A patient with rheumatoid arthritis has normal FEV1 and FVC but MVV is 40% of predicted. The next step in pulmonary function evaluation should be to which test?

A patient with rheumatoid arthritis has normal FEV1 and FVC but MVV is 40% of predicted. The next step in pulmonary function evaluation should be to which test?

• A. Obtain ABGs on room air
• B. Obtain a flow-volume loop
• C. Obtain a measurement of peak flow
• D. Obtain a ventilation/perfusion scan

Answer: (B)

When maximal ventilatory capacity is reduced (MVV) but basic spirometry shows normal FEV1 and FVC, the problem is likely a limitation of the ventilatory mechanics or an airway obstruction rather than a loss of lung volume. To understand where and what kind of obstruction or limitation is present, the next step is to perform a flow-volume loop during spirometry. This dynamic test visualizes airflow during both forced inspiration and forced expiration and can distinguish different patterns of obstruction: a fixed central airway obstruction (both limbs flattened), a variable extrathoracic obstruction (flattened inspiratory limb), or a variable intrathoracic obstruction (flattened expiratory limb). In rheumatoid arthritis, upper airway involvement such as cricoarytenoid arthritis can cause extrathoracic airway obstruction, which the flow-volume loop can detect. If the loop is normal, it suggests the low MVV may reflect poor effort or non-obstructive factors rather than airway obstruction. ABGs, peak flow alone, or a ventilation/perfusion scan don’t provide the needed dynamic pattern to localize airway obstruction or confirm upper airway involvement.

When maximal ventilatory capacity is reduced (MVV) but basic spirometry shows normal FEV1 and FVC, the problem is likely a limitation of the ventilatory mechanics or an airway obstruction rather than a loss of lung volume. To understand where and what kind of obstruction or limitation is present, the next step is to perform a flow-volume loop during spirometry. This dynamic test visualizes airflow during both forced inspiration and forced expiration and can distinguish different patterns of obstruction: a fixed central airway obstruction (both limbs flattened), a variable extrathoracic obstruction (flattened inspiratory limb), or a variable intrathoracic obstruction (flattened expiratory limb). In rheumatoid arthritis, upper airway involvement such as cricoarytenoid arthritis can cause extrathoracic airway obstruction, which the flow-volume loop can detect. If the loop is normal, it suggests the low MVV may reflect poor effort or non-obstructive factors rather than airway obstruction. ABGs, peak flow alone, or a ventilation/perfusion scan don’t provide the needed dynamic pattern to localize airway obstruction or confirm upper airway involvement.