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Biomedical subjects

R B Martin

Publications and source records attributed to R B Martin.

At least 73 records · Page 4Linked to original sources
PubMed1991

Relationships between marrow fat and bone turnover in ovariectomized and intact rats.

It is known that marrow fat content increases in a variety of osteoporoses. This study sought to clarify this phenomenon by combining bone and marrow histomorphometry, and to determine (1) whether the marrow fat increase follows or precedes diminishment of bone volume, and (2) whether the increase in fat volume is due to adipocyte growth or proliferation. The relationship between marrow fat content and bone turnover was studied in the metaphysis and epiphysis of the proximal tibia in 20 ovariectomized and 20 intact 200 gm Sprague-Dawley rats. The results were examined after one and three months. The epiphysis had greater trabecular bone volume than the metaphysis. The metaphysis exhibited a decrease in bone volume with time; the epiphysis did not. Following ovariectomy, the bone volume diminished twice as much in the metaphysis as in the epiphysis. In the epiphysis, as bone volume fraction fell following ovariectomy, the vacated space was filled by both hemopoietic and adipose tissue. In the metaphysis, space-filling was time-dependent: hemopoietic tissue at one month and adipose tissue at three months. Marrow fat content increased with both time and ovariectomy in the metaphysis, but only with time in the epiphysis. Thus, marrow fat increased after bone volume began to decline in the metaphysis, and not at all in the epiphysis. Ovariectomy increased erosion surface in both the epiphysis and the metaphysis, but bone formation rate was increased only in the epiphysis. There was a reciprocal relationship between marrow fat content and bone formation rate.

Adipose Tissue↗
PubMed1991

On the significance of remodeling space and activation rate changes in bone remodeling.

This paper quantifies the relative contributions of the remodeling space and the accumulation of Haversian canals to bone porosity at various ages. It also examines the importance of variations in the rate of bone remodeling that occur during growth and aging, and as a result of trauma and disease. The dependence of the remodeling space (cavities due to resorbing, reversing, and refilling BMUs) and the Haversian canal components of porosity on the Basic Multicellular Unit (BMU) activation frequency are mathematically formulated. A graph is developed using data for the cortex of the human rib which shows the extent to which porosity is primarily due to the remodeling space in children, and to accumulated Haversian canals in adults. It is shown that the diminution of activation frequency between birth and age 35 contributes to the concurrent increase in bone volume fraction, and the increase in activation frequency after age 35 contributes to the subsequent decline of bone volume fraction. An equation is derived for determining the time rate of change of activation frequency using two fluorochrome labels.

Aging↗
PubMed1991

Biomechanical testing of new and old fixation devices for vertical shear fractures of the pelvis.

Malgaigne fractures of the pelvis have been treated with many different methods of fixation. We developed a plate for use on the anterior aspect of the sacroiliac (SI) joint using information obtained from cadaveric dissections and computed tomography (CT) scans of male (50) and female (50) pelvises. We tested each of six pelvises in the Instron, with five different fixation systems. Our results showed that the weakest system was the anterior quadrilateral frame plus two symphyseal plates. When comparing three posterior screws with the SI joint plate, the difference was not statistically significant. However, in both of these systems, a second symphyseal plate added to the overall stability.

Biomechanical Phenomena↗
PubMed1990

Bone marrow fat content in relation to bone remodeling and serum chemistry in intact and ovariectomized dogs.

It was previously shown that 11 months after ovariectomy the volume fraction of trabecular bone in the spine and 11th rib medullary canal of Beagle dogs (6 control, 9 ovariectomized) was significantly reduced. In this paper it is shown that these changes are accompanied by increased marrow fat volume in the 11th rib (59.0 +/- 9.5% vs. 44.3 +/- 10.0%). Conversely, the volume fraction of functional (hematopoietic) cells in the marrow was reduced by ovariectomy. Additionally, variations in marrow fat volume were tested for correlation with 22 other variables pertinent to bone physiology. Marrow fat volume was significantly positively correlated with serum osteocalcin, rib trabecular bone porosity, rib cross-sectional area, and gains in body weight. It was negatively correlated with serum estrogen concentrations and the extent of rib trabecular surfaces labeled with tetracycline.

Adipose Tissue↗
PubMed1990

Linear calibration of radiographic mineral density using video-digitizing methods.

Radiographic images can provide quantitative as well as qualitative information if they are subjected to densitometric analysis. Using modern video-digitizing techniques, such densitometry can be readily accomplished using relatively inexpensive computer systems. However, such analyses are made more difficult by the fact that the density values read from the radiography have a complex, nonlinear relationship to bone mineral content. This article derives the relationship between these variables from the nature of the intermediate physical processes, and presents a simple mathematical method for obtaining a linear calibration function using a step wedge or other standard.

Animals↗
PubMed1990

A mathematical model of cancer chemotherapy with an optimal selection of parameters.

