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Biomedical subjects

J S Allen

Publications and source records attributed to J S Allen.

At least 19 recordsLinked to original sources
PubMed2007

Effects of temperature variation on suicide in five U.S. counties, 1991-2001.

Effects of weather variables on suicide are well-documented, but there is still little consistency among the results of most studies. Nevertheless, most studies show a peak in suicides during the spring season, and this is often attributed to increased temperatures. The purpose of this study is to test the relationship between monthly temperature and monthly suicide, independent of months or seasons, for five counties located across the United States. Harmonic analysis shows that four of the five counties display some seasonal components in the suicide data. However, simple linear regression shows no correlation between suicide and temperature, and discriminant analysis shows that monthly departure from mean annual suicide rates is not a useful tool for identifying months with temperatures that are colder or warmer than the annual average. Therefore, it appears that the seasonality of suicides is due to factors other than temperature.

Climate↗
PubMed2005

Mechanical resonances of bacteria cells.

The quality of the natural vibrations of specific bacteria is investigated using a shell model which accounts for the elastic properties of the membrane and the associated viscosities of the cytoplasma and the surrounding fluid. The motion of the membrane is approximated in terms of the distribution of internal forces over the shell thickness, which is assumed to be much less than the size of the cell. Flexural moments and intersecting stresses are neglected. Using experimentally obtained values for the membrane properties, high-quality resonances are predicted for several types of bacteria which have radii greater than 5 microm. Viscous shear waves are the main source of energy dissipation as has been previously reported in other studies on the natural oscillations of red blood cells, drops, and bubbles. Implications for the acoustic mediated destruction of bacteria are discussed.

Bacteria↗
PubMed2001

Novel MRI contrast agent for molecular imaging of fibrin: implications for detecting vulnerable plaques.

BACKGROUND: Molecular imaging of thrombus within fissures of vulnerable atherosclerotic plaques requires sensitive detection of a robust thrombus-specific contrast agent. In this study, we report the development and characterization of a novel ligand-targeted paramagnetic molecular imaging agent with high avidity for fibrin and the potential to sensitively detect active vulnerable plaques. METHODS AND RESULTS: The nanoparticles were formulated with 2.5 to 50 mol% Gd-DTPA-BOA, which corresponds to >50 000 Gd(3+) atoms/particle. Paramagnetic nanoparticles were characterized in vitro and evaluated in vivo. In contradistinction to traditional blood-pool agents, T1 relaxation rate as a function of paramagnetic nanoparticle number was increased monotonically with Gd-DTPA concentration from 0.18 mL. s(-1). pmol(-1) (10% Gd-DTPA nanoparticles) to 0.54 mL. s(-1). pmol(-1) for the 40 mol% Gd-DTPA formulations. Fibrin clots targeted in vitro with paramagnetic nanoparticles presented a highly detectable, homogeneous T1-weighted contrast enhancement that improved with increasing gadolinium level (0, 2.5, and 20 mol% Gd). Higher-resolution scans and scanning electron microscopy revealed that the nanoparticles were present as a thin layer over the clot surface. In vivo contrast enhancement under open-circulation conditions was assessed in dogs. The contrast-to-noise ratio between the targeted clot (20 mol% Gd-DTPA nanoparticles) and blood was approximately 118+/-21, and that between the targeted clot and the control clot was 131+/-37. CONCLUSIONS: These results suggest that molecular imaging of fibrin-targeted paramagnetic nanoparticles can provide sensitive detection and localization of fibrin and may allow early, direct identification of vulnerable plaques, leading to early therapeutic decisions.

Animals↗
PubMed2001

Optical and acoustical dynamics of microbubble contrast agents inside neutrophils.

Acoustically active microbubbles are used for contrast-enhanced ultrasound assessment of organ perfusion. In regions of inflammation, contrast agents are captured and phagocytosed by activated neutrophils adherent to the venular wall. Using direct optical observation with a high-speed camera and acoustical interrogation of individual bubbles and cells, we assessed the physical and acoustical responses of both phagocytosed and free microbubbles. Optical analysis of bubble radial oscillations during insonation demonstrated that phagocytosed microbubbles experience viscous damping within the cytoplasm and yet remain acoustically active and capable of large volumetric oscillations during an acoustic pulse. Fitting a modified version of the Rayleigh-Plesset equation that describes mechanical properties of thin shells to optical radius-time data of oscillating bubbles provided estimates of the apparent viscosity of the intracellular medium. Phagocytosed microbubbles experienced a viscous damping approximately sevenfold greater than free microbubbles. Acoustical comparison between free and phagocytosed microbubbles indicated that phagocytosed microbubbles produce an echo with a higher mean frequency than free microbubbles in response to a rarefaction-first single-cycle pulse. Moreover, this frequency increase is predicted using the modified Rayleigh-Plesset equation. We conclude that contrast-enhanced ultrasound can detect distinct acoustic signals from microbubbles inside of neutrophils and may provide a unique tool to identify activated neutrophils at sites of inflammation.

