GE Analytical Instruments ©2006 8-17 DLM 14291 Rev. A
is to use a control. Collect exhaled breath from a subject and analyze the bag
immediately after collection. Save this bag and then re-analyze the control along
with the samples. The control will thus provide a measure of how much of a
change in NO might be expected.
Off-Line versus On-Line Exhaled NO Measurements
When the Deadspace Discard Bag Kit is used to collect exhaled NO at an expiratory
flow rate of 50 mL/s, there is no significant difference between off-line and on-
line exhaled NO measurements. When the Vital Capacity Bag Kit is used, an
expiratory flow rate of 350 mL/s gives a significantly lower exhaled NO value than
on-line measurements at 50 mL/s. A linear relationship between off-line and on-
line measurements has been reported (see Silkoff, et al., “A Method for the
Standardized Offline Collection of Exhaled Nitric Oxide.” Chest 1999; 116:754-759
and Canady, et al., “Vital Capacity Reservoir and Online Measurement of
Childhood Nitrosopnea Are Linearly Related.” Am J Respir Crit Care Med. 1998;
159:311-314), but the values are not interchangeable.
Testing Bags for Pinhole Leaks
Mylar bags have been reused over 50 times without problems. The most common
problem in reusing the bags is the development of pinhole leaks usually as a result
of emptying the bags by hand or rough handling. This can be avoided by always
using the vacuum technique to empty the bags and gently handling the bags. The
recommended procedure to test the integrity of the bags is to fill the bags with
varying concentrations of NO, such as exhaled breath from different individuals,
and measuring the NO concentration in the bags over a period of several hours
while also measuring the ambient NO concentration.
WARNING:
DO NOT FILL THE BAGS WITH PPM LEVELS OF NO FOR THESE TESTS. HIGH
CONCENTRATIONS OF NO WILL ABSORB ON THE WALLS OF THE BAGS AND IS
DIFFICULT TO REMOVE.
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