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Biomedical subjects

B L Davis

Publications and source records attributed to B L Davis.

At least 19 recordsLinked to original sources
PubMed2001

Synthesis and structure of tris(alkyl- and silyl-tetramethylcyclopentadienyl) complexes of lanthanum.

In efforts to make sterically crowded tris(peralkylcyclopentadienyl) complexes of lanthanum for the exploration of sterically induced reduction chemistry with a diamagnetic system, the synthesis of (C(5)Me(4)R)(3)La complexes has been pursued with R = Me, Et, (i)Pr, and SiMe(3). The complexes were synthesized in four steps: reaction of LaCl(3) with KC(5)Me(4)R to form (C(5)Me(4)R)(2)LaCl(2)K(THF)(2), addition of allylmagnesium chloride to make (C(5)Me(4)R)(2)La(C(3)H(5)), protonolysis with Et(3)NHBPh(4) to make [(C(5)Me(4)R)(2)La][BPh(4)], and finally the replacement of BPh(4)(-) with C(5)Me(4)R(-) using KC(5)Me(4)R to make (C(5)Me(4)R)(3)La. X-ray crystallographic data were obtainable on the (C(5)Me(4)R)(3)La complexes for R = Me, Et, (i)Pr, and SiMe(3). In each complex, the three C(5)Me(4)R ring centroids define a trigonal planar geometry around La. The average La-(ring centroid) distances are 2.64, 2.65, 2.66, and 2.69 A for the Me, Et, (i)Pr, and SiMe(3) structures, respectively, with La-C distances ranging from 2.857 (3) to 3.029 (2) A. Despite the steric crowding, ligand exchange can be observed by NMR spectroscopy.

Journal Article↗
PubMed2001

An extensometer for global measurement of bone strain suitable for use in vivo in humans.

An axial extensometer able to measure global bone strain magnitudes and rates encountered during physiological activity, and suitable for use in vivo in human subjects, is described. The extensometer uses paired capacitive sensors mounted to intraosseus pins and allows measurement of strain due to bending in the plane of the extensometer as well as uniaxial compression or tension. Data are presented for validation of the device against a surface-mounted strain gage in an acrylic specimen under dynamic four-point bending, with square wave and sinusoidal loading inputs up to 1500 mu epsilon and 20 Hz, representative of physiological strain magnitudes and frequencies. Pearson's correlation coefficient (r) between extensometer and strain gage ranged from 0.960 to 0.999. Mean differences between extensometer and strain gage ranged up to 15.3 mu epsilon. Errors in the extensometer output were directly proportional to the degree of bending that occurs in the specimen, however, these errors were predictable and less than 1 mu epsilon for the loading regime studied. The device is capable of tracking strain rates in excess of 90,000 mu epsilon/s.

Bone and Bones↗
PubMed2001

Motor mechanisms in speech ontogeny: phylogenetic, neurobiological and linguistic implications.

The rhythmic mandible-generated close-open alternations of the mouth, responsible for the series of consonant-vowel alternations characteristic of babbling and of languages, is receiving increased attention as a possible manifestation of an ontogenetic and phylogenetic 'frame' underlying the serial organization of speech. The supplementary motor area appears important for production of this consonant-vowel frame in adults.

Animals↗
PubMed2001

Quantifying muscle activity in non-ambulatory children with spastic cerebral palsy before and after selective dorsal rhizotomy.

Cerebral palsy is a condition that results in varying degrees of functional deficits. The goal of this study was to develop an objective measure of muscle activity during a prescribed voluntary motor task in non-ambulatory children with spastic cerebral palsy. While performing a simultaneous hip/knee flexion task from the supine position, followed by return to the starting position, electromyographic and kinematic data were obtained from the right leg of eight children before and after selective dorsal rhizotomy and compared with eight age-matched controls. The electromyographic and kinematic data were combined to determine for each muscle of interest (tibialis anterior, soleus, vastus lateralis, biceps femoris) the percentage of the movement cycle for which the muscle was acting concentrically, eccentrically, isometrically or was considered inactive. Averaged over the four muscles, isometric activity decreased by 38% post-op and the time the muscles were inactive increased by 37% following surgery. The percentages of concentric and eccentric activity did not differ significantly between pre- and post-op conditions. Post-operatively, the percentage muscle activity patterns of the children with cerebral palsy more closely resembled that of the control children: averaged across all muscles and contraction types, the difference between the control children and the children with cerebral palsy was reduced by 50% following surgery. This measurement technique indicates promise as a method for quantifying muscle activity during voluntary motor tasks in non-ambulatory children with cerebral palsy.

