Effect of Hemorrhage on Blood Flow to Marrow and Osseous Tissue in Conscious Rabbits

The purpose of this experiment was to characterize cardiovascular responses in skeletal tissue 15 minutes and 16 hours following reversible hemorrhagic hypotension and to validate a quantitative method for measuring blood flow rates in marrow and bone. Cardiac output and regional blood flow determinations were made using the radioactive microsphere technique. Microspheres (15 u dia) were injected into unanesthetized rabbits via a chronically implanted left atrial catheter. Blood flow and cardiac output measurements were made by injecting individual microsphere isotopes, each with a different label (®^Sr, 5 1 c r Gr l ^ C e ) , at three specified time intervals: first, as a pretreatment control value; second, 15 minutes following a standardized non-fatal hemorrhage (20 ml blood/kg body wt); and third, 16 hours post-hemorrhage. Results of four standard validations used to test reliability of the microsphere method as applied in this study showed close correlation between blood flow and microsphere distribution. On the day of the experiment both central ear arteries were cannulated. One catheter was used for blood pressure and heart rate recordings. The other v e s se l provided arterial blood for PCO2 , PO2 , pH and hematocrit measurements and also served as the site for collection of free-flowing reference samples used to calculate cardiac output. Each animal was sacrificed immediately following the third isotope injection and the heart, both kidneys, spleen and both femurs (marrow and bone separated) were removed, weighed fresh and ashed overnight at 550° C. Every tissue contained three isotopes, each representing a flow rate measurement during one of the time periods. Dissolved soft tissue samples and bone ash were counted and appropriate equations used to calculate percentage distribution of cardiac output, blood flow and tissue res istance for each time interval. Fifteen minutes after hemorrhage there was a significant decrease in cardiac output, blood pressure, arterial pCC\u3e2 ; while hematocrit and heart rate were significantly increased. These changes were accompanied by significantly reduced blood flows to the heart, kidney, spleen, whole bone, marrow and osseous tissue with corresponding resistance increases in all tissues except the heart. Spleen, whole bone, marrow and osseous tissue received a decreased percentage distribution of cardiac output while there was an increased percentage going to the heart. Renal flow fractions remained unchanged. Sixteen hours following hemorrhage cardiac output, heart rate and arterial pCC\u3e2 returned to normal while pC\u3e2 increased and hematocrit decreased. Arterial pH was unchanged at both post-hemorrhage measurements. Heart and marrow blood flows were significantly increased and kidney flow rates continued to be lower than control values. Perfusion of whole bone, spleen and osseous tissue returned to pretreatment levels. Tissue res istance decreased in the heart, spleen, whole bone and marrow but remained elevated in the renal vascular bed. Osseous tissue resistance decreased but not significantly. Percentage distribution of cardiac output increased in the heart, whole bone and marrow and decreased in the kidney while the spleen and osseous tissue values returned to normal. Normal hemodynamic properties of bone showed parallel blood supplies to marrow and osseous tissue with higher vascular resistance in the latter. It was estimated that total skeletal tissue plus marrow received 16% of resting cardiac output. The response 15 minutes post-hemorrhage demonstrated the characteristic decrease in regional blood perfusion with a relative preservation of flow to the heart. There was a uniform reduction of blood flow within the femur giving no evidence of preferential shunting away from osseous tissue in favor of marrow. Sixteen hours after hemorrhage blood flow to the various soft t is sues reflected continuation of a stress state where both vasodilatory metabolic and vasoconstrictive neurohumoral factors were still operative. A selective blood flow increase not seen in surrounding osseous tissue was observed in marrow. The response seen in marrow may be a preparatory mechanism for the increased metabolism associated with erythropoietic and reticuloendothelial activation and may represent a direct vasoproliferative effec t of erythropoietin on marrow vasculature

The Growth and Governance of American Classical and Christian Schools

Classical and Christian education has proliferated across education sectors over the last decade. As a result, school leaders must implement these timeless philosophies of education and navigate such high demand. This dissertation seeks to equip relevant parties with research about what drives their skyrocketing enrollment and how to support school leaders and their governing boards. My first chapter uses in-person focus groups to understand the school choices of 25 parents whose children are enrolled in Texas-based classical charter schools. I explore the ways in which parents found their children’s school; what made them enroll their children; and whether they are satisfied with their choice. Summarily, most parents report high levels of satisfaction and chose their children’s school because of the classical philosophy of education and commensurate academic program. They claim that their children’s classical charter school provides the education that it claims to offer. In the second chapter, I use conjoint analysis to examine whether academic achievement, education, and experience impact the likelihood of head of school hire by 141 Christian school board members. Conjoint analysis allows researchers to identify whether and to what degree each characteristic has a causal impact on the likelihood that hypothetical candidates will be hired by hiring personnel. I find evidence that board members place a premium on strong academic achievement and qualifications, extensive teaching or leadership experience, and graduation from a postsecondary institution sharing their school’s religious tradition. In my third chapter, I use survey data from the Society for Classical Learning to understand the relationship between 147 heads of school and their governing boards. I use Ordinary Least Squares regression to isolate the board-head relationship and quantify the degree to which mutual trust and perceived care affect head of school health, happiness, stress, and professional well-being. The research shows that mutual trust between classical Christian heads of school and their boards decreases the head’s likelihood of wanting to quit and positively impacts head of school faith, feelings of loneliness, and satisfaction with their governing board. Similarly, heads of school are more likely to flourish when they feel like their board cares for their personal well-being, soul, and family

The Growth and Governance of American Classical and Christian Schools

Classical and Christian education has proliferated across education sectors over the last decade. As a result, school leaders must implement these timeless philosophies of education and navigate such high demand. This dissertation seeks to equip relevant parties with research about what drives their skyrocketing enrollment and how to support school leaders and their governing boards. My first chapter uses in-person focus groups to understand the school choices of 25 parents whose children are enrolled in Texas-based classical charter schools. I explore the ways in which parents found their children’s school; what made them enroll their children; and whether they are satisfied with their choice. Summarily, most parents report high levels of satisfaction and chose their children’s school because of the classical philosophy of education and commensurate academic program. They claim that their children’s classical charter school provides the education that it claims to offer. In the second chapter, I use conjoint analysis to examine whether academic achievement, education, and experience impact the likelihood of head of school hire by 141 Christian school board members. Conjoint analysis allows researchers to identify whether and to what degree each characteristic has a causal impact on the likelihood that hypothetical candidates will be hired by hiring personnel. I find evidence that board members place a premium on strong academic achievement and qualifications, extensive teaching or leadership experience, and graduation from a postsecondary institution sharing their school’s religious tradition. In my third chapter, I use survey data from the Society for Classical Learning to understand the relationship between 147 heads of school and their governing boards. I use Ordinary Least Squares regression to isolate the board-head relationship and quantify the degree to which mutual trust and perceived care affect head of school health, happiness, stress, and professional well-being. The research shows that mutual trust between classical Christian heads of school and their boards decreases the head’s likelihood of wanting to quit and positively impacts head of school faith, feelings of loneliness, and satisfaction with their governing board. Similarly, heads of school are more likely to flourish when they feel like their board cares for their personal well-being, soul, and family

Charter School Funding: Support for Students with Disabilities

The subject of public charter schools and students with disabilities is both important and sensitive. These students have the potential to benefit greatly from the smaller size and specialized focus of many public charter schools, but questions persist regarding whether all or even most charters are as receptive to enrolling students with disabilities as they are to serving students who do not have disabilities. Furthermore, do differences in enrollment of students with disabilities explain differences in funding between the two sectors? To shine a brighter light on this vital question, we have conducted a careful study of the funding surrounding the education of students with disabilities in public charter schools using data from fiscal year 2018 in 18 cities where charters hold a substantial share of K-12 education enrollment. This report provides a summary of our findings. Additional details regarding how special education services are provided to students with disabilities in each of our 18 cities are provided in a separate Appendix of City Snapshots. As public schools, charter schools must adhere to the same federal legal requirements as their traditional public school (TPS) counterparts. When charters are their own local education agency (LEA), the charters themselves ultimately are responsible for ensuring that students with disabilities receive the special education and related services and supports to which they are entitled under the law. When charters are part of another LEA, through their home district or state, the other entity is ultimately responsible for providing services to students who have disabilities. These key realities are part of the context of how funding for special education flows to public charter schools across the country

Making it Count: The Productivity of Public Charter Schools in Seven U.S. Cities

Historically, public education spending in the United States has risen at a steady rate. In 2017-2018 alone, policymakers spent over $780 billion on the public education system. The intent behind education spending is to create more and better opportunities for students to excel academically, thereby improving their life trajectories. However, looming future challenges such as underfunded teacher pension liabilities suggest that policymakers should “economize” their spending wherever possible. The number of public charter schools, concomitantly, has experienced near exponential growth. From 1991 to 2019, charter school legislation passed in 45 states and the District of Columbia. Student enrollments in public charter schools have increased to over 3.3 million. Scarcity, inherent among all resources, makes attention to cost-effectiveness and return-on-investment (ROI) considerations critical to long-term policy success. Therefore, we examine which types of public schooling stand to give each student the greatest “bang for their buck.” Our analysis compares the productivity of different organizations providing a similar service — in this case, public education

Charter School Funding: Dispelling Myths about EMOs, Expenditure Patterns, & Nonpublic Dollars

Three decades after the first charter school law passed in the United States, myths about these public schools not only persist but continue to fuel strong claims and divisive debates. Commentators point to education management organizations (EMOs), for-profit organizations which manage or operate a network of charter schools, as examples of private entities supposedly profiting off public education. In this report, we dispel three common myths about charter schools and their funding, spending, and management (see box). We draw upon comprehensive school funding data collected from traditional public schools (TPS) and public charter schools in 18 cities during fiscal year (FY) 2018. In a November 2020 report, Charter School Funding: Inequity Surges in the Cities, we demonstrated that the public charter schools in those 18 cities received on average one-third less funding than their respective TPS. Here we drill down deeply into those data to test claims about public charter schools and the myths surrounding them

When size matters: differences in demineralized bone matrix particles affect collagen structure, mesenchymal stem cell behavior, and osteogenic potential

Demineralized bone matrix (DBM) is a natural, collagen-based, osteoinductive biomaterial. Nevertheless, there are conflicting reports on the efficacy of this product. The purpose of this study was to evaluate whether DBM collagen structure is affected by particle size and can influence DBM cytocompatibility and osteoinductivity. Sheep cortical bone was ground and particles were divided in three fractions with different sizes, defined as large (L, 1-2 mm), medium (M, 0.5-1 mm), and small (S, <0.5 mm). After demineralization, the chemical-physical analysis clearly showed a particle size-dependent alteration in collagen structure, with DBM-M being altered but not as much as DBM-S. DBM-M displayed a preferable trend in almost all biological characteristics tested, although all DBM particles revealed an optimal cytocompatibility. Subcutaneous implantation of DBM particles into immunocompromised mice resulted in bone induction only for DBM-M. When sheep MSC were seeded onto particles before implantation, all DBM particles were able to induce new bone formation with the best incidence for DBM-M and DBM-S. In conclusion, the collagen alteration in DBM-M is likely the best condition to promote bone induction in vivo. Furthermore, the choice of 0.5-1 mm particles may enable to obtain more efficient and consistent results among different research groups in bone tissue-engineering applications

Demineralized bone matrix-induced ectopic bone formation in rats: in vivo study with follow-up by magnetic resonance imaging, magnetic resonance angiography, and dual-energy X-ray absorptiometry.

Contains fulltext : 57929.pdf (publisher's version ) (Open Access)The aim of this study was to further explore the use of magnetic resonance imaging (MRI), magnetic resonance angiography (MRA), and dual-energy X-ray absorptiometry (DEXA) to assess bone formation and blood circulation in a pedicled bone graft substitute. In 14 Wistar rats, initially 10 weeks old, heterogeneous demineralized femur bone matrix implants were wrapped in pedicled adductor thigh muscle flaps. One rat died after surgery. Subsequently, bone formation and maintenance of blood vessel functionality were evaluated in six rats 6 weeks postimplantation by means of in vivo MRI/MRA and postmortem histomorphometry. The other seven rats were left for 12 weeks, whereafter bone formation was evaluated by in vivo DEXA and postmortem histomorphometry. The results demonstrated that after 6 weeks bone formation was present in four of six animals, quantified as 42 (+/-35)% and 25 (+/-19)% by means of MRI and histomorphometry, respectively. MRA was able to show patency of the pedicles of these four rats only, which suggests that the lack of blood supply in the other two rats is the cause of the failure to form bone. In the 12-week group, histology showed increased bone formation without signs of osteolysis, which was quantified histomorphometrically to be as high as 48 (+/-15)%. DEXA failed to show bone formation. It is concluded that in vivo MRI proved to be a reliable method for monitoring ectopic bone formation in a rat model, whereas in vivo DEXA was unable to detect the implants. Furthermore, in vivo MRA proved to be a useful technique for studying the circulation of muscle flaps in this animal model