Biomedical subjects

R R Mercer

Publications and source records attributed to R R Mercer.

At least 37 records · Page 2Linked to original sources

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↗

PubMed1986

Differential distribution of brush cells in the rat lung.

The distribution of brush cells in the rat lung was studied using electron microscopic morphometry. Samples were taken from six distinctive anatomical regions. Tissue from the trachea, lobar bronchi, terminal bronchioles, first alveolar duct bifurcations, proximal alveolar regions, and the distal alveolar region were isolated and embedded in Epox 812. Aside from the trachea and the lobar bronchi, the other four regions were isolated from embedded tissue using microdissection techniques. Electron micrographs taken from thin sections of these samples were analyzed. It was found that brush cells made up 10% of the volume of epithelium covering the first alveolar duct bifurcation. Approximately 2% of the proximal alveolar epithelium, 1.4% of the terminal bronchiolar epithelium, and 3% of the tracheal epithelium were made up of brush cells. No brush-bordered epithelium was found in the lobar bronchi or in the distal alveolar walls. We conclude that brush cells have a distinct spatial location in the lung, being in high concentration in the trachea and in areas where first generation alveolar ducts bifurcate. The highest density was on the bifurcation of the first alveolar ducts, and their density decreased radially from this region.

Animals↗

PubMed1986

Airway branching patterns influence asbestos fiber location and the extent of tissue injury in the pulmonary parenchyma.

The degree to which various anatomic components of the lung influence the distribution of inhaled particles is not entirely clear. Therefore, we have studied the role intrapulmonary airways play in the localization of respired asbestos fibers and have correlated local asbestos fiber burden with tissue injury in rats following exposure to aerosolized chrysotile asbestos for 7 hours per day, 5 days per week for 12 months. Tissues arising from anatomically distinct pathways of the tracheobronchial tree were isolated by using microdissection. Adjacent tissue blocks from regions immediately distal to the last dissected airway were prepared for light microscopic evaluation or digested in hypochlorite solution to determine alveolar septal tissue density and asbestos fiber concentration respectively. These studies demonstrated regional differences in asbestos fiber number, size, and mass which were inversely related to airway pathlength and to bifurcation number along each airway path. Fiber burden within each region was found to be proportional to the relative degree of tissue injury present. These findings suggest that differences in tissue injury from region to region in the lungs following exposure to asbestos are a result of regional differences in the deposition and retention of these substances in the lungs. These airway characteristics which influence fiber deposition may also play an important role in the deposition and subsequent lung injury caused by other particulates and environmental pollutants.

Animals↗

PubMed1985

Inhalation studies of Mt. St. Helens volcanic ash in animals: respiratory mechanics, airway reactivity and deposition.

Effects of fine volcanic ash aerosol on pulmonary mechanical properties of awake guinea pigs were evaluated during exposure by inhalation. Ash penetration into the lung as well as tissue response to ash were determined by transmission electron microscopy. The reactivity of airway epithelial irritant receptors following ash exposure was assessed using a histamine bronchoprovocation test. Results indicated that breathing 9,4 mg/m3 of ash for 2 hr did not cause a measurable change in pulmonary function of guinea pigs. Electron micrographs showed that ash particles in the lung below the hilus did not seem to produce any acute tissue reaction and were almost all phagocytized by macrophages. Airways of guinea pigs exposed to ash were significantly less responsive to histamine than were the airways of animals exposed only to air. It appears that even though Mt. St. Helens ash was well tolerated by the guinea pig during the exposure, its presence in the inhaled air did change the "histamine sensitivity" of airway epithelial irritant receptors.

Air Pollutants↗

PubMed1985

Inhalation studies of Mt. St. Helens volcanic ash in animals. II. Lung function, biochemistry, and histology.

Rats were exposed by inhalation to 9.4 mg/m3 size-fractionated volcanic ash for 5 days (2 hr/day) and examined for changes in pulmonary function and histology for periods of up to 1 year. Fine-mode volcanic ash, SO2, and a combination of ash and SO2 produced no observable effects in normal rats and rats with elastase-induced emphysema. However, there was a mild irritant response to SO2 which was not influenced by the volcanic ash. Rats injected intratracheally with fine-mode volcanic ash or saline showed no evidence of pulmonary alterations after 6 months. Those injected with coarse-mode volcanic ash showed minor pulmonary functional changes, histologically detectable alveolitis, and small increases in lung weight. In contrast, quartz-injected rats showed large alterations in pulmonary function, lung weight, hydroxyproline levels, and large areas of lung consolidation and fibrosis.

Animals↗

PubMed1985

The role of osteocytes in bone resorption during lactation: morphometric observations.

It has been suggested that osteocytes may resorb bone during the calcium mobilization that occurs during lactation. To test this hypothesis morphometric methods were used to evaluate changes in mature nonmated female rats, 6-day postpartum nonlactating rats, 21-day postpartum nonlactating rats, 6-day lactating rats, 15-day lactating rats, and 21-day lactating rats using femur cross sections in the diaphyseal region. Osteoclast resorption per unit length of periosteal surface, as well as other measures of resorption activity, demonstrated that by 15 days of lactation a significant mobilization of calcium was occurring. The volume density of osteocyte lacunae and individual lacunar volumes from serial section reconstruction showed no increase in the lactating groups. Indeed, the only significant change in lacunae volume was a decrease apparently due to pregnancy. It is concluded from this study that osteocytes do not resorb bone during lactation.

Animals↗