Contrast Media↗
PubMed2001

Echocardiographic characterization of fundamental mechanisms of abnormal diastolic filling in diabetic rats with a parameterized diastolic filling formalism.

Abnormalities of diastolic function (DF) precede systolic dysfunction in diabetic cardiomyopathy. Transmitral Doppler flow analysis is the primary method for noninvasively assessing DF. We used model-based Doppler E-wave analysis to evaluate diastolic function differences between normal and diabetic rat hearts. Control rats and those with diabetes underwent echocardiography with analysis by traditional Doppler indexes and by the parameterized diastolic filling (PDF) formalism, generating 3 parameters, x0, c, and k, that uniquely characterize each E-wave. Significant intergroup differences in the E/A ratios (P <.01), isovolumic relaxation times (P <.01), and the modeling parameter c (P <.05) were found. There were no significant differences in shortening fraction, deceleration time, myocardial collagen content, or the parameters x0 and k between diabetic and control rats. These results indicate that differences in diastolic function may be noninvasively quantified and that diabetic hearts may exhibit defects in uncoupling of the contractile apparatus without concomitant increases in chamber stiffness.

Animals↗
PubMed2001

Shell waves and acoustic scattering from ultrasound contrast agents.

Ultrasound contrast agents are encapsulated microbubbles, filled either with air or a higher weight molecular gas, ranging in size from 1 to 10 microns in diameter. The agents are modeled as air-filled spherical elastic shells of variable thickness and material properties. The scattered acoustic field is computed from a modal series solution, and reflectivity and angular scattering are then determined from the computed fields for agents of various properties. We show that contrast agents also support shell resonance responses in addition to the monopole response, which has been the focus of previous contrast agent studies. Lamb waves appear to be the source of these additional responses. A shell or curvature Lamb wave generates dipole peaks in the 1- to 40-MHz range for 2.5 to 3.5 microns radius agents with elastic properties approximating those of albumin protein. The inclusion of damping affects the lower frequency dipole peaks but is less important for responses occurring above approximately 30 MHz. Moreover, these responses hold untapped potential for clinical ultrasound applications such as tissue perfusion studies and high frequency contrast agent imaging.

Biomedical Engineering↗
PubMed2001

Contextual influences on the internal structure of phonetic categories: a distinction between lexical status and speaking rate.

Previous research has shown that phonetic categories have a graded internal structure that is highly dependent on acoustic-phonetic contextual factors, such as speaking rate; these factors alter not only the location of phonetic category boundaries, but also the location of a category's best exemplars. The purpose of the present investigation, which focused on the voiceless category as specified by voice onset time (VOT), was to determine whether a higher order linguistic contextual factor, lexical status, which is known to alter the location of the voiced-voiceless phonetic category boundary, also alters the location of the best exemplars of the voiceless category. The results indicated that lexical status has a more limited and qualitatively different effect on the category's best exemplars than does the acoustic-phonetic factor of speaking rate. This dissociation is discussed in terms of a production-based account in which perceived best exemplars of a category track contextual variation in speech production.

Adolescent↗
PubMed2000

Lactose digestion capacity in Tokelauans: a case for the role of gene flow and genetic drift in establishing the lactose absorption allele in a Polynesian population.

Throughout the Pacific, lactose absorption occurs at rates of 0-46%. Most authors explain the current rate of lactose absorption in the Pacific in terms of gene flow with Europeans. However, researchers have not been able to determine the exact historical circumstances of the introduction of the lactose absorption gene. The availability of genealogical material, historical information, and mal/absorption frequencies for Tokelau (a Polynesian population) presents a unique opportunity to examine the role of gene flow in establishing lactose absorption in Pacific isolates. In an earlier study, Cheer and Allen ([1997] Am. J. Hum. Biol. 93:1-34) determined lactose digestion capacities for 58 Tokelauans. In the current study, we constructed pedigrees for the same 58 individuals, using the Tokelau Island Migrant Study genealogies (Wessen et al. [1992]). Results indicated that 8 of 13 lactose-absorbing individuals have European ancestors, compared with only 4 of 35 lactose malabsorbers (Chi(2) = 15.75, P < 0.01). Six lactose-absorbing individuals have either American or Portuguese ancestors dating back to the mid-1800s. Historical data were used to establish the contribution of Portuguese and American genetic material to the Tokelau population following massive depopulation after the Peruvian slave raids of 1863. This study provides clear evidence for the role of a population bottleneck followed by gene flow and genetic drift in establishing lactose absorption in the Tokelau population. Furthermore, it is the first study of a Pacific population to directly link lactose absorption with gene flow.

