Diameter, aerodynamic geometric

Activity median aerodynamic diameter h Geometric standard deviation. 

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. ... 

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,... 

Table II. Summary of Mean Monthly Activity Median Aerodynamic Diameters (AMAD) and Geometric Standard Deviations (tfg) of Radon and Thoron Daughter Size Distributions in Ambient Aerosols...

Table III. Median Aerodynamic Diameters (MAD) and Geometric Standard Deviations (Og) of Pb-210 and Be-7 Based on Radioactivity and SO Measured with High-Volume Cascade Impactors...

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).

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. 

The apphcation of the laser diffraction technique is sometimes questioned becanse it measures geometric instead of aerod5mamic particle diameters. However, the aerod5mamic diameter can be calcnlated when the dynamic shape factor and density are known. Moreover, the dynamic shape factor (x) of micronized particles will often be only shghtly higher than 1 and so is the tme particle density (1.0 < pp < 1.4 g cm ). As a conseqnence, the aerodynamic diameter differs only slightly from the eqnivalent volume diameter (see Eq. 3.1). 

Dg is the geometric diameter, pp is the density of the particle, neglecting the buoyancy effects of air, p is the reference density (1 g cm 3), and k is a shape factor, which is 1.0 in the case of a sphere. Because of the effect of particle density on the aerodynamic diameter, a spherical particle of high density will have a larger aerodynamic diameter than its geometric diameter. However, for most substances, pp 10 so that the difference is less than a factor of 3 (Lawrence Berkeley Laboratory, 1979). Particle densities are often lower than bulk densities of pure substances due to voids, pores, and cracks in the particles. 

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... 

The recovered liposomes possess a mean geometric diameter of 0.2 p.m. The aerodynamic diameter of these particles, when emitted from an ultrasonic nebulizer, is 1 xm. 

A solution of insulin is added to an aqueous suspension of Technosphere particles. The insulin is adsorbed to the surface of the particles to form TI. The solvent is then removed from the suspension by lyophilization to produce the bulk drug powder. TI has a mean geometric diameter of 2.0 p,m and an aerodynamic diameter of 2.5 xm. 

AIR particles are low-density lipid-based particles that are produced by spray drying lipid-albumin-drug solutions. These particles are characterized by their porous surface characteristics and large geometric diameter while having a low aerodynamic diameter [176,177], This technology has been used to produce porous particle powder formulations of L-dopa that have been investigated for the treatment of Parkinson s disease [178],... 

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... 

Aerosol properties, such as particle size distribution, aerosol velocity, and hygroscopicity, affect aerosol deposition in the human lungs. Aerosol size distribution, including mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD), is one of the most important variables in governing the site of droplet or particle deposition in the lungs. ... 

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. 

Likewise, particles which appear to be visually of similar size and shape may have different aerodynamic diameter if their densities vary, and geometrically large porous particles can have aerodynamic diameters in the respirable range (between 1 and 5 pm), owing to their low density ... 

Hg. 4. Geometric particle size distributions of different pyrogenic silicas. Correlated aerodynamic diameter can be calculated fiom LD by using an effective density (agglomerate) of0.075 g/cm [8]. 

Three primary mechanisms govern the deposition of aerosols in the respiratory tract inertial impaction, sedimentation, and diffusion (Fig. 7). Early work by Landahl and coworkers showed that both sedimentation and inertial impaction in the mouth, throat, and lungs uniquely depend on the particle aerodynamic diameter [220], Deposition by diffiisional transport is independent of particle density and limited primarily to particles with geometric diameters smaller than 0.5 p,m [221],... 

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