Search PubMed⌕ Search

Biomedical subjects

H T Davis

Publications and source records attributed to H T Davis.

At least 19 recordsLinked to original sources
PubMed2005

Clinical assessment of near-infrared spectroscopy for noninvasive diabetes screening.

BACKGROUND: Current diabetes screening techniques comprise the fasting plasma glucose (FPG) and oral glucose tolerance tests. Both tests demand patient compliance, and neither test has ideal performance. Near-infrared (NIR) spectroscopy is a noninvasive means of interrogating characteristics of a sample and is evaluated as a novel screening method for type 2 diabetes. METHODS: One hundred fifty-four patients with and without type 2 diabetes were recruited. Their forearm skin was measured with the NIR spectroscopic system, and a capillary blood glucose measurement was also taken. Sixty-six patients returned for a second visit at a later date. A multivariate model, generated from a separate training study, was employed to produce a quantitative risk marker of disease for each NIR spectrum. Sensitivity and specificity (the probabilities that the NIR method will correctly identify a subject as having diabetes or as not having diabetes, respectively) were calculated. As the NIR method produces a continuous rather than categorical classification, various thresholds were evaluated to give several sensitivity and specificity pairs. Test reproducibility was also determined. RESULTS: At a false-positive rate of 70%, the NIR test had a sensitivity of 77.7%, which is comparable to the 77.3% sensitivity for the FPG test as reported for the Third National Health and Nutrition Examination Survey (NHANES III) study. The reproducibility of the NIR test was also similar to the FPG test (inter-day agreement rates of 84.2% and 79.2%, respectively). CONCLUSIONS: A noninvasive NIR spectroscopic measurement of the volar forearm was shown to have comparable performance characteristics with the FPG test. The source of the spectroscopic signal is still uncertain and is the subject of ongoing research.

Adult↗
PubMed2002

Enhanced dispersion in cylindrical packed beds.

The effective longitudinal dispersion constant, D(L)(eff), in cylindrical packed beds is larger than in the bulk due to the existence of radial inhomogeneities induced by the cylinder walls. For dense random packed beds, D(L)(eff) can be several times larger than the bulk value, even for arbitrarily large cylinder radius, R. The time-scale for attaining asymptotic dispersion rates in a cylindrical geometry is neither the convective nor the diffusive time-scale, but rather D(T)/R(2), where D(T) is the bulk transverse dispersion rate. Similar effects are predicted for packed beds confined in ducts of any cross-sectional geometry. The case of a rectangular duct, compared with an infinite slit, provides an intuitive model for the influence of walls in the limit as R goes to infinity.

Colloids↗
PubMed2001

Regional variations in skin barrier function and cutaneous irritation due to iontophoresis in human subjects.

The effect of saline iontophoresis on skin barrier function and irritation was investigated on three body sites (abdomen, chest and upper arm) in order to select an appropriate site for iontophoretic delivery of drugs. Thirty healthy human volunteers were recruited according to specific entry criteria. Ten subjects, five males and five females, were assigned to each body site group. Skin barrier function and irritation was examined after 4 h of saline iontophoresis at a current density of 0.2 mA/cm(2) on a 6.5 cm(2) area in terms of the measured responses: transepidermal water loss (TEWL), skin capacitance, skin temperature and visual scores. Alterations in TEWL due to iontophoresis were not observed in the upper arm and chest; however, changes in TEWL at the abdomen were observed and returned to baseline 2 h after patch removal. Similarly, changes in capacitance due to iontophoresis returned to baseline (P>0.05) at the three body sites 2 h after patch removal except under the anode at the abdomen (P<0.05). There was a significant increase in skin temperature due to iontophoresis at the anode and the cathode (P<0.05) at the upper arm. Edema was not observed. At patch removal, the erythema score was significantly (P<0.001) elevated in comparison to baseline at the three body sites. Erythema resolved within 24 h except at the chest under the anode, where the erythema score was still higher (P<0.01) than the baseline. Papules appeared in five subjects at the active anode site on the chest. In three of the subjects, these papules did not resolve until 24 h post patch removal. Thus, there was regional variation in the function of the skin and irritation due to iontophoresis. Irritation was greater at the chest than at the abdomen or upper arm.

Abdomen↗
PubMed2000

Effect of saline iontophoresis on skin barrier function and cutaneous irritation in four ethnic groups.

