Peripheral deposition of a 1 -protease inhibitor using commercial inhalation devices

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1 Eur Respir J 23; 22: DOI: / Prited i UK a rights reserved Copyright #ERS Jouras Ltd 23 Europea Respiratory Joura ISSN Periphera depositio of a 1 -protease ihibitor usig commercia ihaatio devices P. Brad*, H. Beckma #, M. Maas Eriquez #, T. Meyer },B.Müiger }, K. Sommerer }, N. Weber*, T. Weuthe }, G. Scheuch } Periphera depositio of a 1 -protease ihibitor usig commercia ihaatio devices. P. Brad, H. Beckma, M. Maas Eriquez, T. Meyer, B. Müiger, K. Sommerer, N. Weber, T. Weuthe, G. Scheuch. #ERS Jouras Ltd 23. ABSTRACT: Patiets with hereditary a 1 -proteiase ihibitor (a 1 -PI) deficiecy are at risk of deveopig ug emphysema. To prevet the deveopmet of this disease, a 1 -PI repacemet therapy via ihaatio may be a more coveiet ad effective therapy tha the itraveous admiistratio of the drug. I order to optimise this treatmet approach, ug depositio of ihaed radioabeed a 1 -PI (Proasti1) was studied usig four differet commercia ihaatio devices (PARI-LC Star1, HaoLite1, ad AKITA1 system i combiatio with LC Star1 ad Sidestream1) i six patiets with a 1 -PI deficiecy ad mid-to-severe chroic obstructive pumoary disease. The time required to deposit 5 mg of the Proasti1 (5% soutio) i the ug periphery was used as a measure for the efficiecy of deivery. The time was cacuated from measuremets of tota ad periphera ug depositio of the radioabeed a1-pi. This time was shortest for the AKITA1 system (18 24 mi) ad sigificaty higher for the PARI-LC Star1 (44 mi) ad the HaoLite1 (1 mi). The higher efficiecy of drug deivery usig the AKITA1 system is due to the fact that this device cotros breathig patters, which are optimised for each patiet idividuay. Eur Respir J 23; 22: *Ciica Research Group "Aerosos i Medicie" of the GSF-Istitute for Ihaatio Bioogy ad the Askepios Ciic for Respiratory Medicie, # Bayer Vita GmbH, Leverkuse ad } Iamed-Iteiget Aeroso Medicie GmbH, Gautig, Germay. Correspodece: P. Brad, GSF-Istitute for Ihaatio Bioogy, Robert-Koch-Aee 29, D Gautig, Germay. Fax: E-mai: brad@iamed.de Keywords: Ihaatio ihaatio devices a 1 -protease ihibitor repacemet therapy Received: December Accepted after revisio: March This study was supported by Bayer Corporatio, Research Triage Park, NC, USA. Patiets with hereditary a 1 -proteiase ihibitor (a 1 -PI) deficiecy suffer from the ack of a substace that protects the ug from eutrophi eastase, a powerfu protease, which is capabe of ceavig most proteis i the extraceuar matrix. Due to a severey disturbed protease/atiprotease baace, these patiets are at risk of deveopig ug emphysema at a youg age, especiay if they aso smoke [1 3]. I order to prevet the deveopmet of ug emphysema or to sow dow its progressio, smokig cessatio is essetia, ad a 1 -PI repacemet therapy with weeky ifusios has bee show to raise serum cocetratios ad ug epitheium iig fuid a 1 -PI, thus restorig the baace betwee eastase/atieastase activity i the ug biochemicay. Athough the itraveous repacemet therapy showed promisig ciica resuts deayig the progressio of the disease, the therapy [1, 4, 5] has the disadvatage that oy 2% of the admiistered drug reaches the ugs [1]. This is a severe probem sice the wordwide demad caot yet be satisfied by the pharmaceutica idustry9s productio capacities. I pricipe, the drug ca aso be appied directy to the target regio withi the ugs by ihaatio. Nevertheess, a umber of probems have to be soved i order to guaratee efficiet drug deivery: 1) a sufficiet fractio of the drug eeds to be deposited withi the ugs; 2) the drug eeds to be deposited i periphera ug regios i order to achieve sufficiet deivery of protei to the ug iterstitium where a 1 -PI is supposed to act; 3) drug depositio i the