Biomedical subjects

A F Hall

Publications and source records attributed to A F Hall.

At least 19 recordsLinked to original sources

PubMed2004

In vitro dentine permeability: the relative effect of a dentine bonding agent on crown preparations.

OBJECTIVE: The aim of this study was to determine whether a dentine bonding agent (DBA) had an effect in reducing fluid filtration under cemented provisional crowns. METHODS: Crown preparations on 34 premolars, randomly allocated to two equal-sized test and control groups, were assessed for dentine permeability by a fluid filtration technique. In the test group, prepared crowns were acid-etched and then treated with a DBA (Prime & Bond NT). In the control group, no such DBA was applied. Provisional crowns were cemented on both groups of teeth using non-eugenol zinc oxide cement. Fluid filtration rates were measured repeatedly after crown preparation, at cementation, 1 h, 1 day, 1 week and 3 weeks following crown cementation for both groups. Filtration rates were also measured after acid-etching and dentine bonding for the test group. RESULTS: There was insufficient evidence to suggest any statistically significant differences either between the two groups or, on average, across the five time points in each group in terms of the relative percentage of fluid filtration. CONCLUSION: The DBA used did not seal dentinal tubules any more than did the smear layer and provisional crowns luted with a non-eugenol ZnO cement.

Acid Etching, Dental↗

PubMed2002

The intra- and inter-examiner reliability of quantitative light-induced fluorescence (QLF) analyses.

OBJECTIVE: To assess the reliability of the analysis stage of quantitative light-induced fluorescence (QLF). The QLF analysis involves subjective input from the user and this study examines the influence of this on the reproducibility of the QLF data. METHOD: QLF images were taken of 20 human molar teeth that had been previously subjected to a demineralizing solution (phosphoric acid 37%) to create artificial white spot lesions on their buccal surfaces. Following examination of the images, 16 were chosen to represent a range of lesion size and severity. Three copies were made of the images and each was allocated a different filename. 10 examiners in three centres were asked to analyse each of the 16 images on three occasions, with at least seven days between each attempt. Simple instructions describing the analysis procedure were supplied and examiners were asked to adhere to these directions. Examiners were asked to rate each of the 16 teeth on their first attempt both quantitatively (5 point scale) and qualitatively in terms of difficulty of analysis. Data reported were the delta Q at 5% threshold for each tooth on each of three attempts. RESULTS: Using ANOVA and paired t-tests to detect statistical differences, the three attempts of each examiner were used to determine intra-examiner reliability. Only one examiner (a novice at the technique) demonstrated differences between all three attempts and two demonstrated difference between one attempt. When the mean scores were compared to determine the inter-examiner reliability, only one examiner's results were statistically different when compared with two others. CONCLUSION: This study has demonstrated that the analysis stage of QLF is reliable between examiners and within multiple attempts by the same examiner, when analysing in vitro lesions. Novices at the technique should be trained before analysing experimental data.

Analysis of Variance↗

PubMed1999

The effect of saliva on enamel and dentine erosion.

The present study aims to assess the ability of saliva, both in vitro and in situ, to prevent surface mineral loss from enamel and dentine when exposed to an erosive challenge. Fifteen groups of four varnished thin tooth sections were stored in saliva collected from individuals taking part in the in situ study and a further eight groups, each containing four sections, were stored in deionised water. In vitro, sections were stored in saliva or water for 14 days. In addition, fifteen subjects each wore an appliance with four varnished sections. Appliances with sections were worn for 14 days. All sections were exposed to 25 ml of erosion solution for 5 min twice daily. Microradiography and image analysis of the recovered sections demonstrated significant protection of surface mineral loss from enamel and dentine by saliva in vitro and in situ compared with deionised water (p < 0.05). Significantly less mineral loss (p < 0.05) was observed for enamel and dentine stored in situ compared with storage in saliva in vitro. Generalised linear modelling demonstrated both the subject and protocol had significant effect on mineral loss. A weak positive correlation (r = 0.64) was noted when in situ and in vitro mineral loss from enamel were compared, demonstrating greater reactivity of the in vitro enamel specimens to the erosion challenge. The dentine data did not show any linear correlation. Saliva protected against mineral loss by erosion and, for enamel, in vitro results demonstrated a weak positive correlation with in situ results.

Dental Enamel↗

PubMed1998

Evaluation of model-based processing algorithms for averaged transmitral spectral Doppler images.

In an effort to characterize more fully diastolic function using Doppler echocardiography, we have previously developed an automated method of model-based image processing for spectral Doppler images of transmitral blood flow. In this method, maximum velocity envelopes (MVEs) extracted from individual Doppler images are aligned and averaged over several cardiac cycles. The averaged waveform is fit by the solution of a kinematic model of diastolic filling. The results are estimates of the model parameters. As expected, the mean and standard deviation of the model parameter estimates depend on many factors such as noise, the number of cardiac cycles averaged, beat-to-beat variation, waveform shape, observation time and the processing methods used, among others. A comprehensive evaluation of these effects has not been performed to date. A simulation was developed to evaluate the performance of three automated processing methods and to measure the influence of noise, beat-to-beat variation and observation time on the model parameter estimates. The simulation's design and a description and analysis of the three automated processing methods are presented. Of the three methods evaluated, using the inflection point in the acceleration portion of the velocity contour as the first data point to be fit was found to be the most robust method for processing averaged E-wave MVE waveforms. Using this method under nominal conditions, the average bias was measured to be < 3% for each of the model parameters. As expected, the biases and standard deviations of the estimates increased as a result of increased noise levels, increased beat-to-beat variation and decreased observation time. Another important finding was that the effects of noise, beat-to-beat variation and waveform observation time on the parameter estimates are dependent on the location in model parameter space.

Algorithms↗

PubMed1998

Beat averaging alternatives for transmitral Doppler flow velocity images.

To characterize diastolic function from transmitral Doppler data, the image's maximum velocity envelope (MVE) is fit by a model for flow velocity. To reduce the physiologic beat-to-beat variability of best-fit determined model parameters, averaging of multiple cardiac cycles is indicated. To assess variability mathematically, we modeled physiologic noise as a random (normally-distributed) process and evaluated three methods of averaging (1, averaging model parameters from single images; 2, averaging images; and 3, averaging MVEs) using clinical datasets (50 continuous beats from 5 subjects). Method 2 generates a positive bias because low-velocity beats will not contribute to the composite MVE. The difference between Methods 3 and 1 is less than 2.0 E-5 (m/s)2 for uncorrelated model parameters. Input having 10% beat-to-beat variation yields a bias of <4% for model parameter mean. Hence, Method 1 was, in general, more robust than Method 3.

Blood Flow Velocity↗

PubMed1997

Postextrasystolic left ventricular isovolumic pressure decay is not monoexponential.

OBJECTIVE: The relationship between the left ventricular (LV) relaxation time constant and early diastolic filling is not fully defined. This study provides additional evidence that LV isovolumic pressure fall in the normal intact heart in response to certain interventions is not adequately described by a model of monoexponential decay and that its relationship to filling is complex. METHODS AND RESULTS: To gain further insight into the relationship between LV relaxation and early rapid filling we measured LV isovolumic relaxation rate, peak early filling velocity (E), LV volumes, and transmitral pressures at baseline and in the first postextrasystolic beat after a short-coupled extrasystole in 9 anesthetized dogs. Postextrasystolic isovolumic relaxation rate was slowed as measured by 3 commonly used time constants, while E was increased 32%. LV contractility and peak pressure were also increased, while LV end-systolic volume was decreased. LV minimum pressure was deceased, while the early diastolic transmitral pressure gradient was increased. Although all relaxation time constants measured over the entire isovolumic relaxation phase indicated slowed relaxation, direct measurement of isovolumic relaxation time indicated no change in relaxation rate. Calculation of the time constants and direct measurement of isovolumic relaxation time during early isovolumic pressure decay indicated slowed postextrasystolic pressure decay rate compared with baseline, while calculation of time constants and direct measurement of isovolumic relaxation time during late isovolumic relaxation indicated augmented postextrasystolic pressure decay rate versus baseline. CONCLUSIONS: This non-exponential behavior of LV isovolumic pressure decay in postextrasystolic beats after short-coupled extrasystoles provides further evidence that the relationship that exists between ventricular relaxation and early filling is not simple. The results are interpreted in terms of current theoretical formulations that attribute control of myocardial relaxation to the interaction between inactivation-dependent and load-dependent mechanisms.

Animals↗

PubMed1997

Echo machine-imposed limit on transmitral spectral Doppler velocity-profile analysis.

We have previously developed a kinematic model of ventricular filling. Its application to in vivo transmitral Doppler velocity profiles provides a quantitative characterization of filling. However, the model parameters computed by solving the "inverse problem" may depend on ultrasound machine type and setting (e.g., gain, baseline filter, dynamic range). To determine machine-based effects on the computed model parameters, we performed a flow phantom study using Acuson and HP echocardiography machines at various settings. We compared maximum velocity envelopes (MVEs), as well as the model fit to these MVEs, for 3 simulated waveforms imaged by both machines. For all 3 waveforms, the machines generated comparable MVEs, fit by the model within a mean-square difference of 5E-5 (m/s)2. The associated variations in model parameters for the 3 waveforms were not uniform. Two waveforms showed slight variation between machines, with model parameters varying by less than 6%. The shortest duration waveform showed model parameter variations of 10-15%. Analysis of the parameter space for this waveform showed a constant mean-square error contour that was larger than that for the other two, causing similar small variations in measured MVEs to result in larger differences in the parameter estimates for this waveform. Because this method completely eliminates inter- and intraobserver variability, we conclude that, within the limits established, the slight contour variations due to machine type and setting should not affect this method's applicability in clinical Doppler-flow analysis.

Blood Flow Velocity↗

PubMed1997

Relationship of the fourth heart sound to atrial systolic transmitral flow deceleration.

The fourth heart sound (S4) is thought to be due to cardiohemic vibrations, powered by deceleration of transmitral blood flow, that occur when atrial systole leads to a disproportionately high rise in ventricular end-diastolic pressure (relative to diastasis), associated with an enhanced atrial systolic blood filling volume or a stiff ventricular wall. To characterize S4 production, we modeled the cardiohemic system as a forced, damped nonlinear harmonic oscillator. The forcing term used a closed-form expression for the Doppler A-wave contour. We simultaneously recorded transthoracic phonocardiograms and Doppler A waves in subjects with and without audible S4 and compared model predictions for S4 amplitude, frequency, and power spectrum with those of the recorded S4. Excellent agreement was observed between the model-predicted amplitude, duration, timing, and power spectrum and those of the phonocardiographic S4. We conclude that, with a normal mitral valve, there should always be an oscillation of the cardiohemic system during A-wave deceleration. However, oscillations may not have high enough amplitude, frequency, or coupling to the chest wall to be clinically audible as an S4.

Atrial Function↗

PubMed1997

Determination of plaque pH changes within the trough of an in situ appliance used to study mineral changes in early carious lesions.

Plaque pH was measured using a glass combination pH microelectrode of plaque deposits lining the trough of an intra-oral appliance which contained single sections of human teeth with artificial enamel lesions. Plaque exposure to a 10% sucrose solution produced significantly lower plaque pH levels than a solution of sorbitol gum extract. The subsequent flow of saliva over the plaque/pH electrode interface resulted in a significant and rapid increase in pH. Repeat experiments, using deionised water instead of saliva, demonstrated no increase in pH at the plaque/electrode interface. This system may provide a convenient method of producing plaque suitable for repeated pH analysis in intimate association with artificial enamel lesions. This may permit further study of the relationship between plaque acidogenicity, salivary buffering capacity and mineral change within the incipient enamel lesion.

Adult↗

PubMed1997

An in situ interproximal model for studying the effect of fluoride on enamel.

This crossover study determined the ability of an interproximal, intra-oral model to demonstrate a fluoride dose response to 0-, 250- and 1,100-ppm fluoride (sodium fluoride) dentifrices with respect to fluoride uptake into, and remineralization of, incipient subsurface enamel lesions. Following a 1 week 'lead in' period during which 30 panelists were randomly assigned to use one of the products, two enamel specimens with artificial carious lesions were mounted into a specially designed functional partial denture worn by each panelist. Panelists continued to brush three times daily with their test dentifrice for 4 weeks, after which the specimens were removed and analyzed for fluoride uptake and remineralization. The procedure was repeated until each panelist had followed all three treatment regimens. Fluoride analyses were performed using a microdrill biopsy technique, and mineral content changes were determined by transverse microradiography. Fluoride uptake data were significantly different (p < 0.01) for all three products with the effect of 1,100 ppm F > 250 ppm F > placebo. The 1,100 ppm F dentifrice also effected significantly greater remineralization (p < 0.01) than did the 250-ppm-F or placebo dentifrices. Relative efficacy of the three fluoride dentifrices tested in this study was similar to that established in a clinical trial, and, therefore, supports the use of this model for in situ studies of the effects of fluoride-containing products on enamel lesions.

Adult↗

PubMed1997

Relative ability of laser fluorescence techniques to quantitate early mineral loss in vitro.

This in vitro investigation was undertaken to explore two different nondestructive methods to detect very early demineralization. These methods were based on the premise that the clinical detection of caries at a very early stage of formation might permit more efficient reversal of the caries process than may occur when lesions are detected at a more advanced stage, such as a so-called 'white spot'. The methods evaluated in this study were quantitative laser fluorescence (QLF) and an experimental dye-enhanced laser fluorescence (DELF) technique. Prepared and polished bovine enamel specimens were demineralized in a conventional lactic acid-Carbopol solution for varying periods of time between 0 and 24 h with an area of sound enamel retained on each specimen. The coded and randomized specimens were then analyzed for the presence and severity of enamel demineralization using QLF after which they were exposed to a selected dye (Pyrromethene 556) and similarly examined using DELF. The specimens were then sectioned and examined by conventional transverse microradiography and by confocal laser-scanning microscopy. Results were analyzed statistically with sensitivity and specificity determined using sound enamel as the reference. The results indicated that QLF could detect demineralization which occurred as a result of 8 h exposure to the decalcification solution and was able to quantify changes in lesion severity associated with longer demineralization. While DELF was capable of detecting enamel demineralization after only 2 h exposure to the decalcification solution, it was unable to quantify increasing amounts of demineralization associated with longer periods of exposure to the decalcification solution. In summary, while DELF was able to detect very early demineralization, only QLF was capable of detecting and quantifying changes in the extent of the decalcification occurring with demineralization periods up to 24 h.

Animals↗

PubMed1997

Can trasmitral Doppler E-waves differentiate hypertensive hearts from normal?

Physiological models of transmitral flow predict E-wave contour alteration in response to variation of model parameters (stiffness, relaxation, mass) reflecting the physiology of hypertension. Accordingly, analysis of only the E-wave (rather than the E-to-A ratio) should be able to differentiate between hypertensive subjects and control subjects. Conventional versus model-based image processing methods have never been compared in their ability to differentiate E-waves of hypertensive subjects with respect to age-matched control subjects. Digitally acquired transmitral Doppler flow images were analyzed by an automated model-based image processing method. Model-derived indexes were compared with conventional E-wave indexes in 22 subjects: 11 with hypertension and echocardiographically verified ventricular hypertrophy and 11 age-matched nonhypertensive control subjects. Conventional E-wave indexes included peak E, E, and acceleration and deceleration times. Model-based image processing-derived indexes included acceleration and deceleration times, potential energy index, and damping and kinematic constants. Intergroup comparison yielded lower probability values for model-based compared with conventional indexes. In the subjects studied, Doppler E-wave images analyzed by this automated method (which eliminates the need for hand-digitizing contours or the manual placement of cursors) demonstrate diastolic function alteration secondary to hypertension made discernible by model-based indexes. The method uses the entire E-wave contour, quantitatively differentiates between hypertensive subjects and control subjects, and has potential for automated noninvasive diastolic function evaluation in large patient populations, such as hypertension and other transmitral flow velocity-altering pathophysiological states.

Aged↗

PubMed1997

Application of transverse microradiography for measurement of mineral loss by acid erosion.

This paper describes a novel application of transverse microradiography for the detection and quantification of mineral loss due to acid erosion in thin tooth sections. Sixty-four specimens were randomly divided into eight equal-sized groups and exposed to an orthophosphoric-acid-based erosive fluid (pH = 3) for 0, 0.25, 0.5, 1, 2, 5, 12, or 24 hrs. We made microdensitometric scans separately across both enamel and dentin to derive data for the total mineral loss and the minimum mineral content within the eroded area. We then analyzed specimens using a profilometer to determine (1) the area above a plot of penetration depth against distance and (2) the maximum depth of penetration. Correlation coefficients for comparisons between microradiographic and profilometric data for both enamel and dentin specimens varied between 0.87 and 0.96. Two-sample t tests demonstrated that the microradiographic technique could detect early erosion, i.e., discriminate between erosion times of less than 1 hr. It was concluded that this application of transverse microradiography was a useful and acceptable method for the measurement of early mineral loss in vitro, occurring as a result of acid erosion.

Absorptiometry, Photon↗

PubMed1997

In vitro studies of laser fluorescence for detection and quantification of mineral loss from dental caries.

Laser fluorescence (LF) is thought to be a quantitative technique for the measurement of mineral loss from dental caries. These studies aimed to demonstrate the quantitative nature of LF, by means of transverse microradiography (TMR), in addition to the possible use of LF on small specimens suitable for in situ studies. Studies also aimed to determine the ability of LF to detect caries adjacent to amalgam restorations. The results demonstrated reasonable correlation between both the histological depth and mineral loss measured by TMR compared with the % change in mean fluorescence radiance measured by LF (r = 0.70 and 0.83, respectively). Studies with small specimens demonstrated that in vitro remineralization could be observed with LF for comparison of the demineralized specimen with an undemineralized reference. ANOVA showed significant mineral gain (p < 0.0001). The detection and quantification of mineral loss adjacent to amalgam restorations may have potential for the management of recurrent caries. Studies have demonstrated that LF can detect such mineral loss, and, with refinement of the image analysis system, LF was capable of detecting remineralization. Remineralization of such lesions is controversial, but it is suggested that LF may have a role in secondary caries management.

Analysis of Variance↗

PubMed1996

Heart rate variability in a case of pheochromocytoma.

Indices of heart rate variability (HRV) reflect cardiac autonomic tone and may be markedly affected by pheochromocytoma. The effect of pheochromocytoma on HRV was determined by Holter monitoring before diagnosis, under pre-operative alpha-blockade and 5 and 19 months after surgery in a 40 year-old female. Mean heart rates, although higher under alpha-blockade, were unchanged by surgery but indices of HRV reflecting both short term (vagally mediated) and longer term (mediated by vagal, sympathetic and other influences) rhythms were diminished under alpha-blockade and post-surgery. High frequency power (0.15-0.40 Hz), an index of vagal tone, declined from 512 ms2 pre-diagnosis to 220 ms2 under alpha-blockade to just over 100 ms2 post-surgery. Low frequency power (0.04-0.15 Hz), a measure reflecting both vagal and sympathetic tone, declined from 409 ms2 pre-diagnosis to 186 ms2 under alpha-blockade and was just over 200 ms2 post-surgery. SDNN, the standard deviation of normal-to-normal interbeat intervals over 24 hours, declined from 118 ms pre-diagnosis to just over 70 ms both under alpha-blockade and post-surgery. The ratio of low frequency to high frequency power (LF/HF ratio) increased to 0.84 under alpha-blockade, and doubled after surgery (0.79; before, 2.05; after). These changes in HRV may provide insights into the effects of endogenous catecholamines and intrinsic counter-regulatory autonomic mechanisms on HRV.

Adrenal Gland Neoplasms↗

PubMed1996

Interobserver and intraobserver reliability of the proposed International Continence Society, Society of Gynecologic Surgeons, and American Urogynecologic Society pelvic organ prolapse classification system.

OBJECTIVE: Our purpose was to determine the intraobserver and interobserver reliability of site-specific measurements and stages with the proposed international Continence Society, Society of Gynecologic Surgeons, and American Urogynecologic Society 1994 draft prolapse terminology document. STUDY DESIGN: Women who completed informed consent procedures underwent pelvic examinations by two investigators, each blinded to the results of the other's examination. The reproducibility of the nine site-specific measurements and the summary stage and substage were analyzed with Spearman's correlation coefficient (rs) and Kendel tau B Correlation Coefficient (tau b), respectively. Similar analyses were performed on supine and upright examinations performed at two different times by one examiner. RESULTS: Experienced examiners averaged 2.05 minutes per examination and new examiners averaged 3.73 minutes. In the study of interobserver reliability, 48, subjects, mean age 61 +/- 14 years, parity 3 +/- 2, weight 74 +/- 31 kg, comprised the study population. Correlations for each of the nine measurements were substantial and highly significant (rs 0.817, 0.895, 0.522, 0.767, 0.746, 0.747, 0.913, 0.514, and 0.488, p = 0.0008 to < 0.0001). Staging and substaging were highly reproducible (tau b 0.702 and 0.652). In no subject did the stage vary by more than one; in 69% stages were identical. In the study of intraobserver reliability, for 25 subjects correlations for each of the nine measurements were equally strong (rs 0.780, 0.934, 0.765, 0.759, 0.859, 0.826, 0.812, 0.659, 0.431). Measurements from the upright examinations reflected greater prolapse. Staging and substaging were highly reproducible (tau b 0.712 and 0.712). In no subject did the stage vary by more than one; in 64% stages were identical. All stage discrepancies represented an increase in the upright position. CONCLUSIONS: There is good reproducibility of measures with the proposed system. The data suggest that the reliability is independent of examiner experience. Patient position is likely important in maximizing the severity of the prolapse.

Adult↗

PubMed1995

Relationship of the third heart sound to transmitral flow velocity deceleration.

BACKGROUND: The third heart sound (S3) occurs shortly after the early (E-wave) peak of the transmitral diastolic Doppler velocity profile (DVP). It is thought to be due to cardiohemic vibrations powered by rapid deceleration of transmitral blood flow. Although the presence, timing, and clinical correlates of the S3 have been extensively characterized, derivation and validation of a causal, mathematical relation between transmitral flow velocity and the S3 are lacking. METHODS AND RESULTS: To characterize the kinematics and physiological mechanisms of S3 production, we modeled the cardiohemic system as a forced, damped, nonlinear harmonic oscillator. The forcing term used a closed-form mathematical expression for the deceleration portion of the DVP. We tested the hypothesis that our model's predictions for amplitude, timing, and frequency of S3 accurately predict the transthoracic phonocardiogram, using the simultaneously recorded transmitral Doppler E wave as input, in three subject groups: those with audible pathological S3, those with audible physiological S3, and those with inaudible S3. CONCLUSIONS: We found excellent agreement between model prediction and the observed data for all three subject groups. We conclude that, in the presence of a normal mitral valve, the kinematics of filling requires that all hearts have oscillations of the cardiohemic system during E-wave deceleration. However, the oscillations may not have high enough amplitude or frequency to be heard as an S3 unless there is sufficiently rapid fluid deceleration (of the Doppler E-wave contour) with sufficient cardiohemic coupling.

Blood Flow Velocity↗

PubMed1995

Comparison of diastolic filling models and their fit to transmitral Doppler contours.

Anatomic/physiologic and kinematic mathematical models of diastolic filling which employ (lumped) parameters of diastolic function have been used to predict or characterize transmitral flow. The ability to determine model parameters from clinical transmitral flow, the Doppler velocity profile (DVP), is equivalent to solving the "inverse problem" of diastole. Systematic model-to-model and model-to-data comparison has never been carried out, in part due to the requirement that DVPs be digitized by hand. We developed, tested and verified a computerized method of DVP acquisition and reproduction, and carried out numerical determination of model-to-model and model-to-data goodness-of-fit. The transmitral flow velocity of two anatomic/physiologic models and one kinematic model were compared. Each model's ability to fit computer-acquired and reproduced transmitral DVPs was assessed. Results indicate that transmitral flow velocities generated by the three models are 'graphically indistinguishable and are able to fit the E-wave of clinical DVPs with comparable mean-square errors. Nonunique invertibility of the anatomic/physiologic models was verified, i.e., multiple sets of model parameters could be found that fit a single DVP with comparable mean-square error. The kinematic formulation permitted automated, unique, model-parameter determination, solving the "inverse problem" for the Doppler E-wave. We conclude that automated, quantitative characterization of clinical Doppler E-wave contours using this method is feasible. The relation of kinematic parameters to physiologic variables is a subject of current investigation.

Algorithms↗