Regional deposition of inhaled hygroscopic aerosols: in vivo SPECT compared with mathematical modeling

The regional deposition patterns of inhaled hygroscopic aerosols obtained in vivo in the studies of Phipps et al. (P. R. Phipps, I. Gonda, D. L. Bailey, P. Borham, G. Bautovich, and S. D. Anderson. Am. Rev. Respir. Dis. 139: 1516, 1989; and P. R. Phipps, I. Gonda, S. D. Anderson, D. L. Bailey, and G. Bautovich. Eur. Respir. J. 7: 1474-1482, 1994) and Chan et al. (H.-K. Chan, P. R. Phipps, I. Gonda, P. Cook, R. Fulton, I. Young, and G. Bautovich. Eur. Respir. J. 7: 1483-1489, 1994) by using single-photon-emission computerized tomography (SPECT) are compared with the regional deposition predicted by the hygroscopic lung deposition model of Finlay and Stapleton (W. H. Finlay and K. W. Stapleton. J. Aerosol Sci. 26: 655-670, 1995). Three pairs of saline aerosols are considered: isotonic with small [2.6-microns mass median aerodynamic diameter (MMAD), geometric standard deviation (GSD) 1.4] vs. large (5.5-microns MMAD, GSD 1.7) droplets; hypotonic (0.3% NaCl) vs. hypertonic (4.5% NaCl) with 3.7- to 3.8-microns MMAD (GSD 1.4), and hypotonic vs. hypertonic (3.7- to 3.8-microns MMAD, GSD 1.5-1.8) with reduced number of droplets per cubic centimeter. For each of the three pairs of aerosols, no significant difference (P > 0.05) was found between the in vivo and computational results for either the mean value or the variance of the difference in peripheral to central deposition. Thus it appears that theoretical calculations can be used to predict the pattern of lung deposition of hygroscopic aerosols in populations of normal subjects.