Respiratory Variability during Exercise: Associations with Motor Severity in Parkinson's Disease

Respiratory dysfunction is a recognized feature of Parkinson ’ s disease (PD), 1 encompassing alterations in breathing pattern, reduced respiratory muscle strength, and a blunted hypoxic ventilatory response, even in mild to moderate stages. 2,3 These abnormalities likely re fl ect dysfunction across central respiratory networks, chemosensory regulation, and motor activation of respiratory muscles. Because breathing requires precise integration of neural drive and respiratory muscle output, reduced regularity of respiratory muscle activation may contribute to greater breath-to-breath variability in ventilation. Thus, progressive motor dysfunction in PD may also be re fl ected in ventilatory stability. However, the relationship between respiratory variability and motor symptom severity remains unclear. Exercise represents a dynamic physiological challenge to ventilatory control, during which breath-by-breath respiratory variability may serve as a marker of underlying dysfunction. Accordingly, we examined whether respiratory variability during maximal exercise is associated with motor symptom severity in PD. Data were analyzed from 24 participants with idiopathic PD (15 men; 66 (cid:1) 8 years; 78 (cid:1) 18 kg; 170 (cid:1) 10 cm), recruited from the local community for an unrelated study hypothesis. 4 Exclusion criteria included dementia, stroke, recent smoking, type-I diabetes, a self-reported physician diagnosis of autonomic neuropathy, or chronic cardiopulmonary conditions. Participants completed a maximal cardiopulmonary exercise test on an electronically braked cycle ergometer. After a 5-minute warm-up, workload increased continuously using individualized ramp protocols until cadence fell below 50 rpm or volitional exhaustion. 4 All participants were tested during the ON phase of