Respiratory sensation during chest wall restriction and dead space loadingin exercising men

We mimicked important mechanical and ventilatory aspects of restrictive lun g disorders by employing chest wall strapping (CWS) and dead space loading (DS) in normal subjects to gain mechanistic insights into dyspnea causation and exercise limitation. We hypothesized that thoracic restriction with in creased ventilatory stimulation would evoke exertional dyspnea that was sim ilar in nature to that experienced in such disorders. Twelve healthy young men [28 +/- 2 (SE) yr of age] completed pulmonary function tests and maxima l cycle exercise tests under four conditions, in randomized order: I) contr ol, 2) CWS to 60% of vital capacity, 3) added DS of 600 mi, and 4) CWS + DS . Measurements during exercise included cardiorespiratory parameters, esoph ageal pressure, and Borg scale ratings of dyspnea. Compared with control, C WS significantly reduced the tidal volume response to exercise, increased d yspnea intensity at any given work rate or ventilation, and thus limited ex ercise performance. DS stimulated ventilation but had minimal effects on dy spnea and exercise performance. Adding DS to CWS further increased dyspnea by 1.7 +/- 0.6 standardized Borg units (P = 0.012) and decreased exercise p erformance (total work) by 21 +/- 6% (P = 0.003) over CWS alone. Across con ditions, increased dyspnea intensity correlated best with decreased resting inspiratory reserve volume (r = -0.63, P < 0.0005). Dyspnea during CWS was described primarily as "inspiratory difficulty" and "unsatisfied inspirati on," similar to restrictive disorders. In conclusion, severe dyspnea and ex ercise intolerance were provoked in healthy normal subjects when tidal volu me responses were constrained in the face of increased ventilatory drive du ring exercise.