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Biomedical subjects

D E Harrison

Publications and source records attributed to D E Harrison.

174 records · Page 10Linked to original sources
PubMedDate not supplied

A review of biomechanics of the central nervous system--Part III: spinal cord stresses from postural loads and their neurologic effects.

OBJECTIVE: To review literature pertaining to neurologic disorders stemming from abnormal postures of the spine. DATA COLLECTION: A hand search of available reference texts and a computer search of literature from Index Medicus sources was performed, with special emphasis placed on spinal cord stresses and strains caused by various postural rotations and translations of the skull, thorax, and pelvis. RESULTS: Spinal postures will often deform the neural elements within the spinal canal. Spinal postures can be broken down into four types of loading: axial, pure bending, torsion, and transverse, which cause normal and shear stresses and strains in the neural tissues and blood vessels. Prolonged stresses and strains in the neural elements cause a multitude of disease processes. CONCLUSION: Four types of postural loads create a variety of stresses and strains in the neural tissue, depending on the exact magnitude and direction of the forces. Transverse loading is the most complex load. The stresses and strains in the neural elements and vascular supply are directly related to the function of the sensory, motor, and autonomic nervous systems. The literature indicates that prolonged loading of the neural tissue may lead to a wide variety of degenerative disorders or symptoms. The most offensive postural loading of the central nervous system and related structures occurs in any procedure or position requiring spinal flexion. Thus flexion traction, rehabilitation positions, exercises, spinal manipulation, and surgical fusions in any position other than lordosis for the cervical and lumbar spines should be questioned.

Biomechanical Phenomena↗
PubMedDate not supplied

Selection for maximum longevity in mice.

In both mice and men, during the adult life span, aging causes an exponential increase in vulnerability to almost all pathologies. Thus, aging is a serious public health problem. Altering the basic mechanisms that control normal aging would be a powerful approach to reduce damage from aging processes, so research identifying these mechanisms is of vital importance. Because life spans are determined by the first biological system to malfunction, it is likely that basic mechanisms are involved in life span extension of animals already having maximum normal life spans for the species. When life spans of a species are extended, all biological systems must function for unusually long times. If there are a limited number of genes for basic mechanisms that control aging rates in multiple biological systems, then life spans can be extended relatively easily. If not, extending maximum life spans would require changes in impractically large numbers of genes, all genes involved in functional life spans of every biological system. In fact, life spans appear to increase rapidly during evolution, suggesting that changes in only a few genes are required. These genes are likely to control underlying mechanisms timing aging in multiple biological systems. The purpose of selection for increased life span is to identify these genes. An important potential problem is that all species have many defective genetic alleles that can cause early disease and death. Selection studies must be designed to distinguish between altering basic mechanisms of aging, and simply avoiding early pathologies due to defective alleles. Animal models that are short lived for their species should be avoided, because their deaths almost always result from genetic defects unrelated to mechanisms of normal aging. During selection, alleles not causing early pathologies may appear to increase life spans by replacing defective alleles in genetic regions linked to early pathologies; however, these affect early disease, not basic mechanisms of aging. A more subtle potential problem is that caloric restriction increases life spans in mice. Selection for long lived mice should focus on more basic mechanisms than breeding mice that voluntarily consume fewer calories. The fact that aging rates in different biological systems are not necessarily coordinated in different individuals suggests that normal aging is timed by more than one mechanism. Thus, the objective in selection for maximum longevity is to capture the entire set of alleles that increase longevity in a species. Wild populations are not practical to use, despite some theoretical advantages, as genes retarding aging would be confounded with those reducing the stress of captivity. Currently we use four-way crosses of inbred strains that represent maximal genetic diversity. Genetic regions important in increasing longevity will be identified using microsatellite markers distinguishing each of the four starting strains over the entire genome. Other genetic techniques proven useful for studying characteristics that are quantitatively controlled by multiple genes may also be useful in studying mechanisms timing aging; these techniques include diallele crosses, recombinant inbred lines, bilineal congenic lines and correlated genetic markers.

Aging↗
PubMedDate not supplied

Glucose induces closure of single potassium channels in isolated rat pancreatic beta-cells.

The major physiological stimulus for the secretion of insulin from the pancreatic beta-cell is an increase in the plasma glucose concentration. It is well established that glucose-stimulated insulin secretion is associated with the appearance of electrical activity in the beta-cell; glucose concentrations above the threshold level for insulin release produce a slow membrane depolarization followed by either oscillatory bursts of action potentials (5-15 mM glucose) or continuous spiking (greater than 16 mM glucose). Tracer flux studies and microelectrode measurements using intact islets of Langerhans have indicated that the initial depolarization induced by glucose is caused by a decrease in the resting membrane permeability to potassium. Evidence also suggests that the electrical, ionic and secretory responses to glucose are mediated by the metabolism of the sugar within the beta-cell. By using cell-attached membrane patches from isolated rat pancreatic beta-cells, we have now identified a potassium channel (G-channel) that is active at the resting potential and is inhibited by glucose. Closure of this channel requires glucose metabolism. This is the first report of a potassium channel whose activity is modulated by glucose, and which may couple metabolic and ionic events involved in the secretion of insulin.

Action Potentials↗
PubMedDate not supplied

An examination of population changes in Alabama's Black Belt counties: 1960-1970 and 1970-1980.

"Population changes in 11 Alabama Black Belt counties are examined by comparing annual average birth, death, and migration rates during the 1960s with those of the 1970s. The specific focus of the study is migration patterns among the nonwhite segment of the population. Data from the 1980 and earlier censuses are utilized, along with birth and death data from Alabama vital statistics reports." The results show "that net migration losses among nonwhites declined substantially during the 1970s compared with the 1960s and that in two Black Belt counties there was a reversal from heavy net losses to moderate net gains. Whites, on a county-to-county basis, however, were generally characterized by significantly higher rates of loss during the 1970s than in the 1960s."

Black or African American↗
PubMedDate not supplied

A normal sagittal spinal configuration: a desirable clinical outcome.

OBJECTIVE: Traditional forms of chiropractic treatment methods have attempted to restore alignment of vertebrae to proposed "normal" positions. Although this approach has existed throughout chiropractic's 100-yr history, little has been written in the scientific literature in support of this approach. The objective of this review is to study further the rationale behind this approach and evaluate some of the mechanical, anatomical and physiological evidence upon which this chiropractic approach is based. STUDY SELECTION: Articles and studies were selected that discuss analysis of stress and strains in spinal tissues from gravitational loading and experimental deformation in human and animal models. Studies that included radiographic measurements and classifications of spinal configuration in the sagittal plane were reviewed for their relevance to the chiropractic concept of a typical, usual or normal spinal configuration against which to compare patients. CONCLUSION: The usual, typical or normal configuration of the cervical spine in the sagittal dimension is a lordosis with a range of 16.5-66 degrees when measured as tangent lines along the cervical curve of the posterior vertebral body margins of C2 and C7. An analysis of stresses and strains supports this claim, as do studies from the scientific literature that attempt to measure and classify average cervical configuration from large population bases. The use of normative data as a gauge against which to measure patients' structural health and as an outcome of the degree of success or failure of chiropractic interventions seem to be logical consequences of these findings.

Biomechanical Phenomena↗
PubMedDate not supplied

The sacroiliac joint: a review of anatomy and biomechanics with clinical implications.

OBJECTIVE: To examine the biomedical literature pertaining to the anatomy and biomechanics of the sacroiliac (SI) joint to update current concepts and treatment of SI joint dysfunctions. DATA COLLECTION: The biomedical literature was reviewed for articles containing information on the anatomy, mechanics, dysfunction and treatment of the SI articulation. Emphasis was placed on information published in the past decade. Textbooks and prior reviews were used to compare past and present information. RESULTS: The anatomy and mechanics of the SI joint and surrounding tissues are much more complex than taught in chiropractic colleges and technique systems. The motion of the joint is complex, involving simultaneous rotations of 3 degrees or less and translations of 2 mm or less in three dimensions. The axes of motion for the SI joint are not straightforward and are largely dependent upon the surface topography of the joints. Traditional chiropractic types of dysfunctions and displacements are oversimplified and specific SI joint adjustments have not been demonstrated to correct these displacements. The primary function of the integrated SI system is the transmission and dissipation of mechanical forces. History, physical examination and clinical diagnostic tests have failed to demonstrate predictive validity for true SI dysfunction. CONCLUSION: Treatment of the SI articulation is difficult and all known SI joint tests have questionable validity, with the exception of pain provocation tests. Clinical treatment should be aimed at improving the stability of the surrounding soft tissues and at reducing mechanical stresses and strains from poor posture or using orthotics to level the sacral base. Much more research is needed in the treatment of this area.

Biomechanical Phenomena↗
PubMedDate not supplied

Three-dimensional spinal coupling mechanics: Part II. Implications for chiropractic theories and practice.

OBJECTIVE: To compare the current knowledge of 3-D spinal mechanics and abnormal equilibrium states with chiropractic motion theories, chiropractic vertebral letter listing theories, and chiropractic technique theories. DATA COLLECTION: A manual search of available reference texts and a computer search of literature from Index Medicus were collected with an emphasis on 3-D studies of human spinal movements, segmental instability, Euler buckling of the spine, and chiropractic theories concerning vertebral movements. RESULTS: Previous spinal coupling results based upon two-dimensional radiographic studies are inadequate and inaccurate. Therefore, the validity of any chiropractic technique procedure, listing, motion analysis or adjusting style based on the two-dimensional radiograph and coupling studies must be questioned. We have identified four types of spinal subluxations (displacements) in the biomechanical literature: (a) posture main motion and associated segmental coupling, (b) Euler buckling viewed in the anteroposterior view, (c) snap through viewed in the lateral view and (d) segmental instability. CONCLUSIONS: Full three-dimensional investigations of spinal coupling patterns have shown that the vertebrae rotate and translate in all three axes and that previous theories of spinal coupling based upon two-dimensional studies are inaccurate and invalid. Previous chiropractic letter listings (e.g., PRI, PLS, etc.) of spinal displacements are inadequate and invalid. Only one of the four types of biomechanical displacements, segmental instability, is consistent with the traditional chiropractic theory of segmental spinal displacements; in general, this does not respond well to care. In general, vertebrae displacement must be viewed in the context of equilibrium configurations and one vertebra can not be displaced as an individual misalignment. Validity questions arise for any technique methods that use letter listings of displacement taken from motion palpation or two-dimensional radiographic analysis.

Biomechanical Phenomena↗