Mass median aerodynamic diameter

FIGURE 5.28 Estimated overall airway deposition as a function of initial particle size and particle hygroscopicity for particles with mass median aerodynamic diameters (MMAD) between 0.1 and 10 p.m. ° Geometric dispersion, a measure of particle size distribution, principally affects only smaller MMAD,... 

Pb-212 vs S0%- LPI Distributions. Figure 3 presents a summary of the average Pb-212 AMADs and SOj MADs (mass median aerodynamic diameters) determined from a series of LPI measurements made during the period January to October, 1985. The Pb-212 data were derived from collections made at the same time as S0jj and from measurements made to compare Pb-212 vs Pb-214. The mean aerodynamic diameter of Pb-212 was about three times smaller than SoJ . Much less sulfate was found in the aerosol fraction below 0.08 um, compared with Pb-212. While Pb-212 was largely absent above 0.52 um, about 20% of the SoJ occurred above this size. 

The aerodynamic size distributions of Pb-214, Pb-212, Pb-210, Be-7, P-32, S-35-SoJ , and stable SO4 were measured using cascade impactors. Pb-212 and Pb-214, measured by alpha spectroscopy, were largely associated with aerosols small than 0.52 11m. Based on over 46 low-pressure impactor measurements, the mean activity median aerodynamic diameter (AMAD) of Pb-212 was found to be 0.13 11m, while for Pb-214 the AMAD was larger—0.16 lim. The slightly larger size of Pb-214, confirmed with operationally different impactors, was attributed to a-recoil-driven redistribution of Pb-214 following decay of aerosol-associated Po-218. A recoil model was presented that explained this redistribution. Low-pressure impactor measurements indicated that the mass median aerodynamic diameter of SoJ ... 

Published results on the concentration and size distribution of small particles in mainstream smoke vary widely, with concentrations ranging from 107 to 1011 cm-3 and with NMAD (number median aerodynamic diameter) ranging from 0.2 to 0.7 fim (Ishizu et a/., 1978). The MMAD (mass median aerodynamic diameter) of undiluted mainstream smoke particles ranges between 0.93 and 1.00 finl (Langer and Fisher, 1956 Holmes et a/., 1959). Lower values of the MMAD for diluted mainstream smoke, which decreased with degree of dilution, are reported by Hinds (1978). However, the particle size distributions for mainstream smoke appear to have little relevance to its retention and distribution in the lung, for reasons discussed below. Note that the concentration of tars in mainstream smoke is about 1,000 times that of air in smoke-filled rooms. 

Fig. 1. Deposition of inhaled particles of different sizes (mass median aerodynamic diameters) in the three regions of the respiratory tract. Each shaded area indicates the variability of deposition when the aerosol distribution parameter, o, (geometric standard deviation) was varied from 1.2 to 4.5. The assumed tidal volume was 1450 cm3. (Reproduced from Health Physics, vol. 12, pp. 173-207,1966 by permission of the Health Physics Society).

The various pharmacopeias outline appropriate methods for aerodynamic assessment of partiele size distribution. The USP defines the size distribution through mass median aerodynamic diameter (MMAD) and geometrie standard deviation (GSD). 

Both from deposition studies and force balances it can be derived that the optimum (aerodynamic) particle size lies between 0.5 and 7.5 pm. Within this approximate range many different subranges have been presented as most favourable, e.g. 0.1 to 5 pm [24], 0.5 to 8.0 pm [25], 2 to 7 pm [26] and 1-5 pm [27-29]. Particles of 7.5 pm and larger mainly deposit in the oropharynx [30] whereas most particles smaller than 0.5 pm are exhaled again [31]. All inhalation systems for drug delivery to the respiratory tract produce polydisperse aerosols which can be characterized by their mass median aerodynamic diameter (MMAD) and geometric standard deviation (oq). The MMAD is the particle diameter at 50% of the cumulative mass curve. 

Used to derive a chronic inhalation Minimal Risk Level (MRL) of 2 x 10" mg/m nickel for soluble nickel salts dose adjusted for intermittent exposure (6/24 hours, 5/7 days), multiplied by the Regional Deposited Dose Ratio (0.9714 for pulmonary region deposition mass median aerodynamic diameter [MMAD] = 2.5 pm, sigma = 2.4 pm), and divided by an uncertainty factor of 30 (3 for extrapolation from animals to humans, and 10 for human variability). 

