respiratory system remained relatively preserved during exercise in the presence of an increased external dead space. Under these circumstances, DSL-induced increases in exertional dyspnea intensity ratings reflected, at least in part, the awareness of increased neural respiratory drive, contractile respiratory muscle effort and ventilatory output.