What is the most likely cause of reduced vital capacity in a person with quadriplegia at C5–C6?

What is the most likely cause of reduced vital capacity in a person with quadriplegia at C5–C6?

• A. Decreased anterolateral chest expansion due to paralysis of the external intercostals.
• B. Inability to generate negative intrapleural pressure due to denervated diaphragm.
• C. Relatively high resting position of the diaphragm due to paralysis of abdominal muscles.
• D. Reduced rib cage elevation due to paralysis of the anterior scalene and sternocleidomastoid muscles.

Answer: (A)

Vital capacity in high-level quadriplegia is most limited by the ability of the chest wall to expand, not just by diaphragmatic function. At C5–C6, the diaphragm is often still functional, but the external intercostal muscles, which lift the ribs and enlarge the anterolateral chest during inspiration, are paralyzed. This loss of rib cage expansion markedly reduces the volume change of the thorax during inspiration, leading to a smaller vital capacity. The diaphragm can still contract to draw air in, but without the chest wall’s expansion, the overall inspiratory effort is insufficient to achieve normal VC. While diaphragmatic denervation or loss of other neck muscles could contribute, the primary and most impactful deficit at this level is decreased anterolateral chest expansion due to intercostal paralysis.

Vital capacity in high-level quadriplegia is most limited by the ability of the chest wall to expand, not just by diaphragmatic function. At C5–C6, the diaphragm is often still functional, but the external intercostal muscles, which lift the ribs and enlarge the anterolateral chest during inspiration, are paralyzed. This loss of rib cage expansion markedly reduces the volume change of the thorax during inspiration, leading to a smaller vital capacity. The diaphragm can still contract to draw air in, but without the chest wall’s expansion, the overall inspiratory effort is insufficient to achieve normal VC. While diaphragmatic denervation or loss of other neck muscles could contribute, the primary and most impactful deficit at this level is decreased anterolateral chest expansion due to intercostal paralysis.