ugs eeds to be reproducibe ad as idepedet from airway obstructio as possibe; ad 4) ihaatio time shoud be short eough to be coveiet for the patiets. The resuts of previous studies showed that the coditios above may be fufied usig a optimised, cotroed breathig patter [6, 7]. It has bee show that for a deep ad sow ihaatio with sufficiety sma partices ad idividuay cotroed breathig patters, periphera depositio (Dp) as high as 6% of the aerosoised drug ca be achieved [8, 9]. Such high depositio vaues i ciica practice woud cosideraby improve systemic ad topic aeroso therapy ad woud icrease the efficiecy of a 1 -PI repacemet therapy. I this study, i six patiets with a 1 -PI deficiecy ad midto-severe chroic obstructive pumoary disease (COPD), ug depositio of ihaed radioabeed a 1 -PI (Proasti1; Bayer Vita., Leverkuse, Germay) was studied usig four differet commercia ihaatio devices. It was ivestigated whether cotroed ihaatios with carefuy seected breathig patters provide a cosiderabe improvemet of the efficiecy of drug deivery compared with covetioa spotaeous breathig patters. Subjects Methods Six patiets (four mae, two femae) with hereditary a 1 -PI deficiecy (Z-pheotype) ad a midy to severey reduced ug fuctio, aged betwee yrs (media 59 yrs) participated i this study (tabe 1). Four patiets were osmokers

2 264 P. BRAND ET AL. Tabe 1. Athropometric ad ug fuctio parameters of the study popuatio ad two patiets were exsmokers ad had stopped smokig o5 yrs before participatig i the study. A patiets obtaied a 1 -atitrypsi-deficiecy repacemet therapy by weeky i.v. ifusios of Proasti1 ad brochodiators as required. Writte iformed coset was obtaied from each patiet. The study protoco was approved by the Ethics Committee of the Medica Schoo of the Ludwig-Maximiias-Uiversity (Muich, Germay) ad the resposibe reguatory authorities. Pumoary fuctio tests Body pethysmographic ad spirometric parameters of ug fuctio were determied by usig a Jaeger-Masterab (Erich Jaeger GmbH, Würzburg, Germay). The foowig parameters were measured: tota ug capacity (TLC), ispiratory vita capacity, itrathoracic gas voume (ITGV), airway resistace, peak expiratory fow rate ad forced expiratory voume i oe secod. Measured ug fuctio parameters were ormaised to the referece vaues proposed by the Europea Commuity for Coa ad Stee [1]. Nebuiser systems Mea SD (rage) Athropometric data Age yrs Height cm Weight kg Lug fuctio parameters TLC L TLC % pred ITGV L ITGV % pred VC L VC % pred 96 2 FEV1 L (.3 3.1) FEV1 % pred (5 84) PEF L?s PEF % pred Specific airway resistace kpa?s Data represet vaues from six patiets. TLC: tota ug capacity; % pred: % predicited; ITGV: itrathoracic gas voume; IVC: ispiratory vita capacity; VC: vita capacity; FEV1: forced expiratory voume i oe secod; PEF: peak expiratory fow. I this study the foowig commercia ihaatio systems were appied for the ihaatio of radioabeed Proasti1. 1) PARI-LC Star1 Jet ebuiser with "Turbo Boy" Compressor (Pari, Starberg, Germay). The ebuiser is mauay activated at the start of ihaatio. 2) HaoLite1 (Medic Aid, West Sussex, UK). This computer-cotroed device appies the "adaptive aeroso deivery" techique. If the patiets start ihaatio, durig a certai umber of breathig cyces the breathig patter of the patiets is measured by the device. The a aeroso bous is emitted for a certai period withi the first 5% of ihaatio. To coect the exhaed partices, a exhaatio fiter was adopted to the HaoLite1 usig siico fittigs. The proper performace of the device after this maipuatio was tested by the maufacturer. 