Rolf Falk

No Significant Translocation of Inhaled 35-nm Carbon Particles to the Circulation in Humans

Human pulmonary retention of 35 nm 99mTc-labeled carbonaceous particles, produced with a modified Technegas generator, was followed for 24 h using a gamma camera imaging technique. Nine healthy subjects and four asthmatics inhaled the test particles. Particle labeling stability was tested in vitro during 48 h. We also measured in vivo leaching in blood and in urine for 24 h. One additional subject was exposed to particles with unstable labeling. There were no significant differences between healthy and asthmatic subjects in any of the parameters studied. Particle retention after 24 h was 102% (SD ± 4.7). Cumulative in vitro leaching of 99mTc activity from the particles was 1.7% (±1.1) after 24 h. In blood samples, 80 min after exposure, 1.1% (± 0.4) of initially deposited activity was detected and 91% of the activity was not bound to particles. In urine sampled during the first 24 h after exposure, 3.6% (± 0.9) of lung deposited activity was detected. Lung retention was 30% after 1 h in the subject exposed to the leaching aerosol (n = 1). Thirty-one percent of the deposited activity was detected in the blood after 80 min and 80% was not bound to particles. Fifty percent of the activity was excreted with urine within 24 h. On gamma camera images the activity visibly translocated from lungs to thyroid and gastrointestinal tract. In conclusion, over a 24-h period there was no significant translocation of inhaled 35-nm particles to the systemic circulation.

Deposition of Large Particles in Human Lung

Twenty-four nonsmoking males, all without history of pulmonary disease, were randomly divided into four groups of six subjects each. The subjects in each group inhaled monodisperse Teflon particles labelled with 111In (half-life 2.83 days); 8.2, 11.5, 13.7 and 16.4 micron aerodynamic diameter, respectively. Radioactivity in head and throat, lung and stomach was determined after 0, 3 and 24 hrs using a profile scanner. For some subjects radioactivity was also determined using a whole-body scanner at 3.5 and 24 hrs. After the 24-hr determination the subjects inhaled labelled Teflon particles again, this time with a filter in front of the mouth. Average values for total deposition in the body, obtained using a profile scanner, whole-body scanner and filter measurements, agreed fairly well. Lung retention values obtained by whole-body and profile scanning also agreed well. The average deposition in the lung, expressed as a percentage of total deposition, was 49, 31, 21 and 13% for the four particle sizes (8.2-16.4 micron). Alveolar deposition, determined as retention at 24 hrs and expressed in percent of total deposition, was 15, 4, 4 and 1%. For the smallest particle sizes the deposition values agreed with earlier investigations. However, for the larger particles the two deposition values were higher than expected when compared to earlier studies.

Long-term clearance from small airways decreases with age

The prevalence of respiratory symptoms increases with age. Age has been found to be negatively associated with large airway clearance. The small airways region is considered important for development of airway disease. Clearance after the first 24 h was studied in 46 healthy subjects with a wide age distribution, (mean 42, range 19–81 yrs). All subjects inhaled monodisperse 6 μm Teflon particles labelled with 111In, with an extremely slow inhalation flow (0.05 L·s−1). The particles were mainly deposited in the small conducting airways. Lung retention was measured at 0 and 24 h, and at 7, 14 and 21 days after inhalation. Significant relationships were found for the individual 24 h “large” airway clearance in per cent of initial lung deposition with age, forced expiratory volume in one second and forced vital capacity. Age was negatively associated with “small” airway clearance after 24 h as estimated at 2, 7, 14 and 21 days. Using stepwise linear regression only age remained significantly associated to clearance. In conclusion, small airway clearance over 21 days was found to decrease with age. This might be one factor associated with the high prevalence of respiratory symptoms associated among the elderly.

Assessment of long-term bronchiolar clearance of particles from measurements of lung retention and theoretical estimates of regional deposition

Twelve healthy nonsmokers inhaled monodisperse Teflon particles labelled with 51Cr (half-life 27.8 days) with an aerodynamic diameter (dae) of 6.1 microns, 5 at a normal flow, 0.5 L/s, and 7 at an extremely slow flow, 0.05 L/s. Lung retention after 24 hours was measured for about 6 months and could be well described by a 2-component exponential function. After the normal inhalation, 14% of the particles retained after 24 hours cleared with a half-time of 3.7 days and 86% with a half-time of 217 days. After the slow inhalation, 35% of the particles retained after 24 hours cleared with a half-time of 3.6 days and 65% with a half-time of 170 days. Deposition was calculated using 3 different models including the recent Human Respiratory Tract Model (HRTM), adopted by the International Commission on Radiological Protection (ICRP), and a model based on Monte Carlo particle transport, together with an asymmetric lung model. Generally, the 3 models agreed fairly well and predicted a considerably higher deposition in the bronchiolar region (generations 9-15) at the slow flow than at the normal flow. Together, the experimental data and the predictions of the deposition models indicate that about 40% of the particles deposited in the conducting airways during the slow inhalation were retained after 24 hours. They also strongly indicate that the particles which cleared with a half-time of about 4 days were mainly deposited in the bronchiolar region, and that about 25% of the particles deposited in the bronchiolar region cleared in this phase. The experimental data agreed quite well with the HRTM predictions made using its default parameter values for slow clearance in the bronchial tree.