The half-life of nickel in the lungs of rats exposed by inhalation has been reported to be 32 hours for nickel sulfate (mass median aerodynamic diameter [MMAD] 0.6 pm) (Hirano et al. 1994b), 4.6 days for nickel subsulfide ( Ni3S2 activity, median aerodynamic diameter [AMAD] 1.3 pm), and 120 days for green nickel oxide ( NiO, AMAD 1.3 pm) (Benson et al. 1994). Elimination half-times from the lung of rats of 7.7, 11.5, and 21 months were calculated for green nickel oxide with MMADs of 0.6, 1.2, and 4.0 pm, respectively (Tanaka et al. 1985, 1988). 

The Mass Median Aerodynamic Diameter (MMAD) was reported as a lower limit of 0.8 pm and an upper limit of 1.2 pm for an average of 1.0 pm (pg 33 Hartman 1990). The Geometric Standard Deviation (GSD) was reported as a lower limit of 1.2 pm and an upper limit of 1.5 pm for an average of 1.35 or 1.4 pm. The Regional Deposited Dose Ratio (RDDR) from Table HI under the ER (Extrarespiratory effects) column is... 

Minimal data are available from typical inhalation studies in laboratory animals to allow evaluation of extent or dose-dependency in inhaled arsenic absorption. Beck, Slayton and Farr (2002) reported a study in which rabbits were exposed to 0.05, 0.1, 0.22, or 1.1 mg m-3 of arsenic trioxide 8 hours/day, seven days/week for eight weeks. The particle size (mass median aerodynamic diameter, MMAD) ranged from 3.2 to 4.1pm. On the basis of minimal elevation of inorganic arsenic in plasma until exposure levels were at or above 0.22 mg m-3, the authors concluded that systemic uptake of arsenic trioxide following inhalation exposure was low and did not contribute significantly to body burden until relatively high levels of exposure were achieved. 

Aerodynamic diameter Particles suspended in gases typically have irregular shapes. The aerodynamic behavior of an irregularly shaped particle may be modeled with an idealized sphere of uniform composition. The diameter of the sphere is the aerodynamic diameter (compare with mass median aerodynamic diameter). 

Mass median aerodynamic diameter A measure of particle size related to its mass. The aerodynamic diameter of an aerosol, where 50% of the mass of the aerosol has particles with larger aerodynamic diameters and 50 % has smaller diameters. 

The mass median aerodynamic diameter (MMAD) is defined as the aerodynamic diameter which divides the aerosol mass size distribution in half. 

We routinely use nose-only inhalation exposure of B(a)P aerosol to evaluate the consequence of prenatal exposure to this toxicant on physiological and behavioral endpoints. The properties of this B(a)P aerosol are shown in Figure 17.4. The aerosol typically exhibits a trimodal distribution with a 93% cumulative mass less than 5.85 pm, 89% cumulative mass less than 10 pm, 55.3% cumulative mass less than 2.5 pm, and 38% less than 1 pm. Fifty-five percent of the aerosol generally has a cumulative mass less than PM2.5 and the mass median aerodynamic diameter (MMAD) + geometric standard deviation for this mode is consistently 1.7 =E 0.085 pm. For several years we employed a rat model exposing timed pregnant dams to inhalation concentrations of 25, 75, and 100 pg/m. ... 

The various pharmacopoeias outline appropriate methods for aerodynamic assessment of particle size distribution. The USP defines the size distribution through mass median aerodynamic diameter (MM AD) and geometric standard deviation (GSD). None of the pharmacopoeias specify a requirement for particle size. However, the particle size specifications that are set should be appropriate for the intended use of the product. For example, if the particles are intended to reach the deep lung, the MMAD of particles exiting the... 

P3). The average mass median aerodynamic diameter was 3.55 0.07 pm with the geometric standard deviation of 2.55. The test was also conducted to compare the device performance with other small-volume nebulizers,and found to be more efficient in the delivery rate (mass out per minute) than that of other SVNs. 

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