3) AKITA1 (Iamed, Gemüde, Germay). This computer-cotroed device aows idividuaised, cotroed ihaatios i combiatio with covetioa ebuisers. Usig a idividua smart-card for each patiet the ihaatio fow rate, ihaed voume ad a breath-hodig period ca be presicey predetermied. The pressured air for the ebuiser is deivered by a compressor itegrated ito the AKITA1. I this study, the AKITA1 was used i combiatio with either a "PARI-LC Star1" ebuiser or a "Sidestream1" ebuiser (Medic Aid). The order i which the subjects ihaed from the differet devices was radomised. The three differet devices are simiar i size (PARI-LC Star mm, HaoLite mm, AKITA mm), but the AKITA1 system had the highest weight (PARI-LC Star1 2.7 kg, HaoLite1 2.7 kg, AKITA1 7.5 kg). The partice size distributio of each ebuiser used i this study was measured usig a eight-stage cascade impactor (Mark 2) usig radioabeed Proasti1. The foowig vaues for the mass media aerodyamic diameter (MMAD) ad the geometric stadard deviatio were foud. PARI-LC Star1: MMAD=4.4 mm, SD=2; HaoLite1: MMAD=3.7 mm, SD=2; AKITA1 /LC Star1: MMAD=3.8 mm, SD=2; AKITA1/ Sidestream1: MMAD=3.9 mm, SD=2.1. Breathig patters Each ebuiser was fied with 3 ml radioabeed Proasti1 cotaiig 15 mg of Proasti1 ad the patiets ihaed for 5 mi. PARI-LC Star1. Sice a patiets perform orma ihaatios usig jet ebuisers, they were asked to ihae ormay usig the LC Star1 ad to activate the ebuiser durig ihaatio. Exhaatio was performed ito a exhaatio fiter. HaoLite1. Patiets were asked to ihae ormay. Exhaatio was performed ito the device which had a fiter icuded. AKITA1. The breathig patter used i the AKITA1 was derived from i-vivo studies i which the optimum breathig patters for a high periphera ug depositio were ivestigated [8, 9, 11]. From this study, the fow rate was derived as 2 cm 3?s -1 ad the ihaed voume (TLC-ITGV) as.8, idividuay cacuated ad stored o the smart card. The subject was asked to start the ihaatio. If a pressure drop at the mouth is measured the AKITA1 activates the ihaatio by appyig pressure to the ebuiser ozze ad a costat, predefied amout of air is deivered to the ebuiser9s auxiiary air iet at a costat fow rate. The ast 2 ml of the ihaatio were free of drug aeroso to avoid useess drug depositio i the dead space of the ugs. After the predefied ihaatio voume is reached, the air suppy is tured off ad the patiet is istructed to perform a 2-s breath-hodig period. The patiet is istructed via the dispay of the device. The average ihaatio voume cacuated for the AKITA1 was (mea SD) L. For a other devices, othig is kow about the actua breathig patter used for ihaatio. Labeig The prodedure to abe Proasti1 with 99m Tc used i this study was modified from the method pubished by LAFONT et a. [12]; a isotoic NaC soutio cotaiig 5% of Proasti1 was recostituted i a cosed via. From this soutio, a stock soutio of y1 ml was separated. To this soutio, 5 ml of a SC 2 soutio was added as a reducig aget. 99m Tc (185 megabequere (MBq)) was the itroduced by addig a Na 99m TcO 4 soutio. After gete shakig the soutio was icubated for 3 mi. The efficacy of the

3 PERIPHERAL DEPOSITION OF a 1 -PROTEASE INHIBITOR 265 abeig procedure was verified by comparig the size distributios, the radioactivity ad dry mass of Proasti1 usig a Aderse Cascade Impactor (Typ Mark II; Copey Scietific Ltd, Nottigham, UK). The radioabeed Proasti1 soutio was the diuted, for each ihaatio device, i order to imit the radioactivity avaiabe for ihaatio to 1.6 MBq. The stabiity of the abeig was verified usig thi-ayer chromatography as described by LAFONT et a. [12]. It was verified that the size distributio of the partice mass was the same as the distributio of radioactivity usig a cascade impactor. Depositio measuremets Each ihaatio device was fied with 3 ml of radioabeed a 1 -PI with the amout (A) of radioactivity. Each subject the ihaed for y5 mi usig the breathig patter give above. The actua ihaatio time (tih) was recorded. Exhaatio was performed ito a exhaatio fiter. The the amout of radioactivity remaiig i the ebuiser (A9), i the