How are lung volume determination results interpreted in pulmonary function testing?

Updated: May 14, 2020
  • Author: Kevin McCarthy, RPFT; Chief Editor: Nader Kamangar, MD, FACP, FCCP, FCCM  more...
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Answer

Answer

Obstructive lung diseases, particularly emphysema, result in an increase in the RV and RV-to-TLC ratio. In severe emphysema, particularly bullous emphysema, the TLC can show a marked increase. Bronchial spasm, airway inflammation, excessive secretions in the airway, and loss of lung elastic recoil increase airways resistance and result in an insidious progressive increase in the end-expiratory lung volume that results in chronic hyperinflation (elevated RV, TLC, and RV-to-TLC ratio). Other pulmonary causes of increased RV include pulmonary vascular congestion and mitral stenosis. Extrapulmonic causes of increased RV include expiratory muscle weakness as observed in spinal cord injuries and myopathies.

Increased body weight due to increased fat causes an increase in chest wall elastic recoil, which favors a lower end-expiratory lung volume, resulting in less hyperinflation for any degree of airflow obstruction.

Lung volumes can confirm the presence of restriction when a reduced vital capacity is seen on spirometry. A reduced TLC is the hallmark of restrictive lung disease. An isolated reduction of the residual volume may be an early sign of restrictive lung disease. Pulmonary processes that can reduce the TLC include interstitial lung disease, atelectasis, pneumothorax, pneumonectomy, consolidation, edema, and fibrosis. Extrapulmonary causes of restriction include obesity, respiratory muscle weakness, thoracic deformities, and disease of the pleura.


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