Total Alveolar Surface Area Research Articles

Quantitation of lung elastin and collagen in protein and essential fatty acid malnourished rats.

Thirty-nine 40-day old male Sprague-Dawley rats (average wt. 115g) were divided into 4 groups and fed diets A, control; B, essential fatty acid (EFA) deficient; C, protein deficient; D, combined protein and EFA deficient. At the end of 5 weeks, lungs were removed from the animals for collagen and elastin quantitation and for morphometric measurements. The collagen content of the lungs which ranged from 95-100 micrograms/mg dried fat-free (D.F.F.) tissue, was not altered by protein or EFA deficiencies. The elastin content of lungs was markedly increased in diets C and D while the cross-linking (Isodesmosine-desmosine content) expressed as residues per 1,000 (R/1000) was not different in the four groups. The elastin content of lungs from group D animals was greater than group C suggesting an additive effect from the EFA deficiency in diet D. The morphometric measurements indicated no change in alveolar linear diameter (Lm) while the total alveolar surface area (ISAA1V) was decreased by the deficient diets C and D. The protein deficiency and the combined protein and EFA deficiencies produced an increased elastin content in lung. Elastin cross-linking and collagen quantity was not affected by the dietary treatments. The morphometric measurements indicated that protein deficiency in these animals did not produce structural changes in the lungs as indicated by alveolar dimensions.

Morphometric and ultrastructural study of postnatal lung growth and development in calves

Summary The objectives of this study were to characterize basic patterns of postnatal lung growth in 1- to 150-day-old Holstein calves and to identify periods of accelerated lung growth and times of epithelial cell development that might correlate with periods of heightened susceptibility to pulmonary injury by infective agents and dietary toxins. Calves had fully developed alveoli at birth. There was an age-associated increase in total alveolar surface area and alveolar number, which was most marked in calves older than 30 days. Lung volume and body weight increases were also most marked when calves were older than 30 days. Mean bronchiolar cross-sectional area increased significantly (P < 0.05) with age, and there was a significant (P < 0.05) decrease in the percentage of terminal bronchioles with diameters < 3 × 104 μm between 1 and 150 days. In newborn calves, nonciliated bronchiolar epithelial cells retained fetal characteristics of differentiation, including abundant cytoplasmic glycogen and sparse agranular endoplasmic reticulum. Glycogen deposits were depleted, and agranular endoplasmic reticulum was developed in nonciliated cells by the time calves were 30 days old. We concluded that bronchiolar epithelium in calves is well differentiated by the time they are 30 days old and that lung growth in calves raised in semi-isolation begins most rapidly when calves are approximately 30 days old.

Hypophysectomy and Porcine Fetal Lung Development

The effect of hypophysectomy on the development of the lung parenchyma and maturation of pulmonary alveolar type II cells was examined in the fetal pig. In fetuses from four different gilts, hypophysectomy was performed on gestational day 69 or 70. Littermates from the same gilts served as controls. Fetuses were delivered by caesarean section at term (113 +/- 1 days of gestation), and the lungs were fixed by intratracheal instillation. Plasma cortisol and thyroxine concentrations in the umbilical artery were markedly lower for hypophysectomized fetuses compared with control fetuses. Body weight was similar for both groups of fetuses. Total lung volume was 53% smaller in hypophysectomized fetuses compared with control fetuses. However, alveolar septal tissue and capillary luminal volumes were similar in both groups. Total lung alveolar surface area was twice as great in control animals compared with hypophysectomized animals. The volumes of epithelium, interstitium, and endothelium of centriacinar alveolar septa per unit surface area of epithelial basal lamina were 3.7, 4.8, and 2.4 times greater in hypophysectomized fetuses compared with control fetuses. Alveolar type II cell composition also differed significantly between groups. The volume fraction of glycogen in type II cells was 51% for hypophysectomized fetuses and 12% for control fetuses, while lamellar body volume fraction was 8% in hypophysectomized fetuses and 23% in control fetuses. The frequency of alveolar type II cell contact with mesenchymal interstitial cells via foot processes was 5 times greater in the lungs of control animals compared with hypophysectomized animals. These findings demonstrate significant effects of hypophysectomy on the morphogenetic and cytodifferentiation activities of all major tissue compartments of the pulmonary gas exchange area during the final trimester of fetal development.

