What is the role of pulmonary function tests in the workup of hypoventilation syndromes?

Updated: Jul 22, 2021
  • Author: Jazeela Fayyaz, DO; Chief Editor: Guy W Soo Hoo, MD, MPH  more...
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These measurements are required for the diagnosis of obstructive and restrictive lung diseases and for assessment of the severity of disease.

The ratio of forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC) is reduced in airflow obstruction and is the diagnostic variable. The Global Initiative for Chronic Obstructive Lung Disease (GOLD) defines obstructive lung disease as an FEV1/FVC ratio of less than 0.70. Others recommend that obstructive lung disease be diagnosed if the FEV1/FVC ratio is below the lower limits of normal. Note that the FEV1/FVC ratio decreases with age; this helps avoid overdiagnosis of obstructive lung disease in elderly patients. [13]

FEV1 is used to evaluate the degree of airflow obstruction. Generally, when the FEV1 drops to less than 30% (very severe COPD), patients may have hypercapnia. Lung volume measurements may document an increase in total lung capacity, functional residual capacity, and residual volume in obstructive pulmonary disease.

Lung volume measurements are also helpful in the diagnosis of restrictive ventilatory defects. When lung volumes are reduced without a reduction in the diffusing capacity for carbon monoxide, this indicates extrathoracic restriction. Obesity and thoracic cage disorders such as severe kyphoscoliosis may cause this.

Measurement of maximal inspiratory and expiratory pressures may be useful in screening for respiratory muscle weakness and neuromuscular disorders.

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