Morphometric study of the role of pulmonary arterial flow in fetal lung growth in sheep

Hemodynamic management of congenital diaphragmatic hernia: the role of targeted neonatal echocardiography

Congenital diaphragmatic hernia (CDH) is a major congenital anomaly, resulting from the herniation of abdominal contents into the thoracic cavity, thereby impeding the proper development of the lungs and pulmonary vasculature. CDH severity correlates with a spectrum of pulmonary hypoplasia, pulmonary hypertension (PHT), and cardiac dysfunction, constituting the pathophysiological triad of this complex condition. The accurate diagnosis and effective management of PHT and cardiac dysfunction is pivotal to optimizing patient outcomes. Targeted neonatal echocardiography is instrumental in delivering real-time data crucial for the bespoke, pathophysiology-targeted hemodynamic management of CDH-associated PHT.

Fetal pulmonary artery Doppler blood flow velocity measures and early infant lung function. A prospective cohort study

BACKGROUND

Reduced lung function at birth has evident antenatal origins and is associated with an increased risk of wheezing and asthma later in life. Little is known about whether blood flow in the fetal pulmonary artery, may impact postnatal lung function.

OBJECTIVE

Our primary aim was to investigate the potential associations between fetal Doppler blood flow velocity measures in the fetal branch pulmonary artery, and infant lung function by tidal flow-volume (TFV) loops at three months of age in a low-risk population. Our secondary aim was to explore the association between Doppler blood flow velocity measures in the umbilical and middle cerebral arteries, and the same lung function measures.

METHODS

In 256 non-selected pregnancies from the birth cohort study Preventing Atopic Dermatitis and ALLergies in Children (PreventADALL) we performed fetal ultrasound examination with Doppler blood flow velocity measurements at 30 gestational weeks (GW). We recorded the pulsatility index, peak systolic velocity, time-averaged maximum velocity, acceleration time/ejection time ratio, and time velocity integral primarily in the proximal pulmonary artery close to the pulmonary bifurcation. The pulsatility index was measured in the umbilical and middle cerebral arteries and the peak systolic velocity in the middle cerebral artery. The cerebro-placental ratio (ratio between pulsatility index in the middle cerebral and umbilical arteries) was calculated. Infant lung function was assessed using TFV loops in awake, calmly breathing three months old infants. The outcome was the time to peak tidal expiratory flow to expiratory time ratio (t_PTEF/t_E), t_PTEF/t_E <25^th percentile, and tidal volume per kg body weight (V_T/kg). Potential associations between fetal Doppler blood flow velocity measures and infant lung function were assessed using linear and logistic regressions.

RESULTS

The infants were born at median (min - max) 40.3 (35.6 - 42.4) GW, with a mean (SD) birth weight of 3.52 (0.46) kg, and 49.4% were females. The mean (SD) t_PTEF/t_E was 0.39 (0.1) and the 25^th percentile was 0.33. Neither univariable nor multivariable regression models revealed any associations between fetal pulmonary blood flow velocity measures and t_PTEF/t_E, t_PTEF/t_E <25^th percentile, or V_T/kg at three months of age. Similarly, we did not observe associations between Doppler blood flow velocity measures in the umbilical and middle cerebral arteries and infant lung function measures.

CONCLUSION

In a cohort of 256 infants from the general population, fetal third-trimester Doppler blood flow velocity measures in the branch pulmonary, umbilical, and middle cerebral arteries were not associated with infant lung function measures at three months of age.

Histologic identification of prominent intrapulmonary anastomotic vessels in severe congenital diaphragmatic hernia

OBJECTIVE

To determine whether prominent intrapulmonary anastomotic vessels (IPAVs) or bronchopulmonary "shunt" vessels can be identified in lungs from infants with fatal congenital diaphragmatic hernia (CDH).

STUDY DESIGN

We performed histology with immunostaining for CD31 (endothelium) and D2-40 (lymphatics), along with high-precision 3-dimensional (3D) reconstruction on lung tissue from 9 patients who died with CDH.

