How are the results of a lung volume determination expressed 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

All lung volumes are expressed in liters to the nearest hundredth of a liter. FRC is the volume of gas in the lungs at the end of an average resting expiration. It is comprised of the expiratory reserve volume (ERV), the volume of gas that can be voluntarily exhaled beyond the FRC or ITGV, and the RV. The TLC then can be calculated by adding the RV to the vital capacity (VC). RV also is expressed as a fraction of the TLC, the RV-to-TLC ratio (see the image below). The expected repeatability of three repeated same-session measurements of FRC is ± 5%. The standards for expected repeatability of other parameters (RV, IC, TLC) have not been set, but the expected repeatability of the VC is the same as FVC, ≤ 0.15 L difference between the two largest.

This is a graph of lung volumes in health and in d This is a graph of lung volumes in health and in disease, showing the various lung subdivisions. Normal aging results in an increase in functional reserve capacity (FRC) and residual volume (RV) and a normal total lung capacity (TLC) percentage. Obstructive lung diseases cause hyperinflation (increase in RV and FRC) with a relatively normal forced vital capacity (FVC). In severe emphysema, the TLC percentage can exceed 150%, with the RV impinging on the FVC. Restrictive lung diseases exhibit reduced TLC percentage with relative preservation of the RV/TLC percentage in fibrosis, a reduced inspiratory capacity and expiratory reserve volume (ERV) in neuromuscular disease, and severe reduction of the ERV in extreme obesity.

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