Biomedical subjects

R R Mercer

Publications and source records attributed to R R Mercer.

At least 19 recordsLinked to original sources

PubMed1992

Structural changes in elastic fibers after pancreatic elastase administration in hamsters.

Ultrastructural changes in lung parenchymal elastic fibers were studied morphometrically 1, 4, and 12 wk after a single 12-unit dose of pancreatic elastase and in a saline-instilled control group. The mean linear intercept of the parenchymal air spaces was increased in the 1-, 4-, and 12-wk post-elastase instillation groups compared with age-matched controls. The volume of alveolar connective tissue fibers predominantly composed of elastin (elastic fibers) was decreased by 35% 1 wk after the instillation of elastase but returned to control levels by 4 wk. Although the total volume of elastic fibers was normal 12 wk after instillation of elastase, the volume of elastic fibers in alveolar entrance rings remained significantly reduced. In serial sections of elastic fibers, numerous gaps or separations in the normally continuous band of elastic fibers that encircle each alveolus were identified 1 wk after elastase instillation. There were 169 +/- 8 (SE), 62 +/- 32, and 12 +/- 6 gaps per millimeter of alveolar entrance ring circumference at 1, 4, and 12 wk, respectively, in the elastase-treated groups. The number of gaps at 12 wk was equivalent to two gaps or discontinuities in the elastic fibers of every alveolar entrance ring. No gaps or separations in elastic fibers were detected at 1, 4, or 12 wk in the control groups. These defects occur in concordance with the progression of air space enlargement and presumably contribute to the progression of air space enlargement that occurs after the elastin content of the tissue has returned to normal.

Animals↗

PubMed1992

Distribution of injury and microdosimetry of ozone in the ventilatory unit of the rat.

The distribution of ozone-induced injury across ventilatory units of the lungs was determined and compared with the predicted distribution of ozone dose across the same units to evaluate dose-response relationships. Sprague-Dawley rats were exposed to either 0.98 ppm ozone 8 h/day for 90 days or to filtered air only. En bloc microdissection was used to identify and isolate in longitudinal profile the bronchiole-alveolar duct junction, first pair of alveolar duct generations, and intervening bifurcation ridge. The first alveolar outpocketing along the bronchiolar wall of each isolation was used to identify the center of a series of concentric arcs radiating outward at 100-microns intervals across each ventilatory unit. The intercept lengths of each arc with the tissue of alveolar septal tips (edges) and alveolar walls were measured and expressed as a function of distance into the ventilatory unit. Relative ozone dose across the ventilatory unit was estimated using the geometry of the tracheobronchial tree and the volume and surface area distribution within individual ventilatory units. This mathematical model of ozone dose demonstrated a high degree of correlation to this measured tissue injury response. The findings of this study demonstrate that microdosimetry and microtoxicology can be used to determine dose-response relationships within the ventilatory unit and to assess questions of tissue sensitivity in ozone-induced lung injury.

Animals↗

PubMed1992

Distribution of lung cell numbers and volumes between alveolar and nonalveolar tissue.

Although total cell number has been determined for the alveolar region of the lungs of many species, it has not been calculated for the nonalveolar lung tissues. The oriented structure of airways and vessels makes the numerical assessment of cells in nonalveolar tissues difficult. This has led many investigators to use the number of cells in the alveolar region as a direct estimate of total lung cell number. To determine the number of cells in the nonalveolar lung tissues, the lungs of eight rats weighing 230 to 380 g were inflation-fixed and embedded in araldite, and 1.5-microns serial sections of the entire left lobe were cut and stained with methylene blue for light microscopy. The sections were then uniformly point-counted using computer-controlled distances between the fields to determine the fraction of points falling on air, blood, cellular tissue, and noncellular tissue for both the alveolar and the nonalveolar regions. The total volume of cell nuclei in each compartment was determined, and the total number of cells was calculated by dividing the total nuclear volume by the mean cell nuclear volume. It was found that 87% of the lung volume was alveolar, of which 6% was tissue and contained 725 x 10(6) cells. The nonalveolar region constituted 13% of the lung volume, of which 23% was tissue and contained 250 x 10(6) cells. The average rat lung therefore contains 975,000,000 cells, of which 74% was in alveolar tissues and 26% in nonalveolar tissues. On the basis of assays of isolated lung cells, there is an average of 7 pg DNA/cell.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Allometric relationships of cell numbers and size in the mammalian lung.

