Eur Respir J 1989. 2. 846--852.

Total respiratory resistance and reactance in patients with diffuse interstitial lung disease

J.A. van Noord, J. Clement, M. Cauberghs, I. Martens, K.P. Van de Woestijne, M. Demedts

Total respiratory resisJance an.d reactance in patients with diffuse interstitial Dept of Pathophysiology, Laboratory of Pnewnology, lung disease. J .A. van Noord, J. Clement, M. Cauberghs, /. Mer tens, Catholic University, Leuven, Belgiwn. K.P. Van de Woesrijne. M. Demedts. ABSTRACT: In 54 patients with In terstitial lung diseases and no signs of airway obstruction we measured lung volumes, maximal expiratory flows, Correspondence: M. Demedts, Kliniek voor diffusing capacity (DLco), total respiratory resistance (Rrs) and reactance Longziekten, UniversitaiT Zienkenhuis, Weligerveld (Xrs) between 4 and 26 Hz by means of the forced osclllaticm technique. I, B-3041 Pellenbcrg, Belg ium. l n all patients D LCO was less than 75% of the expected val ue. Patients were classified Into two groups depending on total lung capacity (TLC): group A wi th TLC less than 80% of expected, and group n with TLC of 80% or more. Group A demonstrated a decrease of Xrs especlaLJy at low Keywords: Forced oscillation technique; interstitial frequencies, with small, not significant changes In Rrs. ln Lite patients In lung disease; respiratory impedance; respiratory tbls group with the lowest values of TLC (less than 50%), we observed an mechanics. Increase of Rrs at low frequencies causing a negative frequency dependence of Rrs. In group B no distinct changes of Rrs and Xrs occurred. Canonical correlation analysis between routine lung function Received: 4 October 1988; accepted after revision 16 data and forced oscillation parameters, showed tight correlations between May 1989. TLC ln absolute value or VC In percent of the predicted value on the one band and average level of Xrs and average slope of Xrs (and Rrs) vs frequency cur ves on the other hand. Measurements of lung mechanics In five additional patients and compar iso n with a model of the respiratory This study was supponed by a grant from the system suggest that the changes of Rrs and Xrs are not explajned totally Netherlands Asthma Fonds, the Fonds voor Geneeskundig Wetenschappelijk Onder.wek and the by the observed Increase In lung tissue resistance and decrease ln lung European Community for Coal and Steel. compliance. The observed changes ln Rrs and Xrs are not speclnc for restrictive lung disorders; similar changes are met also in moderately advanced obstructive diseases. Eur Respir J., 1989, 2, 846-852

The pathophysiologic pattern in patients with diffuse were qualitatively similar to those in patients with chronic interstitial lung disease is well established: lung volumes obstructive lung disease but were less pronounced. and diffusing capacity are reduced, lung elastic recoil is However, detailed studies relating the amount of increased, airway resistance is nonnal, maximal expira­ restriction (indicated by the reduction in 1LC) to the tory tlows adjusted to volume are usually nonnal or high changes of Rrs and Xrs vs frequency curves in although in some patients a narrowing of small airways well-defmed groups of patients have not been perfonned. has been documented, and lung tissue resistance is Therefore, we studied a group of patients with widely increased [1-11]. Very little infonnation exists about the varying degrees of pulmonary restriction due to intersti­ influence of these disturbances in pulmonary mechanics tial lung disease, in order to compare the Rrs and Xrs vs on total respiratory resistance (Rrs) and reactance (Xrs) frequency curves with lung volumes and maximal flows. measured with the forced oscillation technique. SoBOL Also a model analysis was used to explain the observed [12] measured total respiratory impedance at 6 Hz in 15 changes of the curves. patients with restrictive lung disease and found increased values in 60% of them, while correlation between im­ pedance and airway resistance was poor. FrsHER et al. Patients and methods [13] found, in nine patients with diffuse pulmonary diseases, that mean values of Rrs (measured at the reso­ Patients nant frequency) and of the resonant frequency were nonnal, although three patients showed increased values Fifty-four patients, 24 females, and 30 males, with of Rrs. MOLLER and VooEL [14] detennined Rrs and Xrs clinical, radiological, and functional abnormalities between 5 and 30 Hz in 12 patients wilh a restrictive consistent with interstitial lung disease of various defect and concluded that the changes in Rrs and Xrs etiologies were studied. Lung biopsy was perfonned in INTERSTITIAL LUNG DISEASE AND RESPIRATORY IMPEDANCE 847 case diagnosis could not be made on the basis of the Methods clinical data. Patients with a history or functional evidence of chronic obstructive lung disease were ex­ The pulmonary function measurements performed in cluded, and the ratio forced expiratory volume in I s group A and B consisted of static and dynamic lung