exhaatio fiter (Aexh) ad the activity deposited withi the ugs (A) was measured with a ug couter with four sesitive NaI scitiatio crystas. After 15 mi, a gamma camera image was recorded (Siemes Diacam; Siemes, Erage, Germay). From this picture, the fractio of activity deposited itrathoracicy (Dit) was cacuated usig regios of iterest: Dit~ Athor AtzAh where At is the activity measured i the thorax regios of iterest ad Ah is the activity measured i the head ad stomach area. Durig the foowig 45 h the remaiig ug activity was measured up to eight times with a sesitive ug couter to quatify a fast ad sowy ceared fractio (Asow). Therefore, a doube expoetia fuctio was fitted to the measured decie i ug activity ad the sow compoet of this fuctio was extrapoated to time zero (Asow). This sowceared fractio is assumed to be a measure of the amout of partices beig deposited i the ug periphery, whie the fastceared fractio is assumed to be due to partices ceared by mucociiary cearace from cetra airways. The tota activity ihaed (Aih) by the patiet was cacuated usig: Aih~A{A ð2þ Tota depositio (Dt) i the etire respiratory system of the patiet was give by: Dt~ Aih{Aexh Aih As a measure of Dp the fractio of partices sowy ceared from itrathoracic airways was used [13 15]: Dp~Dt Dit ðasow=aþ ð4þ Depositio, i this study, was defied as the amout of partices deposited i compariso with the amout of partices ihaed. This defiitio of depositio deivers higher vaues tha other defiitios, which reate the deposited drug amout to the amout fied ito the ebuiser. However, the defiitio used i this study was more appropriate to assess the ihaatio time. The time required to deposit 5 mg of a 1 -PI (t5) is give by: t 5 ~ 5 tih ð5þ Dp M where M is the a 1 -PI dose fied i the ebuiser. ð1þ ð3þ Reative retetio Statistics Time h Differeces i depositio ad treatmet time amog the differet devices were tested for statistica sigificace usig a paired t-test. Therefore, the differeces for each subject ad each parameter obtaied for the differet devices were subtracted from each other. For each of the six differeces, the hypothesis that this differece is zero was tested usig the paired t-test. Correatios were cacuated usig Pearso product-momet correatio aaysis. Resuts Fig. 1. Lug retetio of ihaed radioabeed Proasti1 as a fuctio of time for six subjects ihaig with the AKITA1 LC Star1 combiatio. Figure 1 shows, as a exampe, the decie i ug radioactivity over 45 h i a patiets after ihaatio with the AKITA1 LC Star1 combiatio. After 45 h w5% of the radioactivity was sti foud withi the ugs, idicatig the stabiity of the drugs radioabeig. Tabe 2 shows the mea SD Dt ad Dp of radioabeed a1 -PI ihaed with differet ihaatio devices i per cet of ebuised a1-pi i six patiets with a 1 -PI deficiecy ad mid-to-severe emphysema. The mea vaue for Dt for the PARI-LC Star1 ad for the HaoLite1 is i the order of 5 6% (fig. 2) of ebuised Proasti1 ad Dp i the order of 3 35% (fig. 3); both AKITA1 combiatios, AKITA1 Sidestream1 ad AKITA1 LC Star1, reach 75 8% for Dt ad 5 6% Dp. As ca be see from tabe 3, these differeces are statisticay sigificat (paired t-test) whereas there were o sigificat differeces betwee the resuts obtaied for the HaoLite1 ad the PARI-LC Star1 or betwee the AKITA1 Sidestream1 ad the AKITA1 LC Star1 (oy Dt). Due to the higher depositio vaues the time required to deposit 5 mg of Tabe 2. Tota depositio (Dt), periphera depositio (Dp), ad time required to ihae 5 mg of a 1 -protease ihibitor (T5) measured i six patiets with a 1 -protease ihibitor deficiecy after ihaatio with differet devices Device Dt % Dp % T5 mi HaoLite 59 7 (12) 33 1 (3) (41) LC Star (33) (56) (57) AKITA1 Sidestream (11) (21) (54) AKITA1 LC Star1 8 7 (9) 57 9 (16) 18 6 (13) Data are preseted as mea SD (coefficiet of variatio=16sd/ mea).