Allometric studies have shown that lung volume, alveolar surface area, and diffusing capacity increase proportionally with body weight across a broad range of mammalian species. Changes in the number of cells and in average cell size and surface areas with increasing body weight have not been defined. We speculated that cell size is determined more by cell function than by species and body weight. To test this hypothesis, nine species ranging in size from shrew (2 to 3 g) to horse (510 kg) were studied. Random sites from the distal alveolar region of each species were analyzed using morphometric techniques. Six to 10 nuclei from each of the major classes of parenchymal lung cells were three-dimensionally reconstructed to determine their average diameter, volume, and surface area. To calculate the cell density, nuclear profiles were counted using electron microscopy. The number of cells per lung increased with body mass and lung volume with a slope of 1.01 (r2 = 0.99). The lung is unique among organs in the diversity and function of individual cell types, such as mechanical, sensory, secretory, transporting, and circulating cells. Excluding the circulatory cells, the lung has greater than 60 different cell types, making it an ideal organ for examining the varieties in cell characteristics across different species. Up to 6-fold differences in size were found between different lung cell types within a single species; however, for cells having secretory functions, such as type II cells, there was no detectable change in cell size with increasing lung surface area or body mass.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Radon dosimetry based on the depth distribution of nuclei in human and rat lungs.

Calculation of the absorbed dose by different lung cells is necessary for predicting the critical cells that are subject to injury from inhaled Rn and other alpha-particle sources. The absorbed dose was determined for cells in the airways of human and rat lungs, based on airway epithelial thickness and on cell cytoplasm and nuclear volume density as a function of depth from the luminal surface of the airway epithelium. The thickness of the stratified columnar epithelium of human airways varied from 57.8 micron in bronchi to 9.8 microns in bronchioles. The cell populations of all bronchi in human lungs were comparable. The cell populations of trachea and intrapulmonary airways in rats, however, were significantly different. Basal cell populations in rat trachea and human bronchi were similar and formed a nearly continuous layer. In rat bronchi, basal cells were not present in significant numbers. Measurements of epithelial thickness and volume density were used to estimate the absorbed dose for an alpha-particle source (214Po or 218Po) distributed uniformly in the mucus with an equivalent activity of 1 dpm per cm2 of epithelial surface. The following model predictions of dose to human bronchial epithelial cell nuclei for a 218Po alpha-particle source are provided in units of nanogray (nGy) for specific cell types: secretory 158, preciliated 114, ciliated 44, goblet 86, basal 78, and indeterminate cell nuclei 73. The absorbed dose to specific types of rat bronchial epithelial cell nuclei was also predicted: secretory 237, precillated 216, ciliated 203, goblet 204, basal 200, and indeterminate cell nuclei 166 nGy. These and other results indicate that human and rat airway dosimetry have significant differences that may contribute to the differences in cancer cell induction between the two species.

Alpha Particles↗

PubMed1991

Inhomogeneity of ventilatory unit volume and its effects on reactive gas uptake.

This study addressed the question of whether variations in the volume of alveoli and alveolar ducts forming single units of ventilation can significantly influence the distribution and uptake of inspired reactive gases. Quantitative serial section analyses of vascular perfusion-fixed rat lungs were used to determine the anatomic dead space proximal to specific ventilatory units as well as the gas volume of these ventilatory units. Three reconstructions, each consisting of ventilatory units distal to a specific bronchus, were carried out. The number of ventilatory units for each reconstruction varied from 26 to 71. The average ventilatory unit volume for the three reconstructions [0.53 +/- .03 (SE) mm3] was not significantly different from measurements based on random sampling. The distribution of ventilatory unit volume was diverse, with 15% of the population having a volume less than 0.3 mm3 and 9% of the population having a volume greater than 1.0 mm3. For a gas of relatively low reactivity (e.g., oxygen) the predicted oxygen uptake per unit surface area did not vary significantly between ventilatory units. The predicted oxygen uptake was approximately 92% of the uptake in the absence of gradients in oxygen concentration between ventilatory units. For a highly reactive gas (e.g., ozone), the predicted uptake per unit surface area in the proximal portions of larger ventilatory units was significantly greater than the average uptake. These results suggest that focal areas of injury likely result from exposure to inhaled reactive gases.