(FEY 1)/vital capacity (VC) had to be more than 70%. volumes, max imal expiratory now volume curves The diffusing capacity (OLeo) was less than 75% of the (MEFV). diffusing capacity (OLeo), and Rrs and Xrs vs expected value. The patients were classified into group frequency curves. A (n=35) if total lung capacity (TLC) was less than 80% Vital capacity (VC), total lung capacity (TLC). of Lhe expected value, and into group B (n= 19) if TLC functional residual capacity (FRC), residual volume (RV), A ) was more than 80%. Group included 9 pati ents with forced expiratory volume in one second (FEV1 were sarcoidosis, 9 with idiopathic pulmonary fi brosis, 4 wit11 obtained by standard methods of spirometry and exLrinsic allergic alvcolitis, 6 with collagen disease mu 1Libreat11 helium equilibration. Measured values were (without muscular involvement or pleural abnorm alities related to t11e normal values of JoUAssr:r [151. Peak on the chest X-ray), 2 with bleomycin-induced pneumo­ expiratory now (PEF) and maximal now at 50% of the nitis, 2 with .longstanding miLral valve stenosis, 2 witll forced vital capacity (MEF5c) were obtained from MEFV hard metal disease and 1 with silicosis. In group B, 2 curves measured at the moutll and related to the normal patients had idiopathic pulmonary fi brosis, 5 sarcoidosis, values of the ECCS [16]. To obtain MEF50 as a percent­ 9 bleomycin-induced pneumonitis, 2 long standing mitral age of the ex pected value a correcti on for lung volume valve disease and I extrinsic allergic alveolitis. changes was applied: tlle measured MEF was expressed 50 ln fi ve additional male patients wilh restricti ve disease in percentage of Lhe expected llow at the same absolute (TLC: 50-65% of expected) and no signs of airway volume (MEF~ %. Cp ). First. absolute volume was obstruc ti on, pulmonary mechanics were studied. Diagno­ calculated by aoWng '5~% of actual FVC to actual RV. ses included 2 ca<;es of silicosis, 1 of sarcoidosis, I of By subtracting predicted RV (expressed in absolute lymphoid interstitial pneumonitis and 1 of asbestosis values) the percentage of predicted VC witll which this (without pleural involvement). volume corresponds was then derived . Finall y,

Table 1. - Results of the pulmonary function tests

Group A (n=35) Group B (n=19) p(A-B)

Age yrs 44±16 44±16 NS Height cm 168±9 171±11 NS Weight kg 68±16 66±15 NS TLC %expected 63±11 91±11 <0.001 VC %expected 58±15 82±12 <0.001 RV %expected 80±21 118±32 <0.001 FRC{fLC% 57±10 60±8 NS FEVI %expected 62±17 86±12 <0.001 FEY/VC% 80±6 79±5 NS DLCO %expected 58±13 57±11 NS Kco %expected 90±17 65±11 <0.001 PEF %expected 71±21 77±18 NS

MEF50 %expected 238±152 93±30 <0.001 Rrs kPa·t1·s 0.29±0.07 0.24±0.06 <0.05 Rrs0 > kPa·t1·s2 -0.061·1 o·~o.265·1 o·2 0.11 · 10"~0.14·10" 2 <0.01 Rrs<2> kPa-t1-s3 0.015·10"2:t0.092·10"2 o.Ot9·I0·2:to.056·t0·2 NS Xrs kPa·t1·s 0.01±0.05 0.07±0.04 <0.001 Xrs<1> kPa·t1·s2 0.013±0.004 O.Oll±{l.003 <0.05 Xrs<2> kPa·t1-s3 -0.13·I0·2:to.o8-to·z -0.13·10"2:t0.05·10"2 NS