RESULTS

Each patient with CDH required mechanical ventilation, cardiotonic support, and pulmonary hypertension (PH)-targeted drug therapy. All patients were diagnosed with severe PH by echocardiography, and 5 received extracorporeal membrane oxygenation therapy. Death occurred at a median age of 24 days (range, 10-150 days) from refractory hypoxemia with severe PH, pneumonia, or tension pneumothorax. Histology showed decreased alveolarization with pulmonary vascular disease. In each patient, prominent IPAVs were identified as engorged, thin-walled vessels that connected pulmonary veins with microvessels surrounding pulmonary arteries and airways in lungs ipsilateral and contralateral to the CDH. Prominent anastomoses between pulmonary arteries and bronchial arteries were noted as well. The 3D reconstruction studies demonstrated that IPAVs connect pulmonary vasculature to systemic (bronchial) vessels both at the arterial and venous side.

CONCLUSION

Histology and 3D reconstruction identified prominent bronchopulmonary vascular anastamoses in the lungs of infants who died with severe CDH. We speculate that IPAVs connecting pulmonary and bronchial arteries contribute to refractory hypoxemia in severe CDH.

Histologic evidence of intrapulmonary anastomoses by three-dimensional reconstruction in severe bronchopulmonary dysplasia

RATIONALE

Bronchopulmonary dysplasia (BPD) is the chronic lung disease of infancy that occurs in premature infants after oxygen and ventilator therapy for acute respiratory disease at birth. Despite improvement in current therapies, the clinical course of infants with BPD is often characterized by marked hypoxemia that can become refractory to therapy. Preacinar anatomic and functional communications between systemic and pulmonary vascular systems has been established in fetal lungs, but whether increased intrapulmonary anastomotic vessels or their failure to regress after birth contributes to hypoxemia in preterm infants with BPD is unknown.

OBJECTIVES

We sought to find histologic evidence of intrapulmonary anastomotic vessels in lungs of patients who died of severe BPD.

METHODS

We collected lung tissues from fatal BPD cases and performed histology, immunohistochemistry, and high-precision three-dimensional reconstruction techniques.

MEASUREMENTS AND MAIN RESULTS

We report histologic evidence of intrapulmonary vessels that bridge pulmonary arteries and veins in the distal lungs of infants dying with severe BPD. These prominent vessels appear similar to "misaligned pulmonary veins" described in the lethal form of congenital lung disorder, alveolar capillary dysplasia.

CONCLUSIONS

We found striking histological evidence of precapillary arteriovenous anastomotic vessels in the lungs of infants with severe bronchopulmonary dysplasia. We propose that persistence or expansion of these vessels after premature birth provides the anatomic basis for intrapulmonary shunt and hypoxemia in neonates with severe bronchopulmonary dysplasia and may play a significant role in the morbidity and mortality of BPD.

Respiratory disorders in moderately preterm, late preterm, and early term infants

Even when it is just a few weeks before term gestation, early birth has consequences, resulting in higher morbidity and mortality. Respiratory issues related to moderate prematurity include delayed neonatal transition to air breathing, respiratory distress resulting from delayed fluid clearance (transient tachypnea of the newborn), surfactant deficiency (respiratory distress syndrome), and pulmonary hypertension. Management approaches emphasize appropriate respiratory support to facilitate respiratory transition and minimize iatrogenic injury. Studies are needed to determine the impact of respiratory distress coupled with mild-moderate prematurity on long-term outcome.

Lung remodeling in a porcine model of cyanotic congenital heart defect with decreased pulmonary blood flow

BACKGROUND

Hypoperfusion of the pulmonary vascular bed under the condition of congenital cardiac malformations may lead to progressive pulmonary vascular disease. To improve the mechanistic understanding of this disease, we examined the biochemical and morphological changes of the lung in a relevant animal model and provided valuable insights into the underlying mechanisms of the pathogenesis of pulmonary hypotension.