Animals↗

PubMed1991

Quantifying lung structure. Experimental design and biologic variation in various models of lung injury.

The lung is a complex organ composed of a large number of different cell types of varying size and shape. Quantification of lung structure requires an understanding of how the distribution of specific cells and their characteristics affect the accuracy of measurement made on them and how to optimize experimental design for a morphometric study. We have studied lung structural modifications in a variety of lung injuries over the last decade. Extensive quantitative data from EM morphometric studies of pulmonary tissue have been collected. These data provide a unique opportunity to study the accuracy and efficiency of methods used to quantitate lung structure. We present and discuss novel computation-intensive methods for the estimation of biologic variability, sampling error, and measurement error. A new concept, unnested analysis of variance for stratified sampling and the use of computer-based methods for statistical analysis (the bootstrap method) and optimizing experimental design (nonlinear minimization procedure) are described in this report. Examples of experimental designs with their corresponding levels of accuracy and cost are also provided. The number of samples needed for a given level of precision is affected by the volume density of the structure being measured. The most important determinant for the overall accuracy of a morphometric study is the number of animals studied. Biologic variations between samples within an animal and among animals can vary significantly as a function of the model of injury studied.

Animals↗

PubMed1991

Cellular changes in the lungs of adrenalectomized rats following left pneumonectomy.

The time course and nature of the cellular response to left pneumonectomy, with or without prior adrenalectomy, were evaluated in the right lungs of male Sprague-Dawley rats using morphometric techniques. Animals were studied at days 2, 5, and 14 following pneumonectomy, intervals prior to, during the course of, and following significant compensatory changes in right lung mass. The postoperative increase in right lung mass and volume in pneumonectomized animals involved minimal changes in the ratios of most tissue components, when compared to the lungs of sham-operated controls. A transient disproportionate increase in type II cell volume and epithelial thickness was evident on day 14. Postpneumonectomy changes in the type II epithelium were accentuated in the lungs of adrenalectomized-pneumonectomized animals. Adrenalectomy 5 days prior to pneumonectomy resulted in a substantial increase in the volume of all right lung tissue components, associated with thickening of the alveolar wall and with increases in the volume of both cellular and noncellular interstitium. Effects of adrenalectomy on the endothelium also were evident. In both adrenal-intact and adrenalectomized animals, pneumonectomy increased alveolar number by day 14 but had no effect on the volume of individual alveoli. These results confirm a coordinated pattern of compensatory growth following pneumonectomy in the adrenal-intact rat. The data further suggest that in adrenalectomized animals compensatory lung growth is more poorly synchronized, with pronounced postoperative elevations in volume of the interstitial and type II epithelial compartments leading to increased thickness of the alveolar wall. Adrenal hormones thus appear to be required for coordination and control of compensatory lung growth and for rapid restoration of normal tissue structure.

Adrenal Glands↗

PubMed1990

Approximation of surfaces in quantitative 3-D reconstructions.

In serial section reconstructions a series of planar profiles are taken representing curves on the surface of the structure to be reconstructed. For a number of quantitative serial section methods, approximation of a surface is done by the formation of tiles between points of adjacent profiles. As generally proposed, finding this approximation has been difficult due to the inordinately large number of possible solutions resulting from different combinations of tiles between points. Current algorithms have either applied heuristic criteria to force the formation of only one solution or have searched all acceptable combinations for one that minimizes some cost function. The algorithm presented has been developed to choose the tiling which minimizes the estimated error when the tile approximation of the surface is used in subsequent quantitative algorithm such as the calculation of surface area.

Algorithms↗

PubMed1990

Measurement of boundaries using a digitizer tablet.