Pulmonary Development in the Fetal Lamb with Severe Bladder Outlet Obstruction and Oligohydramnios: A Morphometric Study

The lethal feature of male newborns with severe bladder outlet obstruction and oligohydramnios is pulmonary hypoplasia. We report a fetal lamb model of bladder outlet obstruction created in the early second trimester, and morphometric analysis of the profound pulmonary hypoplasia that resulted. At 55 to 65 days of gestation 8 consecutive male fetuses underwent surgical clipping of the urethra and urachus near the abdominal wall. A sham operation was performed in 1 female fetus. The lambs were delivered by cesarean section 10 weeks later. The right lungs were immediately fixed at a distending pressure of 25cm. water. The results of the morphometric studies were compared to control animals from our earlier study of normal fetal lamb lung development; slides for both studies were scored in a blind, randomized fashion by 1 of us (S. G. D.). Although mean body weights for the groups were similar, mean right lung volume in the operated lambs was 63.8cM.3 compared to 158cM.3 in the control animals and 137cM.3 in the sham operated fetus (p less than 0.0005). Relative volume of respiratory tissue was 87 per cent in the operated animals, and 92 per cent in the controls and the sham operated fetus (p less than 0.0005). Microscopic morphometry revealed an increased relative volume of inter-alveolar tissue in the experimental animals (35 compared to 23 per cent in the normal lambs, p less than 0.05), with a corresponding decrease in relative airspace volume. Alveolar numerical density and alveolar surface density were not statistically different between the groups, although total alveolar number and surface area were substantially decreased in the operated lambs due to the reduced mean lung volume. Mean alveolar wall thickness was increased at 3.6μM. in the operated group versus 2.1μM. in the normal group (p less than 0.0005) and 2.8μM. in the sham operated fetus. Thus, the lung in the lamb with severe bladder outlet obstruction is hypoplastic and immature.

Alveolar enlargement in obesity-induced hyperplastic lung growth.

Structural changes underlying obesity-induced pulmonary cellular hyperplasia were evaluated by lung morphometry and stereology in 8-wk-old male Long-Evans rats made obese by nursing in small litters with subsequent feeding of a high-fat diet. Control animals were raised in normal-sized litters and then fed standard rat chow. Compared with controls, obese rats had significant elevations in body weight (31%), fat pad weight (158%), fat pad weight-to-body weight ratio (97%), snout-to-anus length (8%), snout-to-tail length (7%), serum insulin concentration (64%), fixed lung volume (56%), and the ratios of lung volume to body weight (18%) and lung volume to body length3 (24%). Lungs of obese rats had enlarged alveoli, with significant increases in mean (182%) and total (71%) alveolar volume, mean chord length (28%), and mean (89%) and total (25%) alveolar surface area. Surface density (24%), surface-to-volume2/3 ratio (24%), and numerical density (43-53%) of alveoli in obese rats were significantly diminished compared with lungs of control rats. Unchanged were total alveolar number and alveolar volume density. Measurements of perihilar and subpleural alveoli within the obese and control groups were indistinguishable. These results indicate the presence of alveolar enlargement with relatively diminished respiratory surface area in lungs of young rats made obese by diet. This relative decrease in gas-exchanging area may contribute to physiological and functional alterations present in obesity.

An emphysema model in rats treated intratracheally with elastase

Pulmonary functions, morphology, and morphometry were examined in rats at 3, 7, and 10 weeks after a single intratracheal administration of 6.5 units of porcine pancreatic elastase in order to obtain a model of pulmonary emphysema which would be suitable for studying the responses of emphysematous lungs to atmospheric pollutants. Functional residual capacity and residual volume of the elastase-treated rats increased at all the times studied, but their total lung capacity increased only at 7 and 10 weeks compared with those of the saline-treated control rats. The increase in static lung compliance and the decrease in peak flow and maximum flow at 50% of total lung capacity during forced expiration were also observed in all except the 3-week elastase animals. The elastase-treated lungs showed morphological changes characteristic of emphysematous lesions. The increase in mean linear intercept length and the decrease in total alveolar surface area were demonstrated by these elastase-treated lungs. Based on these results, we conclude that an adequate and suitable model of pulmonary emphysema could be obtained in rats 7-10 weeks after treatment with the present dose of elastase.

The effects of intrauterine pneumonectomy in lambs. A morphometric study of the remaining lung at term.

A morphometric study was made of the remaining lung of term lambs that had undergone left pneumonectomy at 60, 80, 100, or 120 days gestation. All pneumonectomy lambs showed some compensatory growth since right lung volume to body weight ratio was higher in all lambs after pneumonectomy than in term controls. In 3 lambs operated at 80, 100, and 120 days, respectively, however, compensatory volume increase was more complete than in the other lamb of each age pair or the 2 lambs operated at 60 days. Despite individual variation, the potential for compensatory lung growth seems greater in the canalicular and later stages than in the pseudoglandular. Measurements indicating distal air-space size (volume density of alveoli, volume density of alveolar duct, surface density of alveolar epithelium, numerical density of alveoli, and mean linear intercept) were similar in all animals, but total alveolar surface area and number increased proportionally to lung volume. The fact that the remaining lung compensates by increasing alveolar number rather than by enlarging air spaces is a model of human developmental abnormalities in which the alveolar number at birth is greater than normal (polyalveolar). At the intraacinar level, a higher than normal proportion of muscularized arteries was found in lambs operated early in gestation and in lambs with smaller compensatory lung growth: an inverse relationship was seen--the lower the lung volume the higher the proportion of muscular arteries. The cause for this is unknown, but may result from the relatively increased flow to a vascular bed smaller than that of two normal lungs.

