Updating the ICRP human respiratory tract model

The ICRP Task Group on Internal Dosimetry is developing new Occupational Intakes of Radionuclides (OIR) documents. 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. Publication of the OIR provides an opportunity for updating the HRTM in the light of experience and new 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.     

Stochastic model of ultrafine particle deposition and clearance in the human respiratory tract

Deposition and clearance of insoluble ultrafine particles, ranging from 1 to 100 nm, were simulated by stochastic models using Monte Carlo methods. Brownian motion is the dominant mode of deposition in human airways. The additional effects of convective diffusion in bifurcations and axial diffusion (convective mixing) primarily affect particle transport and deposition of particles in the 1-10 nm range. Regarding total deposition, the effects of both convective mechanisms are practically compensated by the concomitant effect of molecular radial diffusion (Brownian motion). During the first hours following inhalation, 1 nm particles are predicted to be cleared much faster than particles in the size range from 10 to 100 nm, with a retained fraction of about 80% after 24 h. For 1-10 nm particles, extracellular transfer to blood is the most likely mode of clearance, while uptake and subsequent accumulation in epithelial cells are assumed to be the preferential mechanisms for 10-100 nm particles.     

Comparison of teen and adult driver crash scenarios in a nationally representative sample of serious crashes

Motor vehicle crashes are the leading cause of death and acquired disability during the first four decades of life. While teen drivers have the highest crash risk, few studies examine the similarities and differences in teen and adult driver crashes. We aimed to: (1) identify and compare the most frequent crash scenarios—integrated information on a vehicle's movement prior to crash, immediate pre-crash event, and crash configuration—for teen and adult drivers involved in serious crashes, and (2) for the most frequent scenarios, explore whether the distribution of driver critical errors differed for teens and adult drivers. We analyzed data from the National Motor Vehicle Crash Causation Survey, a nationally representative study of serious crashes conducted by the U.S. National Highway Traffic Safety Administration from 2005 to 2007. Our sample included 642 16- to 19-year-old and 1167 35- to 54-year-old crash-involved drivers (weighted n = 296,482 and 439,356, respectively) who made a critical error that led to their crash's critical pre-crash event (i.e., event that made the crash inevitable). We estimated prevalence ratios (PR) and 95% confidence intervals (CI) to compare the relative frequency of crash scenarios and driver critical errors. The top five crash scenarios among teen drivers, accounting for 37.3% of their crashes, included: (1) going straight, other vehicle stopped, rear end; (2) stopped in traffic lane, turning left at intersection, turn into path of other vehicle; (3) negotiating curve, off right edge of road, right roadside departure; (4) going straight, off right edge of road, right roadside departure; and (5) stopped in lane, turning left at intersection, turn across path of other vehicle. The top five crash scenarios among adult drivers, accounting for 33.9% of their crashes, included the same scenarios as the teen drivers with the exception of scenario (3) and the addition of going straight, crossing over an intersection, and continuing on a straight path. For two scenarios ((1) and (3) above), teens were more likely than adults to make a critical decision error (e.g., traveling too fast for conditions). Our findings indicate that among those who make a driver critical error in a serious crash, there are few differences in the scenarios or critical driver errors for teen and adult drivers.     

An exploratory study of the relationship between road rage and crash experience in a representative sample of US drivers

The phenomenon of road rage has been frequently discussed but infrequently examined. Using a representative sample of 1382 US adult drivers, who were interviewed in a 1998 telephone survey, exploratory analyses examined the relationship between self-reported measures of road rage, generally hazardous driving behaviors, and crash experience. Regarding specific road rage behaviors, most respondents reported having engaged in verbal expressions of annoyance; however only 2.45% reported ever having been involved in direct confrontation with another car or driver. After controlling for gender, age. driving frequency, annual miles driven and verbal expression, an angry/threatening driving subscale of road rage was significantly associated with hazardous driving behaviors that included frequency of driving over the legal blood alcohol limit, receipt of tickets in the past year. and habitually exceeding the speed limit as well as crash experience. However, the verbal/frustration expression subscale was not associated with crash experience or hazardous driving indicators, except for number of tickets, after controlling for other crash-related factors such as gender and age. Direct confrontation by deliberately hitting another car or leaving the car to argue with and/or injure another driver was rarely reported. Results suggest that angry/threatening driving is related to crash involvement; however, after controlling for exposure and angry/threatening and hazardous driving the relationship of milder expressions of frustration while driving and crash involvement was not significant.     

