The principal cause of problems with the PFT testing you will find are due to leaks.

Leaks may occur at any point where there is a detachable junction between two air passages.

While the chamber and valve assembly are shipped with no leaks, the equipment is very fragile and even the jostling during shipping may cause some leakage. However, we have found that the most common place for leaks is the tracheal connection, where the cannula enters the animal. Other common causes for leaks include - equipment being moved from one place to another, and air tubes being connected and disconnected.

Common Symptoms

If any of the following are occurring in your experiment, consider that there may be a leak in your system, and use the “Guide to Fixing Leaks”.

• The system has trouble delivering inspirations (“Unable to inflate to 30 cmH2O”).
• The system has trouble performing forced expirations.
• Hold period does not appear flat, but drifts upwards (in the PV maneuver).
• Expiration does not cross zero volume (also in the PV maneuver).
• The software has trouble analyzing data.

A FLAT volume trace during the Hold Period of (PV test)

Below is an example of what should be seen in FinePointe during the PV test Hold period.  When the animal is at TLC, the volume should be flat (see bottom pane of image below).  A volume that steadily moves up during this period generally means either 1) a leak exists in the manifold, or 2) the flow was not properly zeroed.  

General Suggestions

• In general, make sure that all connections are snug and airtight.
• Check the connection of the tracheal tube to the animal. Make sure the tube is tied in tightly, without any air leaking through. This is a very likely place to find a leak.
• To improve the quality of your seal, try using a greasy substance (like vacuum grease or silicone grease) around the outside of the air tube. Make sure that no grease gets inside the air tube.
• Thin Teflon tape may be applied or wrapped around the area in suspicion, providing a semi- malleable and snug connection. Be careful not to add too much Teflon tape, however, because too much will only prevent you from making the connection completely.

Test for Leaks in the Main Chamber

If you suspect a leak in the PFT chamber, then you can repeat the FRC flow calibration.

If the calibration is successful, then the chamber is likely not leaking.

If you want to verify more thoroughly that the chamber does not leak:

• Plug the tracheal tube port and close the chamber,
• Seal the pneumotach opening with painter’s tape or electrical tape,
• Pull the plunger of a 10 cc syringe back 5 mL,
• Connect the syringe to the syringe port of the chamber and to the calibrator at the same time using a Luer “T” fitting,
• Inject the air, keeping pressure on the plunger to make sure it does not get pushed back,
• Make sure that the water level in the calibrator does not rise and stays steady.

Test for Leaks in the Valve Assembly

If you suspect a leak in the valve assembly (the Lucite manifold that houses all the valve connections, at the end of the chamber). Simply follow the instructions listed in the Pressure Calibration chapter. After pushing the syringe plunger until the calibrator is at 20 cm H₂O, the water level in the manifold should not raise, and the voltage should not drift down. If the voltage drifts down, then you have a leak, and you should identify and fix the leak in the manifold.

Common places to look for a leak in the Valve Assembly:

• N2 Sample port. Make sure it is plugged.
• Mouth Pressure Transducer.

If the leak is not in either of these places, you will need to narrow it down by removing one valve at a time and plugging the hold with tape or a bung. Start with the Slow Expiration, then Inflation, etc.

If you cannot solve your leak problem, then you may have a faulty valve or transducer. Please email support in that situation.

Additional Resources:

FinePointe Pulmonary Function Test (PFT) Manual

Functional Residual Capacity (FRC) Test Troubleshooting

PFT Pressure Volume (PV) Test Troubleshooting

PFT Flow Volume (FV) Test Troubleshooting