Clearance of Particles from Small Ciliated Airways

In recent years, there has been a debate on whether a considerable fraction of particles is retained after 24 h in the tracheobronchial region. In the present study, 8 healthy subjects inhaled 6.2-microns monodisperse Teflon particles labeled with 111 In twice, at flow rates of 0.45 and 0.045 L/s. According to theoretical calculations, the particles inhaled at 0.45 L/s should deposit mainly in large bronchi and in the alveolar region, whereas the particles inhaled at 0.045 L/s should be deposited mainly in small ciliated airways. Twenty-four hours after inhalation, about half of the particles inhaled with both modes of inhalation had cleared. Clearance during the period from 1 to about 30 days after inhalation, could, for both modes of inhalation, be described by the sum of two exponential functions. For the inhalation rate of 0.45 L/s, 15% cleared with a half-time of 3.4 days and 85% with a half-time of 190 days. For the inhalation of 0.045 L/s, 20% cleared with a half-time of 2.0 days and 80% with a half-time of 50 days. The results strongly indicate (1) that a considerable fraction of particles deposited in small ciliated airways had not cleared within 24 h, and (2) that these particles cleared differently from particles deposited in the alveolar region. The experimental data agree quite well with the IRTM predictions made using its default slow clearance fractions.

Long-term lung clearance of 195Au-labeled teflon particles in humans.

Ten healthy males inhaled monodisperse Teflon particles (geometric diameter 3.6 microns, aerodynamic diameter 5.3 microns) labeled with 195Au (half-life 183 days). The leakage of 195Au from the particles in vitro in water was less than 0.2% per year. Retention over the thorax was followed for about 900 days using two separate detector systems. One system consisted of four Ge detectors placed close to the front of the chest over the upper and lower regions of the lungs. The other system consisted of three NaI crystals placed in a ring around the thorax at some distance from the chest wall. Activities of 195Au in feces (24- or 48-h samples) could be measured as long as activities in the thorax could be measured. For the period 7-250 days, the half-times were similar for the two detectors, on the average 740 days for the NaI detectors and 680 days for the Ge detectors. The average half-times estimated from measurements from about 250 days to about 900 days were 1750 days with the NaI detectors and 880 days with the Ge detectors. Clearance curves constructed from measurements from feces agreed very well with clearance measured with the NaI detectors. The excretion via feces was well described by a power function with days after exposure as base. This total clearance from the thoracic region was slower than in earlier studies. No activity could be measured in the urine. The measurements with the two detector systems show that a translocation within the thoracic region occurred. This might be explained by transportation of particles from the lung parenchyma to the regional lymph nodes. The accumulation of particles in the regional lymph nodes was tentatively calculated on the basis of that assumption.

DOES LUNG RETENTION OF INHALED PARTICLES DEPEND ON THEIR GEOMETRIC DIAMETER

Experiments with a bolus technique suggest that retained fractions in the airways are dependent on the geometric diameter of the particles. This view has been adopted by the International Commission on Radiological Protection (ICRP) in its new human respiratory tract model (HRTM). The aim of the present study was to test this view by the use of an inhalation technique, in which particles with an aerodynamic diameter of about 6 microns are inhaled extremely (0.05 l/s) and as a result, the particles are deposited mainly in small ciliated airways. Nine healthy subjects inhaled on one occasion monodisperse 111In-labelled polystyrene particles (geometric diameter 6.05 microns, aerodynamic diameter 6.2 microns) and on another occasion monodisperse 111In-labelled Teflon particles (geometric diameter 4.47 microns, aerodynamic diameter 6.5 microns). Both particles were inhaled at 0.045 L/s and radioactivity in the body was measured after 0, 24, 48, and 72 hours as well as after 1, 2, and, for some subjects, also 3 weeks. The retention in the lungs at 24 hours was slightly lower for the Teflon particles (47%) than for the polystyrene particles (51%). From earlier experimental data with different particle sizes as well as from predictions with theoretical lung models, this difference is reasonably explained by the somewhat larger aerodynamic diameter of the Teflon particles. Clearance of the 2 particle types between 1 day and 2 weeks was similar within each individual as well as in the whole group. The differences between the clearance of 4.5 microns and 6 microns geometric diameter particles observed in the present experiment are significantly different (P < .01) from the differences seen in earlier shallow bolus experiments as well as from the differences for such particles calculated with the HRTM, i.e., our experiment does not support the hypothesis that the fraction retained after 1 day is dependent on the geometric diameter in the size range studied.

