What are common errors in the performance of lung volume determination 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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Two types of errors are known to occur with body plethysmography techniques. One involves the underestimation of mouth pressure swings during respiratory efforts when the airway is occluded. The assumption that when no airflow is present the mouth pressures accurately reflect alveolar pressure has been shown to be not true when respiratory efforts occur at a frequency of greater than 1 Hz (respiratory rate of 60 breaths per minute). Thus, FRCpleth is overestimated if the frequency of the respiratory effort is not kept between 0.5 and 1.0 Hz (30-60 breaths/min) during shutter closure.

The second type of measurement error using body plethysmography involves trying to pace the patient's tidal breathing before shutter closure. The ideal respiratory rate during shutter closure is far in excess of the patient's resting respiratory rate and causes dynamic hyperinflation, increasing the lung volume above the resting lung volume. Patients should breathe at a relaxed spontaneous respiratory rate without coaching before shutter closure.

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