Icrp respiratory tract model-

Rates shown alongside arrows are reference values in units of d —1. The model as shown above would describe the retention and clearance of a completely insoluble material. However, there is in general simultaneous absorption to body fluids of material from all the compartments except ET 1. In the model shown in Fig. For definition of symbols, see text.

This revision was motivated by the availability of increased knowledge of the anatomy and physiology of the respiratory tract and of the deposition, clearance, and biological effects of inhaled radioactive particles, and by greatly expanded dosimetry requirements. Sign In Forgot password? Issue Section:. The ratio of s p to s pt approximates to the fraction that dissolves rapidly. Nuclear Safety Safety of existing facilities Conducting assessments on future facilities Assessing the safety of military nuclear systems, nuclear facilities and defense-related transports. In the absence Jan austen fanfiction indec observations on specific radionuclide compounds, default values for rates of absorption Icrp respiratory tract model blood are given for materials classified as being rapidly, moderately, or slowly absorbed. International institutions Bilateral cooperations. For the ET regions, measured deposition efficiencies were Icrp respiratory tract model to characteristic parameters of particle size and airflow, and were scaled by anatomical dimensions to predict deposition under other conditions e. Abstract - This report describes a revision of the model used in ICRP Publication 30 to calculate radiation doses to the respiratory Icrp respiratory tract model of workers resulting from the intake of airborne radionuclides. Deposition The deposition model evaluates fractional deposition of an aerosol in each region, for all aerosol sizes of practical interest 0.

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Receive exclusive offers and updates from Oxford Academic. Colleague's E-mail is Invalid. The extrathoracic ET airways are divided into ET 1the Icrp respiratory tract model nasal passage, and ET 2which consists of the posterior nasal and oral passages, the pharynx and larynx. Sign in. Article Navigation. With this system, the initial dissolution rate is approximately s p and Icrp respiratory tract model final redpiratory rate is approximately s t. Guidance on obtaining information about absorption of inhaled radionuclides into blood is given in greater detail, Icrp respiratory tract model this is a topic on which ICRP has traditionally given guidance, and because a compilation of such information is not readily available elsewhere. This Guidance Document therefore gives advice Naruto x tsunade doujin applying specific information within the framework of the HRTM for assessing occupational and environmental exposures and for interpreting bioassay data. All rights reserved. Colleague's Email:. Absorption depends on the physical and chemical form of the deposited material. In any particular situation the actual values of many parameters can be considerably different from the reference values. Citing articles Icrl Web of Science The main possibilities under consideration relate to the two main clearance pathways. Save my selection.

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  • Rates shown alongside arrows are reference values in units of d —1.

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Scientific tools. Theses and post-docs. Summary TexteZone1. Application of the Human Respiratory Tract Model HRTM requires a review of the lung-to-blood absorption characteristics of inhaled compounds of importance in radiological protection.

Where appropriate, material-specific absorption parameter values will be given, and for other compounds, assignments to default Types will be made on current information. The main possibilities under consideration relate to the two main clearance pathways.

Recent studies provide important new data on rates of particle transport from the nasal passages, bronchial tree slow phase and alveolar region. The review of absorption rates provides a database of parameter values from which consideration can be given to deriving typical values for default Types F, M and S materials, and element-specific rapid dissolution rates.

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Chapters on each aspect of the model morphometry, physiology, deposition, clearance, gases and vapours, dosimetry provide: - A summary of how the HRTM treats that topic; - Information on the reference values of relevant parameters; - Guidance on choosing between default values; - Information on how doses and bioassay quantities lung retention, urine, and faecal excretion vary with the values of selected parameters, giving guidance on the importance of obtaining specific information; - Simple examples of the use of specific information relating to the topic. Don't already have an Oxford Academic account? To overcome this, the HRTM uses an equivalent system with the same number of variables, but which gives greater flexibility, shown in Fig. Advanced Search. Issue Section:.

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Rates shown alongside arrows are reference values in units of d —1. The model as shown above would describe the retention and clearance of a completely insoluble material. However, there is in general simultaneous absorption to body fluids of material from all the compartments except ET 1. In the model shown in Fig. For definition of symbols, see text. The extrathoracic ET airways are divided into ET 1 , the anterior nasal passage, and ET 2 , which consists of the posterior nasal and oral passages, the pharynx and larynx.