Adolescent↗
PubMed2001

Resonance Raman spectroscopy of mass selected Al2 in an argon matrix.

In an excitation range of 620-760 nm, resonance Raman spectra of aluminum dimers (Al2) in an argon matrix have been obtained for the first time. Temperature annealing experiments were performed to remove Raman lines attributed site effects caused by the Al2/Ar matrix. We observe a single fundamental at 293.3 (5) cm(-1) along with a progression up to 1149 (1) cm(-1). Taking successive differences of band centers we obtain spectroscopic constants for the ground state fundamental, w(e) = 297.5 (5) cm(-1), the anharmonicity, e(e)x(e) = 1.68 (8) cm(-1). Our results are in close agreement with previous experimental results for Al2 which designate the ground state as a 3piu state, and may be considered as confirmation of this assignment.

Aluminum↗
PubMed2001

Urban stress and mental health among African-American youth: assessing the link between exposure to violence, problem behavior, and coping strategies.

This project examines gender differences in exposure to violence, coping strategies and problem behavior among 306 African-American middle and high school students in the state of Virginia. Gender differences in problem behaviors among youth exposed to violence as either victims or witnesses are examined in addition to variations in coping strategies. Relying on recent research examining violent behavior and victimization events, the study focuses on the internalizing and externalizing behavioral characteristics (i.e., academic achievement, anxiety, depression, negative self-esteem, and delinquency) of urban students exposed to violence and the extent to which coping strategies differ. Results show specific gender differences with regard to problem behavior and coping strategy among African-American youth exposed to violence. For adolescent males, exposure to violence and victimization is strongly associated with externalizing problem behaviors such as delinquency, while adolescent females exposed to violence and victimization are more likely to exhibit internalizing symptoms indicative of post-traumatic stress disorder. Among students exposed to violence and victimization, females are more likely to use problem-focused coping (i.e., social support) as an adaptive strategy in comparison to males. Implications for intervention and future research are discussed.

Adaptation, Psychological↗
PubMed2000

On the origin of internal structure of word forms.

This study shows that a corpus of proto-word forms shares four sequential sound patterns with words of modern languages and the first words of infants. Three of the patterns involve intrasyllabic consonant-vowel (CV) co-occurrence: labial (lip) consonants with central vowels, coronal (tongue front) consonants with front vowels, and dorsal (tongue back) consonants with back vowels. The fourth pattern is an intersyllabic preference for initiating words with a labial consonant-vowel-coronal consonant sequence (LC). The CV effects may be primarily biomechanically motivated. The LC effect may be self-organizational, with multivariate causality. The findings support the hypothesis that these four patterns were basic to the origin of words.

Biomechanical Phenomena↗
PubMed2000

Obesity and osteoarthritis of the knee: hypotheses concerning the relationship between ground reaction forces and quadriceps fatigue in long-duration walking.

The principal risk factors of osteoarthritis of the knee are: age, obesity and gender. It is hypothesized that long-duration walking (e. g. 20 min) in the elderly obese will lead to quadriceps fatigue. Changes in the gait pattern due to fatigue will lead to altered knee kinematics at heelstrike and consequently decreased shock absorption. This scenario will result in an increased rate of loading and possibly an increase in the overall magnitude of peak ground reaction forces, both of which could cause articular cartilage degeneration. Obese females are at an overall higher risk of developing osteoarthritis than males. This gender discrepancy may be explained by the fact that females have a higher percentage of body fat content (lower proportion of lean mass) that may increase the rate of quadriceps fatigue. These biomechanical hypotheses can be examined by studying continuous periods of walking in which ground reaction forces, knee kinematics and electromyography data are recorded.

Humans↗
PubMed1999

Characterization of the calcaneal fat pad in diabetic and non-diabetic patients using magnetic resonance imaging.