MATERIALS AND METHODS

A model of congenital heart defect with decreased pulmonary blood flow was implemented into 8 piglets (the cyanosis group). Another 8 piglets underwent a sham operation (the control group). Two months postoperatively, lung biopsy specimens were harvested for the measurement of the expression levels of MMP-2, MMP-9, TIMP-1, VEGF, and type I and type III collagens. Moreover, the light-microscopic morphology, morphometry, and ultrastructure of lobes were examined.

RESULTS

Compared to the controls, the histopathological changes of the pulmonary vasculature in the cyanosis group showed evident hypoplasia and degeneration. The expression levels of MMP-2, MMP-9, TIMP-1, VEGF, and type I collagen, as well as the microvessel density, in the cyanosis group were significantly lower than those in the control group, whereas the level of type III collagen in the cyanosis group was significantly higher than that in the control group.

CONCLUSIONS

The observed morphological changes may represent an adaptive reaction to the prolonged decrease of pulmonary blood flow. The underlying mechanism of lung remodeling may be attributed to the changes in the expression of structural proteins and cytokines in the pulmonary extracellular matrix induced by modulating factors.

Clinical implication of lung fluid balance in the perinatal period

At birth, lung fluid produced during fetal life must be cleared immediately and efficiently before the first breath takes place, in order for infants to achieve a normal and successful transition from prenatal to postnatal life. Postnatal lung fluid resorption is mediated through activation of airway epithelial sodium channels (ENaC). The observation that ENaC expression is a gestational age-dependent process contributes to our understanding of the development of respiratory distress in both term and preterm infants due to impaired clearing of fluid from their lungs. As fluid absorption, mediated by ENaC activity, in postnatal life has a significant biological role in preventing respiratory distress, any strategy that enhances ENaC activity can potentially help to decrease its incidence and associated morbidity.

Analysis of the harmonized growth pattern of fetal organs by multidimensional scaling and hierarchical clustering

The development of an organ may be affected by various growth and differentiation factors released from other organs. These factors are believed to have important effects on the development of multiple organs. To detect and analyze harmonized development among multiple organs, similarities in growth patterns among fetal organs were examined using multivariate analysis. Ninety human fetuses obtained from the Kyoto Collection of Human Embryos were dissected. Harmonized development of organs was evaluated by multidimensional scaling and cluster analysis using measurements (length, width, height, and weight) of the fetal organs. Similar growth patterns were observed between the brain, including cerebrum, diencephalon, and midbrain (cerebrum-to-midbrain [Cer-Mid]), and pituitary (crown-rump length [CRL] 95-155 mm). Further, similar growth patterns were observed between the liver and Cer-Mid and cerebellum (Cb; CRL 156-202 mm), and between Cer-Mid and Cb (CRL 203-253 mm). Similarities in growth patterns were also observed between right and left lungs (CRL 99-235 mm) and between the aorta and heart (CRL 139-187 mm), but not between the lung and pulmonary trunk. These findings revealed synchronized development among fetal organs and suggested a functional and structural relationship among different organs in the prenatal period. These relationships include the existence of common factors in organ development, such as cross-talk mediated by humoral factors, and the presence of an anatomical and functional relationship in the fetal circulatory system.

Vasoreactive response to maternal hyperoxygenation in the fetus with hypoplastic left heart syndrome

BACKGROUND

Cardiopulmonary interactions play an important role in the pathophysiology of hypoplastic left heart syndrome (HLHS). Pulmonary vasculopathy has been identified, especially in those with restrictive/intact atrial septum. Responsiveness of the pulmonary vasculature to maternal hyperoxygenation (MH) may provide a tool to assess the degree of pulmonary vasculopathy present before birth.

