Quantitative aspects of perinatal lung growth

Pulmonary Hypoplasia: Prediction with Use of Ratio of MR Imaging–measured Fetal Lung Volume to US-estimated Fetal Body Weight

PURPOSE

To determine the ratio of fetal lung volume (FLV) to fetal body weight (FBW) by using ultrasonography (US) and magnetic resonance (MR) imaging and to evaluate the usefulness of this ratio in predicting pulmonary hypoplasia (PH) in fetuses at high risk.

MATERIALS AND METHODS

MR imaging lung volumetry and US biometry were performed in 90 fetuses at 25-39 weeks gestation. In the control group of 73 fetuses, normal lung development was confirmed at neonatal follow-up and the normative ratio of MR imaging-measured FLV to US-estimated FBW (FLV/FBW) was determined. The high-risk group included 17 fetuses at risk for PH. The FLV/FBW was compared between the control and high-risk groups and with US parameters for predicting the development of PH in the high-risk group. Measurements 2 or more standard deviations below the mean control group measurement were considered abnormal. Comparisons of the FLV/FBW between groups were made by using the Student t test. The association between development of PH and measurement of each parameter was analyzed by using the Fisher exact probability test.

RESULTS

In the control group, the FLV/FBW decreased with gestational age during the third trimester and had a normal distribution (mean ratio, 0.028 mL/g; range, 0.015-0.444 mL/g). The mean FLV/FBW for the nine fetuses with PH (0.012 mL/g +/- 0.008) was significantly lower (P <.001) than that for the control group (0.028 mL/g +/- 0.007). Fetuses with abnormal FLV/FBW values were at significantly greater risk (P <.05) for PH development. Abnormal FLV/FBW values had higher diagnostic accuracy than abnormal US parameters. Sensitivity of the FLV/FBW was 89% (eight of nine fetuses); specificity, 88% (seven of eight fetuses); positive predictive value, 89% (eight of nine fetuses); negative predictive value, 88% (seven of eight fetuses); and accuracy, 88% (15 of 17 fetuses).

CONCLUSION

The FLV/FBW reflects the adequacy of intrauterine lung growth and can help predict PH.

Comparative biochemistry of gestational and postnatal lung growth and development in the rat and human

We compared the ontogeny of collagen (hydroxyproline), elastin (desmosine), soluble protein, and DNA in the lungs of rate and humans during gestation and postnatal life. In humans, lung weight/body weight ratios declined faster during gestation than postnatally, whereas in rats lung weight/body weight ratio declined little during gestation and then suddenly on the first day of life. Lung weight/body weight ratios may be lower than expected around term in humans, and prediction data are given to assess human pulmonary hypoplasia. Rats and humans differed in water content of their lungs, with rats showing a sharper decline during gestation. In the human lung, collagen and elastin made their appearance at an early stage of gestation; elastin. In particular, increased rapidly during gestation, suggesting a role in intrauterine alveolar formation. In the rat, elastin accumulation is primarily a postnatal event, as is alveolar formation. Hydroxyproline concentrations increased with conceptual age and continued to increase rapidly postnatally between 4 and 7 weeks in the rat, but slowed in the human after 60 weeks of conceptual age. Desmosine concentrations level off at the end of the study period in rats, while these are still increasing, although slowly, in humans. Overall lung growth, as assessed by weight, was linear in humans, but phases of lung growth were apparent in the rat, including one of minimal growth in the immediate postnatal period.