Values are mean ±so. The third column indicates the statistical differences between group A and B; NS: non­ significant (p>0.05); TLC: total lung capacity; VC: viwl capacity; RV: residual volume; FRC: functional residual capacity; FEY : forced expiratory volume in one second; Dt.co: single breath di[fusing capacity for CO; 1 : Kco: Dt.co over lung volume; PEF: peak expiratory Oow ~le; MEF5 max i.mal expiratory now at 50% of forced vital capacity, corrected for lung volumes (see Method!:); Rrs, Rrs< 1) .~<21 : mean value, first (slope) and second derivatives (curvature) of total respiratory resistance; ~ . XrsO>, xr:~<2>: mean vtl)u cs, (irst and second derivatives of total respiratory reactance. 848 I. A. V AN NOORD ET AL.

MEF was Lhen calculated by linear interpolation and Xrs were all measured during tidal breathing at FRC • of Lhe~~~ values of MEF,s. MEF30 and MEF25 Dt.co without previous deep inspirations to 1LC. was obtained with the single brcalh method and related to the reference values of BllllET et al. [17]. Rrs and Xrs were determined by means of a forced Results oscillation technique previously described in detail [18, 19]. Briefly, a pseudo-random noise signal, containing Volumes, maximal flows, diffusing capacity and respi­ all harmonics of 2 Hz up to 26 Hz (2, 4, 6,.... 26 Hz) is ratory impedance applied at the moulh. The impedance of the respiratory Mean values of lung function tests of group A and B system, obtained from pressures and flows measured at are presented in table 1. The groups are well matched for Lhe mouth is partitioned into a real (or Rrs) and an age, height and weight. In group A, mean values of static imaginary part (or Xrs). Rrs is an expression of the and dynamic lung volumes are reduced, RV being least resistive properties of the respiratory system (airways affected, while in group B lung volumes are within normal and tissue deformation resistance), Xrs depends on the ranges. Dtco is reduced to the same extent in both groups, elastic and inertive properties of the system. Only values but Kco is decreased in group B only (p, Xrs(l>, Xrs< >) were in group A and B is shown in fig. 1. In group B mean calculated from 6 to 26 Hz according to a method values of Rrs and Xrs are close to normal. In group A, described previously [20]. The first and second deriva­ tives represent respectively the slope and the curvature of the Rrs-f and Xrs-f relationships. Measured values of Rrs (kPa -t-l.s) Rrs and Xrs were related to the reference values of .4 UNsoillt et al. [20]. Student's Hest was used to deter­ mine the significance of the differences. Canonical correlation analyses were carried out between routine lung function, both in percent of predicted and in absolute values, and forced oscillation parameters. This type of analysis consists of calculating which, out of two sets of .2 parameters, are most closely interrelated [21]. A Welch test was used to determine the significance of differences between group A and B. In five additional patients pulmonary mechanics were also investigated: we measured airway resistance (Raw), 0 specific airways conductance (sGaw), lung resistance pressure compensated integrated flow .2 plethysmograph (Sensormedics) as the chord slopes 1 between inspiratory and expiratory flows of 0.5 /-s- , at a respiratory rate of 0.5 Hz. Static transpulmonary pres­ sure volume curves were determined during apnoea's from volume, obtained by integration of the flow signal at the mouth, and oesophageal pressure (oesophageal balloon: length 10 cm, perimeter 5 cm, containing 0.5 ml of air, positioned at 40 cm from the nares). The static expira­ tory compliance was calculated as the mean slope (of the three curves) between FRC and FRC + 0.5 I. For top inspiratory transpulmonary pressure the highest value of three manoeuvres was selected. RL was obtai.ncd after the isovolume method of FRANK et al. [22) by simultane­ ous recordings of transpulmonary pressure, flow at the 0 30Hz moulh, and volume obtained by integration of the flow Fig. I. - Mean values and standard error of tot.al respiratory resis· tance Rrs and reactance, Xrs, vs oscillatory frequency in group A (Gould Godart compliance test Mark Ill, Hewlett Pack­ (TLc' < SO% pred) and B (TLC > 80% pred). The dotted lines ard 7046A XY recorder). Data from ten measurements at represent the mean values (and standard error) of the 6 patients of _. group A with a TLC value of less than 50% of e~pccted. a respiratory rate of 0.5 Hz were averaged. Raw, R1 Rrs INTERSTITIAL LUNG DISEASE AND RESPIRATORY IMPEDANCE 849

