Aerosol mass median aerodynamic diameter

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 ... 

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. 

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. ... 

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. ... 

Pulmonary deposition of an aerosol preparation is determined primarily by its size. Aerosols with a mass median aerodynamic diameter of 1-5 xm produce the best therapeutic results and are the target particle size for inhalation therapy. These small particles penetrate deep within the respiratory tract to ensure drug deposition in peripheral airways. The cross-sectional area (cm ) of the lung increases dramatically at the level of the respiratory zone therefore, the velocity of gas flow during inspiration rapidly decreases at this level. Moderate-sized particles (5-10 (xm) frequently settle out by sedimentation in larger more central airways because the velocity of gas falls rapidly in the region of the terminal bronchioles. 

Unlike the physical diameter, the is a concept incorporating the size, shape and density of particles [2] and so the pharmaceutical performance of a powder or droplets for pntmonary delivery wonld be defined by the mass median aerodynamic diameter (MM AD) of the particles. MM AD is the equivalent aerodynamic diameter in which 50% of the powder mass falls below [4]. Therefore, the MMAD is representative of the aerodynamic particle size of an aerosol formulation. An MMAD of <5 pm is desirable for deep Inng delivery. 

Thus, Eqs. (2) and (3) enable us to convert the volume-equivalent particle size distribution into aerodynamic-equivalent distribution for any flow regime. The characteristic mean diameters are dy (volume geometric) and (volume aerodynamic). Although dp is numerically close to the mass-median aerodynamic diameter (MMAD) often used for the aerosols, it is better defined for asymmetrical distribution, so often observed for respiratory powders. 

Figure 1 Example of log-normal aerosol size distribution illustrating MMAD, CMAD, GSD, and EPF values for an aerosol with mass median aerodynamic diameter of 5 om and...

Measurements of the quantity and quality of the aerosolized drug allow characterizing the dosing properties of inhalation devices in vitro. Multistage im-pactors are used to assess particle mass and mass distribntion of an aerosol, and methods are available to estimate the mass median aerodynamic diameter (MMAD) of the aerosol as well as the dose of delivered from and retained within an inhalation system. 

The median diameter corresponds with the 50 % value of a cumulative number, volume or mass percent distribution as function of the diameter. Fifty percent of the volume (number or mass) of the aerosol is in larger, and 50 % is in smaller particles than the median diameter. For a volume distribution it is the volume median diameter, for a mass distribution the mass median diameter. When the mass percent is expressed as a function of the aerod3mamic diameter, reference can be made to the mass median aerodynamic diameter (MMAD). 

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