Human fetal lung changes associated with maternal smoking during pregnancy.

Pulmonary impairment in the offspring of smoking mothers is well documented by epidemiologic studies. The morphologic bases for the functional impairment are largely unexplored. We studied 17 infant lungs obtained at autopsy, ten from smoking (group 1) and seven from nonsmoking (group 2) mothers, by light (LM), transmission (TEM), and scanning electron microscopy (SEM). By LM, the alveolar mean linear intercept was similar in both groups; the total lung volume and alveolar surface area increased with the increase in gestational age in all lungs studied. By SEM, the sizes of the neuroepithelial bodies (NEB) were larger in group 1 than in group 2. By SEM and TEM, ciliated cells were increased, but the amount of dense core granules was decreased, in the NEB of the smoking group. Maternal smoking during pregnancy appears to alter the size and cellular composition of fetal NEB. The detailed mechanisms of the alteration in NEB and their implications are unclear from this study and needed further clarification.

The influence of lung volume on gas transfer in scoliosis

Single-breath carbon monoxide transfer factor (DL co) and diffusion coefficient (K co) have been compared with vital capacity and total lung capacity in 119 subjects with scoliosis, 74 with idiopathic scoliosis, 32 with congenital osteogenic scoliosis and 13 with paralytic scoliosis. In each group mean values of DL co were below, and for K co above, predicted values. Furthermore, in each group, DL co was correlated with lung volume and K co inversely correlated with lung volume. The reduction in DL co is probably due to the reduction in the total alveolar surface area and the increased values for K co probably result from an increase in pulmonary capillary blood volume per unit alveolar volume at low lung volumes.

SOLUTE PERMEABILITY OF THE ALVEOLAR EPITHELIUM

Investigations were made of the permeability of the in vivo mammalian alveolar epithelium to determine if restriction of solute diffusion could explain the ability of the alveolar lining cells to maintain the separation of the gas phase of the alveolus from the liquid phase of interstitial and vascular spaces of the lung. Using a split lung preparation, trace amounts of non-electrolyte, lipid insoluble solutes dissolved in normal saline were infused into one lung which was then inflated. Transfer out of the alveolar space was determined by serial samplings of the alveolar liquid and transfer constants were calculated from the change in concentration of each substance with time. The rates of transfer of the various sized substances were analyzed in terms of pore theory to determine an equivalent pore radius for the alveolar epithelium. Individual animals had an equivalent pore radius across the alveolar barrier of 20-40 A with an average of 26 A. The total area of the solute movement was estimated to be only 2×10−8th of the total alveolar surface area, pointing to the intercellular junctions as the anatomic site. Pores of this size impose virtually complete restriction to protein movement, significantly restrict NaCl diffusion, and produce an osmotic gradient favoring free water absorption from the alveolus.

THE EFFECT OF HYPERVENTILATION ON THE SIZE AND SHAPE OF ALVEOLI

SUMMARY Four groups of living anaesthetized guineapigs were artificially hyperventilated for 2 breaths, 5 min, 10 min or 15 min, with a constant negative and positive pressure cycle, and rapidly frozen at the instant of cessation of ventilation at a preselected point on the respiratory cycle. The dimensions of alveoli and alveolar ducts were measured by histological morphometric methods and related to the degree of lung inflation at the instant of freezing. Hyperventilation reduced the alveolar volume fraction, the total alveolar volume and the total alveolar surface area, but did not alter the alveolar duct volume fraction or the total alveolar duct volume. The reduction in the size of alveoli was related to the duration of hyperventilation, being maximal during the first 5 minutes. The alveolar surface-to-volume ratio tended to be reduced following hyperventilation. The possible functional significance of these findings is discussed with particular reference to the actions of pulmonary surfactant.

