Lung growth in health and disease

Br. J. Dis.

LUNG

GROWTH

IN HEALTH LYNNE

S. Burt

Chest

(1984) 78, 113

AND DISEASE

M. REID

Wolbach Professor of Pathology, Harvard Medical The Children’s Hospital Medical Center, Boston,

School and Pathologist-in-chief, Massachusetts, USA

The subject oflung growth in health and disease can be discussed at several levels of anatomical and biochemical resolution. We can concentrate on the interaction between tissues-such as epithelium and mesenchyme: as the lung buds from the foregut, interaction between mesenchyme and epithelium is essential for their subsequent growth and differentiation (Alescio & Cassini 1962; Alescio 1974). Or we can discuss events of cell maturation exemplified by the development of the type II pneumocyte and surfactant system. Or our attention could be to the control mechanisms between cells and tissues. We are familiar with the endocrine system of blood-borne or circulating mediators. The paracrine system describes the cell-cell interaction whereby within a tissue messengers in tissue fluid and cell receptor provide local ‘triggers’ to multiplication and differentiation. Autocrine refers to the feedback between a single cell and its product. Currently it is the pattern ofparacrine control that is of special interest in relation to growth. On this occasion, I have chosen rather to deal with the lung as an organ, to dissect the airways, alveoli and blood vessels separately so that we can identify the nature of disturbed growth. Behind this lie biochemical events still to be elucidated. But as often happens the anatomical analysis of normal and diseased growth offers significant signposts to the biochemist and cell biologist.

Laws of Lung

Development

The newborn lung is not the adult in miniature. The facts of normal lung growth in the human can usefully be summarized by three laws that offer a framework to interpret and diagnose the nature of disturbed growth and its timing (see Hislop & Reid 1981). Law

1

The bronchial tree is developed by the 16th week of intrauterine life (Fig. 1). The first quantitative studies I made were of airways, to identify the level of airway affected in bronchiectasis and to establish the nature of the dilatation (Reid 1950; Hayward & Reid 1952a,b). As a result of such studies, congenital bronchiectasis, a common diagnosis in Tudor Edwards’ day, became recognized for the rarity it is. Bucher later counted the generations in fetal lung which led to the *The 19th Tudor 12

Edwards

Memorial

Lecture--delivered

at the Royal College of Physicians, London.

114

Lynne M. Reid GLANDULAR

CANALICULAR

POST-NATAL

ALVEOLAR

or----T--

alveolar ducts respiratory bronchioli non-respiratory bronchioli

bronchi

TERM

35 38 Weeks Adult 5 IO 15 20 25 30 Fig. 1. Diagrammatic representation of the development of the bronchial tree. Lobar bronchi appear at the 6th week of gestation and by 16 weeks all non-respiratory airways are present. Most respiratory ones appear between 16 weeks and birth, some in infancy. Cartilage and glands appear later

300 “0 X

& 4 200 E 2

Alv. No. II Alv.

5

Age

II Size

o-0 l

(1962)

- - -0 Davies 8 Reid

o-o

7

Dunnill

II

9

(1970)

11

18

II

(years)

Fig. 2. The increase in number and size of alveoli with age using quantitative analysis. The curve of Dunnill’s study is fitted from his figures. The figures for number and size from Davies and Reid, 1970 are shown: size is shown as a reciprocal so the line goes up as size increases

Lung Growth in Health and Disease

115

formulation of this first law (Bucher & Reid 1961). In the longest segments, such as the posterior basal or inferior lingular, the number of generations between the segmental bronchus and the ultimate airways supplying the distal pleural surface is as much as 28. Law II

Alveoli develop after birth, increasing in number until the age of 8 years and in size until growth of the chest wall finishes with adulthood (Fig. 2). Alveolar multiplication is essentially a postnatal story. Alveoli as we know them in the adult are not present at birth. Boyden preferred the term ‘primitive saccule’ to describe the simple air spaces found at the lung periphery (Boyden 1977). Of these about 20 million are present in the newborn and about three hundred million alveoli, the adult number, are found by the age of 8 (Dunnill 1962; Weibel & Gomez 1962; Davies & Reid 1970). There is still discussion as to how lung growth proceeds here and what is the variance in total number in normal young adults. In most cases of disease, however, the reduction in total number is so great that the variance in the normal is relatively unimportant. Alveolar multiplication represents remodelling within the acinus. In the premature but viable lung of the 28-week infant, there are many fewer primitive alveolar spaces than in the term infant. This means that not only are the premature infant’s lungs small by absolute size and weight but the full number of respiratory units is not yet present. The premature infant is not the term infant in miniature (Emery & Mithal 1960; Hislop & Reid 1974). Growth within the alveolar region is, in fact, incomplete. We do not known when the premature infant clocks in to the postnatal timetable, although it certainly does not seem to do it at birth. Law III

The preacinar vessels (arteries and veins) follow the development of the airways, the intra-acinar that of the alveoli. Muscularization of the intra-acinar arteries does not keep pace with the appearance of new arteries (this is discussed later). By using these laws as the timetable ofdevelopment it is possible to decide at what stage in development a given anomaly has appeared and to predict which structures will be susceptible to disease at a given age.

Abnormal Airway Growth In Table I are listed conditions in which the number ofairways is reduced indicating that lung growth was impaired well before the 16th week of intrauterine life. Congenital diaphragmatic hernia

Congenital diaphragmatic hernia illustrates the value of morphometric analysis for precise diagnosis of the nature of disturbed lung growth (Fig. 3). Based on inspection

Lynne M. Reid

116

Table I. Developmental anomalies associated with reduction in bronchial airway generations Bronchial airway generations are reduced congenital diaphragmatic hernia rhesus isoimmunization renal agenesis/dysplasia absent phrenic nerve and diaphragmatic idiopathic hypoplasia agenesis of lung

DIAPHRACMATIC HERNIA

in:

amyoplasia

NORMAL at birth

10 r 1 8+ /jj “0x $

I b! i,::i,I::‘,;; j: ,:,.j.:..: 4 -

2 2

;. .;;,I::.. ::y:,g iit :::.:j,>;j:j:; :::::y:::::j;: :..>,.: ::;.:‘.yi:;:, ::......:.:.I:.: I’.::;:;:g:j :,:.,., :,:.:;:..::, ...:_:( :.> : .A:. :.A:.: :.::*‘ii:‘i;,:. :,j,:,:,:,:,i;::

li Fig.3. Lungs in case of congenital diaphragmatic hernia (left) compared with normal lung at birth (right). Both lungs are reduced in volume, airway number and alveolar number. Shaded bar, number of alveoli; solid bar, number per unit volume

of routine sections it was accepted that in diaphragmatic hernia the main reason for the hypoplasia was growth restriction of alveoli since these appear few and small whereas the airways including their cartilage look normal, suggesting that herniation occurs late. In fact analysis of airway generations in congenital diaphragmatic hernia showed that they are reduced in both lungs sometimes to a greater degree in the ipsilateral lung (Arecchon & Reid 1963; Kitagawa et al. 197 1).

Lung Growth in Health and Disease

117

Reduction is to about half, indicating that interference with lung growth is early, as early as the 10th week, the time that the gut migrates back into the abdomen from the umbilical cord. This is probably when the gut enters the thorax. Alveolar number is reduced but relatively less, in that it is proportional or appropriate for the reduced airway number as judged by the Emery-Mithal count (1960). This means that the programme for airways need not be finished before alveolar multiplication starts. The reduction in airways means that there are fewer respiratory units, i.e. acini. (An acinus is the respiratory unit; it comprises the lung supplied by a terminal bronchiolus.) The total number of alveoli is reduced but the number per acinus is relatively less affected than the total. The alveoli are abnormally small. Arteries also are small and their number and size reduced. If the hernia is corrected and the lung inflated it does not immediately fill the thoracic cavity but usually within weeks to months the radiograph is virtually normal. But it is important to appreciate that the lung will never be normal, it will not show a complete catch-up of growth. The airway and total alveolar number will be down and probably even vessel concentration, and the lower lobe may be hyperlucent (Berdon et al. 1968). Expansion of the lung to fill the chest is associated with emphysema. In a patient in whom the hernia was corrected soon after birth but who died from pneumonia aged 3 months with satisfactory lung expansion judged radiographically, there was emphysema in all lobes and the ipsilateral lung still showed great reduction in diameter of the pulmonary artery (Hislop & Reid 1976). Wohl et al. (1973) studied a series of healthy teenage children after successful correction of a hernia and in all seven patients where perfusion was studied it was reduced to the ipsilateral lung. In the postoperative period pulmonary hypertension not infrequently is a complication: its nature is discussed later. Rhesus isoimmunisation With modern advances in control of the haematological problems most deaths in Rhesus isoimmunization are caused by respiratory insufficiency. We examined the lungs of six infants, all born prematurely and in all of whom lung weights were reduced relatively more than body weight (Chamberlain et al. 1977). Table II shows that although cases 1 and 6 were of similar age the lung volume of case 6 was normal for age, whereas of case 1 it was only about a third. In case 6, alveolar number was reduced, that is the individual alveoli were too large. Although there is variation between cases in most of the features studied the significant reduction in airway number is consistent. This means that interference with airway branching occurred before the 12th week ofintrauterine life, at a time when neither the liver nor spleen is enlarged nor is ascites present, and so suggests a direct immune-mediated injury. Antibodies have been reported in the fetal circulation as early as the 5th week of gestation (Chown 1955; Bergstrom et al. 1967). That the number of alveoli per acinus is sometimes reduced points to continuing injury. Recent advances in treatment aim to prevent the production of antibodies in mother and so the changes that I have described may also be prevented. In manv ofthese conditions surgical correction or treatment cures the patient with good function during childhood and adolescence but often the lungs are not normal.

118

Lynne M. Reid

We do not known whether this level of function will be maintained into adult life or what the effect of other disease might be. Follow-up should be attempted, a difficult task when patients are ‘cured’. Common sense suggests that these patients should be specially warned against the hazards of tobacco smoking and environmental irritants-as were patients with tuberculosis in another era. Renal agenesis and dyplasia-Potter’s

syndrome

In 1946, Edith Potter described the syndrome that now bears her name, pulmonary hypoplasia associated with renal agenesis or with renal dysplasia (see Potter & Craig 1975). Oligohydramnios, usually found in this syndrome, has commonly been blamed for the small lungs. Findings in other clinical conditions and exceptions to this generalization, however, suggest that oligohydramnios is not the whole story. Hislop analysed lung structure in eight such patients, five of renal agenesis and three of renal dysplasia (Hislop et al. 1979). Th e number of airway generations is reduced although not as severely as in the infants with Rhesus isoimmunization, indicating, Table

II. Structural abnormalities shown by morphometric analysis of a series of fatal cases of Rhesus isoimmunization Artery

Gestational age (weeks)

33 28 35 31 26 34

Lung vol.

Airway no.

Alveoli/ acinus

Alveolar maturity

size

f i

f

f

f

f

f” i N

1 1

N 7

7 N N

f i N

WT*

* WT, wall thickness.

however, that airway development is impeded at least as early as the 12th week of intrauterine life. Alveoli are always small, often also too few, even when related to the reduced airway number. Experimental and clinical studies indicate that if amniotic fluid drains away steadily during late pregnancy, the lungs are small and this clearly would be due mainly to interference with alveolar multiplication component (Perlman et al. 1976; Alcorn et al. 1977a). Since the airway number is down, the interference with lung growth must be early. The contribution of the kidney to liquor is only important relatively late in pregnancy. Strang (1977) considers that in the lamb the lung contributes about a third of amniotic fluid. Oligohydramnios probably reflects the lung hypoplasia rather than being its cause. Thorburn (1974) showed that nephrectomy in fetal lambs interfered with subsequent growth without referring to its effect on lung. Clemmons’ studies (1977) have shown that the kidney is an important site of proline synthesis for the use of organs other than the kidney. Clemmons’ interest was in the arginase activity of the developing kidney in the chick embryo, since this enzyme influences production of proline through the

Lung Growth in Health and Disease

119

arginine-ornithine-proline cycle. Since the lung was growing actively at the time that this enzyme increases he examined the lung also. He injected nephrotoxins into the kidney during either the meso- or metanephric stage and, using radiolabel, showed reduced proline production from kidney, and reduced proline uptake and collagen synthesis in the lung which histologically appeared immature. Thus the effect on lung seems to be a nutritional deprivation. The association of kidney with lung defects can now be interpreted in biochemical and metabolic language, offering new ways of investigating the interaction between the organs. Injury to the mesonephros often left no sign in the newborn chick, whereas the lung still carried its stigma: injury to the metanephros continued to be apparent. In cases of unexplained or idiopathic hypoplasia, the kidney is suspect. Agenesis of the phrenic nerve with amyoplasia of the diaphragm

We have analysed morphometrically the lungs of a term infant with agenesis of the phrenic nerve and amyoplasia of the diaphragm associated with small lungs and reduced airway number-to about half the normal complement (Goldstein & Reid 1980). The infant died at 18 hours of age with persistent pulmonary hypertension of the newborn. The halving or so of airway number indicates that the airway branching was disturbed at least by the 10th week, although inspiratory movements in the human fetus are not considered important until about the 20th week (Boddy & Dawes 1975). Fetal phrenectomy studies suggest that impaired respiratory movements later in gestation also lead to small lungs (Alcorn et al. 197713; Desai & Wigglesworth 1979). This clinical case indicates that early in gestation a muscular diaphragm has an important function to increase thoracic volume, to protect the thoracic space from compression by abdominal viscera. In these lungs there was also a major reduction in external diameter afthe small arteries and presence of arterial muscle at a more peripheral level in the arterial tree than is normal. Agenesis of lung

Morphometric studies had been carried out on a single lung present in one patient with agenesis oflung (Ryland & Reid 197 1). In this patient Ryland was able to show that the volume of the single lung and the alveolar number were equivalent to that of two lungs whereas the airway number was again only about half normal. It seems that the early epithelial mesenchyme interaction was associated with lung development, but was deficient even in the one lung that formed, and yet the hypoplastic bronchial tree could respond to the available thoracic space by growing an excessive number of alveoli. The disassociation between the airway and alveolar programme is again evident in this patient. This excessive number of alveoli is unusual. In only one other condition have we seen it-polyalveolar lobe, one form of childhood lobar emphysema (Hislop & Reid 1970). In this condition the increased alveolar number is seen in one region that includes only one or two segments. In view of the recent studies in compensatory growth (Davies et al. 1982) it is possible to make the generalization that in no case

Lynne M. Reid

120

have we seen excessive multiplication of alveoli after birth that fits with the doubling in this case, or with the up to live times increase found in the polyalveolar lobe (Davies et al. 1982). Idiopathic hypoplasia

Airway counts can be carried out by a combination of dissection using a dissecting microscope and microscopic step sections through the more peripheral regions. In cases of hypoplasia such examination is necessary for adequate analysis of the nature of the disturbed growth. Understanding of the causes of idiopathic hyoplasia, either localized or diffuse, is far from complete and justifies careful pathological and clinical studies in such cases.

Abnormal

Alveolar

Growth

Childhood lobar emphysema

Table III lists the various pathological types ofchildhood lobar emphysema (Hislop & Reid 1970, 1971; Hendersen et al. 1971). The interest of the polyalveolar lobe has Table

III.

Types of childhood

lobar emphysema Alveoli

Airway

Overinflation Compensatory Check valve Hypoplasia Atresia of bronchus Polyalveolar lobe

number

number

N N i N N

N N* 1 N* t*

N=normal, t =increased, * Alveoli do not multiply low for age.

i =decreased. normally, so number

size

i

becomes

been discussed above in relation to excessive alveolar multiplication. If resection is delayed to adulthood, the residual lung may not be able to fill the vacated thoracic space (Reid 1967). Clinical symptoms may be so acute and severe in childhood lobar emphysema that indications for surgical excision are clear. Sometimes symptoms are mild or absent and the need for surgery is not apparent but even in asymptomatic cases, the interference with growth of the compressed lung should be weighed by the surgeon in his consideration of resection. In a recent study McBride et al. (1980) followed a series of patients from whom lobes affected by emphysema had been removed in childhood. A better level of compensatory function, hence growth, seemed to be achieved in those children in whom an upper lobe had been removed

121

Lung Growth in Health and Disease

rather than a middle lobe, the suggestion being that resection of the larger volume is a better stimulus to compensatory growth than removal of a small amount. Thoracic deform@

Scoliosis has a devastating effect on lung growth (Reid 1969; Davies & Reid 1971). The lungs model themselves to the distorted space and a striking reduction in alveolar number occurs. The orthopaedic surgeon seems to be less impressed than one would hope with the secondary effect of scoliosis on lung growth. In contrast are the findings in the lungs of an infant with asphyxiating thoracic dystrophy (Jeune’s chondrodystrophy) who died at 4 months of age from hypoxic pulmonary hypertension (hypoxic car pulmonale) (Williams et al. 1984). Lung MUSCULAR

ARTERY

PARTIALLY MUSCULAR

LUMEN

0 Fig. 4. Top:

NON MUSCULAR

0

light microscopy reveals that at the distal end ofany arterial pathway, the complete muscle coat is replaced by a spiral ofmuscle before disappearing in arteries still larger than capillaries. Middle: electron microscopy reveals additional features. In the muscle-free region ofthe wall a pericyte is found in the non-muscular artery, and an intermediate cell in the non-muscular part ofthe partially muscular artery. These are precursor smooth muscle cells. Bottom: cross-sections showing the walls of muscular, partially muscular, and non-muscular arteries

122

Lynne M. Reid

growth was normal in spite of what would appear to be overwhelming odds. The diagnosis of thoracic dystrophy was made at birth, but because the one report in the literature described a hypoplastic lung in this condition, no attempt was made to correct the thoracic wall. During the 4 months of life the diaphragm became progressively depressed, apparent on the radiograph and at autopsy was convex into the abdomen. The lungs were of abnormal shape but their volume was within the normal range for a 4-month-old child as was alveolar and arterial number. The abnormal finding was the increase in pulmonary artery muscle in the large arteries with evidence of the pulmonary hypertension. In this child, in spite of the constriction of the rib cage the lung had achieved normal growth. Alveoli

Alveolar ducts

Respiratory Terminal bronchioli bronchiolus

____-----------_-_____ 28 36 38 40

wks.--j wks. wks. wks.J

FETUS

3 days 4 mths. IO mths. It? mths. 3 yrs. 4 yrs. 5 yrs. IO yrs. II yrs.

CHILD

IQ yrs.

ADULT

Fig. 5. Diagram illustrating the extension of muscle in the walls of arteries within the acinus. The end of the fully muscular region is shown by the black lines. There is no muscle within the acinus in the fetus. With age there is a gradual extension into the acinar region but even at 11 years this is not to adult levels

Normal

Pulmonary

Artery

Remodelling

during

Growth

There are three or four times as many preacinar arteries as there are airways (Davies & Reid 1970; Hislop & Reid 198 1). Usually their numbers are appropriate to airway number so in anomalies associated with reduced airway number, the artery number is reduced to a similar degree. The lungs’ microcirculation not only has a unique function but also a special structure (Fig. 4). Along any arterial pathway a level is reached, still in arteries

123

Lung Growth in Health and Disease

considerably larger than capillaries, where the complete muscular coat of the muscular artery gives way to a spiral ofmuscle-apartial muscular artery. The spiral gives way to an artery, still larger than capillary, with no muscle in its wall-a non-muscular artery. This precapillary alveolar unit or spiral region is found in all mammalian lungs we have studied and in the human lung all at all ages, but its level in the pattern of branching varies with age (Reid & Meyrick 1980, 1982). In the adult the muscular or resistance arteries are found throughout the alveolar walls of the acinus: in the newborn they are all proximal to the alveolar or respiratory region (Fig. 5). In the adult and fetus, the largest partially muscular artery is 15Opm,

I 200

Arterial

A---A

Fetus

o----o

3 Days

o---o

4 Months

I

I

400

External

to Adult

600

Diameter

(ym)

Fig.6. Medial thickness related to arterial external diameter. In the human fetus arteries of any diameter are thicker than in the adult. At birth the compliance of the small resistance arteries (less than 300,um in diameter) increases and wall thickness decreases. It takes some months for the larger arteries to drop to adult values. (From Reid (1979) reproduced with permission.)

whereas in the child, because muscularization lags, the largest partially muscular artery is 450jAm. The muscular arteries in the fetus have thicker walls than the arteries of the same size in the adult (Fig. 6). In the minutes and hours after birth the small arteries increase in external diameter and their wall thins. There is evidently an increase in compliance over the special precapillary segment. We can be sure of the level because we ‘landmark’ the arteries by the airways they accompany. This increase in compliance, or thinning, is the structural counterpart of the drop in pressure and resistance that occurs rapidly in the perinatal period.

Lynne M. Reid

124 Abnormal

Pulmonary

Artery

Persistentpulmonary hypertension of newborn (persistent

Growth

fetal circulation)

One of the major clinical problems in the newborn nursery is so-called persistent fetal circulation or persistent pulmonary hypertension of the newborn. This may occur as a solitary event or be associated with other conditions, such as persistent ductus arteriosus in hyaline membrane disease of the premature infant, meconium aspiration, and certain congenital anomalies of lung or of heart. In three cases where the idiopathic, or unexplained, form of hypertension was Haworth found an abnormal degree of present in the perinatal period,

Normals Term Fetus 3 Days 9 Days PPH 1 Day 1 Day 3 Days 3 Days 3 Days 6 Days Fig. 7. Extension of muscle to adult levels in six patients with persistent pulmonary hypertension (PPH) of the newborn. The length of the bars indicates the level at which partially muscular arteries are found. (From Murphy et al. 1981.)

muscularization of intra-acinar arteries (Haworth & Reid 1976). The youngest death was at 1 week of age. More recently Murphy analysed a series of ten cases who died at the Children’s Hospital Medical Center in Boston within the first week of life, some within the first 24-48 hours oflife (Murphy et al. 1981). Whereas in the normal newborn the alveolar region is virtually free of muscular arteries, in these cases we identified a precocious muscularization of the arterial pathways as far as the pleura, that is muscularization to the adult level even before birth (Fig. 7). That this has

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125

been present for at least some weeks is indicated by the thickness of the muscle layer, the maturity of its staining and by the presence of an internal and external elastic lamina. The small arteries are surrounded by an excessive amount of dense collagen in which lymphatics have developed. In the normal at this level neither of these features is seen. Our original hypothesis had been that persistent fetal circulation represented failure of normal adaptation by dilatation and increase in compliance of the smallest arteries of the lung. Our findings indicate that it is the result of maldevelopment in utero, with excessive muscularization, not just malfunction in the perinatal period. We then examined the lungs of a series of fatal cases of meconium aspiration, expecting in this group to find evidence of maladaptation-that is structurally

NORMAL ARTERIES

PPH

OF THE NEWBORN

AIRWAY Fetal

Perinatal

T. B.

R.B

Cl No muscle I Ma1 development m Muscle II Ma1 adaptation a New muscle III Under development Fig. 8. Diagrammatic representation of the three patterns of persistent pulmonary hypertension of the newborn. Maldevelopment indicates the new and precocious muscularization seen in idiopathic persistent pulmonary hypertension (PPH). Maladaptation represents failure of the increase in compliance in the smallest resistance arteries. Underdevelopment represents the reduced size of arteries seen in congenital anomalies such as congenital diaphragmatic hernia

normal lung at birth save that increase in compliance ofsmall resistance arteries had not occurred (Fig. 8). All but one showed the same type and degree of excessive muscularization we found in idiopathic persistent pulmonary hypertension of the newborn (Murphy et al. 1983). There is evidently one ‘type’ ofmeconium aspiration that is evidence of an abnormal modelling of the pulmonary circulation in utero and not just of perinatal distress. In some cases of congenital heart disease excessive muscularization of peripheral arteries is seen-e.g. hypoplastic left heart syndrome (Haworth & Reid 1977).

126

Lynne M. Reid

Whereas in persistent hypertension of the newborn the veins are normal, in the hypoplastic left heart syndrome there is an excessive muscularization ofveins also as judged both by level of muscle and by wall thickness. The veins have the same nonand partially muscular structure as the artery. In fact, the postcapillary alveolar unit is a mirror image of the arterial precapillary unit. New muscle cells develop from precursor cells under conditions of hypoxia and high flow (Meyrick & Reid 1978; Reid 1979). One case of persistent fetal circulation has been reported after the mother had taken aspirin during pregnancy and the suggestion was made that the drug by interfering with prostaglandin synthesis, had induced partial closure of the ductus, and pulmonary hypertension (Leven et al. 1978). In the guinea pig we have tried to develop an animal model of this condition by exposing the guinea pig mother to hypobaric hypoxia or by giving her daily injections of indomethacin. Hypoxia produced a ‘small for dates’ offspring but no pulmonary hypertension. Nor did indomethacin given for up to 21 days before delivery produce any functional or structural change (Murphy & Reid, preliminary communication). Table

IV. Remodelling in pulmonary arterial microcirculation associated with congenital heart disease

Muscle extension Wall thickness Artery number PBF, pulmonary blood flow; pulmonary arterial pressure; pulmonary vascular resistance.

PBF PAP PVR

t t t

PAP, PVR,

Congenital heart disease

Congential heart defects offer a series of vicarious experiments that indicate the way that the lung’s structure responds to abnormal haemodynamic patterns. The effect of high flow as in ventricular septal defect is an example of serious effect on early postnatal growth. The preacinar arteries fail to increase in size and their muscular coat thickens, both factors leading to reduced lumen diameter: intra-acinar arteries are smaller, more muscular, and too few in number (Hislop et al. 1975). Features of (a) abnormal extension of muscle, (b) increase in medial thickness of normally muscular arteries, and (c) reduced arterial concentration can be reliably assessed in biopsy tissue, since Haworth has shown that these changes occur diffusely and evenly through the lung (Haworth & Reid 1978). Features (a) and (c) are additional to the changes described by Heath and Edwards (1958) (b=grade I of their change) and especially assess the state of lung growth and early vascular remodelling. Extension (a) may occur alone and is often associated only with increase in flow (Rabinovitch et al. 1978, 1980) (Table IV). If medial hypertrophy is present so is extension and then a rise in pulmonary artery pressure is found. If arterial

Lung Growth in Health and Disease

127

concentration is reduced both (a) and (b) are also present with a rise in pulmonary vascular resistance and a more severe degree of pulmonary artery hypertension. These structural features correlate with the findings in clinical angiograms (Rabinovitch et al. 1981). Rendas, by producing an aortopulmonary shunt in the guinea pig, has analysed the haemodynamic and functional effects of high flow, pulmonary hypertension and the effect of closure (Rendas et al. 1979). Closure of the shunt is associated with increased rate ofalveolar and arterial multiplication at least in the first postoperative weeks (Rendas & Reid 1983).

Growth

by ‘Fits and Starts’

In congenital heart disease serious pulmonary hypertension can be present with reduced arterial concentration and yet the alveolar number is normal. This underlines the dissociation between development of arteries and alveoli, which is probably why the vascular changes we have reported in congenital heart disease have been largely overlooked. Meyrick has recently studied lung growth in the rat during the first weeks of life, analysing morphometrically alveolar and also blood vessel growth (Meyrick & Reid 1982). Burri and Weibel advanced our understanding of early postnatal alveolar development in the rat (Burri et al. 1979) by identifying three stages-the first of lung distension, the second marked by a burst of cell multiplication and the third a phase they describe as steady ‘maturation’-the lung grows in size while maintaining a similar overall structure. Meyrick found that in the rat, postnatal remodelling proceeds by a series of steps, each a burst of activity, that affects first one structure, and then another (Fig. 9). Lung volume doubled by 3 days but as alveolar multiplication keeps up alveolar concentration does not change. Then between days 3 and 8 the rate of alveolar growth rises so that concentration of alveoli is dramatically increased. This must represent a new signal, a new instruction, in the programme of lung growth. The lung template has changed but evidently only with respect to alveoli. By day 11 it is the arteries’ turn to receive a signal. They now change their rate of growth and achieve a new and higher concentration in relation to alveoli. The arterial to alveolar ratio is now different from that found before these separate bursts of growth. The large arteries have an unusual pattern of growth. Although lung volume is increasing they show little increase in lumen diameter or wall thickness for some days after birth (except for the fall in medial thickness of the peripheral resistance arteries, as described above). Remodelling of the arteries is marked first by a doubling ofwall thickness at day 15 that encroaches on the lumen and then by day 22 external diameter and the lumen increase and wall thickness drops to the adult level. During the burst of medial increase, the wall thickness of the arteries is greater than anything seen in the fetus. Such structural studies give a lead to which cells to examine in culture to identify the trigger mediators and mechanisms, and the cell to cell interactions responsible for these changes. It is intriguing that a circulatory lung lectin has been shown to increase in concentration particularly at this time but such studies do not help us to

128

Lynne M. Reid

4

% MT (51-100ym

ED) // -

2

Lumen

::j

diameter

*‘I-

12

Alveolar

concentration

Arterial

concentration 11 -

9 6

Alveoli

-I

I

12 3 hrs

1

8

I

11

I 15

I

I

29 22 Days of age

: Artery

36

N//

1

60

Fig. 9. Morphometric analysis of postnatal development of rat lung showing separate step-like change for various features. Dissociation of change of alveolar and arterial concentration especially illustrates this. Lung volume is increasing steadily. MA, muscular arteries; AD, alveolar ducts; MT, medial thickness; ED, external diameter.

decide whether this is evidence that growth is occurring or represents mediator inducing that growth (Powell & Whitney 1980).

Compensatory

Growth

after

Resection-?

More

the trigger or

Alveoli

One of the questions which Tudor Edwards would have pondered many times was the nature of compensatory growth in the residual lung tissue after resection,

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whether pneumonectomy or lobectomy, in the child or the adult. He would have asked this question particularly in relation to resection for childhood bronchiectasis. Although this is no longer a frequent problem, at least in our communities, the question is still relevant when considering repair of developmental anomalies and excision of space-occupying lesions. It has been widely proved that such resection at any age is followed by an increase of volume, of weight and cell number in the residual lung, but not enough to equal two lungs. There had been no resolution of what was considered the key question in Tudor Edwards’ day as to whether or not new alveoli develop after resection. Is compensatory growth by dilatation or by new alveoli? The results of a recent study seem to settle this question at last and also to explain the seeming contradiction in the literature (Davies et al. 1982). Even allowing for species differences the results in the literature were contradictory some studies showing finding of alveolar multiplication after resection, others not. Virtually all previously reported experiments studied a short postoperative period, typically of only a few weeks. Davies analysed morphometrically the residual lung in beagle dogs who had had left pneumonectomy performed at either 6 weeks (young operated) or 1 year of age (adult operated). In each group the animals were followed up for 3-4 years with haemodynamic and respiratory function studies; the controls were 4-5 years old. In the young and adult resection groups, the lung’s weight and volume increased, as did the alveolar size and alveolar surface area, of the order to be expected from dilatation, but the alveolar number in the right lung was the same in both operated groups as in the control (Fig. 10). Certain of the lobes showed a greater degree of distension than others and in these alveolar size was greatest, but there was no increase above the normal alveolar number for lobe. In young mongrel dogs, where the residual lung was studied within a few weeks of resection, an increase in alveolar multiplication was reported by Thurlbeck et al. ( 198 1). It seems that, if follow-up is long enough, no increase in alveolar number is found, but if at the time of resection the animal has not completed its programme of alveolar multiplication, then the effect of resection is to increase the rate ofalveolar formation-but the total achieved is not above the normal. Smith has demonstrated that the serum from rats 3 weeks after pneumonectomy has ‘in culture’ a stimulating effect on type II pneumocytes but not on lung libroblasts: serum from control rats ofa similar age does not (Smith et al. 1980). The compound stimulating the growth is a small peptide (about 5000 dalton), a somatomedin or insulin-like growth factor (Stiles et al. 198313). It seems that the effect of surgery is to reduce serum levels but to increase that in lung tissue. After nephrectomy, he found a similar organ-specific effect on kidney (Stiles et al. 1983a). The fact that the increase is first in the tissue suggests that these growth factors are produced in the tissue, or at least that tissue receptors have changed to increase uptake. There are intriguing and unexplained differences in the arteries of the young and adult operated beagles. The arterial findings of the group operated upon young were normal by our analysis, whereas the adult operated group showed a significant extension of muscle into more peripheral arteries than is normal. Of course, the 13

Lynne M. Reid

130

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increase in lung volume particularly in the young lung means that there has been a remodelling of the circulation in that although the concentration of arteries and alveoli in unit volume is similar to the normal, the increased lung volume represents increase in the total volume of the vascular bed that has followed closely the normal template. The paradox is that there is right ventricular hypertrophy in the young operated group but not in the adult. One possibility is that soon after lung resection the increased flow through the single young lung may have been associated with a greater rise in vascular resistance in the young animals. Later no evidence of pulmonary hypertension was found in these animals but haemodynamic studies were performed only at rest. A surgeon feels intuitively that operation in the young animal must be better than in the old. The trend to greater increase in weight, volume and surface area seen in the young animal (although in our study this does not reach statistical significance), and the normal vascular bed support this. Whether there is an optimum time to maintain volume and structure of the arterial bed has not yet been established. Although bronchiectasis is no longer the serious problem that it was in Tudor Edwards’ day developmental anomalies and immaturity of the lung assume an ever more important role. I have tried to show something of the variety of abnormal patterns of lung growth which we can identify today. We and others are currently exploring these questions by cell and organ culture to construe the mediator language responsible for lung growth and differentiation in health and disease. In many ways we are used to manipulating the endocrine system to correct its dysfunction. With greater knowledge of endocrine and paracrine control of the lung’s metabolic function we can look forward to the time when we can selectively stimulate its cells and tissues, correct faulty growth and ensure appropriate catch-up growth.

References Alcorn,

D., Adamson, T. M., Lambert, T. F., Maloney, J. E., Ritchie, B. C. & Robinson, P. M. (1977a). Morphological effects of chronic tracheal ligation in fetal lamb lung.]. Anat. 123, 649. Alcorn, D., Adamson, T. M., Maloney, J. E., Ritchie, B. C. & Robinson, P. M. (1977b) Morphological effects of phrenectomy in the fetal lamb lung. J. Anat. 124, 526. Alescio, T. (1974) Effect of a proline analogue, azetidine-2-carboxylic acid, on the morphogenesis in vitro of mouse embryonic lung. J. Embry. exp. Morph. 29, 439. Alescio, T. & Cassini, A. (1962) Induction in vitro oftracheal buds by pulmonary mesenchyme grafted on tracheal epithelium. J. exp. Zool. 150, 83. Areechon, W. & Reid, L. (1963) Hypoplasia oflung with congenital diaphragmatic hernia. br. med. J. 1, 230. Berdon, W. E., Baker, D. H. & Amourey, R. (1968) The role ofpulmonary hypoplasia in the prognosis ofnewborn infants with diaphragmatic hernia and eventration. Am. J. Roentgenol. Rad. Ther. Nucl. Med.

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~

Bergstrom, H., Nilsson, L-A., Nilsson, L., & Ryttinger, L. (1967) 39-day old fetus. Am. J. Obstet. Gynecol. 99, 130. Boddy, K. & Dawes, G. S. (1975) Fetal breathing. Br. med. Bull. Boyden, W. A. (1977) Development and growth of the airways. In: W. A. Hodson. In: Lung Biology in Health and Disease, exec. ed. Marcel Dekker.

Demonstration 31, 3. Development

of Rh antigens in a

of the Lung, pp. 3-35, ed. Claude Lenfant. New York & Basel:

Lynne M. Reid Bucher, U. & Reid, L. (1961) Development of the intrasegmental bronchial tree: the pattern of branching and development of cartilage at various stages of intrauterine life. Thorax 16, 207; Burri, P. H., Dbaly, J. & Weibel, E. R. (1979) The postnatal growth ofrat lung. I. Morphometry. Anat. Rec. 178,

711.

Chamberlain, D., Hislop, A., Hey, E. & Reid, L. (1977) P u 1monary hypoplasia in babies with severe rhesus isoimmunization: a quantitative study. J. Path. 122, 43. Chown, B. (1955) On a search for rhesus antibodies in very young fetuses. Archs Dis. Childh. 30, 232. Clemmons, J. J. W. (1977) Embyronic renal injury: a possible factor in fetal malnutrition (abstract). Pediat.

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Davies, G. & Reid, L. (1970) Growth ofthe alveoli and pulmonary arteries in childhood. Thorax 25,669. Davies, G. & Reid, L. (1971) Effects of scoliosis on growth of alveoli and pulmonary arteries and on right ventricle. Archs Dir. Childh. 46, 623. Davies, P., McBride, J., Murray, G. F., Wilcox, B. R., Shallal, J. A. & Reid, L. (1982) Structural changes in the canine lung and pulmonary arteries after pneumonectomy. J. appl. Physiol. resp. exp. Physiol.

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Desai, R. & Wigglesworth, J. S. (1979) Control of lung growth in the fetal rabbit. J. Physiol. 289,66P. Dunnill, M. S. (1962) Postnatal growth of the lung. Thorax 17, 329. Emery, J. L. & Mithal, A. (1960) The number ofalveoli in the terminal respiratory unit ofman during late intrauterine life and childhood. Archs Dis. Childh. 3.5, 544. Goldstein, J. G. & Reid, L. (1980) Pulmonary hypoplasia resulting from phrenic nerve agenesis and diaphragmatic amyoplasia. J. Pediat. 97, 282. Haworth, S. G. & Reid, L. (1976) Persistent fetal circulation-newly recognized structural features. J. Pediat. 88, 614. Haworth, S. G. & Reid, L. (1977) Q uantitative structural study of pulmonary circulation in the newborn with aortic atresia, stenosis or coarctation. Thorax 32, 121. Haworth, S. G. & Reid, L. (1978) A morphometric study of regional variation in lung structure in infants with pulmonary hypertension and congenital cardiac defect. A justification of lung biopsy. Br. heart J. 40, 825. Hayward, J. & Reid, L. (1952a) Observations on the anatomy of the intrasegmental bronchial tree. Thorax

7, 89.

Hayward, J. & Reid, L. (1952b) The cartilage of the intrapulmonary bronchi in normal lungs in bronchiectasis, and in massive collapse. Thorax 7, 98. Heath, D. & Edwards, J. E. (1958) The pathology ofhypertensive vascular disease. Circulation 18,533. Henderson, R., Hislop, A. & Reid, L. (197 1) New pathological findings in emphysema ofchildhood: 3. Unilateral congenital emphysema with hypoplasia-and compensatory emphysema of contralateral lung. Thorax 26, 195. Hislop, A., Haworth, S. G., Shinebourne, E. A. & Reid, L. (1975) Q uantitative structural analysis of pulmonary vessels in isolated ventricular septal defect in infancy. Br. heart J. 37, 1014. Hislop, A., Hey, E. & Reid, L. (1979) The lungs in congenital bilateral renal agenesis and dysplasia. Archs

Dis.

Child.

54, 32.

Hislop, A. & Reid, L. (1970) New pathological findings in emphysema of childhood: 1. Polyalveolar lobe with emphysema. Thorax 2.5, 682. Hislop, A. & Reid, L. (1971) New pathological findings in emphysema ofchildhood: 2. Overinflation of a normal lobe. Thorax 26, 190. Hislop, A. & Reid, L. (1973) Pulmonary arterial development during childhood: branching pattern and structure. Thorax 28, 129. Hislop, A. & Reid. L. (1974) Development of the acinus in the human lung. Thorax 29, 90. Hislop, A. & Reid, L. (1976) Persistent hypoplasia of the lung after repair of congenital diaphragmatic hernia. Thorax 31, 450. Hislop, A. & Reid, L. (1981) Growth and development of the respiratory system: Anatomical development. In: ScientificFoundations ofpaediatrics, 2nd edition, pp. 390-431, eds. J. A. Davis and J. Dobbing. London: Heinemann Medical Publications. Kitagawa, M., Hislop, A., Boyden, E. A. & Reid, L. (1971) Lung hypoplasia in congenital diaphragmatic hernia. A quantitative study of airway, artery and alveolar development. Br. J. Surg.

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Levin, D. L., Fixler, D. E., Moriss, F. C. & Tyson, J. (1978) Morphologic analysis of the pulmonary vascular bed in infants exposed in utero to prostaglandin synthetase inhibitors.]. Pediat. 92,478. McBride, J. T., Wohl, M. E., Strieder, D. J., Jackson, A. C., Morton, J. R., Zwerdling, R. G., Griscom, N. T., Treves, S., Williams A. J. & Schuster, S. (1980) Lung growth and airway function after lobectomy for congenital lobar emphysema. J. clin. Znves&. 66, 962. Meyrick, B. & Reid, L. (1978) The effect of continued hypoxia on rat pulmonary arterial circulation. An ultrastructural study. Lab. Invest. 38, 188. Meyrick, B. & Reid, L. (1982) Pulmonary arterial and alveolar development in normal postnatal rat lung. Am. Rev. resp. Dis. 125, 468. Murphy, J. D., Rabinovitch, M., Goldstein, J. D. & Reid, L. (1981) The structural basis ofpersistent pulmonary hypertension of the newborn infant. J. Pediat. 98, 962. Murphy, J., Vawter, G. F. & Reid, L. (1984) Pulmonary vascular disease in fatal meconium aspiration. J. Pediat. in press. Perlman, M., Williams, J. & Hirsch, M. (1976) N eonatal pulmonary hypoplasia after prolonged leakage of amniotic fluid. Archs Dis. Childh. 51, 349. Potter, E. L. & Craig, J. M. (1975) Pathology of the Fetus and the Infant, 3rd edition. Chicago: Year Book Medical Publishers, Inc. Powell, J. T. & Whitney, P. L. (1980) Postnatal development of rat lung. Changes in lung lectin, elastin, acetyl cholinesterase and other enzymes. Biochem. J. 188, 1. Rabinovitch, M., Haworth, S., Castaneda, A., Nadas, A. & Reid, L. (1978) Lung biopsy in congenital heart disease: a morphometric approach to pulmonary vascular disease. Circulation 58, 1107. Rabinovitch, M., Haworth, S., Vance, Z., Vawter, G., Castaneda, A., Nadas, A. & Reid, L. (1980) Early pulmonary vascular changes in congenital heart disease studied in biopsy tissue. Hum. Path.

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Rabinovitch, M., Keane, J. F., Fellows, K. E., Castaneda, A. R. & Reid, L. (1981) Quantitative analysis of the pulmonary wedge angiogram in congenital heart defects: a correlation with hemodynamic data and morphometric findings in lung biopsy tissue. Circulation 63, 152. Reid, L. (1950) Reduction in bronchial subdivision in bronchiectasis. Thorax 5, 233. Reid, L. (1967) The Pathology of Emphysema. Monograph. London: Lloyd-Luke (Medical Books). Reid, L. (1969) Pathological changes in the lungs in scoliosis. In: Scoliosis, pp. 67-86, ed. P. A. Zorab. London: William Heinemann Medical Books. Reid, L. (1979) The pulmonary circulation: remodeling in growth and disease. The 1978 J. Burns Amberson Lecture. Am. Rev. resp. Dis. 119, 531. Reid, L. & Meyrick, B. (1980) Hypoxia and pulmonary vascular endothelium. In: Metabolic Activities of the Lung (Ciba Foundation Symposium-78)) pp. 37-61. Amsterdam: Excerpta Medica. Reid, L. & Meyrick, B. (1982) Microcirculation: definition and organization at tissue level. Presented at ‘Conference on Mechanisms of Lung Microvascular Injury, Ann. d$‘.Y. Acad. Sci. 384, 3. Rendas, A., Lennox, S. & Reid, L. (1979) Aorto-pulmonary shunts in growing pigs. Functional and structural assessment of the changes in the pulmonary circulation. J. thorac. cardiovasc. Surg. 77, 109. Rendas, A. & Reid, L. (1983) Pulmonary vasculature of piglets after correction of aorto-pulmonary shunts. J. thorac. cardiovasc. Surg. 85, 91 1. Ryland, D. & Reid, L. (1971) Pulm onary aplasia-a quantitative analysis of the development of the single lung. Thorax 26, 602. Smith, B. T., Galaugher, W. & Thurlbeck, W. M. (1980) Serum from pneumonectomised rabbits stimulates alveolar Type II cell proliferation in vitro. Am. Rev. resp. Dis. 121, 701. Stiles, A. D., Sosenko, I. R. S., Smith, B. T. & Dercole, A. J. (1983a) Tissue somatomedin C increased in the regenerating kidney. Pediat. Res. 17, 173a. Stiles, A. D., Sosenko, I. R. S., Smith, B. T. & Dercole, A. J. (198313) Rapid rise in pulmonary somatomedin C levels in the regenerating lung. Pediat. Res. 17, 391a. Strang, L. B. (1977) Growth and development ofthe lung: fetal and postnatal. Ann. Rev. Physiol. 39,253. Thorburn, G. D. (1974) The role of the thyroid gland and kidneys in fetal growth. In: Sire at Birth. Proceedings of Ciba Foundation Symposium Neal Series No. 27, London, March 1974, pp. 185-200, eds. K. M. Elliott and J. Knight. Amsterdam: Elsevier.

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Thurlheck, W. M., Galaugher, W. & Mathers, J. (1981) iZdaptive response to pneumonectomy in puppies. Thorax 36, 424. Weibel, E. R. & Gomez, D. M. (1962) A principle for counting tissue structures on random secti0ns.J. appl. Physiol.

17, 343.

Williams, A. J,, Vawter, G. & Reid, L. (1984) Lung structure in asphyxiating thoracic dystrophy Ueune’s chondrodystrophy). Arch. Path. Lab. Med. in press. Wohl, M. E. B., Griscom, N. T., Schuster, S. R., Zwerdling, R. G. & Strieder, D. (1973) Lung growth and function following repair of congenital diaphragmatic hernia. Pediat. Res. 7, 424.

ERRATUM Efficacy of a Saccharin Test for Screening to Detect Philip Stanley et al. Vol. 78 No. 1 (January 1984).

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