Absorption↗
PubMed2000

Cross-cultural analysis of eventfulness in the lives of people with schizophrenia.

Eventfulness as a strategy for creating a meaningful life is an important component of the attempts of people with schizophrenia to present a positive self-image. This study of patients with schizophrenia shows that the phenomenon of creating eventfulness through normalcy accounts is relevant cross-culturally, with common themes occurring in the speech of participants from Papua New Guinea and New Zealand. Both patient (n = 23) and nonpatient (n = 27) participants from these two countries were interviewed as part of a larger research project. Conversational speech of participants was analyzed for passages that could be defined as normalcy accounts. A total of 61 such accounts were obtained from the conversational samples. The three most common themes of normalcy accounts (educational achievement and goals, national pride, and travel) were characteristic of the self-presentation of nonpatient subjects as well as patients with schizophrenia. Normalcy themes varied slightly depending on nationality and patient or nonpatient status. The similarity of both normalcy account themes and presentation, however, was remarkably consistent across cultures.

Adult↗
PubMed2000

Kinetics of the mucosal antibody secreting cell response and evidence of specific lymphocyte migration to the lung after oral immunisation with attenuated S. enterica var. typhimurium.

The kinetic of mucosal secretory responses elicited by the vaccine vector Salmonella enterica var. typhimurium (S. typhimurium) was examined by enzyme linked immunospot (ELISPOT) and compared with serum responses. Mice immunised orally with BRD509, the aroA, aroD mutant of virulent S. typhimurium SL1344 expressing the C Fragment of tetanus toxin (TT), simultaneously developed an IgA antibody secreting cells (ASC) response in the gastrointestinal lamina propria, the spleen and the lung, against both S. typhimurium lipopolysaccharide (LPS) and TT. The magnitude of the ASC response was greatest in the gut, was boosted by a secondary immunisation at day 25, and the kinetic of the response did not correlate with the appearance of serum antibodies. This study suggests that S. typhimurium can engage the common mucosal immune system to effect mucosal secretory responses at distal sites, however, the magnitude of the responses is both greatest in the gut and antigen-specific. The ASC origin of the serum antibodies specific for S. typhimurium and antigens expressed by the bacterium is yet to be elucidated.

Animals↗
PubMed2000

Left ventricular contractility is impaired following myocardial infarction in the pig and rat: assessment by the end systolic pressure-volume relation using a single-beat estimation technique and cine magnetic resonance imaging.

The end systolic pressure-volume relation (ESPVR) has been shown to be a relatively load independent measure of left ventricular (LV) contractility. Recently, several single-beat ESPVR computation methods have been developed, enabling the quantification of LV contractility without the need to alter vascular loading conditions on the heart. Using a single-beat ESPVR method, which has been validated previously in humans and assumes that normalized elastance is constant between individuals of a species, we studied the effects of myocardial infarction on LV contractility in two species, the rat and the pig. In our studies, LV pressure was acquired invasively and LV volume determined noninvasively with magnetic resonance imaging, at one week postinfarction in pigs and at 12 weeks postinfarction in rats. Normalized systolic elastance curves in both animal species were not statistically different from that of humans. Also, the slope of the ESPVR (Ees) decreased significantly following infarction in both species, while the volume-axis intercept (V0) was unaffected. These results indicate that a single-beat ESPVR method can be used to measure the inotropic response of the heart to myocardial infarction, and that the basis for this method (i.e., constant normalized elastance) is applicable to a variety of mammalian species.

Animals↗
PubMed2000

Dynamics of gas bubbles in viscoelastic fluids. II. Nonlinear viscoelasticity.

The nonlinear oscillations of a spherical, acoustically forced gas bubble in nonlinear viscoelastic media are examined. The constitutive equation [Upper-Convective Maxwell (UCM)] used for the fluid is suitable for study of large-amplitude excursions of the bubble, in contrast to the previous work of the authors which focused on the smaller amplitude oscillations within a linear viscoelastic fluid [J. S. Allen and R. A. Roy, J. Acoust. Soc. Am. 107, 3167-3178 (2000)]. Assumptions concerning the trace of the stress tensor are addressed in light of the incorporation of viscoelastic constitutive equations into bubble dynamics equations. The numerical method used to solve the governing system of equations (one integrodifferential equation and two partial differential equations) is outlined. An energy balance relation is used to monitor the accuracy of the calculations and the formulation is compared with the previously developed linear viscoelastic model. Results are found to agree in the limit of small deformations; however, significant divergence for larger radial oscillations is noted. Furthermore, the inherent limitations of the linear viscoelastic approach are explored in light of the more complete nonlinear formulation. The relevance and importance of this approach to biomedical ultrasound applications are highlighted. Preliminary results indicate that tissue viscoelasticity may be an important consideration for the risk assessment of potential cavitation bioeffects.