Rrs shows a tendency to negative frequency dependence, Table 3.- Clinical characteristics and lung mechanics of and Xrs is reduced especially at low frequencies. O.!!!Y. 5 patients used for interpretation of impedance curves the changes Qf_Xrs in group A differ significantly (Xrs is lower and Xrs< 1> steeper: p, Xrs, Xrsm, Xrs<2>), all expressed in absolute values, shows a highly significant correlation (r=0.83, p + b Xrs + c x.rs<1>+ d (r=0.81, pand Xrs

Kco DLCO MEFSO PEF FEVI TLC

VC -0.52" 0.25 -0.53° 0.50° 0.94" 0.91° 10 20 30Hz TLC -0.60° 0.30• -0.67° 0.33• 0.88° Xrs (kPa·t-l.s) FEV 1 -0.55° 0.25 -0.46° 0.50° PEF -0.14 0.12 0.06 .2 ,.-­ MEFSO 0.38b -0.26 ,."' DLCO 0.50° 1 _,. ,., ..... ,"' ,.-'" Number of patients: 54; all parameters are expressed in % ,.,.-- expected; a: p<0.05; b: p + c (r=0.65, p in kPa·l' 1·s2• respectively (see Discussion). 850 I.A. VAN NOORD ET AL.

Lung mechanics tion analysis [2ll.§.how_~._!hat TLC accounts for 66% of the variance of Rrs<•>, Xrs and XrsO> when all data are Table 3 presents lhe results of pulmonary mechanics expressed in absolute values, and th~VC accounts for in five additional male patients. Mean Raw is at the upper 42% of the variance of Xrs and Xrslung compliance and breathing frequency [24, 25], the a result, tlle mean value of MEFw in percent of the results of these studies are strongly influenced by the predicted value and corrected for lung volume, was much different methods (breathing frequency) and patients. In larger in group A than in group B (p<0.001). lhis light our values of tissue resistance at a frequency of The differences in mechanical properties between group 0.5 Hz are markedly lower lhan tllose found by BACHOFEN A and B are also evidenced by changes in Rrs and Xrs. and SCIIERRER [10] at a comparable respiratory rate. In group B no distinct changes of Rrs and Xrs are Several mechanical properties of lungs and airways observed with respect to tlle expected values, whereas in thus appear to be influenced by interstitial lung disease: group A Rrs is slightly increased at lower frequencies, lung compliance, lung tissue resistance, possibly airway causing a negative frequency dependence, and Xrs is resistance. To investigate which of these changes mainly decreased mainly at lower frequencies. These differences detennines lhe observed modifications of the values of in level and slope of Rrs and Xrs between botll groups Rrs and Xrs we perfonned a simulation of the respiratory are statistically significant (table 1). The changes of Rrs system. A model was used, representing the upper and Xrs are most striking in the patients with the most airway, with a shunt at tlle level of the cheeks, the severe restriction (lLC <50% pred). In general, as TLC intrathoracic airways, taking into account the airway wall (or VC) decreases, Rrs becomes more frequency depend­ compliance and resistance, the alveoli including gas ent and Xrs decreases with steepening of the Xrs­ compressibility, and lhe chest wall (fig. 3). frequency slope. The link between tlle alterations in TLC For the various parameters of the model values were or VC and Rrs and Xrs is tight. A large part of the selected, representative for healtlly male adults. Under variations of TLC or VC can be predicted on the basis of these circumstances tlle Rrs- and Xrs- frequency curves the changes in Rrs and Xrs. Indeed, a canonical correla- obtained from the model satisfactorily reproduced data INTERSTITIAL LUNG DISEAS E AND RESPIRATORY IMPEDANCE 851