METHODS AND RESULTS

Doppler echocardiography was performed in 27 normal and 43 HLHS fetuses. In HLHS, sampling was repeated after 10 minutes of MH with 60% FiO(2) and after 5 minutes of recovery. Sampling was performed in the proximal, midportion, and distal branch pulmonary artery (PA). Pulsatility index (PI) was used as a measure of vascular impedance. Of the HLHS fetuses, 34 had an open interatrial septum and 9 had a restrictive/intact atrial septum. At birth, 5 fetuses underwent immediate intervention on the interatrial septum. Middle cerebral artery PI was lower in HLHS versus normal fetuses (P<0.001). There was no difference in UA, DA, or branch PA PI between normal fetuses and those with HLHS. MH led to a significant decrease in PI at each of the PA sites sampled in fetuses with an open atrial septum (P<0.001); however, there no was significant change in the PI in fetuses that required immediate intervention on the atrial septum at birth. Using a cutoff value of <10% vasoreactivity, the sensitivity of MH testing for determining need for immediate intervention at birth is 100% (0.46 to 1.0); specificity, 94% (0.78 to 0.99); positive predictive value, 71% (0.30 to 0.95); and negative predictive value, 100% (0.86 to 1.0). No untoward effects were seen with MH.

CONCLUSIONS

PA vasoreactivity to MH occurs in the fetus with HLHS. MH testing accurately identifies fetuses requiring urgent postnatal intervention at birth and may be used to select candidates for fetal atrial septoplasty.

Current concepts in fetal cardiovascular disease

This article discusses the unique properties of the fetal cardiovascular system and patterns of blood flow in congenital heart disease. It also explores the complex interactive dependency between the developing heart and pulmonary vasculature, with particular attention to hypoplastic left heart syndrome. The article goes on to highlight some recent advances in the understanding of fetal cardiovascular medicine, specifically the possibilities and prognosis for fetal cardiac interventions. An understanding of the enigmatic process of twin-twin transfusion syndrome may help in elucidating one of the mechanisms for development of cardiac structural abnormalities in the fetus.

Hypoplasia of the Small Pulmonary Arteries in Hypoplastic Left Heart Syndrome With Restrictive Atrial Septal Defect

BACKGROUND

Restrictive atrial septal defect (ASD) (including intact atrial septum [IAS]) has been reported to be a risk factor that negatively impacts survival in hypoplastic left heart syndrome (HLHS). Although lymphangiectasia and "arterialization" of the veins of the lung in HLHS with restrictive ASD have been reported, they cannot fully explain the high mortality. We have introduced a new method of evaluating the development of the pulmonary vasculature in histological sections and used it to assess patients' lungs. We tested the hypothesis that the small pulmonary arteries (SPA), which are pulmonary arteries in a histological section whose radii are approximately 25 microm to 250 microm, in HLHS with restrictive ASD are hypoplastic, but that the alveoli are not, to elucidate the mechanism underlying the poor outcome of these patients.

METHODS AND RESULTS

Fourteen HLHS patients between 1 day and 40 days of age were studied. In 8 cases, the ASD was restrictive [R(+) group], and in the other 6 cases it was not [R(-) group]. Specimens from 12 autopsies of cases with no congenital heart or pulmonary disease were examined as a control group (C group). As a novel histological parameter, we assessed the size of SPA in relation to the size of accompanying bronchioles to identify SPA underdevelopment. To evaluate the development of alveoli and interstitial tissue, radial alveolar counts (RAC), which reflect alveolar maturity and complexity, were also performed. Statistical comparisons between groups were made by analysis of covariance with age as a covariant factor. When the radius of the accompanying bronchiole was 100 microm, the radius of the SPA was 34.0+/-10.8 microm in the R(+) group, and significantly lower than the 46.6+/-8.5 microm in R(-) group (P=0.0022) and 70.5+/-8.4 microm in the C group (P<0.0001). The RAC was in 3.5+/-0.9 in the R(+) group, 3.4+/-0.6 in the R(-) group, and 3.7+/-0.9 in the C group (no significant differences between groups).

