Pattern of extra-diaphragmatic respiratory muscle activity during exercise in patients with unilateral diaphragm dysfunction.

Whether extra-diaphragmatic respiratory muscle output is altered in patients with unilateral diaphragm dysfunction (UDD) remains unclear. We compared respiratory pressures and muscle activity during symptom-limited cardiopulmonary exercise testing (CPET) in 10 patients with UDD and 10 matched controls. Ventilatory variables, dyspnea, and electromyography (EMG) of the diaphragm, scalene, sternocleidomastoid, and parasternal intercostals were assessed at iso-ventilation and peak ventilation. Compared to controls, patients with UDD showed lower peak workload and oxygen consumption (p < 0.029), with a 10% lower but not statistically different peak ventilation (p = 0.078). At peak, they were more likely to report high dyspnea (p = 0.050). EMG patterns were similar between groups at iso-ventilation (40 L/min). At peak, controls had greater diaphragm (p = 0.007) and parasternal intercostal (p = 0.042) activity, while UDD patients showed earlier activation of scalene (p = 0.021) and sternocleidomastoid (p = 0.049), and greater expiratory muscle recruitment (p = 0.004). These findings suggest that patients with UDD rely on earlier and increased activation of extra-diaphragmatic and expiratory muscles to compensate for reduced diaphragm function during intense exercise. Targeting these compensatory mechanisms may be beneficial in managing diaphragm dysfunction.