DSI Buxco FinePointe - How It Works

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The FRC tests measures the FRC lung volume by using Boyle’s Law. FRC lung volume is the Functional Residual

Capacity. This is the volume of air that remains in the lung at the end of a normal expiration. This lung volume is

important because by knowing this lung volume, it is easy to know all the other lung volumes.

See Section FRC for list of common parameters reported.

The PV test allows the researcher to know the static lung properties. Static lung properties are described by the

pressure-volume relationship of the lung. The slope of the Volume-Pressure curve is the instantaneous compliance

at a given pressure. See Section Quasistatic Pressure VolumeFRC Test for list of common parameters reported.

The FV test allows the researcher to know the dynamic lung properties. Dynamic lung properties are described by

the flow-volume relationship of the lung. The Flow-Volume curve shows the flow at a given expired volume. Since

the pressure across the lung is essentially constant during the acquisition of the flow-volume data, the flow value is

proportional to the conductance of the limiting airways at a given expired volume. See Section Fast Flow Volume

for list of common parameters reported.

See Section Resistance & Compliance for list of common parameters reported.

How It Works

The subject has a tracheotomy performed (or is intubated) and placed in the supine position on the bed within the

plethysmograph. The trach tube is connected to the face plate where fresh air is provided either via bias flow or

through ventilation. The face plate contains a manifold of valves which are actuated to perform the PFT tests.

Also, supporting the manifold is a pressure panel which provides flows at safe pressures to the manifold. The

pressure panel also contains preamplifiers necessary to condition the flow and pressure signals needed for the

data analysis.

With the plethysmograph placed around the subject, the subject breathes through the wall of the face plate and

the chest expands with the air entering and contracts as the air exits the lungs. This expansion forces an equal

amount of air out of the plethysmograph through a screen pneumotach. The pneumotach resists the movement

of air, and so, pressure in the chamber is created as a result of the air being forced through the pneumotach. This

pressure is linearly related to flow of air passing through the pneumotach, and since that is the same as the

volume inspired by the subject, the pressure is related to the flow in and out of the subject.

The lung pressure is measured in the tracheal line. Normally, the pressure is referenced to atmosphere, but it can

optionally be referenced to the subject’s esophagus or even to the intrapleural cavity using a needle.