title: Physiological mechanisms of dyspnea during exercise with external thoracic restriction: role of increased neural respiratory drive.
abstract: We tested the hypothesis that neuromechanical uncoupling of the respiratory system forms the mechanistic basis of dyspnea during exercise in the setting of "abnormal" restrictive constraints on ventilation (VE). To this end, we examined the effect of chest wall strapping (CWS) sufficient to mimic a "mild" restrictive lung deficit on the interrelationships between VE, breathing pattern, dynamic operating lung volumes, esophageal electrode-balloon catheter-derived measures of the diaphragm electromyogram (EMGdi) and the transdiaphragmatic pressure time product (PTPdi), and sensory intensity and unpleasantness ratings of dyspnea during exercise. Twenty healthy men aged 25.7 ± 1.1 years (means ± SE) completed symptom-limited incremental cycle exercise tests under two randomized conditions: unrestricted control and CWS to reduce vital capacity (VC) by 21.6 ± 0.5%. Compared with control, exercise with CWS was associated with 1) an exaggerated EMGdi and PTPdi response; 2) no change in the relationship between EMGdi and each of tidal volume (expressed as a percentage of VC), inspiratory reserve volume, and PTPdi, thus indicating relative preservation of neuromechanical coupling; 3) increased sensory intensity and unpleasantness ratings of dyspnea; and 4) no change in the relationship between increasing EMGdi and each of the intensity and unpleasantness of dyspnea. In conclusion, the increased intensity and unpleasantness of dyspnea during exercise with CWS could not be readily explained by increased neuromechanical uncoupling but likely reflected the awareness of increased neural respiratory drive (EMGdi) needed to achieve any given VE during exercise in the setting of "abnormal" restrictive constraints on tidal volume expansion.
authors.affiliation: Clinical Exercise and Respiratory Physiology Laboratory, Department of Kinesiology and Physical Education, McGill University, Montréal, Québec, Canada.
authors.forename: Cassandra T
authors.initials: CT
authors.lastname: Mendonca
authors.forename: Michele R
authors.initials: MR
authors.lastname: Schaeffer
authors.forename: Patrick
authors.initials: P
authors.lastname: Riley
authors.forename: Dennis
authors.initials: D
authors.lastname: Jensen
mesh_terms: D000328:Adult; D018592:Cross-Over Studies; D004328:Drive; D004417:Dyspnea / Q000503:physiopathology* / Q000523:psychology; D004576:Electromyography; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D017079:Exercise Tolerance; D005260:Female; D006801:Humans; D008176:Lung Volume Measurements; D008297:Male; D012129:Respiratory Function Tests; D015656:Respiratory Mechanics / Q000502:physiology; D012143:Respiratory Physiological Phenomena; D035441:Thoracic Wall / Q000502:physiology; D013909:Thorax / Q000502:physiology*; D055815:Young Adult
keywords: chest wall strapping; diaphragm EMG; dyspnea; exercise; neural respiratory drive; respiratory mechanics; thoracic restriction