CONCLUSIONS

The SPA in HLHS with restrictive ASD were underdeveloped compared with the SPA in HLHS with nonrestrictive ASD and the controls, but their alveoli were not hypoplastic. Based on these results, it is speculated that SPA hypoplasia may be responsible for the poor outcome of HLHS with restrictive ASD.

[An update on the fetal circulation]

The fetal circulation has been an exciting area of study for centuries. The principles which grew from the period of hypotheses have been demonstrated in several animal models. These experiments have shaped the major concept of fetal circulation. More recently, the improvement in ultrasound technology has allowed a non invasive study of the fetal circulation in humans. Although the general schema of the fetal circulation has been confirmed in humans, in some aspects some substantial differences have been demonstrated. They may not only reflect some inter-species differences, but also underscore the limitation of chronically instrumented animal studies.

Induction of pulmonary angiogenesis by adenoviral-mediated gene transfer of vascular endothelial growth factor

BACKGROUND

We hypothesized that gene transfer of vascular endothelial growth factor (VEGF) mediated by an adenovirus vector might induce pulmonary artery angiogenesis in a lamb model of pulmonary artery hypoplasia.

METHODS

Thirteen fetal lambs had left pulmonary artery banding at 106 days of gestation. Following birth, 3 groups were divided: VEGF group (n = 5) and beta-GAL group (n = 4) received an adenoviral vector encoding respectively for human VEGF165 and for galactosidase A. A control group (n = 4) had neither gene nor virus. Viral suspensions were selectively instilled in the left bronchus 6.5 days after birth. Five nonoperated lambs constituted the normal group. Euthanasia was performed at 30 days of age. Gene transfer was confirmed by blue coloration of left lung obtained with Xgal solution in an additional experiment. Histomorphometric evaluation was performed. All groups were compared with ANOVA test and paired test was used to compare right and left lung in each animal.

RESULTS

Left lung was similarly hypoplastic in all operated lambs. Left pulmonary artery hypoplasia present in all operated groups was significantly less pronounced in VEGF group. The number of pleural arteries was similarly increased in left lung of all operated lambs. Left lung arterial density was higher in VEGF group than in all other groups. The percentage of parenchyma of left lung was lower in beta-GAL group than in all others, partially returned to normal in VEGF group.

CONCLUSIONS

In this model, transbronchial VEGF gene transfer induces pulmonary angiogenesis, proximal pulmonary artery growth and contributes to lung parenchyma recovery.

Hypoplasia of the small pulmonary arteries in total anomalous pulmonary venous connection with obstructed pulmonary venous drainage

OBJECTIVE

Preoperative pulmonary venous obstruction has been reported to be a risk factor negatively impacting survival in total anomalous pulmonary venous connection. We examined lung tissue from total anomalous pulmonary venous connection patients with pulmonary venous obstruction and demonstrated hypoplasia of small pulmonary arteries to elucidate the mechanism underlying the poor outcome.

METHODS

Ten total anomalous pulmonary venous connection patients with preoperative pulmonary venous obstruction between the ages of 2 days and 10 months were studied. As histological parameters, we assessed the size of small pulmonary arteries in relation to the size of accompanying bronchioles to identify small pulmonary artery underdevelopment. Other parameters, such as the radial alveolar count, which reflects alveolar maturity, intimal lesions, lymphangiectasia, and the medial thickness of small pulmonary arteries and small pulmonary veins, were also examined. As a control group, we examined 24 autopsy cases with no congenital heart or pulmonary disease.

RESULTS

When the radius of the accompanying bronchiole was 100 microm, the radius of small pulmonary artery in the control group was found to enlarge for the first 2 months and then remain stable at approximately 80 microm from 2 to 10 months. In total anomalous pulmonary venous connection with preoperative pulmonary venous obstruction, the radius was significantly lower than in the control (47.0 +/- 21.8 microm versus 75.9 +/- 9.8 microm, P <.001), and the difference between dead and surviving patients was significant at P <.001 (33.0 +/- 14.6 microm versus 68.2 +/- 9.2 microm). Examination of the alveoli yielded an radial alveolar count of 4.6 +/- 1.5 in the control group and 4.4 +/- 0.8 in the total anomalous pulmonary venous connection patients, and the difference was not significant (P =.71).