Rheology of stimulated whole saliva in a typical pre-orthodontic sample population

The dynamic viscosity () of stimulated whole saliva in a typical pre-orthodontic sample population was characterized as a function of temperature (T). Samples were collected from 30 adolescents or young adults, after screening for factors that are known to have an effect on salivary viscosity. Using a cone and plate viscometer, 1.5 ml of stimulated whole saliva was evaluated at a constant shear rate of 450 s^-1 from T=20°C to T=40°C. Data from the -T plots showed a negative dependence of the form, =a–bT, over a range of from 1.08 to 2.45 centipoise (cps) at 34°C. Most of the samples fell into a narrow envelope, where the mean of the saliva samples ranged from 2.42±0.61 cps at 20°C to 1.57±0.32 cps at 37°C. With regard to sample stability, viscosity-time plots indicated that a small but predictable decrease in occurred during the 3 h period. The -T plots generated from fresh and frozen saliva samples demonstrated an appreciable change in as a result of refrigeration. With regard to sample reproducibility, viscometric data obtained from a typical pre-orthodontic patient over a 1-week period fluctuated within a fairly broad envelope of values.Presented, in part, at the 21st Annual Meeting and Exhibition of the A.A.D.R., Boston, Massachusetts, March, 1992.     

Estimation of Weibull parameters by omission of some data in a sample

Methods of estimating Weibull parameters by omission of some data in a sample are considered for various functions for survival probability in linear Weibull plots. Computer simulation is used for the consideration. A use of the survival probability function, (P(i) = 1 – (i – 0.5)N, in whichP(i) is survival probability,i is thei-th order of failure strength andN is the total number of data in the sample, and the omission of 2 to 4% of the data, which are of the smallest value, the largest one and their neighbours, are recommended to get the best value of the Weibull parameters.     

Deposition and clearance for radon progeny in the human respiratory tract

In vivo counting of 214Pb was conducted to estimate the deposition and retention of radon progeny in the human respiratory tract. Two volunteer subjects were exposed to high radon concentrations. After the exposures, activity deposited in the extrathoracic (ET) region for each subject was measured using a NaI(Tl) detector. According to the International Commission on Radiological Protection (ICRP) model, a reference value for particle transport rate from ET2 to the GI tract is 100 d(-1) (half-time, 10 min). The effective half-time of 214Pb deposited in the ET region was calculated for pure nose and mouth breathers, using the ICRP reference transport rate. While the measured half-times for nose breathers were generally consistent with the calculated values, those for mouth breathers were significantly larger than the calculated values. The results indicated that the particle transport rate from ET2 to the GI tract was much smaller than the reference value in the ICRP model.     

最小二乘拟合法在生物电阻抗模型参数提取中的应用

运用最小二乘拟合圆法提取生物组织电阻抗模型参数,此算法为显式公式,具有计算速度快、数值拟合精度高等优点.能够实现快速、精确地提取阻抗模型参数Re、Ri、Cm和α,在生物电阻抗虚拟仪器的应用与开发中有很大的价值.通过对RC模型的测量及拟合,结果表明,利用此方法所编写的程序可以精确提取生物电阻抗参数,且运行速度也很快.     

A multi-compartment model for slow bronchial clearance of insoluble particles--extension of the ICRP human respiratory tract models

To incorporate the various mechanisms that are presently assumed to be responsible for the experimentally observed slow bronchial clearance into the HRTM, a multi-compartment model was developed to simulate the clearance of insoluble particles in the tracheobronchial tree of the human lung. The new model considers specific mass transfer paths that may play an important role for slow bronchial clearance. These include the accumulation of particulate mass in the periciliary sol layer, phagocytosis of stored particles by airway macrophages and uptake of deposited mass by epithelial cells. Besides the gel layer representing fast mucociliary clearance, all cellular and non-cellular units involved in the slow clearance process are described by respective compartments that are connected by specific transfer rates. The gastrointestinal tract and lymph nodes are included into the model as final accumulation compartments, to which mass is transferred via the airway route and the transepithelial path. Predicted retention curves correspond well with previously published data.     

Oscillatory behaviour in a three-component plankton population model

We examine the qualitative behaviour of an NPZ (nutrient-phyto- plankton-zooplankton) model for parameter ranges consistent with values used in the literature. The wide range of values partly reflects variations of conditions in different environtments for the plankton, but in many cases is a measure of the difficulties in making observations and consequent uncertainties. We pay particular attention to the bifurcational behaviour of the system, and to the regions of parameter space for which oscillatory behaviour is possible; such oscillatory behaviour has recently been found in both observational data and in more complex ecosystem models. In some regions of parameter space, we also find that multiple attractors occur. Finally, we examine in more detail the behaviour for a range of values of nutrient input.     