The thoracic regions are bronchial BB: trachea and bronchi , bronchiolar bb , and alveolar-interstitial Al: the gas exchange region. The deposition model evaluates fractional deposition of an aerosol in each region, for all aerosol sizes of practical interest 0. For the ET regions, measured deposition efficiencies were related to characteristic parameters of particle size and airflow, and were scaled by anatomical dimensions to predict deposition under other conditions e.

To model particle deposition, the regions are treated as a series of filters, during both inhalation and exhalation. The efficiency of each is evaluated by considering aerodynamic gravitational settling, inertial impaction and thermodynamic diffusion processes acting competitively. Deposition parameters are given for three reference levels of exertion for workers sitting, light exercise, heavy exercise. For inhalation of radionuclides by workers, the reference subject is taken to be a normal nose-breathing adult male at light work.

Material deposited in ET 1 is removed by extrinsic means such as nose-blowing. In other regions clearance is competitive between the movement of particles towards the GI tract and lymph nodes particle transport , and the absorption into blood of material from the particles in the respiratory tract. Removal rates due to particle transport and absorption to blood are taken to be independent. It is assumed that particle transport rates are the same for all materials.

A single compartment model is therefore provided to describe particle transport of all materials Fig. Reference values of rate constants were derived, so far as possible, from human studies, since particle transport rates are known to vary greatly among mammalian species. Figure 11 as it stands would describe the retention and clearance of a completely insoluble material.

However, as noted above, there is in general simultaneous absorption into blood. Absorption depends on the physical and chemical form of the deposited material. It is assumed to occur at the same rate in all regions including the lymph nodes except ET 1 , where it is assumed that none occurs. A limitation of the system in Fig. To overcome this, the HRTM uses an equivalent system with the same number of variables, but which gives greater flexibility, shown in Fig. With this system, the initial dissolution rate is approximately s p and the final dissolution rate is approximately s t.

The ratio of s p to s pt approximates to the fraction that dissolves rapidly. The system shown in Fig. Uptake to body fluids of dissolved material can usually be treated as instantaneous. In some situations, however, a significant fraction of the dissolved material is absorbed slowly into body fluids because of binding to respiratory tract components.

However, it is assumed by default that uptake is instantaneous, and this is reflected in the reference values.

Reference values for each are specified in terms of the parameters s p , s pt and s t , and are given in Table 5.

These absorption rates, expressed as approximate half-times, and the corresponding amounts of material deposited in each region that reach body fluids can be summarised as follows:. Regional deposition does not need to be assessed for such materials, because in dose calculations they can be treated as if they were injected directly into body fluids.

The small amounts transferred to lymph nodes continue to be absorbed into body fluids at the same rate as in the respiratory tract. Guidance on the choice of default Type, and hence of the reference values of the absorption parameters, is given in ICRP Publication 68 [36] for occupational exposure and in ICRP Publication 71 [33] for exposure of the public for the 31 elements covered. Absorption type. F fast. M moderate. S slow. Initial dissolution rate d Transformation rate d Final dissolution rate d Fraction dissolved rapidly.

Rapid d Slow d Fraction to bound state. Gases and Vapours. For radionuclides inhaled as particles solid or liquid the HRTM assumes that total and regional depositions in the respiratory tract are determined only by the size distribution of the aerosol particles.

The situation is different for gases and vapours, for which deposition in the respiratory tract depends entirely on the chemical form. In this context, deposition refers to how much of the material in the inhaled air remains behind after exhalation.

The fraction of an inhaled gas or vapour that is deposited in each region thus depends on its solubility and reactivity. Class SR-0 insoluble and non-reactive: negligible deposition in the respiratory tract. Class SR-1 soluble or reactive: deposition may occur throughout the respiratory tract. For Classes SR-1 and SR-2, subsequent retention in the respiratory tract and absorption to body fluids are determined by the chemical properties of the specific gas or vapour.

By default, reference values for an Absorption Type are used, normally Type F absorption rate d -1 or Type V instantaneous absorption. Measuring techniques Biokinetic models Dose assessment References. Human respiratory tract model Alimentary tract model Absorption through intact skin Wounds Biokinetic models for systemic activity Excretion pathways Biokinetic functions. Deposition The deposition model evaluates fractional deposition of an aerosol in each region, for all aerosol sizes of practical interest 0.