The perimeter is the most error prone of the primary measurements (length, perimeter and area) made when using a device such as a digitizer tablet to trace profiles on micrographs. To allow for minimization of this error an expression is developed relating the error in the perimeter to the digitizer resolution plus other errors in the entry process. The predictions of this expression are shown to be in good agreement with the results of computer simulation of the tracing process, as well as results from manual tracing using a digitizer tablet. This analysis of the digitizer entry process also provides a method by which an optimal choice of the sample spacing between digitizer coordinates can be made.

Computer Simulation↗

PubMed1990

Spatial distribution of collagen and elastin fibers in the lungs.

Surface tension forces acting on the thin-wall alveolar septa and the collagen-elastin fiber network are major factors in lung parenchymal micromechanics. Quantitative serial section analysis and morphometric evaluations of planar sections were used to determine the spatial location of collagen and elastin fibers in Sprague-Dawley rat and normal human lung samples. A large concentration of connective tissue fibers was located in the alveolar duct wall in both species. For rats, the tissue densities of collagen and elastin fibers located within 10 microns of an alveolar duct were 13 and 9%, respectively. In human lung samples, the tissue densities of collagen and elastin fibers within 20 microns of an alveolar duct were 18 and 16%, respectively. In both species, bands of elastin fibers formed a continuous ring around each alveolar mouth. In human lungs, elastin fibers were found to penetrate significantly deeper into alveolar septal walls than they did in rat lungs. The concentration of connective tissue elements in the alveolar duct walls of both species is consistent with their proposed roles as the principal load-bearing elements of the lung parenchyma.

Adult↗

PubMed1990

Neonatal hyperoxia alters the pulmonary alveolar and capillary structure of 40-day-old rats.

High inspired oxygen concentrations during the neonatal period profoundly inhibit rat lung development, an effect that is partly reversed during recovery in air. Persistent effects of neonatal hyperoxia on the size and number of alveoli or the structure of pulmonary capillaries have not been well defined. Using light and electron microscopic morphometry plus quantitative three-dimensional reconstructions of alveoli, we examined the lungs of 40-day-old rats that were exposed to more than 95% oxygen for the first 7 days after birth. Neonatal hyperoxia administered to rats resulted in abnormally enlarged air spaces at age 40 days. The fraction of the lung consisting of parenchyma was significantly increased and alveolar surface area was 13% lower than controls. There was an abnormal enlargement of alveolar ducts, which reduced by 24% the relative amount of air in the alveoli, compared to that in the alveolar ducts. The number of alveoli per lung and the mean volume of an alveolus were not different between the groups, but alveolar size class distributions were different, with significantly more very small and very large alveoli in 40-day-old rats after neonatal hyperoxia. By scanning electron microscopy, the alveolar surface of the exposed animals had a corrugated appearance, which was especially evident along alveolar ducts. Transmission electron microscopy revealed a greater density of capillaries, particularly in the alveolar regions close to terminal airways. Based on a random sample of the entire parenchymal region, capillary blood volume per cm2 of alveolar basal lamina was 18% greater. The results demonstrate that neonatal exposure to hyperoxia can cause abnormalities in the pulmonary alveolar and capillary structure of 40-day-old rats, and that these changes are similar to some features of broncho-pulmonary dysplasia.

Animals↗

PubMed1989

Postnatal growth of pulmonary acini and alveoli in normal and oxygen-exposed rats studied by serial section reconstructions.

Three-dimensional reconstructions from serial sections were used to examine postnatal lung development of rats reared in air (control) or oxygen. From birth to age 21 days, control lung volume increased ninefold, and the average volume of each ventilatory unit (all airspaces distal to a single respiratory bronchiole) increased seven times. There were approximately 5,000 ventilatory units at birth and on day 21, indicating that the lung grew by enlargement and subdivision of ventilatory units and not by their multiplication. Growth in hyperoxia (greater than 97%) for 7 days had no effect on the number of ventilatory units but, compared to controls, total lung volume and ventilatory unit volume were reduced 32% and 16%, respectively. At birth there were 0.6 x 10(6) alveoli, and at age 7 days in controls alveolar number increased 16-fold while the average volume of a single alveolus fell to one-sixth that at birth. Exposure to hyperoxia for 7 days stopped alveolarization; the surface area to volume ratio (Sa/V) of the ventilatory unit was lower, alveolar number was the same as at birth, and the alveoli present were large. At age 21 days, after 14 days of recovery in air, lung volume and ventilatory unit volume were greater than in controls but the Sa/V of the ventilatory unit was still depressed 20%. Alveoli from oxygen-exposed lungs were larger than in controls, and a greater size distribution coefficient showed them to be more variable. A shape coefficient for alveoli did not change as a function of the animal's age or oxygen treatment; it demonstrated proportional growth of alveolar height and diameter.

