Chest wall kinematics, respiratory muscle action and dyspnoea during arm vs. leg exercise in humans

Aim: We hypothesize that different patterns of chest wall (CW) kinematics and respiratory muscle coordination contribute to sensation of dyspnoea during unsupported arm exercise (UAE) and leg exercise (LE). Methods: In six volunteer healthy subjects, we evaluated the volumes of chest wall (V-cw) and its compartments, the pulmonary apposed rib cage (V-rc,V-p), the diaphragm-abdomen apposed rib cage (V-rc,V-a) and the abdomen (V-ab), by optoelectronic plethysmography. Oesophageal, gastric and trans-diaphragmatic pressures were simultaneously measured. Chest wall relaxation line allowed the measure of peak rib cage inspiratory muscle, expiratory muscle and abdominal muscle pressures. The loop V-rc,V-p/V-rc,V-a allowed the calculation of rib cage distortion. Dyspnoea was assessed by a modified Borg scale. Results: There were some differences and similarities between UAE and LE. Unlike LE with UAE: (i) V-cw and V-rc,V-p at end inspiration did not increase, whereas a decrease in V-rc,V-p contributed to decreasing CW end expiratory volume; (ii) pressure production of inspiratory rib cage muscles did not significantly increase from quiet breathing. Not unlike LE, the diaphragm limited its inspiratory contribution to ventilation with UAE with no consistent difference in rib cage distortion between UAE and LE. Finally, changes in abdominal muscle pressure, and inspiratory rib cage muscle pressure predicted 62% and 41.4% of the variability in Borg score with UAE and LE, respectively (P < 0.01). Conclusion: Leg exercise and UAE are associated with different patterns of CW kinematics, respiratory muscle coordination, and production of dyspnoea.