- Email: [email protected]
A new device for aerosol and gas inhalation studies and its application in lung investigations
The biomedical influence of the aerosol
237
THE L I G H T SCATTERING O F AEROSOLS H. STRAUBEL
Vorderhindelang, West Germany The response of light scattering instruments can only be calculated for spherical particles. Natural aerosols, however, consist of non-spherical particles. In case the constituents are water-soluble, they can change size and shape due to water absorption or evaporation, before they reach the screening volume of the instrument. Consequently the light scattering signal is different from the signal which would be obtained from the particle outside the instrument. Often the aerosols consist of cristalline aggregates. The initial water uptake of these particles is due to capillary condensation between the cristalline surfaces. Therefore, the intensity and the angular intensity distribution changes rapidly although the diameter of the aggregate is almost unchanged. This is due to a reduced total reflection on these surfaces. There are certain substances which show an unsteady water uptake. For instance, NH4C1 forms "dendrites" at a certain relative humidity (r.h.). The change of the particle mass cannot be measured with a device as shown in Fig. 5, but with a device, as previously described (Straubel, 1973) in which the particle is electrically levitated and thus spatially stable. The change of the particle mass can be easily determined from the levitation voltage at each moment. The water uptake of a levitated NH4CI crystal was studied in a movie picture. The formation of dendrites occurred in a time of less than 100 msec. The same phenomenon could be observed when the crystal was supported by a cover glass. The water uptake by the crystal was associated with a change in its light scattering pattern (Fig. 6, on p. 239). It is the purpose of this paper to demonstrate which errors could be associated with light scattering measurements. It should be emphasized that the detection of the water uptake on a single surface depends on the orientation of the particle in the light beam. REFERENCE Straubel, H. (1973) Staub 33, 174.
LOllr I
. . . . . . . . . . . . .
Cover
gloss
//I .%, (//~I 1~'6, .I.6ll I~\\~ s',t l I ! .,, / ~ / I I I
II/I///I//
| I ~
I I
X \
~, ~. ~ .
Film
Fig. 5. Observation of crystal.
A NEW DEVICE FOR AEROSOL AND GAS INHALATION STUDIES A N D ITS APPLICATION IN LUNG INVESTIGATIONS J. GEBHART, G. HEIGWER, J. HEYDER, C. ROTH and W. STAHLHOFEN Gesellschaft f6r Strahlen- und Umweltforschung m.b.H., Neuherberg, Abteilung ffir Biophysikalische Strahlenforschung, 6000 Frankfurt/M, Paul-Ehrlich-Str. 20, West Germany Total deposition, DE, is the average probability of an inspired particle touching a surface of the respiratory tract and thereby being deposited. It can be calculated from the ratio of the number of exhaled (Ne) to inhaled (N~) particles per breath according to: DE = 1 - N~ = 1 Ni
S"elcfZ dt S(,i~ c 12 dr"
where t~ = t, is the period for inspiration respiratory expiration. Consequently, deposition can either be determined indirectly by continuous monitoring of the particle number concentration, c, and the volumetric flow rate, 12,(analog method) or directly by counting the number of inspired and expired particles (digital method). The analog method has been already described elsewhere (Heyder et al., 1973). For the digital method a novel photometer has been developed which counts the number of particles in the main stream of the in- and exhaled air close to the entrance of the respiratory tract (see Fig. 7). The beam of an argon ion laser (3 W) is optically shaped into
238
i ~lJ Ar,~t AI ('OSJ:~RE~Cr
o~
] HI! GAFF
/ if--\ "x PHOTOMULTIPLIER ,
\
\
'N
_
FLEISCH
TUBE
~
IGHT
TN~P
MOUTHPIECE
LASER B E A M
Fig 7 The schematic diagram of the photometer.
