Comparative analysis of lung function in supine and sitting positions in patients with moderate multiple sclerosis

Multiple sclerosis (MS) is a progressive disease that may affect respiratory muscle function. Pulmonary dysfunction may be subclinical, and posture changes can reduce lung volumes, especially in the presence of respiratory muscle weakness.

To determine whether lung function differs between sitting and supine positions in individuals with moderate MS, and to explore associations with respiratory muscle strength and disability.

Forty-eight participants with moderate MS (13 men, 35 women; median Expanded Disability Status Scale (EDSS) 4.5, range: 4.0-6.5) underwent spirometry (VC, FVC, FEV₁, PEF) in sitting and supine positions. Respiratory muscle strength was assessed using maximal inspiratory (MIP) and expiratory pressures (MEP).

VC and FVC did not differ significantly between positions. FEV₁ and PEF were slightly reduced in the supine position (p ≤ 0.001), with median relative decreases of -6% and -10%, respectively. These changes did not correlate with EDSS, MIP, or MEP. No sex-related differences were observed.

FEV₁ and PEF are reduced in the supine position in individuals with moderate MS, indicating early positional respiratory changes. These alterations appear independent of disability level or respiratory muscle strength. However, it remains uncertain whether these changes differ from those of healthy individuals. Controlled studies are warranted to clarify their clinical significance.