CONCLUSIONS

The small pulmonary arteries of total anomalous pulmonary venous connection patients with preoperative pulmonary venous obstruction were underdeveloped compared with controls but their alveolae were not hypoplastic. These results suggested that the small pulmonary artery hypoplasia may be responsible for the poor outcome of these patients.

The fetal lung. 1: Developmental aspects

A literature survey is presented on normal fetal development during the embryonic, pseudoglandular, canalicular, saccular and alveolar stages in the human fetus. Normal anatomical and physiological aspects of fetal lung development including the fetal pulmonary circulation are described. Factors which may influence fetal lung growth and consequently may play a role in the development of pulmonary hypoplasia are discussed, such as intrauterine and intrathoracic space, lung fluid, fetal breathing movements, normal balance of volume and pressure in the lung and interference with the blood supply.

Cardiac malposition, redistribution of fetal cardiac output, and left heart hypoplasia reduce survival in neonates with congenital diaphragmatic hernia requiring extracorporeal membrane oxygenation

OBJECTIVE

To evaluate cardiac position, left ventricular (LV) mass, and distribution of fetal cardiac output in infants with congenital diaphragmatic hernia (CDH) who required extracorporeal membrane oxygenation (ECMO), and in control subjects.

STUDY DESIGN

Echocardiograms were performed on 23 neonates with CDH shortly after birth, and repeated within 5 days of repair on ECMO in 21 infants,aand on 12 infants receiving ECMO for other diagnoses, and on 10 healthy, term neonates. Cardiac angle between the midline saggital plane and the interventriculak septum was measured, and deviation from normal (45 degrees) was determined. The ratio of cross-sectional areas (proportional to flows) across the pulmonary (PV) and aortic (AV) valves was determined (PV2/AV2) in 19 infants with CDH and in the healthy control subjects.

RESULTS

Thirteen (57%) infants with CDH survived and 10 (43%) died, with no difference in cardiac deviation before surgical repair (35 +/- 13 degrees vs Cardiac deviation persisted after repair in nonsurvivors (27 +/- 14 degrees vs 800.01 and LV mass was significantly less (1.68 +/- 0.39 vs 3.05 +/- 1.20 gm/kg, p00.0005). Neonates requiring ECMO for other diagnoses and well term babies did not have cardiac angle deviations; both these groups had a greater LV mass than did the infants with CDH. The PV2/AV2 flow ratios were higher in infants with CDH (median, 1.73; range, 1.25 to 16.50) compared with those of the healthy infants (0.96, 0.79 to 1.69, p < 0.0002).

CONCLUSIONS

Cardiac malposition persisted despite CDH repair in nonsurvivors with low LV mass, and fetal cardiac output was redistributed away from the left ventricle. Lung hypoplasia with reduced pulmonary flow returning to the left atrium and altered left atrial hemodynamics may result in LV hypoplasia

Developmental changes in water permeability across the alveolar barrier in perinatal rabbit lung