It is well known that diabetic patients have a high incidence of foot ulceration. The purpose of this study was to determine whether magnetic resonance (MR) imaging can detect changes in the composition of the calcaneal fat pad in diabetic feet. MR data were collected in vitro from amputated specimens (eight from diabetic patients and eight from non-diabetic patients) as well as in vivo from age-matched diabetic and control subjects (four subjects each group.) Three types of images were acquired: spin lattice (T1), spin-spin (T2), and magnetization transfer (MT). The in vitro results showed statistically significant differences in the T1, T2, and MT parameters between the two disease groups. The same trends were shown in the study of live subjects but the differences were not statistically significant. The differences are believed to arise from changes in the composition of the tissues as a result of the progression of diabetes.

Adipose Tissue↗
PubMed1999

A biomechanical evaluation of one-stage vs two-stage bilateral knee arthroplasty patients.

In this study the functional abilities of eight one-stage bilateral total knee replacement (TKR) patients were compared to five two-stage bilateral TKR and nine control subjects. The TKR individuals were an average of 62 months post-operative. Based on gait analysis, ground reaction force profiles during walking and isometric knee strength assessment, the one-stage individuals did not differ significantly from the control subjects. The two-stage individuals had significantly less knee range of motion during gait and smaller vertical ground reaction forces during the braking phase than the control and one-stage individuals. To compare left and right sides, a symmetry index was computed and there were no significant differences among the three groups. Based on the variables tested in this biomechanical evaluation it can be concluded that for individuals facing bilateral knee replacement a one-stage procedure can result in functional capabilities at least comparable to a two-stage procedure.

Aged↗
PubMed1998

Nasalization of vowels in nasal environments in babbling: evidence for frame dominance.

An emerging concept for the characterization of the form of babbling and early speech is 'frame dominance': most of the variance arises from a frame provided by open-close mandibular oscillation. In contrast, the tongue - the most versatile articulator in adults - plays only a minor role in intersegmental and even intersyllabic changes. The contribution of another articulator - the soft palate - to time-domain changes in babbling was evaluated in an acoustic analysis of 433 consonant-vowel-consonant sequences produced by 3 infants. Strong nasal effects on vowels in symmetrical consonantal environment were observed in the form of a lower frequency first formant region in low vowels and a lower frequency second formant region in front vowels. These results, the first of which also occurs in adults, were complemented by perceptual tendencies for transcribers to transcribe more mid vowels relative to low vowels and more central vowels relative to front vowels in nasal environments. Thus the soft palate is like the tongue in making only minor contributions to time-domain changes in babbling, and this is considered to be additional evidence for the frame dominance conception.

Female↗
PubMed1998

Inhaled nitric oxide versus conventional therapy: effect on oxygenation in ARDS.

A randomized, controlled clinical trial was performed with patients with acute respiratory distress syndrome (ARDS) to compare the effect of conventional therapy or inhaled nitric oxide (iNO) on oxygenation. Patients were randomized to either conventional therapy or conventional therapy plus iNO for 72 h. We tested the following hypotheses: (1) that iNO would improve oxygenation during the 72 h after randomization, as compared with conventional therapy; and (2) that iNO would increase the likelihood that patients would improve to the extent that the FI(O2) could be decreased by > or = 0.15 within 72 h after randomization. There were two major findings. First, That iNO as compared with conventional therapy increased Pa(O2)/FI(O2) at 1 h, 12 h, and possibly 24 h. Beyond 24 h, the two groups had an equivalent improvement in Pa(O2)/FI(O2). Second, that patients treated with iNO therapy were no more likely to improve so that they could be managed with a persistent decrease in FI(O2) > or = 0.15 during the 72 h following randomization (11 of 20 patients with iNO versus 9 of 20 patients with conventional therapy, p = 0.55). In patients with severe ARDS, our results indicate that iNO does not lead to a sustained improvement in oxygenation as compared with conventional therapy.

Administration, Inhalation↗
PubMed1998

Is there a "trochaic bias" in early word learning? Evidence from infant production in English and French.

Studies of speech perception and segmentation in the prelinguistic period, early word production, and patterns of function word omission in early syntax have all recently emphasized the role of the trochaic accentual pattern in English, sometimes positing a universal trochaic bias. We make use of perceptual and acoustic analyses of words and babble from 9 children acquiring English and 5 acquiring French in the late single-word period (13-20 months) to provide a direct test for the existence of such a bias. Neither English nor French infant vocalizations were exclusively trochaic. The iambic productions of American infants were traced to the presence of iambic phrases in the input. Differences between English and French in the acoustic realization of accent in infant vocalizations were also traceable to adult patterns. However, the almost bipolar distribution of trochaic and iambic patterns in the data from English-learning infants was ultimately traceable to the integration of prosodic and segmental patterning in individual child word production templates, themselves arguably the product of an earlier acting articulatory filter.

