Coupled Nanomechanical and Raman Microspectroscopic Investigation of Human Third Molar DEJ.

The dentino-enamel junction (DEJ) connects enamel, that covers the outer surface of a tooth, to a thicker underlying dentin. The DEJ is a critical interface that permits joining these materials that have widely dissimilar mechanical properties. AFM-based nanoindentation and Raman microspectroscopy were used to define the width and composition of human molar DEJ. Indentation elastic modulus and hardness of enamel, dentin, and DEJ were determined along lines of indents made at 2 µm intervals across the DEJ. Indents made at maximum loads at each end of the indent lines were used to make visible markers allowing Raman microspectroscopy at 1 µm intervals across the DEJ, while using the nanoindent markers for orientation and location. Functional DEJ width estimates were made based on results from nanoindentation and Raman microspectroscopy. DEJ width estimates ranged from 4.7 (±1.2) µm to 6.1 (±1.9) µm based on hardness and 4.9 (±1.1) µm to 6.9 (±1.9) µm based on modulus. DEJ width based on Raman peak intensity variations were 8.0 (±3.2) µm to 8.5 (±3.1) µm based on the phosphate peak, and 7.6 (±3.2) µm to 8.0 (±2.6) µm for C-H stretching mode. These estimates are in the range of DEJ width estimates reported using nanoindentation.

Optical spectroscopy and imaging of the dentin-enamel junction in human third molars.

A 351-nm laser excitation source was used to perform autofluorescence microscopy of dentin, enamel, and the dentin-enamel junction (DEJ) to obtain information regarding their morphology and spectral characteristics. The emission spectra of these calcified dental tissues were different from one another, and this enabled the DEJ to be imaged and dimensionalized. The DEJ displayed sharp and clearly delineated borders at both its enamel and dentin margins. The dentinal tubules and the enamel prisms appeared to terminate abruptly at the DEJ. The median DEJ width was 10 microm, ranging from 7 to 15 microm, and it did not appear to depend on intratooth position.

Mechanical properties of the dentinoenamel junction: AFM studies of nanohardness, elastic modulus, and fracture.

The dentinoenamel junction (DEJ) is a complex and poorly defined structure that unites the brittle overlying enamel with the dentin that forms the bulk of the tooth. In addition, this structure appears to confer excellent toughness and crack deflecting properties to the tooth, and has drawn considerable interest as a biomimetic model of a structure uniting dissimilar materials. This work sought to characterize the nanomechanical properties in the region of the DEJ using modified AFM based nanoindentation to determine nanohardness and elastic modulus. Lines of indentations traversing the DEJ were made at 1-2 microm intervals from the dentin to enamel along three directions on polished sagittal sections from three third molars. Nanohardness and elastic modulus rose steadily across the DEJ from bulk dentin to enamel. DEJ width was estimated by local polynomial regression fits for each sample and location of the mechanical property curves for the data gradient from enamel to dentin, and gave a mean value of 11.8 microm, which did not vary significantly with intratooth location or among teeth. Nanoindentation was also used to initiate cracks in the DEJ region. In agreement with prior work, it was difficult to initiate cracks that traversed the DEJ, or to produce cracks in the dentin. The fracture toughness values for enamel of 0.6-0.9 MPa . m(1/2) were in good agreement with recent microindentation fracture results. Our results suggest that the DEJ displays a gradient in structure and that nanoindenation methods show promise for further understanding its structure and function.

Analysis of the right ventricular function in the exercising horse: use of the Fourier Transform.

The objective of this study was to develop and test a technique to allow dynamic cardiac function to be studied during exercise in the horse. Blood pressure waveforms in the exercising horse are difficult to interpret because of the large influence of stride and respiration. A method has been devised to study dynamic right ventricular variables during high-speed exercise in the horse. A Fast Fourier Transform was performed on the digitised pressure waveforms and the frequency components associated with stride and respiration were removed. An inverse Fourier Transform was then performed to generate a time-domain pressure signal. Several dynamic right ventricular variables were calculated using the derived signal. Various parameters associated with removing frequencies from the frequency-domain pressure signal were changed to determine their influence on the variables. Most of the variables were not sensitive to these parameters. When compared during separate exercise bouts, some variables differed among runs, while others were not significantly different. Using the signal separation technique described here, right ventricular function of an exercising horse can be critically analysed.

Use of a turbine in a breath-by-breath computer-based respiratory measurement system.

The Computer-Based Respiratory Measurement System (CBRMS) is capable of analyzing individual breaths to monitor the kinetics of oxygen uptake, carbon dioxide production, tidal volumes, pulmonary ventilation, and other respiratory parameters during rest, exercise, and recovery. Respiratory gas volumes are measured by a calibrated turbine transducer while the respiratory gas concentrations are measured by a calibrated, fast-responding medical gas analyzer. To improve accuracy of the results, the inspiratory volumes and gas concentrations are measured and not assumed to be equal to expiratory volumes or ambient concentrations respectively. The respiratory gas volumes and concentration signals are digitized and stored in arrays. The gas volumes are converted to flow signals by software differentiation. These digitized data arrays are stored as files in a personal computer. Time alignment of the flow and gas concentration signals is performed at each breath for maximum accuracy in analysis. For system verification, data were obtained under resting conditions and under constant load exercises at 50 W, 100 W, and 150 W. These workloads were performed by a healthy, male subject on a bicycle ergometer. A strong correlation existed between the CBRMS steady-state results and the standard end-expirate bag collection technique. Thus, there is reason to believe that the CBRMS is capable of calculating respiratory transient responses accurately, a significant contribution to an understanding of total respiratory system function.

A computer-based instrumentation system for measurement of breath-by-breath oxygen consumption and carbon dioxide production.

Improvements are implemented (Version 4) in a Computer-Based Respiratory Measurement System (CBRMS) identified as Version 3. The programming language has been changed from Pascal to C. A Gateway 2000 desktop computer with 486 DX2/50MHz CPU and a plug-in data I/O board (KEITHLEY METRABYTE/ASYST/DAC's DAS-HRES 16-bit Analog and Digital I/O board) replaces an HP 9836 system used in Version 3. The breath-by-breath system consists of a mass spectrometer for measuring fractional concentrations of oxygen and carbon dioxide and the accommodation of a turbine or pneumotachometer for measuring inspiratory and expiratory flows. The temperature of the inspiratory and expiratory gases can be monitored if temperature corrections are necessary for the flow measurement device. These signals are presented to the PC via the data acquisition module. To compare the two Versions, ten significant respiratory parameters were investigated and compared for physiological resting states and steady states obtained during an exercise forcing. Both graphical and statistical (analysis of variance, regression, and correlation) tests were carried out on the data. The results from the two versions compared well for all ten parameters. Also, no evidence of a statistically significant difference was found between the resting and steady-state results of the present CBRMS (Version 4) and the previous CBRMS (Version 3). This evidence suggests that Version 3 (Pascal) has been successfully converted to Version 4 (C). Implementation of the CBRMS in C on a PC has several advantages.(ABSTRACT TRUNCATED AT 250 WORDS)

ECG data compression with wavelet and discrete cosine transforms.

When applying transform techniques in data compression, an efficient approximation of the original signal using fewer transform coefficients is desired. The Discrete Cosine Transform (DCT) has been an effective tool in such applications. It decomposes a signal into a set of sinusoidal waveforms that are global in time. The DCT is not as efficient for signals with only local variations. The Wavelet Transform (WT) is a new technique that can decompose a signal into a set of small waveforms called wavelets. These wavelets possess local supports in the time domain, which makes the WT suitable for representing signals with local variations. Even though the ECG is dominated by low frequencies, its QRS complex exhibits strong localized characteristics. In this study, the effectiveness of the two transforms in compressing ECG data is investigated. Having noted the weakness of each transform, the two techniques are combined in two ways to compress the ECG data. It is observed that with the new techniques, better visualization quality can be achieved with the same total number of transform coefficients.

Definition of reference frames on human skeleton.

In our modeling study of the human cardiovascular system, some forms of subject motion or posture, e.g., those experienced or assumed by a fighter pilot, can not be neglected in considering the overall system dynamics. This investigation aims at establishing a set of reference frames on the human skeleton which are based on the observations and measurements taken on four skeleton systems. These frames are coupled together at the articulation positions to form a base of operation of 3-D translation and rotation. The coupling at a specified reference position was verified against the proportional measurements taken from X-ray films, CAT scan films, atlases and two human cadavers. A program was written to perform the forementioned transformations on the frames coupled at the reference position such that any posture can be achieved as long as the necessary angular anthropometric measurements are provided. If a set of angular profiles at all involved joints are given, the human motion can be mathematically animated to a certain degree of accuracy appropriate for specified computer simulation studies. Under this definition, any major segment of our cardiovascular system model can be specified in terms of spatial position and orientation. [table: see text]

A mobile real-time bioengineering front end system.

In the study of physiological system dynamics, a mobile Front End System is needed in faithfully monitoring and recording physiological signals at various experimental sites. Local real-time mode operation is required at the site of the experiment such that the significant dynamic response or event from the subject can be easily captured and displayed as the experiment progresses. An additional requirement is the interfacing with the campus computer network such that numerous network computing resources can be employed in further processing of the captured data. The system is configured by using general-purpose components such as a 50MHz PC-486, a DAS-HRES data acquisition board and some other necessary peripheral devices. An algorithm has been developed for the continuous manipulation of two queues to maintain the real-time task scheduling. Traces can be played back in forward or reverse mode at varied speed after the recording has been made. As desired, any trace segment can be picked up in the play back mode from the huge data files. The system is incorporated in a live subject bioinstrumentation laboratory and has the capability of monitoring signals from four simultaneously experimental setups. The signal types involved are membrane potentials, ECG, EMG, blood pressure, and respiratory flows and gas concentrations.

Theory of gas exchange in the avian parabronchus.

To understand the distribution of oxygen and carbon dioxide in the avian lung, a theoretical treatment of gas exchange in the parabronchus of the avian lung is described. The model is modified after Zeuthen (1942). In addition to bulk flow through the parabronchial lumen, diffusion through the air spaces of both the parabronchial lumen and air capillaries is treated. The relationship of PO2 and PCO2 within the blood capillaries, air capillaries, and parabronchial lumen to parabronchial blood flow and ventilation is graphically shown. The results indicate that the variations of PO2 and PCO2 along an air capillary are less than one torr under resting conditions. Removal of diffusion resistance within the air space of the air capillaries increases calculated parabronchial gas exchange by less than 0.1% at rest. At high or resting ventilation rates the partial pressure profile along the parabronchial lumen calculated considering bulk flow only agrees well with the profile calculated considering bulk flow and axial diffusion, but as the ventilation rate decreases there is increasingly large disagreement. Forward diffusion of O2 toward the parabronchus reduces pre-parabronchial PO2 and backward diffusion of CO2 from the parabronchus increases PCO2. Neglecting diffusion within the air spaces of both the lumen and the air capillaries increases calculated parabronchial gas exchange by less than 2% (CO2) or 6% (O2) at rest.