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Pulmonary Function Test • Publication 014181-001 Rev 02 • www.datasci.com ©2023 Data Sciences International
Measuring Dead Space in the Manifold
In the FRC test, the Pressure and Volume changes caused by the animal’s attempts to breathe help us derive the
entire volume occluded from atmosphere. This volume is made up of the animal’s lung volume at the time of the
occlusion plus the dead space. So, if the animal is occluded at FRC, then after we determine the occluded volume,
we only need to subtract out the dead space to compute FRC.
The following procedure describes how to measure the dead space. Keep in mind that you should only need to
measure this if it is the first time you are using this apparatus or if you change the type of tracheal tube you are
using (the dead space of your apparatus should be constant unless you change your apparatus). Once you have
measured the dead space, this value must be entered into your hardware configuration in FinePointe Control Panel.
Boyle’s Law Method
Before you perform the measurement, make sure the mouth pressure transducer is properly calibrated.
You will need:
• A tracheal catheter with the end sealed (airtight)
• A small syringe, perhaps 100µL or 50µL for a rat chamber. You should plan on injecting 20µL into the
valve assembly.
• The current atmospheric pressure P
atm
, in cm H
2
O
• FinePointe open acquiring data so that you can view the mouth pressure signal
Procedure:
1. Attach your sealed tracheal catheter to the tracheal port, on the inside of the chamber. Make a
guess at the dead space and set your syringe to roughly 0.02 or 0.03 times that amount. For
example, if you guess that there is 0.85 mL of dead space, set the syringe for 20µL.
2. Attach the syringe onto the N
2
sample port.
3. Turn on the FRC valve (to close it).
4. Freeze the waveform in FinePointe Station and use on the cursor to read back the stable pressure.
Check it is at zero. If not, make note of the current value. Return the trace to Live.
5. Inject the syringe. The Mouth pressure signal should rise, and if there are no leaks, it will remain
steady at that level. If there is a leak, please use the suggestions in the chapter “Test for leaks in
the valve assembly”.
6. Freeze the waveform in FinePointe and use on the cursor to read back the stable pressure. Find the
difference from that stable value to the pressure before you injected the syringe. Use this difference
as ΔP in the following equation.
=
×
∆
P
atm
and ΔP must be in the same unit (cmH2O).
The computed Dead space is in the same units that V
injected
is specified.
Note the following to ensure a good measurement:
• Make sure the pressure signal did not get saturated. If it did, then you should repeat this process
with a smaller volume. If you do, make sure your V
injected
reflects what you injected.
• Your ΔP should be more than 10cm H
2
O. If not, try increasing the volume you inject. If you do, make
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