Final answer:
To distinguish between obstructive and restrictive lung disease when FVC is <80%, the FEV1/FVC ratio is used; it is less than 69% in obstructive and 88 to 90% in restrictive diseases. Spirometry, not a nebulizer, is used to measure this ratio for diagnosis.
Step-by-step explanation:
Obstructive lung disease can present with Forced Vital Capacity (FVC) less than 80% when there is airway obstruction that results in slow exhalation. To distinguish obstructive lung disease from restrictive lung disease, one would look at the Forced Expiratory Volume in one second (FEV1) to FVC ratio. In obstructive lung disease, this ratio is usually less than 69 percent due to the impaired ability to quickly expel air. Conversely, in restrictive diseases like respiratory distress syndrome and pulmonary fibrosis, the lungs are stiff or fibrotic with decreased compliance, making the FEV1/FVC ratio typically higher (88 to 90 percent), even though the overall FVC might be reduced.
Spirometry is a tool used to diagnose these conditions by measuring the rate at which air can be expelled from the lung. A nebulizer might be mistakenly referred to for diagnosis; however, it's primarily used for delivering medication rather than diagnostics. In contrast to restrictive conditions, where the intrinsic lung tissue is affected, obstructive diseases are characterized by increased airway resistance which can be detected by the decreased FEV1/FVC ratio using spirometry.