Acoustics↗
PubMed2000

Effects of chewing betel nut (Areca catechu) on the symptoms of people with schizophrenia in Palau, Micronesia.

BACKGROUND: Although millions of people with schizophrenia live in betel chewing regions, the effects of betel chewing on their symptoms are unknown. Betel nut alkaloids include potent muscarinic cholinomimetics: recent research suggests that these agents may be therapeutic in schizophrenia. AIMS: To compare the primary and extrapyramidal symptom profiles and substance-using habits of betel chewing v. non-chewing people with schizophrenia. METHOD: A cross-sectional study of 70 people with schizophrenia. Symptom ratings measured by the Positive and Negative Syndrome Scale (PANSS) and Extrapyramidal Symptom Rating Scale (ESRS), and demographic and substance-use data, were compared for 40 chewers and 30 non-chewers of betel nut. RESULTS: Betel chewers with schizophrenia scored significantly lower on the positive (P = 0.001) and negative (P = 0.002) sub-scales of the PANSS than did non-chewers. There were no significant differences in extrapyramidal symptoms or tardive dyskinesia. CONCLUSIONS: Betel chewing is associated with milder symptomatology and avoidance of more harmful recreational drugs. These initial results indicate that longitudinal research is merited.

Adult↗
PubMed1999

Social deficits associated with schizophrenia defined in terms of interpersonal Machiavellianism.

The social deficits of schizophrenia have been interpreted in an evolutionary context of Machiavellian social dexterity, stressing deficits in evolved psychological mechanisms that mediate the interpretation of affect and deceptive intention in others. A complementary hypothesis was tested, that patients with schizophrenia will be relatively non-Machiavellian compared to controls, and that social problems associated with the condition may reflect this relative social credulity. This hypothesis was addressed by assessing Mach IV psychometric scale performance in a group of 51 patients with schizophrenia and in 93 controls. Males, but not females, with schizophrenia scored significantly lower on the Mach IV scale than control groups. This result is interpreted in conjunction with the existing literature on social competence and sex differences in the symptomatology of patients with schizophrenia.

Adolescent↗
PubMed1999

Effects of syllable-initial voicing and speaking rate on the temporal characteristics of monosyllabic words.

Two speech production experiments tested the validity of the traditional method of creating voice-onset-time (VOT) continua for perceptual studies in which the systematic increase in VOT across the continuum is accompanied by a concomitant decrease in the duration of the following vowel. In experiment 1, segmental durations were measured for matched monosyllabic words beginning with either a voiced stop (e.g., big, duck, gap) or a voiceless stop (e.g., pig, tuck, cap). Results from four talkers showed that the change from voiced to voiceless stop produced not only an increase in VOT, but also a decrease in vowel duration. However, the decrease in vowel duration was consistently less than the increase in VOT. In experiment 2, results from four new talkers replicated these findings at two rates of speech, as well as highlighted the contrasting temporal effects on vowel duration of an increase in VOT due to a change in syllable-initial voicing versus a change in speaking rate. It was concluded that the traditional method of creating VOT continua for perceptual experiments, although not perfect, approximates natural speech by capturing the basic trade-off between VOT and vowel duration in syllable-initial voiced versus voiceless stop consonants.

Female↗
PubMed1998

Patterns of prehistoric human mobility in polynesia indicated by mtDNA from the Pacific rat.

Human settlement of Polynesia was a major event in world prehistory. Despite the vastness of the distances covered, research suggests that prehistoric Polynesian populations maintained spheres of continuing interaction for at least some period of time in some regions. A low level of genetic variation in ancestral Polynesian populations, genetic admixture (both prehistoric and post-European contact), and severe population crashes resulting from introduction of European diseases make it difficult to trace prehistoric human mobility in the region by using only human genetic and morphological markers. We focus instead on an animal that accompanied the ancestral Polynesians on their voyages. DNA phylogenies derived from mitochondrial control-region sequences of Pacific rats (Rattus exulans) from east Polynesia are presented. A range of specific hypotheses regarding the degree of interaction within Polynesia are tested. These include the issues of multiple contacts between central east Polynesia and the geographically distinct archipelagos of New Zealand and Hawaii. Results are inconsistent with models of Pacific settlement involving substantial isolation after colonization and confirm the value of genetic studies on commensal species for elucidating the history of human settlement.

Animals↗