Implementation of Charged Particles Implementation of Charged Particles Deposition in Stochastic Lung Model Deposition in Stochastic Lung Model

and Calculation of Enhanced and Calculation of Enhanced DepositionDeposition

Dr. Hussain Majid

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This presentation will cover

• Background of the study

• Overview of the published work

• Conclusions

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BackgroundBackground

• A system of solid or liquid particles suspended in air or other gaseous environment called aerosol.

Dust Smoke

Fume Mist

Clouds Pesticides

Types Natural Aerosol

- Soil Dust- Soil Dust

- Sea Salt- Sea Salt

- Volcanic Dust- Volcanic Dust

- Oceanic Sulphates - Oceanic Sulphates Anthropogenic Aerosol

- Industrial Sulphates- Industrial Sulphates

- Soot (Black carbon)- Soot (Black carbon)

- Organic particles- Organic particles

Aerosols

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Charged ParticlesCharged Particles• The Boltzmann equilibrium charge distribution represents the

charged distribution of an aerosol in charge equilibrium with bipolar ions surrounding it.

• Freshly generated aerosols in workplace atmosphere may have charges well above the Boltzmann equilibrium (Forsyth et al. 1998) .

• Aerosols produced by commercial metered dose inhalers can produce elementary charges up to several ten thousands (Kwok et al. 2005).

• In-vivo experimental studies have shown that lung deposition of particles is significantly effected by particle charges (Yu and Chandra 1977, Cohen et al. 1998).

• The significance of charged particles deposition may be of more concern for aerosol therapy than for inhalation toxicology.

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LungLung deposition calculations-deposition calculations-ImportanceImportance

• Evaluating the efficiency of dose deliverance i.e. how much and how long will particles remain in the lung.

• Assessing toxic effects of airborne pollutant depositing in certain regions of the lung.

• Estimation for the location of potentially induced cancer due to exposure in radiation environment.

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Deposition Fraction

Deposition fraction is the ratio on aerosol inhaled to the total aerosol deposit in the lung. This is affected by the entry point, the orientation of the flow to the entry point, the flow rate and particle size.

Original aerosol Aerosol inhale DF =

Inhaling

HumanHuman LungLung

Head airway (HA)

Air is inspired through nose or mouth down to larynx and rest of the lung.

Parent Branch

Major daughter Minor daughter

Bifurcation

Tracheaobronchial (TB)

Bronchial tree is the first part of the lung. This part directs air in to the lung Each branch in the tree splits into 2 parts

Alveolar or Pulmonary (Al)

Alveoli are located at the end of the bronchial tree and is region where gas exchange occurs. 7

Lung deposition mechanismsLung deposition mechanisms

Major:• Diffusion• Sedimentation• Inertial Impaction

Minor:• Interception• Electrostatic

Naso-pharyngeal: impaction, sedimentation, electrostatic (particles > 1 μm)Tracheo-bronchial: impaction, sedimentation, diffusion (particles < 1 μm)Pulmonary:sedimentation, diffusion (particles < 0.1 μm) 9

Factors that effect Factors that effect depositiondeposition

1. Aerosol properties• Size distribution (MMD, AMD. etc)• Concentration• Particle hygroscopicity• Gas particle interaction• Chemical reaction• Particle surface charge

2. Air flow properties• Lung capacity• Breathing frequency• Tidal Volume

3. Respiratory tract• Structure of the extrathorcic region• Lung structure and morphology• Models used: Weibel, Raabe, and Horsfield

Numbering scheme of asymmetric lung model of Raabe et al. (1974).

Particle properties

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Stochastic Lung Dosimetry Model- Stochastic Lung Dosimetry Model- IDEALIDEAL

• Deposition fractions and distribution within airways generations are modeled by the stochastic lung model-IDEAL

• Particles inhaled follow random path in the lung– Random selection of actual path out of millions of possible pathway by tracing

histories of a large number of particles

• The model uses asymmetric nature of branching pattern of the lung. – Variability of lenghts and diameter of airways are described by log-normal

frequency distributions

• Analytical (deterministic) formulas are used for computing deposition by diffusion, sedimentation and impaction

• Monte Carlo process continues even after deposition of particles within a given airway by decreasing the statistical weight of particles

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Objectives of the studyObjectives of the study

1. to implement charge particle deposition in the stochastic human lung model (TB and Al regions),

2. to predict enhanced deposition for various charged particle at airway generation level and to compare results with previous studies

3. to quantify the breathing effects on charged particle deposition and

4. to calculate enhancement factors for various breathing conditions.

Charged Particles deposition Charged Particles deposition ModelModel

Tracheobronchial (TB) region• Enhanced deposition in TB region is obtained by implementing the following

efficiency equation:

where B is the mechanical mobility of the particles, t0 is the is the mean residence time, εo is the electric permittivity of air.

Alveolar (Al) region• For the spherical shaped Al region, enhanced deposition is calculated by

implementing the following

where t0 is the particles mean residence time [in sec].

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0

2/1

030

8qqt

d

B

tq

3/1

00

251

t

Bq

dalvq

ResultsResults• Particle sizes

– Unit density monodisperse charge particles of 0.3, 0.6 and 1 µm diameter.

• Flow rates – For sitting and light exercise conditions 18 and 50 L min-1 respectively

(ICRP 1994).

• Tidal volumes – 750 and 1250 mL and breathing cycle times are 5 and 3s respectively.

• The effect of breath-hold – 2-8 Seconds

• Threshold charge limit– The enhanced deposition due to particle charges q is considered

proportional to increase in threshold charge limit (q – q0).

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Results (continued..)Results (continued..)

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Enhanced deposition in TB and Al regions as function of loaded Enhanced deposition in TB and Al regions as function of loaded particle charges. Deposition is calculated for different particle sizes particle charges. Deposition is calculated for different particle sizes at oral tidal volume of 1000 cmat oral tidal volume of 1000 cm33 and 15 breaths per minute (Flow and 15 breaths per minute (Flow rate of 30 L minrate of 30 L min-1-1).).

Results (continued..)Results (continued..)

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Enhanced deposition of 0.6 µm particles in the lung airway generations at various particle charge loading.

The effect of breath hold times on charged particle deposition for 1.0 µm size particles and 100 elementary charges.

Results (continued..)Results (continued..)

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Enhanced deposition within the TB and Al regions as function of Enhanced deposition within the TB and Al regions as function of particle charge loading. The deposition is calculated for different particle charge loading. The deposition is calculated for different particle sizes under sitting (tracheal flow rate 18 L minparticle sizes under sitting (tracheal flow rate 18 L min -1-1) and light ) and light exercised (Flow rate 50 L minexercised (Flow rate 50 L min-1-1) breathing conditions.) breathing conditions.

Results (continued..)Results (continued..)

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Enhanced deposition within the TB and Al regions as function of loaded particle charges at various tidal volumes. The deposition is calculated for different particle sizes and fixed breathing frequency of 15 min-1.

Results (continued..)Results (continued..)Enhancement factorsEnhancement factors

ConclusionConclusion• The enhanced deposition of charged particles in the Al region is

up to five times higher than in the TB region and reaches a saturation level.

• Within the TB-region, enhanced deposition is higher under sitting breathing than under light exercise breathing conditions.

• The enhanced deposition increases with increase in VT and flow rate in Al region.

• The introduction of pause time during inhalation increases the probability of increased enhanced deposition at targeeted loaction of the respiratory tract.

• Hence, by introducing charged particles during inhalation, further control on targeted deposition in the respiratory tract is possible in addition to the already applied modulation of breathing and aerosol parameters.