Re le Rp lp Ct· Rti Rth Cth oscillation technique appears to be an interesting tool to 009 13 0 126 0 4 I 03 0 052 0 .0 5 0 .25 investigate pulmonary mechanics, also in interstitial lung disease. Indeed, the technique is sensitive to the degree

R ~I 0 of pulmonary restriction. However, the alterations of the sh ··o' '--"NVVv------l1~,_ Rrs and Xrs vs frequency curves in advanced restrictive ,0.01 disorders are comparable with those in mild obstructive Rb Cb disease [29], i.e. the method on its own does not 1Csh :.. o.o3 0 14 0 05 distinguish a small increase in airway resistance from the combined effects caused by interstitial lung disease. Fig. 3. - Electrical analog of th e respiratory system. Bor.h the central Accordingly, the results of the forced oscillation and r.he peripheral airways are represented by a series resistance and technique cannot be used in clinical practice to incnance (R , I , and R , 1 respet:tivcly), and a shunt: R h and C differentiate obstructive and restrictive disorders. correspond ib &c shunr re~ i stan ce and compliance at r.hc level Jr cheeks, Rb and Cb to the bronchial waU resistance and compliance. 1he lungs are simUl ated by a compliance (CL)' lung tissue resistance References ('\;) and gas compressibility (C ), the chest wall by a resistance and a compliance (R111 and Clh respef:tively). For R + R . CL, C and R 11 1. Keogh BA, Crystal RG. - Pulmonary function testing in r.he mean values determaned in the S subjccu' wiuf intcrstif.al lung interstitial pulmonary disease. Chest, 1980, 78, 856-865. disease were used, for the other parameters values representive for 2. Yemault JC, De Jonghe M, De Coster A, Englert M. - h e~~ hhy aduh subjects: R h' C (two values depending whether the cheeks are supported (upPer va'f'ues) or not [26), Cb [271. ~ (2.5, 271, Pulmonary mechanics in diffuse fibrosing alveolitis. Bull Phys­ 1 and J [19], Rill !1 9] and Clh (28). Resistances are in kPa·11·s iopath Respir, 1975, 11, 231-244. c~npl i wfccs in f.k l'a' 1, inenances in Pa·lt·s2• 3. Macklem PT, Becklake MR. - The relationship between the mechanical and diffusing properties of the lung in health and disease. Am Rev Respir Dis, 1963, 64, 47- 56. measured in vivo [20]. When the parameters were modi­ 4. Boushy SF, North LB. - Pulmonary function in infiltra­ fied in agreement with the mean results obtained in the tive lung disease. Chest, 1973, 64, 448-453. 5. Gibson GJ, Pride NB. - Pulmonary mechanics in fibrosing five subjects with interstitial lung disease in whom alveolitis. Am Rev Respir Dis, 1977, 116, 637-647. pulmonary mechanics were measured, the model yielded 6. Ostrow D, Chemiack RM. - Resistance to airflow in pa­ values of Rrs and Xrs which satisfactorily simulated the tients with diffuse interstitial lung disease. Am Rev Respir Dis, measured data, both with and without support of the 1973, 108, 205- 210. cheeks (fig. 2), provided that a value was attributed to 7. Jaymanane OS, Epstei.n H, Goldring RM. - The influence peripheral airway resis tance markedly higher than that of lung volume on expiratory now rates in diffuse interstitial accepted for healthy subjects [301 (0.1 26 instead of 0.014 lung disease. /\mer J Mcd Sci, 1978, 275, 329-336. kPa·/·1·s) and chest wall compliance was halved. Indeed, 8. Tan CSH, Tashkin DP. - Supernormal maximal mid in the model represented in fig. 3 a negative frequency expiratory flow rates in diffuse interstitial lung disease. Respi­ dependence of Rrs is simulated only if the summed value ration, 1981, 42, 200-208. 9. Murphy MF, Hall DR. Peterson MR. Lapp NL. - The of peripheral airways, R , and tissue resistance, RaJ . is effect of diffuse pulmonary fibrosis on lung mechanics. Bull sufficiently high. Keeping the values of the parameters Europ Physiopath Respir, 1981, 17, 27-41. indicated in the fi gure, except for R and R . , a frequency 10. Bachofen H, Scherrer M. - Lung tissue resistance in dif­ dependence of Rrs similar to that o"f fi g. 2ucan be repro­ fuse interstitial pulmonary fibrosis. J Ciin Invest, 1967, 46, duced by an isolated increase in R . (R being 0.0 14 133- 140. k.Pa·l'1·s), onl y if its value reaches 0 .1 ~ kPa·f·1·s, a figure 11. Marshal! R, DuBois AB. - The viscous resistance of lung about three times higher than the mean of the values tissue in patients with pulmonary disease. Clin Sci, 1956, 15, measured in the present study. In the model a negati ve 473-483. frequency dependence of Rrs is accompanied by a 12. Sobol BJ. - TesLs of ventilatory function not requiring maximal subject effort II. The measurement of total respiratory decrease in Xrs. The latter is diminished further by the impedance. Am Rev Respir Dis, 1968, 97, 868-879. reduction in lung compliance. However, to achieve the 13. Fisher AB, DuBois AB, Hyde RW. - Evaluation of the reduction in Xrs observed experimentally (fig. 2) an forced oscillation technique for the determination of resistance additional decrease in chest wa ll compliance, est>. has to to breathing. 1 Clin Invest, 1968, 47, 2045- 2057. be assumed. Both assumptions, an increase in 1< and a 14. MUller E, Vogel J. - Messung und Modellinterprctation decrease in clh, are not unrealistic in patient<; wi th neurer atemmechanischer Parameter. Z Erkrank.Atm Org, 1981, interstitial lung disease. A narrowing of the peri pheral 157, 340-344. airways has been documented by FvtMER et al. L31J in 15. Jouasset D. - Normalisation des epreuves fonctionnelles idiopathic pulmonary fibrosis, and in sarcoidosis as well respiratoires dans les pays de la Communaute Europeenne du as in occupational disease. Because functional residual Charbon et de l'Acier. Pownon Coeur, 1960, 10, 1145-1159. 16. Standardization lung function testing. Report Working party capacity is decreased, Cllj which tendS LO decrease with Standardization of lung function tesLs (Ph. Quanjer, Ed Euro­ decreasing lung volwne t1 9] may, indeed, be reduced. pean Community for Coal and Steel, Luxembourg. Bull Europ The model study thus suggests that, besides an increase Physiopath Respir, 1983, 19, Suppl 5. in lung tissue resistance and the decrease in pulmonary 17. Billict L, Baisier W, Naedts JP. - Effect de la taille, du compliance, other factors contribute to the changes in sexe, et de !'age sur la capacite de diffusion pulmonaire de Rrs and Xrs in interstitial lung diseases. l'adulte normal. 1 Physioi Paris, 1963, 55, 199- 200. In conclusion, this study confirms that the forced 18. Landser FJ, Nagels J, DemedLs M, Billiet L. Van de 852 J.A. VAN NOORD ET AL.