Acoustics↗
PubMed1997

Early prediction of prolonged ventilator dependence in thermally injured patients.

BACKGROUND: Recent studies suggest that when prolonged ventilator dependence (PVD) can be predicted in trauma or intensive care unit patients, early tracheostomy may reduce hospital stay and improve utilization of resources. This study was performed to develop criteria predictive of PVD (> 14 days) in burn patients. METHODS: We reviewed burn patients aged > or =16 years admitted between 1990 and 1994 who required ventilator support for > or =3 days. Using the variables full-thickness burn size, age, inhalation injury, and worst PaO2/FiO2 on ventilator day 3, an equation predicting PVD was created using logistic regression. The equation was tested by applying it to 1995 patients. RESULTS: When a probability of >0.5 was considered predictive of PVD, the equation correctly predicted PVD in 82% of 1990 to 1994 patients (n = 110) and 90% of 1995 patients (n = 29). CONCLUSION: PVD in burn patients can be predicted using objective variables in the early postburn period. Predictions can be used to select patients for prospective studies of early tracheostomy.

Adult↗
PubMed1997

Production constraints on utterance-final consonant characteristics in babbling.

In order to evaluate hypotheses regarding production constraints on final consonants in babbling, 721 utterance-final consonants produced by 6 infants in consonant-vowel-consonant (CVC) syllables were examined and compared with the preceding consonant in the CVC. Consistent with earlier studies, major patterns were observed for each of the three main consonantal properties--place and manner of articulation and voicing. These patterns included a strong tendency for final consonants to repeat the place of articulation of nonfinal consonants and a tendency for relatively more fricative, nasal and voiceless consonants to occur in final position than in nonfinal position. The high frequency with which final consonants shared place of articulation with the preceding consonant was considered to reflect 'frame dominance' or the tendency of a relatively constant mandibular cycle (the frame) to determine the structure of utterances with very little contribution from other active articulators. The manner and voicing effects were attributed to an overall terminal energy decrease in the vocal production system.

Child Language↗
PubMed1997

Effects of age, density, and geometry on the bending strength of human metatarsals.

In this basic study, we investigated the relative roles of donor age, bone density, and bone geometry in determining structural strength of human metatarsals tested in a four-point bending configuration. Density measurements were made noninvasively using dual energy X-ray absorptiometry, and geometric measurements were made by digitally imaging cross-sections of specimens. Correlations between area bone mineral density and metatarsal strength were strong (r2 = 0.83, 0.81 for second and third metatarsals, respectively) and were not improved by including cross-sectional area or minimum moment of inertia in multiple regression analyses. Increased donor age was associated with decreased bending strength (r2 = 0.51 and 0.45, respectively), which was expected because increased age correlated significantly with decreased bone density (r2 = 0.69 and 0.80, respectively). These results indicate that the strength of human metatarsals generally decreases with age and that this decrease is likely attributable to decreased bone density. Moreover, the results indicate that noninvasive dual energy x-ray absorptiometry measurements of metatarsal density are useful for assessing metatarsal strength and that additional measurements of bone geometry are not required.

Absorptiometry, Photon↗
PubMed1996

Frequency content of normal and diabetic plantar pressure profiles: implications for the selection of transducer sizes.

How small do pressure transducers need to be in order to faithfully measure the plantar pressure profiles (PPPs) under normal and diabetic feet? In this study, pressures were collected from five diabetic and six non-diabetic subjects using a commercial measurement system with 25 mm2 transducers. Discrete Fourier Transform techniques were then used to determine (i) the spatial frequency content of diabetic and non-diabetic PPPs, and (ii) the effects of quadrupling the transducer area (from 5 mm x 5 mm to 10 mm x 10 mm). When the data were filtered to represent the effects of using 10 mm x 10 mm transducers, it was found that the ensuing reductions in peak pressure in the toe region (50 kPa) were significantly greater than in all other regions of the foot (p < 0.05). There was a significant correlation between pressure underestimations and measured peak pressures in the metatarsal regions. Based on data collected with 25 mm2 transducers it was concluded that transducer sizes greater than 6.36 mm x 6.18 mm (medio-lateral and antero-posterior directions) would result in sub-optimal sampling of PPPs.

Adult↗