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Instructions,
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A comparison of techniques to assess regional deposition of aerosol particles in individuals with compromised lung function. A new technique has recently been
proposed, called the Single Breath Regional Deposition (SBRD).
This technique quantifies intrapulmonary distribution of particles
deposited in the lungs using monodisperse inert and non-radioactive aerosols
by measuring particle number concentrations of inhaled and exhaled test
particles. This measurement
allows the quantification of particle deposition as a function of the
volumetric lung depth. The authors used a fast mass spectrometer that measures
the concentrations of various gases (respiratory and non respiratory) within
the respired air as a function of the respired air volume to calculate dead
space. When the individual
functional dead space of the lung is known, the fraction of particles
deposited proximal and peripheral to the dead space can be calculated.
This represents deposition in the conducting airways and in the
alveolar space, respectively. This
method was originally developed for aerosol boluses and has been generalized
for single breath inhalations. These authors investigated the use of
this SBRD test in patients with compromised lung function since these tests
are purported to be influenced by lung disease. The results were compared to
those values obtained by the CRD method, which has been validated for use in
patients with COPD. A comparison
of the CRD and SBRD methods have been previously done in healthy subjects and
the results showed good agreement.
Furthermore, prior studies between healthy and Chronic Obstructive
Pulmonary Disease (COPD) patients, revealed that after 24 hours, the results
were identical using the CRD method. Therefore,
it was concluded that CRD was a valid test in persons with COPD.
Thus, the CRD method has been tested in both healthy subjects and those
with compromised lung function. To
date, the SBRD technique has only been performed in healthy subjects. Brand et al. measured the deposition
of monodisperse test particles with aerodynamic diameters of 2,3, and 4 um
(di-2-ethylhexylsebacate droplets) in 12 patients (8 males & 4 females)
with homozygote alpha-1 antitrypsin deficiency and symptoms of moderate to
severe chronic obstructive pulmonary disease. Notwithstanding a slightly different
technique to measuring dead space (usingC18O2 as a
tracer gas as opposed to nitrogen gas), the SBRD also showed promise as a
method to use in patients with COPD. However,
the validation has to be generalized in future studies to patients with
differing lung diseases and different breathing patterns as well as with
different aerosol particle sizes. In conclusion, this study compared the
SRBD technique with the CRD technique. Their results showed that both
techniques yielded very similar results with respect to total and alveolar
deposition. The CRD method used
the kinetics of particle clearance within the first 24 hours after inhalation
to determine bronchial and alveolar deposition.
In contrast, the SBRD method used the longitudinal distribution of
deposited inert test particles to calculate the particle fraction deposited
within and distal to the dead space. The
authors suggested that because of controlled slow and deep inhalations, the
alveolar deposition was as much as 50% in patients with COPD.
They concluded that SBRD should be considered an easy tool to study
alveolar deposition in patients whose lung function is compromised. By: Arlene L. Weiss, MS DABT |