Biochemical, clinical, and morphologic studies on lungs of infants with bronchopulmonary dysplasia

We correlated clinical, biochemical, and morphologic findings in the lungs of 48 infants dying of either bronchopulmonary dysplasia (BPD) or hyaline membrane disease (HMD) to obtain a better idea of the disease process. The infants ranged from 24 weeks of gestation to 1 1/2 postnatal years. The lungs of BPD and HMD infants had higher contents of DNA, alkalisoluble protein, hydroxyproline, and desmosine, as well as increased concentrations of DNA, hydroxyproline, and desmosine when compared with the lungs of 72 control infants. BPD was classified histologically into 4 groups: Group I was a phase of acute lung injury, Group II the proliferative phase; Group III the phase of early repair, and Group IV the phase of late repair. We saw a significant increase in hydroxyproline concentration in Groups II and III. The ratio of type I/III collagen decreased in BPD Groups II to IV. Desmosine was significantly higher only in Group III than in controls. When the pathological classification was related to biochemical and clinical features of BPD, the classification showed dependence on the number of days the infant survived postnatally and not on the gestational age of the infant. The number of days on assisted ventilation was a slightly better predictor of the disease classification than days on > 60% oxygen. A statistical model correctly predicted the pathologic classification 83% of the time.

"Silent" patent ductus arteriosus and bronchopulmonary dysplasia in low-birthweight twins

During a screening protocol of early echocardiographic diagnosis (ATL MK 600) and treatment of "silent" PDA in RDS preterms with BW < or = 1.750 kg, clinical data on premature twins were collected, including diagnosis of both PDA and BPD, to investigate whether twin birth influences PDA incidence and BPD development. Out of the 290 RDS preterms evaluated, 96 (33%) showed evidence of PDA, and a total of 79 (27%) developed BPD, 47 (16%) with associated PDA and 32 (11%) without PDA. Out of 238 singletons, 74 (31%) presented "silent" PDA and a total of 75 (31%) developed BPD, 44 (18%) with associated PDA, and 31 (13%) without PDA. In 52 other twins (18% of the total number of babies studied), 22 (42% of this subgroup) presented evidence of "silent" PDA, and 4 (8% of the subgroup), developed BPD, 3 with associated PDA (6% of the subgroup), and 1 without PDA (2% of the subgroup). From these data, it is inferred that that low-birthweight twins are at high risk for PDA hemodynamic complications during RDS, and may benefit from early induced ductal closure. Instead, in RDS twins, BPD was statistically less frequent (at the 99% C.L.) probably because twinning enhances fetal lung maturity, influencing enzymatic and nonenzymatic protective systems of lung defence.

Mechanisms of phosphatidylcholine acyl remodeling by human fetal lung

The molecular specificity of phosphatidylcholine (PC) synthesis by the de novo pathway in postmortem samples of human fetal lung (15 to 20 wk of gestation) was determined from the incorporation pattern in isolated microsomal preparations of CDP:[14C]choline into individual molecular species of PC. These analyses are based on the assumption that the molecular species composition of the pool of endogenous diacylglycerol used for PC synthesis by isolated microsomes reflects that of the authentic pool of diacylglycerol converted to PC by intact cells. Comparison of this microsomal incorporation pattern of radiolabel into PC with tissue PC composition suggested that even at this early stage of gestation 50% of lung dipalmitoyl PC was derived from synthesis de novo, with the remainder coming from acyl remodeling mechanisms. Analysis of PC synthesis de novo by organ cultures of human fetal lung showed that these acyl remodeling mechanisms were lost in culture. Despite evidence for differentiation of type II alveolar epithelial cells in culture, equilibrium labeling of PC with [14C]choline over 18 h resulted in a progressive decline in fractional incorporation into dipalmitoyl PC with time in culture. By 4 days in culture, this value was no different from the fractional incorporation of CDP:[14C]choline into microsomal PC in vitro over 3 h. The pattern of PC synthesized was not altered when total PC synthesis was stimulated by exposure of cultures to dexamethasone and tri-iodothyronine but was readily manipulated by exposure to exogenous fatty acids. These results demonstrate for the first time the activity of PC acyl remodeling mechanisms in human fetal lung, well before the initiation of surfactant production.(ABSTRACT TRUNCATED AT 250 WORDS)

