pulmonary plethysmography; total body plethysmography

Indications

• measures pulmonary functional residual capacity & total lung volume
• a flow-loop can calculated to assess pulmonary compliance
• restrictive lung disease
• chronic obstructive pulmonary disease
• respiratory muscle weakness
• useful for patients who have air spaces which do not communicate with the bronchial tree

Procedure

• the patient sits in a small, airtight room known as a body box & breathes against a mouthpiece
• clips are put on the nose to shut off the nostrils
• the mouthpiece may be open at first, & then closed
• breathing changes the pressure of air in the room & against the mouthpiece
• at the end of normal expiration, the mouthpiece is closed
• the patient is then asked to make an inspiratory effort
  • the lungs expand, decreasing pressure within the lungs & increasing lung volume
  • this increases pressure within the box since it is a closed system & the volume of the box has decreased to accommodate the new volume of the lungs

More general terms

• plethysmography