DSI Buxco FinePointe - Alternate Boyles Law Method Without P

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Pulmonary Function Test • Publication 014181-001 Rev 02 • www.datasci.com ©2023 Data Sciences International
sure your V
injected
reflects what you injected.
• Be sure to specify P
atm
in cm H
2
O units—it should be somewhere near 1030 cm H
2
O
Alternate Boyle’s Law Method Without P
atm
If P
atm
is not known, you can use this method to measure the dead space. This method requires you to make two
injections, and to find two ΔP values. The two injections that you make must differ by a known volume (referred
to here as V
b
).
Ideally, you would want to make that known volume about ¼ the volume of the estimated dead space. And the
volume you will inject (V
injected
) could be 10 times smaller. It is desirable to use the same syringe to both provide
the V
b
and to allow you to inject V
injected
.
So, if you estimate the dead space is 0.85ml, then you might want V
b
to be around 200µL and you will want to
inject about 20µL. This will require you to use a 250µL syringe, and so the accuracy of the 20µL injection is
diminished from what it would be if you used a 50µL syringe. In short, you need to make a tradeoff between
accuracy of the V
injected
and the accuracy of V
b
.
To improve the situation, instead of injecting only 20µL, inject 50µL. This will improve your ability to have accurate
values for both V
injected
and V
b
. However, it requires that you recalibrate the mouth pressure to be less sensitive,
to avoid saturation.
Procedure:
1. Calibrate Mouth Pressure so that you get an Effective Range of +/- 90 cmH2O. You will have to reduce
the gain on the M Pressure preamplifier.
2. Attach your sealed tracheal catheter to the tracheal port, on the inside of the chamber.
3. Turn off the FRC valve (to open it).
4. Attach the syringe onto the N
2
sample port.
5. Pull the plunger of the syringe back 50µL (or V
injected
)
6. Turn on the FRC valve (to close it).
7. 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.
8. 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”.
9. Freeze the waveform in FinePointe Station 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
0
in the equation below.
10. Turn off the FRC valve (to open it).
11. Pull the plunger of the syringe back 250µL (or V
injected
+ V
b
)
12. Turn on the FRC valve (to close it).
13. 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.
14. Inject the syringe 50µL (V
injected
) to 200µL (V
b
) plunger position. The Mouth pressure signal
should rise, and if there are no leaks, it will remain steady at that level.
15. Freeze the waveform in FinePointe Station and use on the cursor to read back the stable pressure.