a sheet of light of 80/am thickness and 15 m m height which passes the aerosol flow in such a way that the viewing tteid of the photometer covers a large part of the cross-section of the aerosol channel. The sheet of light is inclined at an angle of 60 ° to the direction of the aerosol flow and coincides with the observation plain of the receiver optic J hc light flashes scattered from single particles traversing the light sheet are received by a photomultiplier and transformed into electrical signals which, according to their height, are stored in a multichannel device. The signals during in- and expiration are stored separately• Simultaneously, a computer counts the number of signals during i n and expiration and calculates deposition for each breath• When the photometer is operated in the digital mode concentrations less than 5 c m - 3 are required and a iowe! detection limit of about 0.3/am is achieved• At higher concentrations ( > 100 c m - 3) it can also be operated m ~,he usual analog mode and used to record aerosol concentration profiles• Due to its high sensitivity the photometer can distinguish between gases which differ in Rayleigh-scattering. Therefore dispersions of inhaled pulses of tracer gases in the respiratory tract can also be analysed with the instrument. The advantages of the digital photometer for inhalation studies are the following (1) The method of determining total deposition is straightforward. No calibration, no correction ,,r any unpr,~v,~d assumption are required. (2) Since only particle concentrations below 5 cm - ~ are needed deposition studies can be carried out with Joy, i~n~burdens of the subjects, even if particles up to 10/am are used. (3) Separate records of size distributions of inspired and expired aerosols allow growth studies c,f hygroscopic.: particles in the respiratory tract, (4) Using insoluble particle materials monodisperse fractions of aerosols suitable for deposimm studies can b~.: selected out of polydisperse size distributions in the in- and exhaled air. REFERENCE J. Heyder, 3. Gebhart, G . Heigwer. C Roth and W. Stahlhofen (1973) .L Aerosol Sci. 4, 191
MEASUREMENTS WITH
OF
THE
RESPIRABLE
A CYLINDRICAL
AEROSOL
FRACTION
CENTRIFUGE
D, SE[ HARS Eraunhofer-Gesettschaft lnstitut ffir rroxikologie und Aerosolforschung, 5948 Schmallenberg-Grafschaft, West G e r m a n y A cylindrical centrifuge for the collection of the respirable aerosol fraction is described. According to the definition m "Technische Anleitung zur Reinerhaltung der Luft" an aerodynamic diameter of 7/am was theoretically designed as a separation limit between coarse and fine particles• This means a significant upward shift of the Johannesburg separation function from a lower 50% - value of sampled particle size (5 ,urn). The actual separation function points to the typical character of a parabolic elutriator efficiency curve• The dimensions of the deposition channel were calculated in such a way that particle sizes of 1.5/am penetrated the channel to an a m o u n t of 50')o• The centrifuge was similar to an instrument, which was designed in England some years ago (Wolff and Roach, 1961). The most important components are an annular inlet slit and a cylindrical deposition channel and finally a non-rotating filter device. Thus, in comparison to the English instrument, the actual centrifuge is a two-stage sampling and separation system• Another difference concerns the suction of aerosol throughout the instrument, i.e the English is a "self-pumping" system acting as a centrifugal pump, whereas in our case a membrane p u m p is used t~ minimize the collection time. As a result of the centrifugal force at the inlet slit coarse particles are hindered frotp, entering the instrument. The fine particles entering the centrifuge are induced by centrifugal forces n;~deposil on rb,:
237
THE L I G H T SCATTERING O F AEROSOLS H. STRAUBEL
Vorderhindelang, West Germany The response of light scattering instruments can only be calculated for spherical particles. Natural aerosols, however, consist of non-spherical particles. In case the constituents are water-soluble, they can change size and shape due to water absorption or evaporation, before they reach the screening volume of the instrument. Consequently the light scattering signal is different from the signal which would be obtained from the particle outside the instrument. Often the aerosols consist of cristalline aggregates. The initial water uptake of these particles is due to capillary condensation between the cristalline surfaces. Therefore, the intensity and the angular intensity distribution changes rapidly although the diameter of the aggregate is almost unchanged. This is due to a reduced total reflection on these surfaces. There are certain substances which show an unsteady water uptake. For instance, NH4C1 forms "dendrites" at a certain relative humidity (r.h.). The change of the particle mass cannot be measured with a device as shown in Fig. 5, but with a device, as previously described (Straubel, 1973) in which the particle is electrically levitated and thus spatially stable. The change of the particle mass can be easily determined from the levitation voltage at each moment. The water uptake of a levitated NH4CI crystal was studied in a movie picture. The formation of dendrites occurred in a time of less than 100 msec. The same phenomenon could be observed when the crystal was supported by a cover glass. The water uptake by the crystal was associated with a change in its light scattering pattern (Fig. 6, on p. 239). It is the purpose of this paper to demonstrate which errors could be associated with light scattering measurements. It should be emphasized that the detection of the water uptake on a single surface depends on the orientation of the particle in the light beam. REFERENCE Straubel, H. (1973) Staub 33, 174.
LOllr I
. . . . . . . . . . . . .
Cover
gloss
//I .%, (//~I 1~'6, .I.6ll I~\\~ s',t l I ! .,, / ~ / I I I
II/I///I//
| I ~
I I
X \
~, ~. ~ .
Film
Fig. 5. Observation of crystal.