Biochemical and morphometric analyses in hypoplastic lungs

We report the results of biochemical and morphometric studies on lungs of infants with bilateral lung hypoplasia either with or without oligohydramnios (OH or NOH) in comparison with findings in normally grown lungs. The OH and NOH lungs were equally hypoplastic in terms of DNA content but OH lungs had a significantly lower disaturated phosphatidylcholine (DSPC) concentration than NOH or normal lungs, apart from a subgroup with gastrointestinal or airway obstruction. Hydroxyproline concentration in OH lungs was higher than that in NOH or normal lungs. Desmosine concentrations did not differ significantly between groups despite the obvious lack of elastin in the septal crests of the OH group on histology. Morphometry revealed low lung volume, low radial alveolar counts, low alveolar numbers, and low alveolar surface area in both OH and NOH groups. Alveoli and alveolar ducts constituted a higher proportion of lung volume in NOH than in OH lungs. The similarity of most morphometric indices in the two groups implies that maturation does not depend on quantitative elaboration of airways and alveoli. The finding of impaired epithelial maturation despite the high hydroxyproline concentration in the OH lungs suggests an abnormality in epithelial-mesenchymal interaction that is not present in the equally small lungs of the NOH group.

Surfactant-associated glycoproteins accumulate in alveolar cells and secretions during reparative stage of hyaline membrane disease

Surfactant-associated (SA) glycoproteins are lung-specific proteins produced in the human lung by alveolar type II cells and Clara cells. The distribution of these proteins was studied immunohistochemically in lung tissue obtained postmortem from 12 stillborn fetuses and 49 infants with hyaline membrane disease (HMD). By 21 weeks of gestation, SA glycoproteins were detected in the fetal alveolar epithelium and within Clara cells. The staining increased in intensity and extent with advancing gestational age. Infants with HMD who survived less than 48 hours did not generally exhibit stainable material either within type II cells or secretions, but staining was often noted in Clara cells as well as focally beneath hyaline membranes. In infants surviving more than 48 hours, intense staining of hyaline membranes, alveolar secretions, proliferating alveolar type II cells, and Clara cells was evident. Immunoreactivity was intense in hypertrophic type II cells that formed a continuous alveolar epithelial lining in lungs with bronchopulmonary dysplasia. Included in the population of infants with HMD were 15 infants with pulmonary hypoplasia. The lungs of these infants showed minimal staining for SA glycoproteins regardless of postnatal survival time. The results provide an immunomorphologic basis for defining normal and abnormal lung maturation. They also indicate that enhanced SA glycoprotein production is a sustained response of regenerating and hypertrophic type II cells in premature infants.

Assessment of elastin maturation by radioimmunoassay of desmosine in the developing human lung

Desmosine has been quantitated in the normally grown fetal and early infant lung by radioimmunoassay. Desmosine could first be detected at 22 weeks gestation: the concentration of desmosine expressed per milligram lung DNA increased in approximately linear form up to about 55 weeks postconceptional age. The concentration in peripheral lung was approximately half that in whole lung homogenates. Lungs of infants dying with acute HMD and lungs of growth retarded infants showed no significant differences from the normals, although there was a tendency for higher desmosine concentrations in prematurely born growth retarded infants.

Fetal lung growth in congenital laryngeal atresia

Morphometric and biochemical indexes of lung growth were measured in 2 cases of uncomplicated laryngeal atresia at 27 and 30 weeks gestation and in 1 case of cryptophthalmos syndrome with anomalies including laryngeal atresia and renal agenesis. Findings were compared with those in normally formed fetuses and newborn infants. The cases of pure laryngeal atresia showed a marked increase in surface area and lung volume for age, associated with an increase in alveolar number and apparent advance in elastin maturation, but little increase in cell population as measured by lung DNA content. Alveolar walls were thin but there was no increase in disaturated phosphatidylcholine (DSPC) content. Similar features were observed in the case of cryptophthalmos in marked contrast to the lung hypoplasia expected to result from renal agenesis. The results give further support to the importance of lung liquid retention for normal fetal lung growth. Overdistention with lung liquid appears to promote alveolar development by redistribution of cells rather than increase in cell population.