MEMBRANE DIFFUSING CAPACITY A N D PULMONARY CAPILLARY BLOOD VOLUME IN

PULMONARY SARCOIDOSIS

G. Saumon, R. Georges, A . Loiseau, and J. Turiaf

Groupe de Recherches U 82 Institut National de la Santt et de la Recherche Mkdicale et

Facultt de Mtdecine Xavier Bichat H6pital Bichat Paris, France

Granulomas of sarcoidosis are mainly localized in the peribronchiovascular sheaths, but by their consequences they can modify the alveolus-capillary ex- change membrane. Alterations of transfer capacity may thus be found; their fre- quency and their reversibility during the different stages of the disease have been the subject of several studies since the initial work of Svanborg.' Few studies, however, have attem ted t o characterize the ways in which the alveolar capillary

The present study analyzes 77 patients suffering from mediastinopulmonary sarcoidosis, classified according to their roentgenographic appearance. The fol- lowing points are examined:

1) The frequency and nature of the modification of the air/blood barrier and the value of x-ray classification.

2) The difference from a pathological process localized essentially in the lung interstitium; a good model of this being provided by diffuse interstitial fibrosis (DIF).

membrane is altered. &

MATERIALS AND METHODS

Selection and Classification of Patients

Diagnosis of sarcoidosis was based on the conjunction of clinical and radio- graphic signs, bronchial biopsy, and Kveim test. The patients were classified into three stages according to x-ray appearance:

Stage I (SI), isolated involvement of mediastinal nodes (19 cases). Stage I1 (S2), diffuse reticulonodvlar images (49 cases). These lesions were

completely reversible under corticosteroid therapy maintained for an average of 2 yr. The functional data employed were those obtained before starting the treatment.

Stage I11 (S3), the infiltration of parenchyma is stable (9 cases). It appears as micro- or macronodular images, sometimes confluent, associated with aspects of retraction, bronchial stenosis (2 cases), or increased transparence, evoking micro- cysts. Prolonged corticosteroid therapy is practically inefficient.

These three groups of patients will be compared to 24 cases of DIF either of unknown origin authenticated by biopsy or due t o systemic sclerosis.

284

Saumon et al.: Capillary Membrane Alteration 285

Methods

Vital capacity (VC) and forced expiratory volume-I sec (FEV,) are measured by a spirographic method and residual volume (RV) by helium dilution in a closed circuit. The standards employed are those of the CECA.'

Intrapulmonary air distribution is measured by single-breath technique (SB) using a tracer gas (Ar) inspired to the total lung capacity (TLC) level from func- tional residual capacity (FRC) and is expressed by the variation of the A r / N 2 ratio between 750 and 1250 ml of expired volume.6 Based on laboratory standards the value of this distribution index (ID) is estimated as being less than 10% in normal subjects.

Respiratory mechanics are studied using a real-time computerized system that allows determination at the frequency of spontaneous breathing of effective com- pliance (Ce) and total expiratory and inspiratory pulmonary resistances (RLE and RLr). The principle of this method is equivalent to the flattening of the pressure- volume loop proposed by Mead and Whittenberger.7 C e is expressed as a specific value using the TLC.

The CO-transfer method utilized is that described by Roughton and Foster.' The single-breath technique is performed in a sitting position.

The CO mean venous pressure level in the blood (PVco) for assessing CO capil- lary pressure Pcco) a t time t = 0 is measured by rebreathing. At each alveolar 0 2

pressure level PA^^) the diffusing capacity of the lungs for CO ( D L ~ ~ ) is deter- mined in duplicate a t 10-15-min intervals.

Membrane conductance (Dm) and capillary blood volume (Qc) estimations are performed using the classical equation D DL = l / D m + I/OQc. The numerical values for OCO are calculated by the equation l / K O = a + 0.0057 Po2. If it is postulated that the ratio of membrane permeability t o that of the red blood cell interior has a finite value of 2.5, a = 0.73. Exchange Po, is calculated from alveolar sample measurement ( P E ~ , ) by the following equation proposed by Forster:

Po2 = PEo2 - VO,/(DLCO X 1.23).

Vo2 and D L ~ ~ are measured under basal conditions with an inspired O2 fractional concentration ( F I ~ , ) = 0.21. In order to calculate D m and Qc the following con- ditions should be fulfilled:

I ) At least 6 D L ~ ~ determinations a t increasing PA^^. 2) The first PAo2 level 2 200 mmHg; this condition is required for a linear relationship between I/DL,, and I/OCO. The last level is > 500 mmHg. 3) A satisfactory reproducibility of measured alveolar volume and exchange time for the 6 DL determinations. 4) A correlation coefficient r of DL = f( l/OCO), significant a t least a t 0.01.

For each patient, Qc is corrected according to the hemoglobin concentration.

RES u LTS

Physical Characteristics (TABLE 1)

The patients in groups S3 and D I F are significantly older than those in groups S1 and S2. Body surface area (BSA) does not significantly differ.

286 Annals New York Academy of Sciences

TABLE I PHYSICAL CHARACTERISTICS OF PATIENTS

Sl s 2 s 3 D I F

Number 19 49 9 24 Sex

(number males/number females) 10/9 22/27 6/3 14/10 Age (yr) 29.6* f 6.32 34.2 + 10.81 40.8 f 13.78 39.2 + 14.82 BSA (m2) 1.72*+0.163 1.75*0.195 1.83f0.182 1.73*0.217

*The values for each group are the mean =t S.D.

Lung-Function Data (TABLE 2)

The mean TLC value is normal in groups S1 and S2. A restrictive syndrome (TLC < 80%) is observed in 2 cases of group S1 and in 5 cases of the S2 group. The mean TLC value is decreased in group S3 and in the DIF group. The RV/TLC ratio is often higher than 30% in groups S2, S3, and DIF. The FEV, /VC ratio is

TABLE 2 LUNG-FUNCTION DATA

SI s 2 53 D I F VC % of predicted 11Of 18.6 lOO+ 23.5 77 * 22.8 77* 17.6

19t 49 9 24

Number of patients 19t 49 9 24 with abnormal 2 5 0 12 parameter of <800/,

T L C % of predicted 9 4 i 11.7* 103+ 18.0 82 * 22.8 77 f 21.0

RV/TLC % 24 f 4.2* 27 + 8.5 38 f 7.5 37 + 9.8 Number of patients 19t 49 9 24

with abnormal I 16 4 13 parameter of > 30%

FEVl /VC 80 + 6.9* 77 + 7.8 65 f 12.3 67 + 12.8 Number of patients 19t 49 9 24

with abnormal 1 7 4 I 1 parameter of <70%

Ce/TLCf 0.055 f 0.0179* 0.045 f 0.0184 0.034 j, 0.0180 0.038 f 0.0091 17t 46 9 18

R LEQ 2.78 f 0.812* 2.81 f 1.267 5.57 j, 3.067 4.93 + 4.418 Number of patients 1st 47 5 16

with abnormal 1 5 4 10 parameter of > 3.5

ID % 6.6 f 2.31* 7.9 f 3.32 16.3 * 3.02 14.7 + 6.62 Number of patients 14t 45 8 15

with abnormal I 3 5 10 parameter of > 10%

*Data expressed as means + S.D. Predicted values from CECA. ?Number of patients for whom information was available.

f Ce/TLC = (dm ’/ h Pa)

dm3

Saumon et af.: Capillary Membrane Alteration 287

disturbed in groups S3 and DIF, which are significantly different from SI and S2 (p < 0,001). The frequency of the obstructive syndrome (FEVI/VC < 70%) is greater in groups S3 (44%) and DIF (46%) than in group S2 (14%). These results suggest an alteration of the bronchi, confirmed by RLE measurement.

The mean value of Ce/TLC can be considered as normal except in groups S3 and DIF.

The distribution index (ID) is higher in groups S3 and DIF than in groups S1 and S2 ( p < 0.001) and is greater than the normal limit in 62% of the cases in group S3 and 67% in group DIF.

The values of the transfer parameters are compared to those obtained in a

TABLE 3 DIFFUSING CAPACITY FOR co

s1 s 2 s 3 D I F Normals (n = 19) (n = 49) (n = 9) (n = 20) (n = 52)

*DLCO

§ Dmco

BSA-', 14.2 f 3.39f 14.1 f 3.987 9.0 + 3.587 8.2 i 2.48t 17.3 f 3.06 mSA- ,364 f 0.07591 .357 f 0.0814t ,253 f 0.0843t ,213 f 0.0586t .414 f 0.0607

BSA-I 31 .4k4.72 31 .4 f 12.31 20 .0f9 .64t 24.0f9.64t 37 .4 f9 .99 N.S . 11

mSA-l .737 f 0.25311 ,767 f 0.23681 ,567 + 0.2391t ,635 f 0.2754t ,893 f 0.2013

BSA-' 42.8 + 12.43 40.4f 13 .1 25.7 f 8.477 19 .4 f 7.49t 43.3 f 9.72

mSA-l 1.092 f 0.2844 1.03 f 0.3105 ,735 0.2137t .499 f 0.171 It 1.037 f 0.2197

TQc

N.S. N.S.

N.S . N.S .

cm3/min

mmHg/m2 * D L ~ ~ =

?All data are expressed as means f S . D . In comparison between this group and normals,

1 In comparison between this group and normals, p < 0.01.

5Dmco =

cm3 (Qc = -

m2 1) Not significant.

p < 0.001.

cm'/min

mrnHg/m2

group of normal subjects using the same technique and the above-mentioned hypothesis concerning 0 CO. This group is made up of 40 male and 10 female sub- jects (mean age 32.7 yr * S.D. 14). To provide a biometric reference DL, Dm, and Qc are expressed in relation to both body surface area (BSA) and alveolar surface (mSA) as estimated by Weibel formula.' This latter reference will be used to ascertain whether transfer parameter variations are related to a total exclusion of certain exchange units. The choice of these references is justified, since the linear correlation coefficients of DL, Dm, and Qc in relation to BSA (r = 0.66, 0.41, and 0.62 respectively, p < 0.001) and to mSA (r = 0.77,0.61, and 0.67 respectively, p < 0.001) are statistically significant. Because the reference to mSA takes into

288 Annals N e w Y o r k A c a d e m y of Sciences

TABLE 4 MEMBRANE CONDUCTANCE VALUES*

Experimental Significant Difference Groups Mean + S.D.

SI s2 s 3 DIF Normals

SI ,737 f 0.2531 - N.S.? N.S. N.S. p < 0.01

s 3 ,567 f 0.2391 N.S. N.S. - N.S. p < 0.001 DlF ,635 =t 0.2754 N.S. p < 0.05 N.S. - p < 0.001

s 2 .767 rt 0.2368 N.S. - N.S. p < 0.05 p < 0.01

Normals ,893 =t 0.2013 p < 0.01 p < 0.01 p < 0.001 p < 0.001 -

a Dm/mSA. ? N o t significant.

account the age of the subject, it provides the best fit with DL, Qc, and especially Dm.

The results from the pathological groups in relation to BSA (TABLE 3) show a significant decrease of D L ~ ~ in all cases, with no significant difference between S1 versus S2 and S3 versus DIF. In groups S1 and S2, only Dm is altered, without significant difference between them. The analysis of individual cases (adopted nor- mal range limit: iii - 2 S.D.) reveals the rarity of the capillary network impair- ment in groups S1 and S2 (5.3 and 12.2% of cases) and its frequency in groups S3 (33.3%) and DIF (65%)).

A similar analysis with mSA supports these results (TABLE 3). D L ~ ~ is di- minished in groups S1 and S 2 without significant difference between them. The de- crease is more important and significant in group S3 and in the D I F group. D m decreases more than mSA in the 4 groups. The mean Qc value is not reduced in S1 and S2. However, a decrease of Qc is observed in 5 cases of group S2 ( 1 1.2% of cases). By contrast, the decrease of Qc is important and frequent in group S3 and D I F (TABLES 4 and 5). TABLES 4 and 5 summarize these data, allowing a com- parison between the pathological and control groups.

DISCUSSION

Interest of Separate Dm and Qc Measurement

Pathological studies have shown the frequency of Qc impairment in DIF lungs. This finding is fundamental, since the impairment is probably irreversible. In

TABLE 5 CAPILLARY BLOOD VOLUME*

Experimental Significant Difference G~~~~~ Mean + S.D.

S1 s2 s 3 DIF Normals SI I .092 + 0.2844 -- N.S.? p < 0.01 p < 0.001 N.S. s2 1.030 =t 0.3015 N.S. - p < 0.01 p < 0.001 N.S. s 3 ,735 & 0.2137 p < 0.01 p < 0.01 - p < 0.01 p < 0.001 DIF .499 & 0.171 I p < 0.001 p < 0.001 p < 0.01 - p < 0.001 Normals 1.037 + 0.2197 N.S. N.S. p < O . O O l p < 0.001 ~

*Qc/mSA. t N o t significant.

Saumon et al.: Capil lary M e m b r a n e Alterat ion 289

addition, theoretical studies" have shown that in contrast with isolated modifica- tions of the exchange membrane, capillary-network impairment may have impor- tant consequences for the efficiency of the lung exchange process.

These anatomic data are confirmed by our experimental determinations in- volving 22 cases of systemic sclerosis, a pathological process that presents a char- acteristic modification of the i n t e r s t i t i ~ m . ~ The results obtained in pulmonary sarcoidosis differ greatly from those observed in DIF. However, in order t o draw justifiable conclusions the validity of Dm and Qc measurements must be discussed.

Validity of Dm and Qc Measurements

The hypotheses required for experimental measurement have different effects on Dm and Qc estimations. The most important consequence arises from K O . But if the approximation made on OCO has a crucial influence on Dm estimation, its influence is much less on the slope of the relation I/DL,, = f(l/OCO), thus on Qc determination. This may also be true for experimental errors on different D L , ~ measurements a t increasing PA^^. In our experiment the reproducibility of Dm, even in normal subjects, is in fact less than that of Qc.

Furthermore, the existence of a distribution inhomogeneity of DL/VA (lung diffusing capacity/volume of alveolar gas) and Dm/Qc could notably influence the experimental evaluation of Dm and Q c . ~ As a matter of fact, these inhomo- geneities are obvious in pathological processes. We have investigated the in- fluence of these inhomogeneities on Dm and Qc determination in a recent theoreti- cal paper,4 using the simulation of a multicompartmental lung model. If the Dm/Qc distribution is homogeneous, the establishment of an increasing DL/VA inhomogeneity leads to a higher underestimation of measured Dm, whereas the Qc estimation remains acceptable. If the local alveolar volume is not reduced, such a distribution inhomogeneity can be created by the suppression of some capillary segments resulting in a functional suppression of the corresponding membrane. On the other hand, distribution inhomogeneity of Dm/Qc leads to an underestimation of not only Dm but also Qc. However, if the morphological findings observed in D I F " are taken into account, modifications in the part of the membrane involved in gas exchange are compatible with a good Qc estimation. Finally, the two types of distribution inhomogeneity distort D L , ~ estimation.

Thus the interest of separate Dm and Qc determination is obvious. On the one hand, D L ~ ~ determination provides no information on the capillary network impairment that is fundamental in prognosis and diagnosis. On the other hand, Qc estimation appears much more valid than that of D L ~ ~ or Dm, especially in a pathological lung where the properties of the alveolus-capillary membrane have necessarily an inhomogeneous distribution.

A nalysis

The analysis of the results and the study of the conditions for a valid deter- mination of the transfer parameters lead to the following statements:

In Stage I , sarcoidosis rarely alters the static and dynamic characteristics of the pulmonary system. Nevertheless, the decrease of D L ~ ~ is significant even when considering eventual alterations of the gas exchange volume, but the pul- monary capillary network is altered in only l of 19 cases.

290 Annals New York Academy of Sciences

In Stage 11, mainly functional alterations expressing bronchial impairment as well as a restrictive syndrome are observed. D L ~ ~ is significantly decreased even more than would be accounted for by the destruction of some exchange units (TABLE 3). Only D m is impaired without significant difference from Stage I (TABLE 4). However, in a limited number of cases, the diminution of Qc (< fii - 2 S.D.) demonstrates a n alteration of the capillary network (10.2% of cases). The decrease of D L ~ ~ and D m may possibly be linked in part to DL/VA distribution inhomogeneity. This correlation seems likely considering the functional modifica- tions observed. However, the possibility of alterations of the capillary network should be emphasized. In the series studied it is not possible to confirm whether or not the alteration is more frequent in Stage I1 than in Stage I.

These findings concerning the alveolus-capillary membrane are very different from those obtained in D I F as analyzed in this study or in systemic sclerosis with pulmonary l o ~ a l i z a t i o n . ~ They are, however, in agreement with pathological find- ings. Electron microscopic analyses of pulmonary biopsies as previously described by Basset et al." show the effects of sarcoid granulomas on alveolar tissue. The granulomas are generally found in the peribronchiovascular sheaths or in the sub- pleural region and more rarely in the alveolar interstitium. At the periphery of a granuloma the alveolar structure may be either totally destroyed or simply mod- ified. Whatever the anatomic mechanism, this may therefore lead to an increase in the diffusing distance and t o a modification or destruction of the alveolar capil- laries, but exclusively in proximity t o the granulomas.

At Stage I11 the pathological studies have shown the polymorphism of the sclerosis and the impairment of the bronchiolar and alveolar structures. The func- tional characteristics analyzed are in agreement. Furthermore, the ' decrease of D L ~ ~ and D m is significant and impairment of the capillary network is signifi- cantly more frequent than in Stage I1 (33% of cases), but less important than in the D I F process (TABLES 4 and 5).

SUMMARY AND CONCLUSIONS

Most CO-transfer data from patients suffering from sarcoidosis agree well with pathological findings. The roentgenographic appearance seems to be in- adequate for the estimation of pulmonary involvement and the establishment of a valuable classification based on such an estimate. This is well shown considering the fact that measured transfer properties may be diminished in Stage I due to extension of the sarcoid process t o the lung.

The accuracy and the importance of Qc measurement is demonstrated both by theoretical considerations of the effect of the distribution inhomogeneity of trans- fer properties and by the results obtained from patients whose diseases mainly affect the pulmonary interstitium. We observe that Qc is normal in most of the cases of sarcoidosis before reaching Stage 111. Then it appears that the lowering of DLCO may be due either t o Dm impairment or pulmonary inhomogeneity.

This is an important point, which makes a distinction between sarcoidosis and interstitial lung diseases that destroy the capillary network.

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