A NEW DEVICE FOR AEROSOL AND GAS INHALATION STUDIES A N D ITS APPLICATION IN LUNG INVESTIGATIONS J. GEBHART, G. HEIGWER, J. HEYDER, C. ROTH and W. STAHLHOFEN Gesellschaft f6r Strahlen- und Umweltforschung m.b.H., Neuherberg, Abteilung ffir Biophysikalische Strahlenforschung, 6000 Frankfurt/M, Paul-Ehrlich-Str. 20, West Germany Total deposition, DE, is the average probability of an inspired particle touching a surface of the respiratory tract and thereby being deposited. It can be calculated from the ratio of the number of exhaled (Ne) to inhaled (N~) particles per breath according to: DE = 1 - N~ = 1 Ni
S"elcfZ dt S(,i~ c 12 dr"
where t~ = t, is the period for inspiration respiratory expiration. Consequently, deposition can either be determined indirectly by continuous monitoring of the particle number concentration, c, and the volumetric flow rate, 12,(analog method) or directly by counting the number of inspired and expired particles (digital method). The analog method has been already described elsewhere (Heyder et al., 1973). For the digital method a novel photometer has been developed which counts the number of particles in the main stream of the in- and exhaled air close to the entrance of the respiratory tract (see Fig. 7). The beam of an argon ion laser (3 W) is optically shaped into
238
i ~lJ Ar,~t AI ('OSJ:~RE~Cr
o~
] HI! GAFF
/ if--\ "x PHOTOMULTIPLIER ,
\
\
'N
_
FLEISCH
TUBE
~
IGHT
TN~P
MOUTHPIECE
LASER B E A M
Fig 7 The schematic diagram of the photometer.
a sheet of light of 80/am thickness and 15 m m height which passes the aerosol flow in such a way that the viewing tteid of the photometer covers a large part of the cross-section of the aerosol channel. The sheet of light is inclined at an angle of 60 ° to the direction of the aerosol flow and coincides with the observation plain of the receiver optic J hc light flashes scattered from single particles traversing the light sheet are received by a photomultiplier and transformed into electrical signals which, according to their height, are stored in a multichannel device. The signals during in- and expiration are stored separately• Simultaneously, a computer counts the number of signals during i n and expiration and calculates deposition for each breath• When the photometer is operated in the digital mode concentrations less than 5 c m - 3 are required and a iowe! detection limit of about 0.3/am is achieved• At higher concentrations ( > 100 c m - 3) it can also be operated m ~,he usual analog mode and used to record aerosol concentration profiles• Due to its high sensitivity the photometer can distinguish between gases which differ in Rayleigh-scattering. Therefore dispersions of inhaled pulses of tracer gases in the respiratory tract can also be analysed with the instrument. The advantages of the digital photometer for inhalation studies are the following (1) The method of determining total deposition is straightforward. No calibration, no correction ,,r any unpr,~v,~d assumption are required. (2) Since only particle concentrations below 5 cm - ~ are needed deposition studies can be carried out with Joy, i~n~burdens of the subjects, even if particles up to 10/am are used. (3) Separate records of size distributions of inspired and expired aerosols allow growth studies c,f hygroscopic.: particles in the respiratory tract, (4) Using insoluble particle materials monodisperse fractions of aerosols suitable for deposimm studies can b~.: selected out of polydisperse size distributions in the in- and exhaled air. REFERENCE J. Heyder, 3. Gebhart, G . Heigwer. C Roth and W. Stahlhofen (1973) .L Aerosol Sci. 4, 191
MEASUREMENTS WITH
OF
THE
RESPIRABLE
A CYLINDRICAL
AEROSOL
FRACTION
CENTRIFUGE
D, SE[ HARS Eraunhofer-Gesettschaft lnstitut ffir rroxikologie und Aerosolforschung, 5948 Schmallenberg-Grafschaft, West G e r m a n y A cylindrical centrifuge for the collection of the respirable aerosol fraction is described. According to the definition m "Technische Anleitung zur Reinerhaltung der Luft" an aerodynamic diameter of 7/am was theoretically designed as a separation limit between coarse and fine particles• This means a significant upward shift of the Johannesburg separation function from a lower 50% - value of sampled particle size (5 ,urn). The actual separation function points to the typical character of a parabolic elutriator efficiency curve• The dimensions of the deposition channel were calculated in such a way that particle sizes of 1.5/am penetrated the channel to an a m o u n t of 50')o• The centrifuge was similar to an instrument, which was designed in England some years ago (Wolff and Roach, 1961). The most important components are an annular inlet slit and a cylindrical deposition channel and finally a non-rotating filter device. Thus, in comparison to the English instrument, the actual centrifuge is a two-stage sampling and separation system• Another difference concerns the suction of aerosol throughout the instrument, i.e the English is a "self-pumping" system acting as a centrifugal pump, whereas in our case a membrane p u m p is used t~ minimize the collection time. As a result of the centrifugal force at the inlet slit coarse particles are hindered frotp, entering the instrument. The fine particles entering the centrifuge are induced by centrifugal forces n;~deposil on rb,: