Biology Reference
In-Depth Information
CO
2
and O
2
analyzers) and to convert them into digital numeric
values that can be processed by a computer. There are several
acquisition systems commercially available and each of them
has its pros and cons. The main concerns for the experi-
menter in a choice of acquisition system is the compatibility
with analyzing software (especially in term of acquisition fre-
quency) and measurement devices connections (usually BNC
connectors).
10. Once converted by the acquisition system, the collected data
should be registered and then analyzed on a computer. Several
comprehensive software are available for data acquisition and
real-time analysis. Some software present two distinct mod-
ules, a first one which register the data inputs and a second one
devoted to data analysis. Usually, the software used for plethys-
mography analysis generate both a stream file of the registered
traces and data files containing numeric values obtained from
the traces or calculated from them.
11. Although this is not necessary the gas content of the experi-
mental cylinders to be certified, it would increase the homoge-
neity in the results (especially if one would compare experiments
done by using more than one gas cylinder). If mixing the gases
in the lab, we strongly recommend the use of an appropriate
gas analyzer(s) located within the system to specifically assess
the gas content of the air entering in the plethysmography
chamber.
12. The caliber (internal and external diameter) of the tubing
should be optimized as much as possible in order to avoid
over-pressure and to limit the air dead volume within the air
path. Also in order to limit the air dead volume, the length of
the tubing should be kept at the necessary minimum.
13. A wide variety of connectors is necessary to properly and con-
veniently interconnect tubing together or with devices.
14. It is essential to dry the air before its arrival in the gas analyzers
because evaporated water causes interference with CO
2
mea-
surement which is carried out by infrared optical detection.
For this reason, an air dryer should be inserted in the air path
just before entering in the CO
2
analyzer.
15. Our experience teaches us that between 6 and 10 mice per
group is usually sufficient to obtain satisfying and representa-
tive plethysmography results. Nevertheless, the sample size
has to be determined empirically for each experimental design
and increased until the standard errors are reasonable in com-
parison to means. If wild-type mice are used, the extrapolation
and comparison with previous or published results should be
carefully leaded since some differences in the breathing phe-
notype of different mice strains has been reported (
15
).
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