COMPARISON OF CLEARANCE OF PARTICLES INHALED WITH BOLUS AND EXTREMELY SLOW INHALATION TECHNIQUES

Ten healthy nonsmokers inhaled 6-Ten healthy nonsmokers inhaled 6-microm (aerodynamic diameter) Teflon particles labelled with 111In twice, once with the shallow bolus technique (volumetic lung depth 76+/-20 mL ([+/- SD]) and once with the extremely slow inhalation technique (0.05 L/s). The radioactivity in the lungs was measured at 1 and 24 hours as well as at 1, 2, and 3 weeks after both inhalations. The 24-hour lung retention a percentage of lung deposition was significantly lower for the bolus inhalation, 46%+/-9% (+/- SD) than for the extremely slow inhalation, 56%+/-11%. The retention after 21 days as a percentage of the 24-hour retention was 55%+/-9% for the shallow bolus inhalation and 56%+/-10% for the extremely slow inhalation. Also within the subjects, clearance was similar for the 2 modes of inhalation. Deposition of particles inhaled with the 2 modes of inhalation was calculated with 2 model, one being based on Monte (Carlo particle transport together with an asymmetric lung model. Deposition predicted with this model agreed well with the experimental data under the assumption that there are large retained fractions only in small ciliated airways (bronchioli) and not in large ones. For the bolus inhalation, the model predicted 43% to 50% deposition in the bronchial (BB) region of initial lung deposition, 33% to 38% in the bronchiolar (bb) region, and 16% to 22% in the alveolar region. For the extremely slow inhalation, the model predicted 31% to 34% deposition in the BB region, 45% to 47% in the bb region, and 21% to 22% in the alveolar region. In addition, it predicted about the same ratio between bb and alveolar depositions for the 2 modes of inhalation. Thus, both the experimental and theoretical data indicate that the shallow bolus particles to a considerable extent reach both the bb and the alveolar regions and that they do that at about the same extent as the particles inhaled extremely slow. This conclusion is concerning the experimental data based on the assumption that there are no large retained fractions in the BB region. Another interpretation of the similar clearance for the two modes of inhalation is that there are large retained fractions in both the BB and the bb regions and that individual charactristics of clearance of these fractions are of importance rather than the site of deposition.

Retention of Particles Inhaled in Boli with and Without Induced Bronchoconstriction

Large lung retentions (up to 50%) of particles < or = 4 microns inhaled with a bolus technique at a penetration depth less than dead space have been reported to occur after 24 h. This retention may be due to retarded clearance of particles deposited in the airways of the tracheobronchial tract; an alternative explanation could be that particles are deposited in the alveolar region. The purpose of the present study was to confirm the occurrence of retained fractions and to study the influence of a cholinergic drug, which is assumed to give a more central particle deposition, on these retentions in human lungs after shallow aerosol bolus inhalation. Twelve healthy subjects inhaled, with a bolus technique, monodisperse Teflon particles (2.4 microns geometric diameter, 3.5 microns aerodynamic diameter), labeled with 111In. The volumetric lung depth of the inspired bolus was around 60 mL and flow rate was about 300 mL/s. Six subjects inhaled the test particles after a provocation with a cholinergic aerosol, which induced a threefold increase in airway resistance. The other six subjects inhaled a cholinergic aerosol after inhalation of the test particles or inhaled no cholinergic aerosol at all. Radioactivity in the body was measured after 0.5, 24, 48, and 72 h with a whole-body scanner with three 127 x 101-mm Nal detectors. The investigation confirmed results obtained earlier by a group in Frankfurt claiming that great retentions occur after 24 h. The retentions tended to be lower in the group receiving a bronchoconstricting drug before the bolus inhalations. There was a significant lung clearance of particles between 24 and 72 h, in contrast to the findings in earlier studies in healthy subjects and asthmatics who inhaled Teflon particles in large volumes. On the other hand, the clearance agreed well with the clearance in healthy subjects with extensive deposition of Teflon particles in the small ciliated airways, obtained by means of an extremely low inhalation flow rate. The results suggest that a considerable fraction of the particles in the bolus inhalation have been deposited in small ciliated airways in which the mucociliary transport is less efficient or in the alveolar region.

Phagolysosomal morphology and dissolution of cobalt oxide particles by human and rabbit alveolar macrophages.

The effect of phagolysosomal size on dissolution of cobalt oxide particles was evaluated in two different macrophage systems: alveolar macrophages (AM) of human smokers with phagolysosomes enlarged by ingested cigarette smoke products, and rabbit AM incubated in vitro with sucrose, which causes swelling of the phagolysosomes by osmosis. Human AM from smokers and nonsmokers were studied in vitro. There was no significant difference in particle dissolution between AM obtained from smokers and nonsmokers, although there was a clear difference in the morphological appearance of AM, including significantly larger phagolysosomes in smokers. Rabbit AM were incubated for 24 or 72 h with or without 80 mM sucrose in the medium. The sucrose-treated cells had 3-4 times larger phagolysosomes than untreated cells, with no major change in phagolysosomal pH. The increased size of the phagolysosomes did not affect the ability of the AM to dissolve cobalt oxide particles. Furthermore, rabbit AM showed the same ability as human AM to dissolve the cobalt oxide particles, in spite of the fact that they had markedly smaller phagolysosomes. Another difference between human and rabbit AM was that phagolysosomes in human AMs increased in size with time in culture, while rabbit AM phagolysosomes decreased in size.