A RAPID METHOD FOR ASSESSING REGIONAL LUNG DEPOSITION

KN Chang (1), SH Huang (1), CP Chang(2), CW Chen(2), CC Chen (1)

(1) Institute of Occupational Medicine and Industrial Hygiene, National Taiwan University (2) Institute of Occupational Safety and Health, Taiwan

Introduction The serial bolus delivery methods were commonly used to measure the regional deposition of inhaled particles in the human respiratory tract. This technique is versatile and can provide important data, such as fraction of lung deposition and morphological dimension of the airways. However, the process is time-consuming because only one aerosol size and one regional deposition rate can be measured each time.

ObjectivesThe aim of this study was to develop an experimental system for rapid measurement of regional lung deposition.

Materials and methodsThe main sampling train consisted of a mouthpiece, a flow meter, and a particle counter (Fig 1). The mouthpiece was attached to the pneumotachograph in line with a minimum dead space. In the present study, an aerosol size spectrometer (Welas 2000H) with sampling rate up to 100 Hz was used in this work to cover size ranging from 0.3 to 40 m. A condensation particle counter (TSI 3025A) was used for aerosols smaller than 0.3 m. During respiration, the aerosol was sampled continuously into the counter via the sidearm port attached to the mouthpiece. Nine people volunteered to be test subjects. The breathing patterns generated by the cylinder-piston breathing machine were shown on a monitor in front of subjects for them to follow. It took about an hour for subjects to practice and to tract the breathing curves reasonably well.

To calculate the longitudinal distribution of aerosol deposition, the lung volume can be divided into infinitesimally small volume elements, or n elements. Aerosol particles within each volume element of the respiratory tract system are assumed to deposit with an efficiency of xi as they are inhaled and exhaled again with the same deposition efficiency penetrating through the same volume element (i). Aerosol recovery from the ith

volume element, RCi, can be obtained by

Note that aerosol deposition fraction in ith volume element (DFi) is the sum of depositions during inspiration and expiration. The local deposition fraction in the ith volume element, LDFi, can then be expressed as

Results and discussionFigure 2 shows local deposition values for each 50 ml volumetric regional as a function of penetration volume. Those data were repeated more than five times. The local deposition efficiency was calculated for each 50 ml volumetric region to compare with the data reported by Kim et al. (1996). The trend of our data was similar to that of Kim’s (solid line). This difference may be due to the different subjects and breathing flow conditions. The average body height for previous study was above 180 cm and the constant flow rates were used. However, the cyclic flow rates were used in this study.

Local deposition fraction was calculated as shown in figure 3. In theory, inertial impaction plays an important role in the first few generations of bifurcation where the velocity is high. For the rest of the regions, the gravitational settling becomes dominant. Therefore, the local deposition efficiency increases with volumetric lung regions.

2)1(1

kxi

kiRC

n

jiDF

niLDF1

1

Figure 1. Schematic of experimental set-up.

Exhaust

Mixing Chamber

Dilution AirAm-241

Aerosol Generator

Δ P

CPC

Dc Dc=78 mm

Breathing PatternVisual Feedback

Humidifier

Vacuum Pump

1.255.11854.094.796518022M9

2.134.32882.743.1148.415823F8

2.883.93843.454.096917025M7

14.96903.844.276017024M6

1.094.34813.724.66017223M5

1.253.83853.954.646817533M4

1.283.33852.93.437917429M3

1.42.57832.793.376216029M2

0.924.42984.044.146016837M1

Raw, cm H2O/l/sec

FRC, ml

FEV1/FVCFEV1,

mlFVC,

mlWeight,

kgHeight,

cmAgeGender

Subject No.

Table 1. Subject characteristics and lung function test results

FVC, forced vital capacity; FEV1, forced expiratory volume in 1 s; Raw, airway resistance

Volumetric Lung Region, mL

0 100 200 300 400 500 600

Loca

l Dep

ositi

on E

ffici

ency

0.00

0.02

0.04

0.06

0.08

0.10

0.12Kim et al. 1996Present study

Fb15 bpm

Vt 500 mL

1 m

Figure 2. Local deposition efficiency (for each 50 ml volumetric region) as a function of penetration volume.

Figure 3. Deposition fraction in local volumetric regions (for each 50-mL volumetric region) as a function of penetration volume.

Volumetric Lung Region, mL

0 100 200 300 400 500

Loca

l Dep

ositi

on F

ract

ion

0.00

0.01

0.02

0.03

0.04

15 bpm

Vt 500 mL

1 m

Kim et al. 1996

Present study