Animals↗

PubMed1988

Effects of low levels of NO2 on terminal bronchiolar cells and its relative toxicity compared to O3.

This report describes structural changes occurring in the terminal bronchioles of rats exposed to low levels of NO2 continuously for 6 weeks. In addition, the relative susceptibility of epithelial cells to oxidants and the comparative toxicity of NO2 and O3 are discussed. Terminal bronchioles isolated from rats exposed 5 days/week to 2.0 ppm NO2 (plus two 1-hr daily spikes to 6.0 ppm) were found to have 19% less ciliated cells per unit area of epithelial basement membrane. The remaining ciliated cells had a reduced mean surface area (-29%). The shape of the Clara cell changed with reduced size of the dome protrusions but increased cell contact with the basement membrane. These data indicate that exposure to 2.0 ppm NO2 (+ spikes) for 6 weeks caused injuries to cilia and ciliated cells and possible Clara cell differentiation in the terminal bronchioles of adult rats. Exposures of adult or juvenile rats to 0.5 ppm NO2 (+ two 1-hr daily spikes 5 days/week to 1.5 ppm) did not cause morphologically measurable injuries in the terminal bronchioles. The severity of the concentration-dependent epithelial cell reactions to NO2 and O3 in adult rat terminal bronchioles were compared to those occurring in the proximal alveolar regions (PAR). Epithelial cells in the PAR appeared to be more susceptible to oxidant insult since both 0.5 ppm NO2 and 0.25 ppm O3 were found to cause epithelial injury only in the PAR. Comparison of epithelial reactions to 6-week exposures to either NO2 or O3 indicated that 0.25 ppm O3 caused four times as much increase in the number of type I epithelial cells as did 2 ppm (+spikes) NO2. Therefore, O3 could be 40 times more toxic than NO2 in the PAR on the basis of the inspired concentration and the focal response. On the other hand, there was no loss of ciliated cells following the 0.25 ppm O3 exposure. This suggests that the ratio of O3 to NO2 toxicity in the terminal bronchioles is considerably less than 10. The relative toxicity of the two oxidant gases appears to be site specific.

Animals↗

PubMed1988

Evaluation of lung diffusing capacity by physiological and morphometric techniques.

Determinations of pulmonary diffusing capacity for CO (DLCO) by physiological and morphometric techniques have resulted in substantially different values for both DLCO and its major components. To evaluate the differences in these methods of measurement of DLCO, measurements were made under controlled conditions on isolated perfused dog lungs. Multiple gas-rebreathing techniques were used to measure DLCO, the membrane component of the diffusing capacity for CO (DmCO), and pulmonary capillary blood volume (Vc) in both anesthetized dogs and after isolation and perfusion of their lungs. The isolated perfused lungs were than perfusion fixed for morphometric analysis of the components of DLCO. The values obtained morphometrically for Vc were similar to those measured by physiological techniques. Perfusion fixation did not substantially alter the morphometric estimate of DmCO when compared with previous values obtained on inflation fixed lungs. However, the morphometric estimate of DmCO was over 10 times higher than that estimated physiologically. Analysis of the potential errors in the techniques suggests that the correct value for DmCO is substantially higher than that commonly estimated by use of physiological techniques and that the explanation for the difference is due to a number of factors that can influence the binding of CO to hemoglobin under in vivo conditions. The net effect of these factors can be represented by an unknown in each component of the Roughton-Forster relationship so that 1/DL = 1/(U1.Dm) + 1/(U2.theta Vc), where theta is the binding rate for CO to hemoglobin. Because the magnitudes of the unknown terms (U1 and U2) in the Roughton-Forster relationship are likely to be large, this relationship cannot be reliably used to determine Dm and Vc.