4 266 P. BRAND ET AL. Tota depositio % HaoLite AKITA Fig. 2. Tota depositio measured i six patiets with a 1 -protease ihibitor deficiecy usig differet ihaatio devices. Side.: sidestream. Periphera depositio % HaoLite a 1 -PI i the ug periphery was sigificaty shorter for both AKITA1 devices compared with HaoLite1 ad LC Star1 (fig. 4 ad tabe 2). The itersubject variabiity for each parameter was highest for the LC Star1 device ad owest for the AKITA1 LC Star1 combiatio (tabe 2). Athough there was a tedecy that patiets with the most AKITA Fig. 3. Periphera depositio measured i six patiets with a 1 - protease ihibitor deficiecy usig differet ihaatio devices. Side.: sidestream. Tabe 3. Leves of sigificace of the differeces betwee the parameters uder cosideratio ad differet ihaatio devices cacuated usig a paired t-test p-vaues Dt Dp T5 HaoLite1 versus LC Star HaoLite1 versus AKITA Sidestream1 HaoLite1 versus AKITA1.42 v.1.3 LC Star1 LC Star1 versus AKITA Sidestream1 LC Star1 versus AKITA LC Star1 AKITA1 Sidestream1 versus AKITA1 LC Star1 Dt: tota depositio; Dp: periphera depositio; T5: time required to ihae 5 mg of a 1 -protease ihibitor. Time to deposit 5 mg mi HaoLite impaired ug fuctio eeded the ogest time to deposit 5 mg of Proasti1 i the ug periphery, this tedecy faied statistica sigificace, which may be due to the sma umber of subjects. Discussio AKITA Fig. 4. Time required to ihae 5 mg of a 1 -protease ihibitor measured i six patiets with a 1 -protease ihibitor deficiecy usig differet ihaatio devices. Side.: sidestream. This study has show that the highest Dt ad Dp of ihaed radioabeed a 1 -PI ad the shortest ihaatio times ca be obtaied usig a optimised breathig patter, which is cotroed by a device ike the AKITA1. If a covetioa ebuiser is used without cotro of the breathig patter, depositio is quite heterogeeous. Some patiets show high Dp vaues simiar to the cotroed case, but i others, depositio v2% is foud. As a previous study has show [6], these heterogeeous depositio vaues ca be expaied by the hetereogeeity of the breathig patter. Basicay, it was foud that depositio is highest if the patiet is ordered to ihae deepy o1.5 L [8, 9, 11]. I this case, most of the drug is abe to peetrate ito the ug periphery ad its residece time is og eough for compete depositio by sedimetatio. Such deep ihaatios ca be maitaied usig the AKITA1 device which aows a programmig of the ihaed voume accordig to the idividua ug fuctio of the patiet. Usig this idividua approach, each patiet ihaes the argest possibe voume that is sti coveiet for them. Additioay, the ihaatio fow rate is fixed to vaues which are sow eough (2 ml?s -1 ) to prevet depositio by impactio i obstructed proxima airways [6]. The resuts obtaied with the AKITA1 device seems to be idepedet of the ebuiser actuay used. Athough the AKITA1 LC Star1 combiatio teded to show higher depositio ad ower ihaatio times tha the AKITA1 Sidestream1, these sma differeces were ot statisticay sigificat. I the HaoLite1 device, ihaatio is aso cotroed. However, this cotro is passive ad maitaied by a adaptatio of the ebuisig process to the patiets arbitrary breathig patter. A aeroso bous is itroduced ito the ihaatio at the begiig of each breath. The patiet is ot ed through the ihaatio uder optimum coditios, but is free to ihae sowy or fast, shaow or deep. However, the mai disadvatage of this device is the bous appicatio of the drug aeroso. Due to this techique, oy a sma fractio of the ihaed air cotais aeroso ad the drug amout appied by each breath is imited. This is the reaso for the very og times ecessary to deposit 5 mg of drug usig this

5 PERIPHERAL DEPOSITION OF a 1 -PROTEASE INHIBITOR 267 device. This time was o averagey5-times oger tha the times obtaied with the AKITA1 combiatios. The HaoLite1 may be a appropriate device for the dosig of ow amouts of a potet drug, but i situatios where a arge amout of drug has to be appied, the bous techique seems to have sigificat disadvatages. I this study, the time to deiver 5 mg of Proasti1 was cacuated from the amout deposited i 5 mi. This extrapoatio may overestimate the rea time, sice i the course of time the drug remaiig i the ebuiser may be cocetrated due to water evaporatio ad therefore, the ebuiser output may chage. However, this extrapoatio of time seems to be reasoabe if