Human Variation in Spontaneous Breathing Deposition Fraction: A Review

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Abstract
The fractional deposition of inhaled particles during spontaneous breathing is an important parameter in defining lung dose of inhaled particles for occupational and clinical exposures. Yet few investigators have studied particle deposition under spontaneous breathing conditions. Variability in spontaneous breathing deposition fraction (DF) may play a role in the variability of lung response to inhaled particles. This review attempts to address the degree of variability in spontaneous breathing DF measured in normal human subjects at rest, but more specifically attempts to address the causes of this variability. There are primarily two factors which likely contribute to variability in spontaneous DF, breathing pattern and the size of the airspaces. Included is a review of these factors only as they relate to spontaneous DF of particles depositing primarily in the periphery of the lung. This author concludes that present evidence, as set forth in this review, suggests that breathing pattern variability in humans is greater than variability in peripheral airspace size, and as a result plays a greater role in the variability observed in spontaneous breathing DF.

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