Thoracic fraction

Thoracic fraction Particles with aerodynamic diameters of 5-10 pm, which enter the lungs but not the alveoli. 

In the past 20 years size-selective sampling has been applied to ambient sampling as well as personal sampling [John (1984), EPA (1987)]. A method known as the PM-10 method samples particles into two size segments, one greater than 10 pm and the other less than 10 pm (the thoracic fraction). If a conventional mass respirable sampler operates at a flow rate of 1.7 L/min to collect 3.5-pm particles with a 50 percent efficiency, what flow rate would be necessary to collect 10-pm particles with a 50 percent efficiency Assume unit-density spheres. 

Kauffer E, Vigneron JC, Fabrics JF, et al. 1996. The use of a new static device based on the collection of the thoracic fraction for the assessment of the airborne concentration of asbestos fibres by transmission electron microscopy. Arm Occup Hyg 40 311-319. 

The penetration of inhaled particles in human airways depends on their size. As defined by new standards (European EN 481 and International ISO 7708), the cut-off aerodynamic diameter of the total thoracic fraction is 10 pm it is related to the smallest particles penetrating beyond the larynx. Because these particles are strongly responsible for the inhalation risk, their on-line measurement must be representative. The variations in intensities of deposited fractions as a function of particle diameter is shown in Fig. 9.11. 

Shaw EG, McGinnis WL, Jett JR, et al. Pilot study of accelerated hyper-fractionated thoracic radiation therapy plus concomitant cisplatin chemotherapy in patients with unresectable stage M non small cell lung cancer. J Natl Cancer Inst 1993 85 321-323. 

Critical to vitamin D3 action is its further metabolic conversion to more active compounds (Figure 1.3). Via its transport by DBP, vitamin D3 accumulates in the liver [48]. In rats, as much as 60-80% of an injected or oral dose of vitamin D3 locates to the liver [49-51], Intestinal absorption of vitamin D3 is in association with the chylomicron fraction via the lymphatic system. Vitamin D3 is delivered to the liver in blood from the thoracic duct only a few hours post ingestion [44], A specific portion of hepatic vitamin D3 in the rat is converted to 25-OH-D3 by a 25-hydroxylase system in the endoplasmic reticulum of hepatocytes [52, 53]. This enzyme (Km 10"8 M) is regulated to an extent by 25-OH-D3 and its metabolites. Higher concentrations of vitamin D3 are handled by a second 25-hydroxylase located in liver mitochondria [54], This enzyme, also known as CYP27, 27-hydroxylates cholesterol and thus appears less discriminating than the microsomal 25-OHase which does not use cholesterol as substrate [55, 56]. In humans, however,... 

A similar peptide, SchistoFLRFamide, was recently isolated from extracts of the locust (Schistocerca gregaria) thoracic nervous system by gel filtration followed by RP-HPLC on a C-18 column. Samples were initially fractionated with a water acetonitrile gradient using heptafluorobutyric acid as the ion-pairing agent. 

Pickrell, J.A., Harris, D.L., Hahn, F.F., Belasich, J.J., Jones, R.K. (1975). Biological alterations resulting from chronic lung irradiation III. Effect of partial Co thoracic irradiation upon pulmonary collagen metabolism and fractionation in Syrian hamsters, Radial Res. 62 133 4. 

PAHs reach more-perfused tissues rapidly following exposure and are eliminated more slowly from lessperfused tissues (Bartosek et al. 1984). A large fraction of orally absorbed benzo[a]pyrene is believed to be transported by lipoproteins from the gastrointestinal tract to the blood via the thoracic duct lymph flow (Busbee et al. 1990). 

Head and thoracic ganglia from eighty cockroaches (P. americana) were homogenized in ice-cold 0.25M sucrose (buffered to pH 7.2 with Tris.HCl) and fractionated as far as the crude synaptosomal... 

Ciliary action removes deposited particles from both the bronchi and bronchioles. Though it is generally thought that mucocilliary action rapidly transports most particles deposited here toward the pharynx, a fraction of these particles are cleared more slowly. Evidence for this is found in human studies. For humans, retention of particles deposited in the lungs (BB and bb) is apparently biphasic. The slow action of the cilia may remove as many as half of the bronchi- and bronchiole-deposited particles. In human bronchi and bronchiole regions, mucus moves more slowly the closer to the alveoli it is. For the faster compartment, it has been estimated that it takes about 2 days for particles to travel from the bronchioles to the bronchi and 10 days from the bronchi to the pharynx. The second (slower) compartment is assumed to have approximately equal fractions deposited between BB2 and bb2 and both with clearance half-times estimated at 20 days. Particle size is a primary determinant of the fraction deposited in this slow thoracic compartment. A small fraction of particles deposited in the BB and bb regions is retained in the airway wall for even longer periods (BBseq and bbseq). 

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