Lung fluid is reabsorbed rapidly at birth to permit alveolar respiration. We reported previously that expression of aquaporins (AQP) 1, 4, and 5 in rat lung increased just after birth. The hypothesis was tested that the increased AQP expression is associated with increased osmotic water permeability (Pf) between the airspace and capillary compartments. Pf was measured in isolated perfused fetal and newborn rabbit lungs using a pleural surface fluorescence method (Carter, E.P., M.A. Matthay, J. Farinas, and A.S. Verkman. 1996. J. Gen. Physiol. 108:133-142). In response to perfusate osmolality increase from 300 to 600 mosM, initial rates of osmotic equilibration were 1.13+/-0.13 mosM/s at 0-12 h after birth, increasing to 1.52+/-0.19 mosM/s at 12-24 h, and 1.83+/-0.10 mosM/s at 24-84 h. Corresponding Pf values (in cm/s x 10(-2)), computed from d[mosM]/dt and alveolar surface-to-volume ratios, were 1.03+/-0.11 (0-12 h), 1.51+/-0.16 (12-24 h), and 1.88+/-0.09 (24-84 h). Pf was relatively low in prenatal (1.22-1.27, fetal days 29 and 31) and adolescent (1.25+/-0.08, 21-d) rabbit lungs. To test for involvement of molecular water channels, measurements were made of Arrhenius activation energy (Ea), mercurial inhibition, diffusional water permeability (Pd), and AQP expression. Temperature-dependence measurements showed a 25% decrease in Ea for Pf in lungs < 1 d vs. 4 d. Pf was decreased 30% by 0.5 mM HgCl2 in < 1-d lungs and 44% in 4-d lungs. Pd was 1.0 x 10(-)5 cm/s and did not change when Pf was increased by 75%. RNase protection assay showed increased transcript expression in the first 24 h after birth for rabbit isoforms of AQP1 and AQP4. These results provide the first functional data on water permeability in perinatal lung. The increased water permeability after birth may facilitate the maintenance of dry alveoli.

Pulmonary vascular abnormalities in experimentally induced congenital diaphragmatic hernia in rats

In infants with congenital diaphragmatic hernia (CDH), abnormalities of the pulmonary arteries are present consisting of increased medial wall thickness and decreased external diameter. This forms the morphological substrate for persistent pulmonary hypertension, one of the leading causes of the high mortality in these patients. To elucidate the significance of these abnormalities, experimental models are required that mimic as close as possible the human situation. In our rat model we are able to study the hypoplastic CDH lungs extensively. In this study we performed a histological evaluation of the pulmonary arterial bed in the control group and the nitrofen-treated group in which the latter was divided into two subgroups, CDH and normal diaphragm. We examined the newborn rats after perfusion of the pulmonary arteries with barium gelatine and subsequent fixation. At the level of the respiratory bronchioles significant differences in the vessels were found consisting of decreased external diameter and increased wall thickness as percentage of the external thickness in CDH lungs compared with controls. Abnormal muscularization of the peripheral branches of the CDH pulmonary arteries was also found. We concluded that the rat model strongly resembles the human situation concerning the arterial bed in the lungs.

Development of alveolar septa and cellular maturation within the perinatal lung

To quantitate fetal lung cellularity and regional variation in alveolar maturation, guinea pig lungs were studied at 55, 60, and 65 d of gestation or within 2 h of birth (term = 68 d), and the data were analyzed for intralobar, interlobar, and age-group differences. Nine blocks from each left cranial and caudal lobe were all measured for volume, numerical, and surface densities in tissue (Vv(i,t), Nv(i,t), and Sv(i,t], and total volumes, numbers, and surface areas per lung (V, N, and S) of type I and type II epithelia, presumptive progenitor epithelium (cuboidal cells lacking lamellar bodies [LB]), interstitium, and endothelium. Total fixed lung volume, VL, increased 3-fold from day 55 through birth. At each age, there were no consistent intralobar or interlobar differences in Vv(i,t), Nv(i,t), or Sv(i,t) for any cell type. Within a septal tissue volume of 580 to 670 microliters at all ages, the N and V of type I cells did not vary with age, although their S increased from 1,240 cm2 at day 55 to 3,967 cm2 at birth. The N of morphologic type II cells per lung increased 7-fold from day 55 to day 60 and was constant thereafter, while the N of cuboidal cells decreased proportionally; type II cells contained only 4.8% (vol/vol) of LB at 55 d compared to 18.0% at birth. The N and V of interstitium did not vary by age. While endothelial V was constant over these ages, endothelial S increased from 897 cm2 to 3,398 cm2, and the V of capillary blood and the V of alveolar airspace each increased 4-fold.(ABSTRACT TRUNCATED AT 250 WORDS)