Robust trend parameters in a multivariate spatial linear model

This article gives a robust estimator of the trend parameters in multivariate spatial linear models. This estimator is presented as an alternative to the classical one which is obtained by using cokriging. The goal focuses on improving predictions of spatial variables when data contain both atypical and high influence observations. The procedure consists of extending robust methods used in linear regression models to the multivariate spatial context. The resulting estimator belongs to the class of GM-estimators and then, it is a bounded influence estimator and it has good robust properties, in particular, a high breakdown point and a high efficiency. An illustrative example is given to show how the proposed estimator works. Research partially supported by Ministerio de Ciencia y Tecnología, Project AGL2000-0978.     

The role of parental alcohol consumption on driving under the influence of alcohol: results from a longitudinal, nationally representative sample

Purpose

Many studies have examined the role of peer and parental alcohol use on drinking behaviors among adolescents. Few studies, however, have examined parental influences on driving under the influence (DUI) of alcohol. The current study uses data from a longitudinal study to examine the role of parental alcohol use during adolescence on the risk for DUI among young adult men and women.

Methods

Data were derived from 9559 adolescents and young adults who participated in the National Longitudinal Study of Adolescent Health (Add Health) Waves I and III. Survey logistic regression was used to examine the relationship between multilevel risk and protective factors and self-reported DUI. Analyses were stratified by gender and frequency of parental alcohol consumption to understand the role of parental alcohol use on risk for DUI among their youth.

Results

Risk and protective factors for DUI were very similar among men and women. Parental alcohol use significantly predicted DUI among women (OR = 1.39, p < 0.01) and men (OR = 1.33, p < 0.05). When parents did not report alcohol use, peer alcohol use significantly increased risk for DUI for both women (OR = 1.26, p < 0.05) and men (OR = 1.31, p < 0.001). When parents reported alcohol use, however, peer alcohol use was not a significant independent predictor.

Conclusions

Findings suggest remarkable similarities in risk and protective factors for DUI across gender groups. For men and women, parental alcohol consumption was a risk factor for DUI. Peers’ alcohol use predicted DUI only when parents did not use alcohol.     

On the stability of some equilibrium points in a plankton population model

It is proved that the equilibrium point (N₀, 0, 0) for the plankton population model given in Edwards and Brindley, (1996, Dynamics and Stability of Systems, 11(4): 347-370) is unstable in the case of two negative and one zero eigenvalues, thus correcting an assertion on its stability in the above quoted paper.     

上呼吸道流场及颗粒物沉积规律的模拟

基于医学CT扫描图像得到的真实人体上呼吸道模型,采用大涡模拟方法计算了上呼吸道内部的气流流动,分析了气流流速和涡旋的特征.在拉格朗日框架下计算了可吸入颗粒物的沉积,对颗粒的局部沉积位置进行了直观显示.研究结果表明,舌咽部位涡旋和回流最多,狭窄结构处流速最大,且产生了气流喷射现象;大部分的颗粒沉积在鼻腔和喉部,颗粒粒径对沉积率有很大影响.     

Approximate model of a heat exchanger with distributed parameters

The construction of an approximate model of a type of heat exchanger described by partial differential equations is discussed. A form of transfer function for this approximate model is proposed together with a calculation method and a block diagram for analog simulation purposes.     

In vivo measurement of unattached radon progeny deposited in the human respiratory tract

Seven nose breathing and seven mouth breathing volunteers were exposed to atmospheres enriched with unattached radon progeny (218Po, 214Pb and 214Bi). The activity of these radionuclides deposited in the respiratory tract was measured in vivo after the exposures. The results of these measurements are in agreement with predictions calculated with the ICRP Publication 66 Human Respiratory Tract Model. Temporal analysis of the activity deposited in the heads of the volunteers leads to the conclusion that a significant amount of the deposited activity associated with particle diameters of about 1 nm is not subject to a fast transport to the gastrointestinal tract as generally reported for larger aerosol particles.     

Estimation and test for the parameters of the arrhenius model

Estimation and test procedures are given for the parameters of the Arrhenius model. The assumed failure distribution is of exponential or Weibull type with fixed and temperature independent shape parameter. The approach is based on failure terminated experiments on at least two different tempera-ture levels with pre-assigned and equal number of failures for each temperature level. Estimation consists of two steps, modified maximum likelihood estimation followed by ordinary least squares regression. Statistical tests are defined on acceptance regions given in the particular parameter space by circles or ellipses depending only on the experimental design.