Chemical Analysis of Deep-Lung Fluid Derived from Exhaled Breath Particles

Breath particles generated deep within the lung provide
noninvasive
access to sampling nonvolatiles in peripheral airway lining fluid.
However, background contamination, their variable production among
subjects, together with a huge unknown dilution when using the common
breath condensate method for collection has limited their use for
quantitative biomarker analysis. Instead, we first capture and dry
the particles in a flexible chamber followed by accurate optical particle
characterization during their collection for chemical analysis. By
decoupling breathing and aerosol sampling airflows, this sequential
approach not only accommodates all types of breathing routines but
also enables the use of a variety of aerosol samplers for downstream
biomarker analysis. Using 23Na NMR, we measured 0.66 M
Na in dry particles collected on a filter, which suggests that dehydration
reduces their volume by a factor of ∼ 5.5 based on known Na
levels in lung fluid. 1H NMR revealed 0.36 and 0.68 M phosphocholine
lipids in dried particles collected from two volunteers, presumably
enriched to these levels relative to literature values derived from
bronchoalveolar lavage fluid due to the film-bursting mechanism that
underlies breath particle generation. Decoupling of breath collection
and aerosol capture enabled the design of an impactor sampler with
72% efficiency. This impactor minimizes reagent and handling-related
contamination associated with traditional filters by collecting dry
particles directly in a microreactor for subsequent derivatization
and quantification by mass spectrometry. The method is demonstrated
by quantifying subnanogram amounts of urea from breath particles,
corresponding to lung fluid urea concentrations consistent with literature
blood plasma values.