THE EFFECT OF HYPERVENTILATION ON THE SIZE AND SHAPE OF ALVEOLI

SUMMARY Four groups of living anaesthetized guineapigs were artificially hyperventilated for 2 breaths, 5 min, 10 min or 15 min, with a constant negative and positive pressure cycle, and rapidly frozen at the instant of cessation of ventilation at a preselected point on the respiratory cycle. The dimensions of alveoli and alveolar ducts were measured by histological morphometric methods and related to the degree of lung inflation at the instant of freezing. Hyperventilation reduced the alveolar volume fraction, the total alveolar volume and the total alveolar surface area, but did not alter the alveolar duct volume fraction or the total alveolar duct volume. The reduction in the size of alveoli was related to the duration of hyperventilation, being maximal during the first 5 minutes. The alveolar surface-to-volume ratio tended to be reduced following hyperventilation. The possible functional significance of these findings is discussed with particular reference to the actions of pulmonary surfactant.

The effect of changes in lung volume on the size and shape of alveoli.

1. A technique is described by which living anaesthetized guinea-pigs were artificially ventilated with a positive and negative pressure cycle, and rapidly frozen at the instant of cessation of ventilation at a preselected point on the respiratory cycle.2. The dimensions of alveoli and alveolar ducts were measured by histological morphometric methods, and related to the degree of lung inflation at the instant of freezing.3. The alveolar volume fraction increased from 0.52 at low lung volumes, up to 0.62 at lung volumes in the mid-inflation range, then decreased to 0.51 at high lung volumes. The alveolar duct volumetric fraction remained constant at all lung volumes.4. The total volume of alveoli increased linearly with increase in lung volume. The total alveolar duct volume increased little until the lungs were 40% inflated, above which it increased steeply.5. The total number of alveoli was linearly related to the body weight.6. The total alveolar surface area increased steeply between lungs of low lung volume and those which were up to 50% inflated, above which the increase levelled off. The absolute values of total alveolar surface depended on the body weight as well as the degree of lung inflation.7. The mean alveolar duct diameter was 40% greater, and the mean alveolar mouth diameter 35% greater in lungs which were fully inflated than in lungs which were nearly collapsed. The average geometrical shape of alveoli was not related to the degree of lung inflation.8. The harmonic mean thickness of the air-blood barrier was 33% less in lungs which were fully inflated than in lungs which were nearly collapsed. The alveolar surface membrane was smooth whether the lungs were fully inflated or collapsed.

Mammary Gland Growth and the Initiation of Lactation in Dairy Goats

Summary The efficacy of estradiol, oxytocin, and bovine somatotrophin to initiate lactation in goats with artificially induced mammary gland growth was tested. In a second experiment, the amount of mammary gland growth resulting from the oral administration of diethylstilbestrol (DES) and 6-methyl-17 acetoprogesterone (MAP) was determined. In the first experiment, the milk production of goats previously treated for 120 days with estradiol and progesterone was not increased by the injections of either estradiol, oxytocin, or bovine somatotrophin. In the second experiment, no marked milk secretion occurred in goats fed DES or MAP for 150 days until a dose of 1.0 mg estradiol had been injected daily for a 7-day period. The oral administration of DES or MAP alone, or a combination of the two, resulted in some mammary gland growth and milk production, but the production was much lower than that resulting from pregnancy. The combination of both compounds was no more effective than either one alone. The feeding of MAP to goats for the last 60 days of pregnancy resulted in higher levels of milk production for the first 4 wk of lactation, but the difference was not statistically significant (P > 0.10). Thereafter, the milk production was approximately equal in the treated and the normal pregnant groups. The correlation between previous milk production and total alveolar surface area was 0.935.

Histological Changes During Involution of the Mammary Glands of Ovariectomized and Intact Lactating Goats

Summary Udders were removed from intact and ovariectomized lactating goats at various times after parturition, to determine the histological changes occurring during involution and the effect of ovariectomy on involution. It was found that ovariectomy and sham ovariectomy caused a drop in milk production, but that ovariectomy did not retard involution after the animals recovered from the operation. The total alveolar surface area decreased in proportion to the milk production. The correlation coefficient between previous 4-wk milk production and total alveolar surface area was high. The decrease in the alveolar surface area is probably the most important cause of the decline in milk production. No histological abnormalities or other histological differences were observed between groups or times of udder removal. No increase in connective tissue was found during the involution process.

Effect of Somatotrophin and Oxytocin on the Mammary Gland Development of Goats Treated with Estrogen and Progesterone

Summary Neither the addition of somatotrophin nor oxytocin to estradiol and progesterone injections caused an increase in the udder alveolar surface area or milk production of virgin yearling goats as compared to estradiol and progesterone alone. The total alveolar surface area and milk production resulting from any combination of hormones used for inducing mammary gland growth was less than half of that of the goats whose udders were developed through pregnancy. All hormone-treated groups showed a deficiency of total alveolar surface area. The correlation of previous 4-wk. milk production and total alveolar surface area was 0.947. Goats injected with growth hormone started out at a higher level of milk production than the two other hormonally induced groups. No histological abnormalities were observed in the hormone-treated groups.