MMAD mass median aerodynamic

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. 

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,... 

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. 

Can failures occur from time to time. The release of fission products from them depends on the temperature and type of fuel. If the fuel is uranium metal, as in the Windscale and Magnox reactors, and the can fails, the uranium will oxidise in air or C02. In laboratory experiments, the mass median aerodynamic equivalent diameter (MMAD) of the particles produced by oxidation of uranium increased from about 40 ptm when the temperature of oxidation was 600°C to 500 jum at 1000°C (Megaw et al., 1961). At high temperature, a coherent sintered oxide layer formed on the uranium and this hindered the formation of particles. 

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... 

The FisoNeb and Pulmosonic nebulizers both operate at a frequency of 1.3 MHz that generates a mass median aerodynamic diameter (MMDA) of 4-6 pm [9,10]. The Pulmosonic nebulizer has been reported not to deliver many particles smaller than 2 pm and, therefore, is unsuitable for pentamidine administration [10]. The Portosonic (DeVilbiss) device is a 2.3-MHz ultrasonic nebulizer and may offer the combination of less than 2-pm MMAD and a high output. In any study using ultrasonic nebulizers, the output and particle size of each device need to be periodically sampled, because the frequency of the piezoelectric crystal may alter with age [10]. Any MMADs between 0.5 and 2 pm are available. The Respirgard nebulizer II has one-way valves that control a drug reservoir, allow entrainment of room air in patients whose minute ventilation is... 

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. 

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