The effect of saline iontophoresis on skin barrier function and irritation was investigated in four ethnic groups (Caucasians, Hispanics, Blacks and Asians). Forty healthy human volunteers were recruited according to specific entry criteria. Ten subjects, five males and five females, were assigned to each ethnic group. Skin barrier function was examined after 4 hours of saline iontophoresis at a current density of 0.2 mA/cm(2) on a 6.5 cm(2) area in terms of the measured responses: transepidermal water loss (TEWL), skin capacitance, skin temperature and visual scores. There were significant differences in TEWL among the ethnic groups prior to patch application. TEWL at baseline in ethnic groups was in the rank order: Caucasian>Asian>Hispanic>Black. Iontophoresis was generally well tolerated, and skin barrier function was not irreversibly affected by iontophoresis in any group. There was no significant skin temperature change, compared to baseline, in any ethnic groups at any observation point. Edema was not observed. At patch removal, the erythema score was elevated in comparison to baseline in all ethnic groups; erythema resolved within 24 hours. Thus, saline iontophoresis produced reversible changes in skin barrier function and irritation in healthy human subjects.

Adolescent↗
PubMed2000

A pilot study of methylphenidate, clonidine, or the combination in ADHD comorbid with aggressive oppositional defiant or conduct disorder.

A pilot comparison of the safety and efficacy of methylphenidate (MPH) combined with clonidine, clonidine monotherapy, or MPH monotherapy in 6- to 16-year-old children diagnosed with attention deficit hyperactivity disorder (ADHD) and comorbid aggressive oppositional defiant disorder or conduct disorder was completed. Study design was a 3-month, randomized, blinded, group comparison with eight subjects per group. No placebo comparison was used. All three treatment groups showed significant improvements in attention deficits, impulsivity, oppositional, and conduct disordered symptoms as assessed by parent and teacher rating scales and laboratory measures. Significant differences among treatment groups were found only on a few measures. Only the clonidine monotherapy group showed significantly decreased fine motor speed. These results suggest the safety and efficacy of clonidine alone or in combination with MPH for the treatment of ADHD and aggressive oppositional and conduct disorders.

Adolescent↗
PubMed1998

Paramagnetic tracer concentration evolution by NMR relaxation time mapping: application to Aris-Taylor dispersion.

A procedure to study tracer dispersion was proposed and tested for the case of tracer spreading in tube flow. Concentration maps of paramagnetic tracers Gd3+ were measured in time through direct measurements of spin lattice relaxation time T1 obtained by using a two-point stimulated echo pulse sequence. The procedure was used to test the linear dependence of Peclet number on inverse velocity in the range of flow rates 0.3-1.2 cc/min.

Contrast Media↗
PubMed1996

A compendium of potential energy maps of zeolites and molecular sieves.

We present potential maps of xenon in 20 different zeolites and molecular sieves. The potential maps reveal both the accessible pore volume and localized adsorption sites and so are important in understanding adsorption and diffusion processes in nanoporous materials. We examine zeolites and molecular sieves with one-dimensional channel-like nanopores (zeolite-Theta 1, AlPO4-5, zeolite-Omega, zeolite-L, ZSM-12, AlPO4-8, and VPI-5), with two-dimensional intersecting channel-like nanopores (ZSM-5 [silicalite], ZSM-11, ferrierite, mordenite, and zeolite-Beta), and with three-dimensionally connected cagelike nanopores (zeolite-A, zeolite-Rho, zeolite-Y, sodalite, chabazite, cloverite, cation-poor zeolite-A, and cation-rich zeolite-A). We report the fraction of pore volume accessible, the maximum energy well depth at the adsorption sites, and the activation energy to move between sites. We note several examples of surprising similarities and differences between various molecular sieves. In several instances, we show that these potential profiles are relevant for other small Lennard-Jones-like molecules. By comparison with published Monte Carlo and molecular dynamics simulations, we show that the density distributions of adsorbates at low density are well predicted by the potential maps.

Cations↗
PubMed1996

Dispersion of paramagnetic tracers in bead packs by T1 mapping: experiments and simulations.

NMR imaging was used to study dispersion in 6 mm bead pack. T1 maps were employed to measure the rate of axial spreading of paramagnetic tracers (GdCl3) inside the bead pack in the range of flow rate from 0.015 mL/s to 0.175 mL/s. From the T1 maps, tracer concentration profiles were obtained, which yielded dimensionless axial dispersion coefficient and mean transit time. Spatial variations in the dispersion coefficient were observed at flow rates above 0.08 mL/s. We hypothesized that the observed spatial oscillations in the dispersion coefficient arise from the spatial variations of the velocity distribution. To validate this mechanism we showed by simulation that similar dispersion coefficient variation occur in a layered network.

Contrast Media↗
PubMed1993

Zeolite adsorption site location and shape shown by simulated isodensity surfaces.

The graphics software package Ribbons is used to display isodensity surfaces of Xe atoms adsorbed in the alpha cage of zeolite NaA. The location, size, and shape of the adsorption sites are highly dependent on the loading and the crystal cation content. When the zeolite has a high number of cations, ellipsoidal sites arrange in a cuboctahedron. When the zeolite has fewer cations, cone-shaped sites arrange in an octahedron at low loading, but at high loading the sites become ellipsoidal and new sites form at cuboctahedral positions. The effect of the nature of the adsorption site on the development of a universal adsorption model is discussed.

Adsorption↗
PubMed1988

Controlled environment vitrification system: an improved sample preparation technique.

The controlled environment vitrification system (CEVS) permits cryofixation of hydrated biological and colloidal dispersions and aggregates from a temperature- and saturation-controlled environment. Otherwise, specimens prepared in an uncontrolled laboratory atmosphere are subject to evaporation and heat transfer, which may introduce artifacts caused by concentration, pH, ionic strength, and temperature changes. Moreover, it is difficult to fix and examine the microstructure of systems at temperatures other than ambient (e.g., biological systems at in vivo conditions and colloidal systems above room temperature). A system has been developed that ensures that a liquid or partially liquid specimen is maintained in its original state while it is being prepared before vitrification and, once prepared, is vitrified with little alteration of its microstructure. A controlled environment is provided within a chamber where temperature and chemical activity of volatile components can be controlled while the specimen is being prepared. The specimen grid is mounted on a plunger, and a synchronous shutter is opened almost simultaneously with the release of the plunger, so that the specimen is propelled abruptly through the shutter opening into a cryogenic bath. We describe the system and its use and illustrate the value of the technique with TEM micrographs of surfactant microstructures in which specimen preparation artifacts were avoided. We also discuss applications to other instruments like SEM, to other techniques like freeze-fracture, and to novel "on the grid" experiments that make it possible to freeze successive instants of dynamic processes such as membrane fusion, chemical reactions, and phase transitions.

Microscopy, Electron↗
PubMed1987

Use of risk assessment methods in the certification of decontaminated buildings.

Accidental events such as fires, explosions, and leaks often result in large-scale contaminations of buildings with toxic chemicals. After decontamination, the certification for original use requires testing for residual contamination. The two basic kinds of sampling plans in use up to recently both fall short of the required performance. Their deficiencies are analyzed in terms of the scientific questions implicit in both the sampling plan and the subsequent statistical evaluation. A sampling strategy of a new kind is proposed and discussed in the same context. It is motivated by concern for the long-term safety of the building's occupants and is, therefore, based on factors important in risk assessment. Three different sampling plans are derived in the framework of this methodology, two of which have already been used in actual certification proceedings.

Algorithms↗
PubMed1986

Graphical analysis of multivariate pain data in analgesic trials.

In order to compare analgesic treatments effectively one must measure pain over time. In a single-dose clinical analgesic trial one typically obtains repeated pain measurements from each patient during a relatively short period (4-6 hours). Such measurements constitute multivariate data, which are usually reduced by simple addition to a single derived pain measure for analysis of between-treatment differences. In this article we consider graphical procedures for the display of multivariate, clinical analgesic data. The first of these are the traditional time-effect curves, with added "standard error bars." We also examine a multivariate display, the biplot, which is based on principal component analysis. This technique provides a representation of the raw pain scores at each time of measurement by a vector originating from the origin of a two-dimensional graph. The multivariate pain scores of individual patients are summarized by points on the graph. Differences in pain scores over time (or between treatment groups) may be examined by relating points (or ellipses representing treatment groups) to different vectors. Using actual data from a postsurgical analgesic trial, we compare the two approaches and show that the multivariate approach is a useful addition to the standard technique for display of such data.

Analgesics↗
PubMed1984

Gallbladder disease: risk factor for colorectal carcinoma?

The relation between gallbladder disease and the risk of colorectal carcinoma (CRC) is examined in light of 864 consecutive adult postmortem examinations analyzed for significant associations between the state of the gallbladder (normal, cholelithiasis, and cholecystectomy) and the presence of colorectal carcinoma. Our findings supported the known association between female sex and gallbladder disease (p = 0.02) and revealed a significant association between cholelithiasis and/or cholecystectomy and colorectal cancer (p less than 0.02). The frequency of CRC was higher in patients who had a cholecystectomy than in those still with stones, but this difference was not statistically significant. The data suggests a sex-linked dependence between the state of gallbladder and CRC. However, the proper statistical test for this dependence was not significant (p less than 0.25), no doubt as a result of the relatively small amount of data for persons with gallbladder disease. We conclude that the state of gallbladder may modify the risk for colorectal carcinoma.

Cholecystectomy↗
PubMed1983

Somatosensory thresholds in monkeys exposed to acrylamide.

Six monkeys were trained to report detection of a vibratory or electrical stimulus applied to the fingertip. The vibratory stimuli were presented at two frequencies (40 and 150 Hz). Thresholds were determined with a tracking procedure before, during, and after dosing. Each monkey served as its own control. Four monkeys were dosed orally with 10 mg/kg of acrylamide 5 days a week until the appearance of toxic signs. The total administered dose varied between 320 and 450 mg/kg. The other two monkeys served as time-matched controls. All the monkeys were observed 5 days a week. They were also weighed and presented with a visuomotor task (pickup test) twice a week. Weight loss usually preceded the onset of gross behavioral disturbances, such as loss of balance, tremor, or decreased activity. Impaired coordination, as revealed with the pickup test, paralleled weight loss. Electrical sensitivity was not affected. Vibration sensitivity, however, fell during dosing and remained impaired for several months after dosing ceased, outlasting all the other effects. Recovery of the other indices occurred relatively soon after dosing ended. These data indicate that vibration sensitivity testing can trace the time course of intoxication and recovery in toxic peripheral neuropathies. Furthermore, the differential results obtained with vibratory and electrical stimulation are consonant with a primary effect on end-organ receptors.

Acrylamides↗
PubMed1982

Imaging vesicular dispersions with cold-stage electron microscopy.

A fast-freeze, cold-stage transmission electron microscopy technique which can incorporate in situ freeze-drying of the sample is described. Its use in elucidating structure in unstained and stained, hydrated and freeze-dried, aqueous vesicular dispersions of biological and chemical interest is demonstrated with vesicles of L-alpha-phosphatidylcholine (bovine phosphatidylcholine) and of the synthetic surfactant sodium 4-(1'-heptylnonyl)benzenesulfonate (SHBS). The contrast features observed in transmission electron microscope images of frozen, hydrated samples are identified and explained with the dynamical theory of electron diffraction. Radiolysis by the electron beam is shown to increase contrast in vesicle images and to change their structure and size. Micrographs illustrate the freeze-drying of a dispersion in the microscope; the process causes vesicles to shrink and collapse.

Animals↗
PubMed1982

The chronology and suddenness of cardiac death after myocardial infarction.

A prospective postinfarction study of 978 patients less tha 66 years of age followed from 1 to 5 years was utilized to evaluate the chronology (interval from hospital discharge to demise) and suddenness (elapsed time from the onset of terminal symptoms to demise) of cardiac death. Clinical information including the patient's history and CCU, 6-hour Holter electrocardiographic, medication, and mortality event data was available on 112 cardiac deaths, with 56% of those with witness deaths dying suddenly (less than or equal to 1 hour). During the first postinfarction year 50% of the nonsudden deaths occurred within the first month after hospital discharge, whereas 84% of the sudden deaths occurred in the 2 to 12 month period after infarction (Chi Square = 6.25, p less than 0.02). There were no clinical variables including Holter-recorded ventricular premature beats that distinguished between early and late or sudden and nonsudden cardiac death. These findings indicate that the chronology and suddenness of the terminal cardiac event are more difficult to predict than had previously been appreciated. The therapeutic implications of these observations are discussed.

Aged↗