The influence of breathing patterns on particle deposition in a nasal replicate cast

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Abstract

The purpose of these experiments was to measure the differences in total deposition in the nose arising from differences in the breathing patterns. Monodisperse droplets (from 1.7 to 10μm) were deposited in an artificial nasal cavity (cast) using different human breathing patterns as well as under constant flow rate conditions. The human breathing patterns were recorded from a volunteer and then reproduced by a breathing simulator. The nasal cast was made from Magnetic Resonance images of the same volunteer, which were digitised and milled into consecutive plates to form a cavity.

The results for small particles (1.7 and 3μm) show much higher deposition at high constant flow rates than at fast human breathing. The difference becomes less pronounced with increasing particle size, but is still significant at high flow rates. This suggests that it might not be sufficient to take the average flow rate of the breathing pattern for comparison with constant flow. Therefore, the breathing patterns were partitioned into small segments and deposition was calculated for each segment. Adding deposition of each segment gives a theoretical predicted total deposition caused by the particular breathing pattern. However, the theoretical deposition is higher than the measured deposition at high flow rates, and again this is more pronounced for small particles.

An explanation was given for this behaviour.

Introduction

Since the nose is an effective filter for inhaled air, it has a large influence on the amount of particulate matter reaching the lungs, and for soluble materials may be an important route of entry into the systemic circulation. Several authors (Etherington et al., 1998; Heyder & Rudolf, 1977; Hounam, Black, & Walsh, 1969; Kesavanathan & Swift, 1998; Lippman, 1977; Stahlhofen et al., 1989) have, therefore, performed in-vivo nasal deposition studies using radio-labelled particles. Measurements of regional deposition in the nose require relatively large amounts of radioactivity and, therefore, a high radiation dose for the participants. To avoid giving such doses and to obtain more reproducible results, complementary studies on artificial nasal cavities (nasal casts) have been carried out (Cheng, Yeh, Smith, Cheng, & Swift, 1998; Gradon and Podgorski, 1992; Itoh et al., 1985; Strong & Swift, 1987; Swift, 1991; Zwartz & Guilmette, 1999). Studies on nasal casts allow measurements of the influence of a single factor on deposition, but these studies so far have been limited by their methodology in several ways. Nasal passages have in the past been made from cadavers rather than living human beings. A cadaver's anatomy is physically different from a living human, and use of such casts excludes the possibility of comparison with deposition measurements of the human volunteer from whom the cast was made. A method to reproduce human airways from magnetic resonance imaging scans (MRI scans) of human volunteers was therefore developed by (Swift, 1991) and refined by Guilmette and Gagliano (1994). Deposition studies using these casts were performed, but realistic breathing patterns were not used (Cheng et al., 1998; Swift, 1991; Zwartz and Guilmette, 1999). The particles were usually inhaled using a pump that produced constant flow rather than cyclic flow patterns or realistic human breathing.

The purpose of these experiments was to compare total deposition in a nasal cast with several human breathing patterns and also constant flow. To simulate human breathing, a breathing simulator has been designed and constructed (Häußermann et al., 2000). It is computer controlled, and also allows artificial breathing patterns to be implemented. Furthermore, an artificial nasal cavity was built utilising MRI to replicate the nasal anatomy of a human volunteer, whose various breathing patterns were also recorded.

Section snippets

Material and method

Monodisperse sebacate oil droplets of various aerodynamic diameters dae (1.7, 3, 6 and 10μm) were drawn through the cast using different flow rates. Oil droplets rather than solid particles were used because of the tendency of the latter to bounce off the surface of the cast. The droplets were produced using a Vibrating Orifice Aerosol Generator (VOAG) Model 3450 from TSI Inc. An ionising source (85Kr) was used to bring the charge level of the particles to Boltzmann equilibrium.

The cast was

Results

Fig. 3, Fig. 4, Fig. 5, Fig. 6 show the total deposition in the cast for constant flow and human breathing. To be able to compare constant flow with the cyclic patterns, average flow rates were taken for the latter.

Fig. 3 shows the total deposition of 1.7μm dae particles. While deposition at constant flow reaches 100% at a flow rate of 30L/min, deposition for human breathing never reaches more than 40%. Fig. 4 shows the deposition of 3μm dae particles. The difference in deposition for the two

Discussion

The results show that deposition caused by constant flow is generally higher than deposition caused by cyclic human breathing with the same average flow rate. The difference is greatest for 1.7μm dae particles and diminishes when the particles become larger, but is still observable.

The influence of breathing patterns on the deposition efficiency could have different explanations. The cyclic flow patterns have a high proportion of very low flows and comparing constant flow to the average flow

Conclusions

This work shows that breathing pattern influences the total amount of nasal deposition and probably also the deposition sites. The total deposition for constant flow is significantly higher than that of human breathing. This is surprising because similar experiments by others with lung casts showed the opposite results (Gurman, Lioy, Lippmann, & Schlesinger 1984a, Gurman, Lippmann, & Schlesinger 1984b). The impaction factor is normally an indicator of deposition by impaction. The results in

Acknowledgements

The authors wish to thank Dr. R. Guilmette for his active help and advice to produce the artificial nasal cavity. This work was partly supported by the CEC under contract F14P CT950026.

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