Functional Residual Capacity (FRC) is the volume of air that remains in the lung at the end of a normal expiration. During the FRC test with PFT, the subject should be able to breathe on their own. The airway is occluded at the end of expiration, and based on Boyle’s law, the residual volume is derived from the subject’s attempts to breathe. The residual volume resulted from Boyle’s law calculation is made of FRC plus the total dead space  (that includes the dead space in the manifold and in  the tracheal tube. )

The total dead space must be introduced in Fine Pointe under the PFT hardware configuration (see the screenshot below).  Fine Pointe subtracts this dead space automatically to report the FRC values directly.

The dead space introduced by the user in Fine Pinte has to be accurately measured. If during a study, the length of the tracheal tube that is used is changed, this has to be considered in the calculation of the dead space introduced in Fine Pointe.

If the user overestimates the dead space, the reported FRC values are too small, even negative.

Conversely, if the dead space is underestimated, the reported FVC values are too large.

Attached are the instructions on how to measure the dead space in the manifold.