Animals↗

PubMed1988

Effects of inhalation of 0.25 ppm ozone on the terminal bronchioles of juvenile and adult rats.

Cells of the terminal bronchioles are particularly susceptible to the effects of inhalation of low levels of ozone (O3). One-day-old (juvenile) or 6-week-old (adult) rats were exposed to 0.25 ppm O3 for 12 h/day or to continuous room air for 6 weeks. Morphometric analysis of perpendicular cross sections of terminal bronchioles demonstrated that exposure to O3 produced alterations in the surface characteristics of ciliated and nonciliated (Clara) cells in both groups of rats. There were significant losses (20-30%) of the surface area contributed by cilia and the luminal surface of Clara cells was decreased by 16-25%. O3 exposure also produced significant decreases in the number of brush cells per square millimeter of terminal bronchiolar basement membrane. The results of this study indicate that the normal structure of terminal bronchiolar epithelial cells is significantly altered by inhalation of 0.25 ppm O3. No statistically significant interactions between the effects of O3 and animal age at the beginning of the exposure were found.

Aging↗

PubMed1987

Three-dimensional reconstruction of alveoli in the rat lung for pressure-volume relationships.

To determine alveolar pressure-volume relationships, alveolar three-dimensional reconstructions were prepared from lungs fixed by vascular perfusion at various points on the pressure-volume curve. Lungs from male Sprague-Dawley rats were fixed by perfusion through the pulmonary artery following a pressure-volume maneuver to the desired pressure point on either the inflation or deflation curve. Tissue samples from lungs were serially sectioned for determination of the volume fraction of alveoli and alveolar ducts and reconstruction of alveoli. Alveoli from lungs fixed at 5 cmH2O on the deflation curve (approximating functional residual volume) had a volume of 173 X 10(3) microns3, a surface area of 11,529 microns2, a mouth opening diameter of 72.7 microns, and a mean caliper diameter of 91.8 micron (SE). Alveolar shape changes during deflation from total lung capacity to residual volume was first (30 to 10 cmH2O) associated with little change in the diameter of the alveoli (102.7 +/- 2.4 to 100.3 +/- 3.3 microns). In the range overlapping normal breathing (10 to 0 cmH2O) there was a substantial decrease in diameter (100.3 +/- 3.3 to 43.3 +/- 2.3 microns). These measurements and others made on the relative changes in the dimensions of the alveolus suggest that the elastic network, particularly around the alveolar ducts, are predominant in determining lung behavior near the volume expansion limits of the lung while the elastic and surface tension properties of the alveoli are predominant in the volume range around functional residual capacity.

Animals↗

PubMed1987

Three-dimensional reconstruction of the rat acinus.

This study provides a quantitative description of the small airways and alveolar duct-alveolar architecture of the rat lung. To accomplish this, quantitative three-dimensional reconstructions were made of small airways, the alveolar duct system, and alveoli. The branching pattern of the small airways immediately proximal to the alveolar ducts varied significantly. For example, the number of bronchiole-alveolar duct junctions per parent bronchus (terminal bronchiole) ranged from two to six. The number of bronchiole-alveolar duct junctions per lung was 7,280 +/- 250 (mean +/- SE). The general shape of the ventilatory unit arising from each bronchiole-alveolar junction was that of a space-filling sphere with an outer diameter of 1,490 +/- 130 microns. The average distance from the bronchiole-alveolar duct junction to alveoli at the end of the alveolar sac termination was 1,290 +/- 100 microns. Numerous trifurcations were found in the branching pattern of the alveolar ducts. The branching of the alveolar ducts did not fit a regular dichotomous pattern. The volume of the terminal branches (alveolar sacs) accounted for 64 +/- 5% of the volume of the ventilatory unit. Both of these factors, the pattern of branching and the substantial volume distributed in the most peripheral branches, contribute to the uniform distribution of gas within the ventilatory unit and thus minimize potential diffusion limitations to gas exchange.

Animals↗