Respiratory sensation during chest wall restriction and dead space loading in exercising men

Abstract

We mimicked important mechanical and ventilatory aspects of restrictive lung 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 increased ventilatory stimulation would evoke exertional dyspnea that was similar in nature to that experienced in such disorders. Twelve healthy young men [28 +/- 2 (SE) yr of age] completed pulmonary function tests and maximal cycle exercise tests under four conditions, in randomized order: 1) control, 2) CWS to 60% of vital capacity, 3) added DS of 600 ml, and 4) CWS + DS. Measurements during exercise included cardiorespiratory parameters, esophageal pressure, and Borg scale ratings of dyspnea. Compared with control, CWS significantly reduced the tidal volume response to exercise, increased dyspnea intensity at any given work rate or ventilation, and thus limited exercise performance. DS stimulated ventilation but had minimal effects on dyspnea and exercise performance. Adding DS to CWS further increased dyspnea by 1.7 +/- 0.6 standardized Borg units (P = 0.012) and decreased exercise performance (total work) by 21 +/- 6% (P = 0.003) over CWS alone. Across conditions, 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 inspiration," similar to restrictive disorders. In conclusion, severe dyspnea and exercise intolerance were provoked in healthy normal subjects when tidal volume responses were constrained in the face of increased ventilatory drive during exercise.

Sex differences in the perceived intensity of breathlessness during exercise with advancing age

“…Certainly, younger healthy individuals can tolerate increases in exercise V E during dead space loading that are comparable to the age-related increases in this study with minimal or no increase in breathing discomfort (36). However, we cannot exclude the possibility that even small increases in ventilatory demand (and therefore muscular effort) of this magnitude, in the setting of progressive age-related decline in respiratory muscle strength and dynamic mechanical restriction, may lead to greater respiratory difficulty in the elderly.…”

Effect of salmeterol on the ventilatory response to exercise in chronic obstructive pulmonary disease

“…Thus, in hyperinflated COPD patients, close intercorrelations were found between the reduced resting IC, reduced peak VT and reduced symptom-limited peak oxygen uptake (V9O 2 ) [6]. It was reasoned that bronchodilator-induced increases in resting IC should result in greater VT expansion throughout exercise, with greater ventilatory capacity and improved exercise ability.Similarly, it was previously hypothesised that the inability to expand VT appropriately in response to the increasing central drive of exercise can contribute to both the intensity and quality (unsatisfied inspiration) of exertional dyspnoea [7,8]. During exercise, inspiratory effort and central drive increase progressively in the face of increasingly restricted VT expansion in COPD.…”

“…Similarly, it was previously hypothesised that the inability to expand VT appropriately in response to the increasing central drive of exercise can contribute to both the intensity and quality (unsatisfied inspiration) of exertional dyspnoea [7,8]. During exercise, inspiratory effort and central drive increase progressively in the face of increasingly restricted VT expansion in COPD.…”

“…The ratio of inspiratory effort (tidal oesophageal pressure relative to maximum) to VT displacement is increased during exercise in COPD compared with health, and correlates well with intensity of inspiratory difficulty [7]. Similarly, in health, when VT is constrained by chest wall strapping during exercise, dyspnoea also intensifies [8]. When chemical drive is augmented further during exercise in volume-restricted individuals, by adding dead space, dyspnoea and the sense of unsatisfied inspiration increase dramatically [8].…”

“…Similarly, in health, when VT is constrained by chest wall strapping during exercise, dyspnoea also intensifies [8]. When chemical drive is augmented further during exercise in volume-restricted individuals, by adding dead space, dyspnoea and the sense of unsatisfied inspiration increase dramatically [8]. The corollary of this is that an improved ability to expand VT (due to an increased IC) for a given muscular effort or drive should ameliorate respiratory…”