differet devices are compared with each other. I this study Dp was quatified by cacuatig the sow ceared partice fractio Asow. This parameter was chose istead of the usua 24-h retetio vaue with regard to the soubiity of the used drug. Sow cearace ca be attributed to both partice cearace as we as drug trasocatio ito the bood circuatio. If the sow partice cearace kietics are extrapoated to time zero to assess Asow, this vaue quatifies the iitia amout of partices, which are ot subject to fast mucociiary cearace regardess of whether sow cearace is due to partice cearace or absorptio. However, the assessmet of aveoar depositio by the measuremet of sow partice cearace is based o the assumptio that brochiay deposited partices are fast ceared by mucociiary cearace, whereas partices beig deposited i the aveoar space are ceared sowy by macrophages. However, some studies idicate that there is cosiderabe sow cearace from presumaby periphera brochi [15 19]. Therefore, it has to be cosidered that some drug icuded i the fractio preset after 24 h may be deposited withi this periphera, coductig airway. Whether this drug fractio is reay "ost" for a 1 -PI repacemet therapy, however, is yet ucear. I additio, it is possibe that respiratory brochioes may beefit from a restoratio of the protease/atiprotease baace. I this study it has bee show that high periphera depositio of radioabeed a 1 -protease ihibitor ca be obtaied usig a optimised ad cotroed breathig patter. Ihaatio devices usig this cocept aow efficiet drug depositio i a cosideraby shorter time period tha covetioa devices or devices with differet optimisatio cocepts, ad guaratee a costat dosig with ow iterpatiet variabiity. Refereces 1. Hubbard RC, Crysta RG. Strategies for aeroso therapy of apha1-atitrypsi deficiecy by the aeroso route. Lug Supp 199; 168: Permutter DH, Pierce JA. The apha1-atitrypsi gee ad emphysema. J App Physio 1989; 257: L Pierce JA. Atitrypsi ad emphysema. JAMA 1988; 259: Hubbard RC, McEvaey NG, Seers SE, Heay JT, Czerski DB, Crysta RG. Recombiat DNA-produced a1-atitrypsi admiistered by aeroso augmets ower respiratory tract atieutrophi eastase defeses i idividuas with a1- atitrypsi deficiecy. J Ci Ivest 1989; 84: Wewers MD, Casoaro MA, Seers SE, et a. Repacemet therapy for apha1-atitrypsi deficiecy associated with emphysema. New Eg J Med 1987; 316: Brad P, Frieme I, Meyer T, Schuz H, Heyder J, Häußiger K. Tota depositio of therapeutic partices durig spotaeous ad cotroed ihaatios. J Pharmaceutica Sci 2; 89: Brad P, Meyer T, Sommerer K, Weber N, Scheuch G. Aveoar depositio of moodisperse aeroso partices i the ug of patiets with COPD. Exp Lug Res 22; 28: Scheuch G, Meyer T, Müiger B, et a. Cotroed ihaatio improves periphera ug depositio. J Aeroso Med 21; 14: Sommerer K, Meyer T, Brad P, et a. Evauatio of a optima device for periphera depositio i patiets with ug emphysema. Drug Deiv Lugs 21; XII: Quajer PH, Tammeig GJ, Cotes JE, Pederse OF, Pesi R, Yeraut JC. Lug voumes ad forced vetiatory fows. Eur Respir J 1993; 6: Müiger B, Meyer T, Sommerer K, et a. Patiet idividuized ihaatio optimizes periphera ug depositio. Drug Deiv Lugs 21; XII: Lafot P, Beo G, Mei Tappoier N, Meurisse G, Barbier Y. Apha 1 atitrypsi abeig with techetium 99m for moitorig the depositio of apha 1 atitrypsi i aeroso therapy. Nuc Med Bio 1998; 25: Stahhofe W, Gebhart J, Heyder J. Experimeta determiatio of regioa depositio of aeroso partices i the huma respiratory system. Am Id Hyg Assoc J 198; 41: Kreyig WG, Scheuch G. Cearace of partices deposited i the ugs. I: Gehr P, Heyder J, eds. Partice-Lug Iteractios. New York, Marce Dekker, 2; pp Stahhofe W, Koebrich R, Rudof G, Scheuch G. Shortterm ad og-term cearace of partices from the upper huma respiratory tract as fuctio of partice size. J Aeroso Sci 199; 21: S47 S Svartegre M, Sommerer K, Scheuch G, et a. Compariso of cearace of partices ihaed with bous ad extremey sow ihaatio techique. Exp Lug Res 21; 27: Gehr P, Im Hof V, Geiser M, Schürch S. The fate of partices deposited i the itrapumoary coductig airway. J Aeroso Med 1991; 4: Stahhofe W, Scheuch G, Baiey MR. Ivestiagatios of retetio of ihaed partices i the huma brochia tree. Radiat Prot Dosimetry 1995; 6: Scheuch G, Stahhofe W, Heyder J. A approach to depositio ad cearace measuremets i huma airways. J Aeroso Med 1996; 9: