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Biomedical subjects

B L Davis

Publications and source records attributed to B L Davis.

At least 37 records · Page 2Linked to original sources
PubMed1996

Use of an instrumented treadmill for real-time gait symmetry evaluation and feedback in normal and trans-tibial amputee subjects.

The purpose of this research was to evaluate a newly developed system for assessing and providing feedback of gait symmetry information in real time to subjects walking on a motorised treadmill (the CCF Treadmill). The advantages of the system are that it allows the rapid collection and comparison of temporal and kinetic parameters of gait for multiple successive strides, at a constant known speed, without forcing subjects to target their footsteps. Gait asymmetries of six normal (mean age 42.7 years) and six unilateral transtibial amputee subjects (mean age 41.7, and average 6.0 years using a prosthesis) were quantified. The amputee group was the reevaluated after receiving five minutes of training with each of three different types of real-time visual feedback (RTVF). Asymmetries in the measured parameters before feedback were 4.6 times greater in the amputee population than in the normal group, and were consistent with the finding of previous authors. Significant decreases in gait asymmetry were demonstrated for all forms of feedback after amputees received feedback training. Results, however, indicated that gait asymmetries for different variables are not necessarily related, and that more work needs to be done to identify those variables for which attaining a more symmetrical gait pattern is most beneficial. Further work also needs to be done to determine the long term effects of such RTVF training. The CCF Treadmill and RTVF were shown to be potentially useful tools both for defining rehabilitation targets and for quantifying patients' progress towards those goals.

Adult↗
PubMed1996

Ground reaction forces during locomotion in simulated microgravity.

BACKGROUND: Significant losses in bone density and mineral, primarily in the lower extremities, have been reported following exposure to weightlessness. Recent investigations suggest that mechanical influences such as bone deformation and strain rate may be critically important in stimulating new bone formation. HYPOTHESIS: It was hypothesized that velocity, cadence, and harness design would significantly affect lower limb impact forces during treadmill exercise in simulated zero-gravity (0G). METHODS: A ground-based hypogravity simulator was used to investigate which factors affect limb loading during tethered treadmill exercise. A fractional factorial design was used and 12 subjects were studied. RESULTS: The results showed that running on active and passive treadmills in the simulator with a tethering force close to the maximum comfortable level produced similar magnitudes for the peak ground reaction force. It was also found that these maximum forces were significantly lower than those obtained during overground trials, even when the speeds of locomotion in the simulator were 66% greater than those in 1G. Cadence had no effect on any of the response variables. The maximum rate of force application (DFDTmax) was similar for overground running and exercise in simulated 0G, provided the "weightless" subjects ran on a motorized treadmill. CONCLUSIONS: These findings have implications for the use of treadmill exercise as a countermeasure for hypokinetic osteoporosis. As the relationship between mechanical factors and osteogenesis becomes better understood, results from human experiments in 0G simulators will help to design in-flight exercise programs that are more closely targeted to generate appropriate mechanical stimuli.

Adult↗
PubMed1995

Visual guidance to force plates does not influence ground reaction force variability.

Gait analysis methods commonly require the subject to avoid visual guidance, that is, targeting, the force plate upon which a foot-strike is necessary. The putative rationale underlying the preference for not using targeting is the unsubstantiated contention that gait is altered. This study evaluated the influence of force plate targeting on the variability of ground reaction forces (GRF) in 15 normal subjects. Secondary factors of single vs multiple steps to the force plate and whether or not subjects were informed of the study's primary purpose were also examined. ANOVA main effects revealed that targeting did not significantly affect GRF variability (p > 0.05). A significant main effect of the number of steps required to reach the force plate on AP force variability was found (p = 0.002). Prior knowledge of the purpose of the study did not significantly affect GRF variability (p > 0.05). It was concluded that the variability of ground reaction forces is not significantly affected by targeting the force plate. Thus, targeting would not be expected to influence the variability of calculated kinetic variables that are subservient to GRF.

Adult↗
PubMed1995

The articulatory basis of babbling.

This article evaluates the "Frames, then Content" hypothesis for speech acquisition, which states that much of the patterning of babbling is a direct result of production of syllabic "Frames" by means of rhythmic mandibular oscillation, with relatively little of the intrasyllabic and intersyllabic "Content" of the syllable-like cycles under mandible-independent control. Analysis was based on a phonetically transcribed corpus of 6,659 utterances of 6 normally developing infants obtained from one-hour weekly audio-recordings over a 4-6 month period. Intrasyllabic predictions were that front vowels would preferentially co-occur with front (alveolar) consonants, back vowels with back (velar) consonants, and central vowels with labial consonants, with the latter effect presumably resulting from mandibular oscillation alone. Intersyllabic predictions were for more variegation in tongue height for vowels than in front-back tongue movement, and for consonant manner changes to predominate over place changes (related primarily to mandibular oscillation). All 30 individual predictions from both hypotheses were confirmed, leading to a conception of the articulatory basis of babbling as "Frame Dominance."

Child Language↗
PubMed1994

Locomotion in a rotating space station: a synthesis of new data with established concepts.

Despite technical problems associated with designing a rotating space station it is still thought that such a device may provide a more tolerable work environment and prevent some of the physiological changes that currently pose a threat to long-duration space missions. In the present analysis four case studies are presented and the results show that centrifugal and Coriolis effects could hinder one's ability to walk or run in a natural way in such an environment. In a rotating station that has a nominal 'G-level' equal to that on earth it can be shown that a person running at 3.8 m s -1 could experience foot 'heaviness' effects that range from 1 to 3 g and fore-aft foot 'forces' that range fom -0.5 to +0.5 g. In contrast the hip region could sense a relatively constant 'force' equal to 2 g. With regard to the body as a whole there would be 'weight changes' that depended on the direction of gait. While these conditions imply that locomotion in a rotating space station would be different from normal gait, it is likely that given sufficient training, astronauts could learn optimal strategies to account for centrifugal and Coriolis effects on individual body segments. The learning process would also entail developing strategies on which route to take when moving from one location to another, since in many cases the shortest route would not be the least energy consuming. Such training would be justified if it were shown that artificial gravity was an effective countermeasure to the problems of muscle atrophy and bone loss.

Coriolis Force↗
PubMed1993

Foot ulceration: hypotheses concerning shear and vertical forces acting on adjacent regions of skin.

During gait the plantar surface of the foot experiences distributed shear and compressive stresses due to tangential and vertical forces respectively. At any given point under a foot, the ratio of tangential/vertical forces gives a value (mu Rmin) for the minimum coefficient of friction required to prevent slipping. If mu Rmin is greater than the actual coefficient of friction (mu A), then localized slipping will occur. Three possible scenarios exist which could lead to skin ulceration: at a localized area the skin may tend to slip (i) towards, (ii) away from or (iii) parallel to a neighboring skin region where mu Rmin < or = mu A (i.e. a region that doesn't slip). The first of these possibilities is similar in concept to the loading conditions that lead to a carpet becoming 'wrinkled', i.e. one region of the carpet slips towards another that is stationary. The second and third possibilities would tend to cause tearing in the carpet or shearing of its fabric respectively. In terms of skin breakdown the relative importance of each of these biomechanical hypotheses needs to be determined.

Biomechanical Phenomena↗
PubMed1993

Developing a career trajectory: research and community service.

The faculty of historically black colleges and universities (HBCUs) assume a major role in educating the largest share of the country's minority students. These institutions have traditionally focused upon teaching and learning processes which most result in student successes; conversely, their faculty's focus has suffered a decreased emphasis in the areas of research and community service. The Project for Faculty and Community Enhancement (FACE) has been designed to meet this decreased interest and activity in the areas of research and community service. This article will discuss the design and effectiveness of Project FACE among nursing faculty at twenty-two HBCUs.

Black or African American↗
PubMed1993

Simulating reduced gravity: a review of biomechanical issues pertaining to human locomotion.

In the decade preceding Apollo missions to the Moon, extensive studies were conducted on human locomotion in reduced gravity. These investigations focused primarily on issues of maneuverability and energy expenditure and not on musculoskeletal loading, which is of more interest to planners of long-duration space missions. The techniques have included water immersion, parabolic aircraft flights, supine and erect cable suspension and centrifugal methods. The practical implications of the findings from these studies are: 1) the present shuttle treadmill running surface would not suffice if one wanted to run with a natural style at levels greater than 0.6 G; 2) in terms of attempting to replicate typical ground reaction force profiles during locomotor exercise at reduced gravity levels, it appears as though it is easier to match the peak rates of change of force (maxDFDT) than it is to match values for the peak force magnitudes (maxGRF).

Biomechanical Phenomena↗
PubMed1992

Qualitative holographic study of hemi-pelvic deformation caused by loading different hip prostheses.

The dynamic biological response of bone can materially influence the longevity of artificial implants. This paper presents a series of in vitro experiments conducted on epoxy resin models of human hemi-pelves. Different commercially available acetabular components were implanted and used for the construction of simplified three-dimensional models of the artificial hip joint. Boundary conditions included simulation of muscle groups and femoral loading. Real-time holographic interferometry, a stress analysis technique permitting whole-field simultaneous inspection of deformation patterns, was used as the experimental method. The holographic interferograms were interpreted qualitatively rather than quantitatively. High stresses were identified in the hemi-pelvis and it is postulated that these stresses may be implicated in the mechanical pathogenesis of loosening. The observed changes in the detected stress levels could influence both future design of acetabular prostheses and surgical techniques.

Biomechanical Phenomena↗
PubMed1992

A biomechanical perspective on exercise countermeasures for long term spaceflight.

Many systems of the body undergo adaptation on exposure to hypogravity, with the lower extremity skeleton experiencing considerable mineral loss during relatively short periods of hypogravic exposure. To date, a variety of countermeasures have had limited success in preventing demineralization, though it is now accepted that mechanical deformation is critical for bone homeostasis on Earth. In the present study, three exercises under active consideration for use in the Space Station were compared in 1 G in terms of the peak loads and rates of change of load elicited under the feet. Peak loading rates were in the ratio of 34.7:1.9:1 for running, rowing, and cycling, respectively. With regard to peak foot loads, the corresponding values were in the ratio of 5.3:1:1.2. These results suggest that exercise during spaceflight must be considered from both biomechanical and physiological perspectives if optimal response is to be obtained.

Adult↗
PubMed1992

Professional nursing and Operation Smile International.

Operation Smile International (OSI) has a commitment to make a difference in the quality of life for people in third world countries by performing reconstructive surgeries on patients with birth defects and other deformities. Faculty members from the Hampton University School of Nursing and a graduate student were volunteers on two African medical missions. This article focuses on two of these faculty members as they provided nursing care services during reconstructive surgeries in Monrovia, Liberia and as they conducted lecture series, surveys, a research study and a day-long scientific symposium. Additionally, a model for human resource development was established in Monrovia, in conjunction with OSI, to upgrade the level of nursing education for Liberian.

Education, Nursing↗
PubMed1991

Noradrenergic innervation to the VMN or MPN is not necessary for lordosis.

The purpose of the present study was to determine the importance of noradrenergic neurons terminating in the ventromedial nucleus (VMN) and medial preoptic nucleus (MPN) of the hypothalamus for lordosis behavior in ovariectomized, estrogen/progesterone-treated female rats. Seven days following bilateral injections of the noradrenergic neurotoxin 5-amino-2,4-dihydroxy-alpha-methylphenylethylamine (5-ADMP) into the ventral noradrenergic bundle (VNAB), norepinephrine (NE) concentrations (ng/mg protein) were reduced to 30-35% of control in the VMN and MPN. 5-ADMP-induced lesions of the VNAB also reduced lordosis quotients in these animals, and this effect was reversed by intracerebral ventricular administration of the alpha 1-adrenergic receptor agonist phenylephrine. These results indicate that neurotoxin-induced disruption of noradrenergic neurons in the VNAB is associated with a deficit in sexual receptivity in female rats. To determine if the reduction in sexual receptivity following 5-ADMP-induced lesions of the VNAB resulted from loss of noradrenergic neuronal projections specifically to the VMN or MPN, lordosis quotients were determined in ovariectomized, estrogen/progesterone-treated rats in which noradrenergic terminals in these hypothalamic nuclei were selectively lesioned. Injection of 5-ADMP directly into either the VMN or MPN reduced NE concentrations to 17% of control in these hypothalamic nuclei, but failed to alter lordosis. Furthermore, injection of phenylephrine into either the VMN or MPN of VNAB-lesioned rats failed to reinstate lordosis to the levels comparable to sham-lesioned controls. Taken together, these results indicate that noradrenergic neurons terminating in either the VMN or MPN are not essential for gonadal steroid induction of sexual receptivity in ovariectomized female rats.

Animals↗
PubMed1990

Acquisition of correct vowel production: a quantitative case study.

There have been relatively few studies of the course of acquisition of correct vowel production. The present study suggests this gives an illusory impression that vowels are acquired easily and are of little theoretical interest. Despite a relatively precocious rate of vocabulary acquisition over the period from 14 to 20 months, the subject studied produced less than 60% of her vowels correctly according to evidence from phonetic transcriptions. A complex pattern of vowel preferences and errors was only partially related to typical prespeech babbling preferences, but was strongly related to word structure variables (monosyllabic vs. disyllabic) including stress patterns of disyllabic words, as reflected in patterns of relative frequencies of vowels in stressed and unstressed syllables. Consonant-vowel interdependence was observed, in both the favoring of high front vowels in the environment of alveolar consonants, and a reciprocal relation between vowel reduplication and consonant reduplication in disyllabic words.

Child Language↗