An optimal parameter selection model of cancer chemotherapy is presented which describes the treatment of a tumor over a fixed period of time by the repeated administration of a single drug. The drug is delivered at evenly spaced intervals over the treatment period at doses to be selected by the model. The model constructs a regimen that both minimizes the tumor population at the end of the treatment and satisfies constraints on the drug toxicity and intermediate tumor size. Numerical solutions show that an optimal regimen withholds the bulk of the doses until the end of the treatment period. When a drug used is of either moderate or low effectiveness, an optimal regimen is superior to a schedule that delivers all of the drug at the beginning of the treatment. This study questions whether the current method for the administration of chemotherapy is optimal and suggests that alternative regimens should be considered.

Antineoplastic Agents↗
PubMed1990

Interlocking femoral components for revision arthroplasty with allografts.

The use of interlocking screws has been advocated to fix major proximal femoral allografts to femoral prostheses. This study examines the effect of interlocking screws on strength of the component. Model femoral components were tested in axial compression. Drilling one hole diagonally (lateral to medial), drilling one hole anterior to posterior, or drilling one diagonal hole plus one anterior-to-posterior hole did not significantly decrease failure load compared to controls with no holes. However, two diagonal holes or horizontal, medial-to-lateral holes were weaker. Four cases have been done with proximal femoral allografts fixed to porous-coated femoral components with proximal and distal interlocking screws. Initial results in these cases are good.

Adult↗
PubMed1990

Emotional coping, age, and physical disorder.

Traditional ideas suggest that emotional expression is healthy, but empirical support for this position is mixed. Adult subjects participated in a telephone interview to examine the relationships among age, emotional coping (ie, laughter and crying), physical disorder, sex, and income level. Results indicated that cry-coping in women and in low-income participants was associated with increased disorder as age increased. Humor-coping had no relationship to physical disorder across the adult lifespan. These results indicate that emotional weeping does play a role in the prediction of physical disorder, especially in certain groups. In the future, researchers need to concentrate on more subtle physiological effects as well as on the psychological and social consequences of emotional expression.

Adaptation, Psychological↗
PubMed1990

The physiological and psychological effects of the expression and inhibition of emotion.

Previous work has indicated that humor enhances immunity, but the immunological effects of overt crying have not been studied. Thirty-nine women viewed sad and humorous videotapes and either inhibited or expressed overt expressions of laughter and weeping; these were observed and timed. Moods and immunity (S-IgA) were repeatedly measured. The humorous stimulus resulted in improved immunity, regardless of the overt laughter expressed; overt crying was immunosuppressive, whereas the inhibition of weeping in the context of the same sad stimulus was not. Moods were more negative following the sad stimulus and in the expression condition. The results with respect to humor are consistent with previous research; the immunosuppressive effect of overt crying is discussed in the context of various types of crying that may have different effects.

Adaptation, Psychological↗
PubMed1990

Simulated swimming: a useful tool for evaluation the VO2 max of swimmers in the laboratory.

This study was designed to develop a simulated swimming exercise (SS) so that peak VO2 would be assessed on swimmers in a laboratory setting. The subjects assumed a prone position on an incline bench and performed arm cranking on a Monark Rehab Trainer while performing a flutter kick against tension supplied by elastic cords. The SS test was compared to four peak VO2 tests: treadmill running (RN), tethered swimming (TW), bicycle ergometry (B), and arm cranking (AC). Eleven male varsity swimmers underwent each of the five VO2 max tests, and maximal cardiorespiratory indicators (HR, VE, VO2, O2 pulse, and RQ) were measured. The percentage of peak VO2 obtained during SS was compared to RN, TW, B, and AC. The SS test achieved 78 percent of RN, 91 percent of TW, 81 percent of B, and 124 percent of AC. There were no significant differences in VO2 in ml/kg.min between SS and TW. As expected, RN and B were significantly higher, while AC was lower. Ten subjects performed the SS test twice on two separate days within one week. The reliability of VO2 max in ml/kg.min was 0.95. the validity of VO2 max in ml/kg.min in the SS test vs. RN was 0.68. The SS test is reliable and can be used as effectively as TW to assess the VO2 max of swimmers in a laboratory setting.

Adult↗
PubMed1989

Oxidation of substituted N,N-dimethylanilines by cytochrome P-450: estimation of the effective oxidation-reduction potential of cytochrome P-450.

Rates of N-demethylation of N,N-dimethylaniline and of eight meta- or para-substituted N,N-dimethylanilines by rat liver cytochrome P-450PB-B (P-450) were determined under conditions where oxidation was supported by iodosylbenzene or NADPH-P-450 reductase. The rates of dimethylaniline oxidation were found to correlate with the substrate oxidation-reduction potential within each series of substrates supported by a particular oxygen activation protocol; the kcat for each substrate studied was approximately 20-fold faster in the iodosylbenzene-supported system relative to the NADPH-P-450 reductase supported system. Since the N-demethylation of amines is believed to proceed via an initial electron-transfer step, a kinetic scheme for P-450 was proposed that enabled evaluation of the data according to theoretical treatments that correlate rates of electron transfer with extrakinetic parameters. In these analyses, the data could be fitted to the Rehm-Weller and Agmon-Levine equations, providing lambda values (for the energetics of enzyme-substrate reorganization) of 22-26 kcal mol-1 and apparent E1/2 (oxidation-reduction potentials) of 1.7-2.0 V (vs saturated calomel) for the oxidized enzyme. The apparent E1/2 for the enzyme is composed of contributions from the intrinsic potential of the active prosthetic core of the enzyme, the Fe = O - porphyrin species, and a coulombic factor that is a function of the charge-separated radical anion/radical cation pair produced upon electron transfer.(ABSTRACT TRUNCATED AT 250 WORDS)

Aniline Compounds↗
PubMed1989

Errors in bone remodeling: toward a unified theory of metabolic bone disease.

Recent evidence suggests that skeletal adaptation is organized by a functional unit that includes cells of diverse origin working in coordination. Genetic and metabolic factors control and regulate the processes of modeling and remodeling, only rarely acting on the isolated individual functions of specific cell lines. Errors in the genetic or metabolic regulation of the functional unit affect the entire process of skeletal adaptation rather than specific elements of it. Viewed in this way, some metabolic bone diseases can be understood as relatively simple errors in factors that control the coordinated activities of the entire functional unit. This paper reviews the modeling and remodeling processes and demonstrates how abnormal morphological characteristics of bone tissue can be viewed as products of specific errors in the adaptive process.

Aging↗
PubMed1989

The relative effects of collagen fiber orientation, porosity, density, and mineralization on bone strength.

This investigation determined the relative importance of collagen fiber orientation, porosity, density, and mineralization in determining the tensile strength of bovine cortical bone. Thirty-nine specimens were tested for failure stress and the values of eight histologic and compositional parameters: collagen fiber orientation, wet and dry apparent density, percent mineralization of the bone matrix, and several components of porosity (Haversian canals, Volkmann's canals, and plexiform vascular spaces). Linear regression analysis showed that collagen fiber orientation was consistently the single best predictor of strength. Mineralization of the bone matrix was generally a poor predictor of strength. Density and porosity ranked between these variables in importance. Multiple regression equations containing all significantly correlated variables achieved correlation coefficients of 0.607 for plexiform bone and 0.881 for osteonal bone. Also, separate analysis of plexiform and osteonal specimens showed that the latter group was weaker even though it was less porous, apparently because it had collagen fibers which were less longitudinally oriented. This study suggests it is feasible to develop better empirical formulae for the prediction of cortical bone strength than are currently available if a variety of variables is introduced. Additional data are needed to confirm these results.

Animals↗
PubMed1989

Effects of bone ingrowth on the strength and non-invasive assessment of a coralline hydroxyapatite material.

The dependence of strength on the amount of bone growth into a hydroxyapatite material made from coral was investigated. Block and granular forms of the material were implanted into cortical and trabecular regions of the skeletons of 16 dogs. The results were examined after 4, 8, 12 and 16 wk, with four dogs in each experimental group. When implanted into cortical bone, the bending strength of the implant material was found to be highly correlated with the amount of pore space which had become occupied by bone (r = 0.92, P less than 0.005 for the block form; r = 0.84, P less than 0.005 for the granular form). Multiple regression analysis showed that six histomorphometric measures of ingrowth accounted for 96% of the variability in bending strength of the block material, and there were no significant differences between block and granular forms of the material. On the other hand, when implanted into trabecular bone, the block form of the material achieved greater compressive strength than the granular form. While both strength and ingrowth increased with time, there were poor correlations between these two variables. Finally, when the material is implanted into trabecular bone, it becomes stronger in compression than the surrounding bone; when implanted in cortical bone, linear modelling suggests that resorption and replacement of the implant would be required to approximate the bending strength of the surrounding bone.

Animals↗
PubMed1989

Label escape theory revisited: the effects of resting periods and section thickness.

A mathematical theory is developed for the effects of section thickness and resting periods on "label escape"--that is, the tendency for some bone formation sites to display only one label when a double fluorochrome marker is given. It is demonstrated that when section thickness is greater than the interlabel distance, many double labels will appear to be fused, so that they will be counted as single labels. Thus, thinner sections allow more accurate measurement of labeled surfaces, but it turns out that thicker sections yield a better estimate of apposition rate. It is also shown that if the refilling of BMU resorption cavities is interrupted by resting periods of arbitrary frequency and duration, the number of single labels will be increased in proportion to the total duration of the interruptions. Equations are derived which allow one to predict the magnitude of these effects, and to calculate the average total duration of resting periods during refilling from the ratio of single to double labeled surfaces. When the theory is applied to existing experimental data, it is found that substantial resting periods must be present to explain the amount of excess single label which is usually observed.

Bone Development↗
PubMed1988

Ternary hydroxide complexes in neutral solutions of Al3+ and F-.

Especially in G protein systems AlF4- has been claimed as an activating species serving as a tetrahedral phosphate analog. However, in aqueous solutions (H2O)2AlF4- is hexacoordinate with two bound water molecules. In neutral solutions five different mixed OH- and F- complexes of Al3+ comprise the main species under usual experimental conditions. Comparison of the mole fraction distribution curves with limited results on the activity as a function of ambient F- concentrations suggests an activating complex composed of Al3+ with three F- and uncertain geometry. Even fewer activity data suggest a tetrahedral Be2+ complex with three F-.

Aluminum↗