Woestijne KP. -A new method to determine frequency char­ resistance in healthy man. J Appl Physiol, 1975, 38, acteristics of the respiratory system. J Appl Physiol, 1976, 41, 427-435. 101-106. 31. Fulmer ID, Robcrts WC. -Small airways and interstitial 19. Nagels J, Landser FJ, Van der Linden L, Clement J, Van pulmonary disease. Chest, 1980, 77, 470-473. de Woestijne KP. -Mechanical properties of lungs and chest wall during spontaneous breathlng. J Appl Physiol: Respiral Resistance respiratoire totale et reactance, chez des patien1s Environ Exercise Physiol, 1980, 49, 408-416. atteints de maladie pulmonaire interstitielle diffuse. J. van 20. Landser FJ, Clement J, Van de Woestijne KP.- Normal Noord, ]. Clement, M. Cauberghs, I. Mertens, K. Van de values of total respiratory resistance and reactance determined Woestijne, M. Demedts. by forced oscillations. Influence of smoking. Chest, 1982, 8, RESUME: Chez 54 patients atteints d'affection pulmonaire 586-591. interstitielle sans signes d'obstruction des voies aericnncs, nous 21. Mardia KV, Kent IT, Bibby JM.- Canonical correlation avons mesure les volumes pulmonaircs, les debits expiratoires analysis. In: Multivariate analysis. Academic Press London, maximaux, la capacite de diffusion (DLco), la resistance New York, 1979, pp 281- 295. rcspiratoire totalc (Rrs) et la reactance (Xrs), entre 4 et 26 Hz. 22. Frank NR, Mead J, Ferris BG Jr. - The mechanical behav­ par la technique d'oscillation forcee. Chez tous les patients, la iour of the lungs on healthy elderly persons. J Clin Invest, DLCo etait inferieure a 75% des valeurs prooites. Les patients 1957, 36, 1680-1687. ont ete classes en deux groupes selon J'etat de leur capacite 23. Schofield NMcC, Davies RJ, Cameron IR, Green M. - pulmonaire totale: dans le groupe A, la CPT est inferieure a Small airways in fibrosing alveolitis. Am Rev Respir Dis, 1976, 80% des valeurs prooites; dans le groupe B, elle est egale ou 113, 729-735. superieure a 80%. Dans le groupe A, !'on a note une 24. Hoppin FG Jr, Stothert JS Jr, Greavcs lA, Yih-Loong L, diminution de Xrs, particulicrement aux basses frequences, avec Hildcbrandt J. - Lung recoil: clastic and rheological properties. des modifications faibles et non significatives de Rrs. Chez Jes In: Handbook of Physiology. Section 3. The respiratory sys­ patients de ce groupe ayant les valeurs Jes plus basses de CPT tem, volume ID, Mechanics of breathing (Macklem PT, Mead (inferieures a 50%), nous avons observe l.!nc augmentation de J Eds). Bethesda, Am Physiol Sci, 1986, pp 195- 215. Rrs aux basses frequences, provoquant une frequence­ 25. Bobbaers H, Clement J, Van de Woestijne KP. - Dynamic dependance negative de Rrs. Dans le groupe B. l'on n'a observe viscoelastic properties of the canine trachea. J Appl Physiol. aucune modification nette de Rrs ou de Xrs. L'analyse de 1978, 44, 137-143. correlation canonique entre Jes donnees de fonction pulmonaire 26. Cauberghs M, Van de Woestijne KP. - Mechanical prop­ de routine et les parametres d'oscillation forcee, a montre des erties of the upper airways. J Appl Physiol: Respiral Environ correlations etroites entre CPT en valeur absolue ou CV en % Exercise Physiol, 1983, 55, 335- 343. de la valeur theorique d'une part, et d'autre part le niveau 27. Mead J. - Contribution of compliance of airways to fre­ moyen Xrs et la pente moyenne de Xrs (et de Rrs) vs des quency-dependent behaviour of lungs. J Appl Physiol, 1069, courbes de frequcnce. Les mesures de la mecanique 26, 670-673. pulmonaire chez cinq patients supplementaires et la 28. Van Noord JA, Demedts M, Clement J, Caubcrghs M, comparaison avec un modele du systeme respiratoire, Van de Woestijne KP. - Effect of rib cage and abdominal suggerent que les modifications de Rrs et de Xrs ne sont pas restriction on total respiratory resistance and reactance. J Appl totalement expliquees par !'augmentation observee de la Physiol, 1986, 61, 1736-1740. resistance du tissu pulmonaire ni par la diminution de la 29. Clement J, Landser FJ, Van de Woestijne KP. - Total compliance pulmonaire. Les modifications observees en ce qui resistance and reactance in patients with respiratory complaints conceme Rrs et Xrs ne sont pas specifiques aux maladies with and without airways obstruction. Chest, 1983, 83, pulmonaires restrictives; des modifications du meme type ont 215-220. cgalement ete rencontrees dans des maladies obstructives 30. Bobbaers H, Clement J, Pardaens J, Van de Woestijne KP. moyennernent avancees. - Simulation of frequency dependence of compliance and Eur Respir J., 1989, 2, 846-852.