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 FinePointe Pulmonary Function Test (PFT) Manual Section Fast Flow Volume for list of common parameters reported. 

With this test, more than any other, you should be concerned about the position and comfort of the animal.

Common Reasons

The inspiration to 30 cm H20 phase of the FV test is not triggered

This can happen if the end of the breaths cannot be determined during the breath history phase. The slow expiration phase is triggered when the breath hold phase ends.

Make sure the calibration is good for all leads.

Check the system for leaks (See the Leaks section in the PFT Manual).

30 cm H20 of pressure cannot be achieved during the inspiration phase

• • There could be a leak in the tracheal tube surgery. Check the surgery site and the tubing connection to the manifold.
  • The inspiration flow rate is too low. Increase in inspiration flow slightly and repeat the test (See the Setting Inspiration Flow section on page 25).
  • There could be a leak in the valves (See the Leaks section below)
  • If you have a test lung for your species type, connect it and attempt the PV test. If the test passes, the issue was probably with the tracheal surgery or the connection to the manifold. If it still fails, try the other items in this list.
  • 30 cm H20 must be reached within a unique specified time for each species, or the inspiration will time out. Keep in mind that the rate you need to achieve for a “good” test is usually less than the time out value (See the Setting Inspiration Flow section on page 25). For example, with mice the inspiration time out is 5 seconds. However, the best inspiration rate for the average sized mouse is to reach 30 cm H20 in 1-2 seconds.

The fast expiration phase failed

• • • Check the connection from the fast flow valve to the negative pressure reservoir.
    • Ensure the negative pressure dial is set to -40 on the PFT controller. It can be set as high as -50 cmH20 if needed.
    • Check the system for leaks (See the Leaks section below).

Animal Breathes During Tests

If your animal is breathing throughout the tests, consider the following possibilities:

• Inspiratory Flow Rate is too low.
• Expiratory Flow Rate is too low.
• Anesthesia dose should be increased.

Ripples or Squiggles Near the End of the Flow-Volume Curve

If you observe squiggles near the end of the Flow Volume curve, it is probably because there is mucus, goo, or condensation in the lung or trach tube. For larger animals, we recommend you suction it out. For mice, just change either the trach tube or the mouse.

A Flat Top of the Flow Volume Curve

This does not occur often, but if you look at a Flow-Volume curve, and it is perfectly flat at the top, this is most likely a saturated flow transducer. What to do:

• Make sure the calibration procedure was performed properly.
• Make sure that the High Flow input is connected to Lead 1.
• Reduce the gain on the flow preamp and recalibrate the High Flow, Flow, and FRC flow.
• Make sure that there are no obstructions in the tracheal line of the manifold.

Dip in the Center of the Flow-Volume Curve

A dip in the flow near mid volume of the Flow-Volume curve could be a real result of a physiological condition, however, when it is observed you should check a couple things to make sure it is not something else. This shape is caused by a temporary obstruction in the expiration line. One example may be a collapsed tube either in or outside the lung. A balloon without cotton inside will almost always do this as the flabby piece of balloon covers the hole in the trach tube temporarily. You might just try repositioning the animal to make sure the tracheal line is straight and not putting the trachea at any angles.

Generally Rounded Flow-Volume Curve

The FVC parameter (forced vital capacity) should not be too far from what you expect. If the tracheal tube is inserted too deeply in the lung, the end of the tracheal tube may pass the first bifurcation of the lung. The result is that you are performing your test on only one half of the lung.

FVC Value is Wildly Different Than IC

Though rare, we have seen data where the expired volume is very small when compared to the inspired volume. While this can be caused by a physical obstruction in the airway or tubing, for example, a tube crimps during the expiratory phase, you may want to confirm the calibration for the Flow and High Flow signals. In general, the effective range of the High Flow should be 8 times larger than the effective range of the Flow signal. A jumper on the Signal Generator card can change this to 4 times.

4 times has been recommended for mouse systems. The High Flow signal is only used during expiration of the FV test, so problems with the High Flow calibration should not impact other tests.

Additional Resources:

FinePointe Pulmonary Function Test (PFT) Manual

Functional Residual Capacity (FRC) Test Troubleshooting

PFT Pressure Volume (PV) Test Troubleshooting

PFT Troubleshooting Leaks