Respiratory tract deposition of diesel engine exhaust particles for healthy subjects and subjects with COPD
Abstract
Both epidemiological and toxicological studies have shown a correlation between adverse health responses and exposure to diesel exhaust particles. A key factor for determining the health effects is the deposition of the particles in the respiratory tract during breathing. It is therefore important to investigate the deposited fraction and dose for different aerosol sources during various conditions. It has been suggested that certain subpopulations are more susceptible to adverse health effects of airborne particles. One such group is those diagnosed with chronic obstructive pulmonary disease (COPD). The objective of this study was to examine the deposited fraction and dose of fresh diesel exhaust particles for healthy subjects and subjects with COPD. The size-resolved deposited fraction and deposited dose of diesel engine exhaust particles were measured with the RESPI instrument (Londahl et al. 2006). In RESPI particle concentrations in inhaled and exhaled air is measured with a scanning mobility particle sizer (SMPS). The measurements were done on 10 healthy subjects (5m/5f) and 10 subjects (7m/3f) with varying degree of COPD, from mild to moderate. One healthy male was excluded because of difficulties to breathe relaxed in the instrument. A Volvo diesel engine (Volvo TD40 GJE, 4.0 L, four cylinders, 1996) with no exhaust after-treatment was used with a typical MK1 diesel fuel (sulphur content ≤10 ppm). The engine was operated in a motor test bench to simulate different operating conditions. The deposited fraction was measured for two different diesel aerosols: idling and transient load conditions according to the urban driving part of the standadized European Transient Cycle (ETC) protocol. The deposited fraction according to the International Comission for Radiological Protection model (ICRP, 1995) was calculated for each subject and compared to the measured values. The deposited dose was calculated (normalized to one hour exposure at 100 μg/m for both aerosols). The average deposited fraction and dose for the two groups and aerosols are presented in Table 1. The study showed a statistically significant difference in deposited fraction between the groups. For both studied driving conditions, the deposited fraction is lower for the subjects with COPD compared to the healthy subjects, but the deposited dose is higher. The higher deposited dose for the subjects with COPD is expected as they breathed with a higher minute volume than the healthy subjects. The difference in deposited fraction between the two aerosols can most probably be explained by the different size distributions. The aerosol from the idle engine mode contained more nucleation mode particles for which the probability of deposition is high.