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PubMed1999

Stability of implants as anchorage for orthopedic traction.

The aim of this animal study was to investigate the stability of osseointegrated fixtures when used as anchorage for orthopedic traction with extreme force magnitude. Three Brånemark fixtures were placed in the left zygomatic arch and three in the right of five adult dogs. An orthopedic nonaxial force of 5 N was applied using an intraoral coil system. The initial displacement immediately after force application was measured by means of speckle interferometry. After 2 months of continuous loading, bone adaptation and mineralization around all implants were analyzed. All the loaded implants were immobile. Significant marginal bone loss at the abutment-fixture interface (<1 mm) was observed around each loaded fixture implant. Bone remodeling was significantly more pronounced at the tension side of the implants, irrespective of fixture length. Radiographical and histological analyses showed bone with normal trabecular pattern around the implants.

Adaptation, Physiological↗
PubMed1996

Acoustically induced vibrations of the Reissner's membrane in the guinea-pig inner ear.

In the inner ear, the Reissner's membrane separates the scala vestibuli from the scala media and is thus of importance for maintaining a positive endocochlear potential. The motion of the membrane is thought to be driven by the vibrations of the underlying hearing organ caused by a hydromechanical coupling between the structures. Since the Reissner's membrane is relatively easily accessible in the cochlea its vibratory response has been used as a measure of the micromechanical behaviour of the hearing organ. To determine whether this indirect measure revealed the true characteristics of the hearing organ, experiments were performed using laser heterodyne interferometry in an in vitro preparation of the guinea-pig temporal bone. Interferometric measurements at the Reissner's membrane and at the surface of the hearing organ directly beneath made it possible to compare the mechanical tuning characteristics of both structures. It was found that the mechanical response characteristics of the Reissner's membrane differed considerably from the hearing organ. The tuning frequency was different and only minor changes in the maximal vibration amplitude were seen when measuring at different radial locations. However, the shape of the response curve changes with location. The Reissner's membrane response appeared to be affected by the mechanical vibrations originating both at the middle ear ossicles and at the hearing organ. It is concluded that the Reissner's membrane response is a poor indicator of cochlear mechanics and that investigations of cochlear micromechanics should be performed directly at the level of the hearing organ.

Acoustic Stimulation↗
PubMed1998

[Value of optical coherence tomography in diagnosis of age-related macular degeneration. Correlation of fluorescein angiography and OCT findings].

BACKGROUND: Age-related macular degeneration (AMD) is the leading cause of blindness in industrialized countries. In this study, we used optical coherence tomography for evaluation of patients with AMD. METHODS: Optical coherence tomography imaging is analogous to ultrasound, except that reflected light instead of sound is used. The analysis of the reflected light is processed with the technique of low-coherence interferometry. In this study, 33 patients with different stages of AMD were examined with optical coherence tomography. The classification of AMD was according to the guidelines as proposed by the "International ARM Epidemiological Study group". RESULTS: With this method we were able to identify drusen, alteration of the retinal pigment epithelium, and secondary retinal changes. Other structures such as basal laminar (linear) deposits could not be identified with this method. Choroidal neovascularization was evident in the tomogram. Classic choroidal neovascular membranes presented with well-defined boundaries on optical coherence tomography and occult choroidal neovascular membranes had a less delineable structure with optical coherence tomography. CONCLUSION: Optical coherence tomography cannot replace conventional diagnostic techniques. This method provides no additional information in patients with non-exsudative AMD. In patients with choroidal neovascular membranes secondary to AMD optical coherence tomography may be able to characterize the relation of the membrane to the retinal pigment epithelium and imaging may be possible through hemorrhage. The interpretation of the optical coherence tomogram needs further studies including clinicopathologic correlation.

Aged↗
PubMed2002

Coherent infrared emission from myoglobin crystals: an electric field measurement.

We introduce coherent infrared emission interferometry as a chi(2) vibrational spectroscopy technique and apply it to studying the initial dynamics upon photoactivation of myoglobin (Mb). By impulsive excitation (using 11-fs pulses) of a Mb crystal, vibrations that couple to the optical excitation are set in motion coherently. Because of the order in the crystal lattice the coherent oscillations of the different proteins in the crystal that are associated with charge motions give rise to a macroscopic burst of directional multi-teraHertz radiation. This radiation can be detected in a phase-sensitive way by heterodyning with a broad-band reference field. In this way both amplitude and phase of the different vibrations can be obtained. We detected radiation in the 1,000-1,500 cm(-1) frequency region, which contains modes sensitive to the structure of the heme macrocycle, as well as peripheral protein modes. Both in carbonmonoxy-Mb and aquomet-Mb we observed emission from six modes, which were assigned to heme vibrations. The phase factors of the modes contributing to the protein electric field show a remarkable consistency, taking on values that indicate that the dipoles are created "emitting" at t = 0, as one would expect for impulsively activated modes. The few deviations from this behavior in Mb-CO we propose are the result of these modes being sensitive to the photodissociation process and severely disrupted by it.

Animals↗
PubMed1997

Effects of changes in intraocular pressure on human ocular haemodynamics.

PURPOSE: Myogenic autoregulation is the ability of a vascular bed to maintain blood flow despite changes in perfusion pressure. Ocular perfusion pressure is defined as the difference between ocular arterial pressure and ocular venous pressure, the latter dependent on intraocular pressure (IOP). The aim of the present study was to investigate the effect of moderate increases in IOP on ocular haemodynamics. METHODS: Changes in IOP (+ 10 mmHg, +20 mmHg) were induced by a suction cup in 10 healthy subjects. Ocular fundus pulsations in the macula and the optic disc were measured by laser interferometry; blood flow velocities in the central retinal artery (CRA) and in the ophthalmic artery (OA) were measured by Doppler sonography. RESULTS: Changes in IOP caused a significant reduction in fundus pulsations, which was more pronounced in the macula (at +10 mmHg: -9 +/- 2%, p < 0.01; at +20 mmHg: -19 +/- 3%, p < 0.001) than in the optic disc (at +10 mmHg: -5 +/- 2% (ns); at +20 mmHg: -9 +/- 3%, p < 0.01). Mean flow velocity in the CRA was reduced by -5 +/- 3% at +10 mmHg (ns) and by -14 +/- 5% at +20 mmHg (p < 0.005), resistive index was increased by +4 +/- 1% at +10 mmHg (p < 0.05) and by +6 +/- 2% at +20 mmHg (p < 0.01). In contrast, a rise in IOP did not affect blood flow parameters in the OA. CONCLUSIONS: Our results from fundus pulsation measurements indicate that choroidal blood flow decreases when IOP is increased. The Doppler sonographic findings in the CRA indicate reduced blood flow velocity in this artery during raised IOP.

Adult↗
PubMedDate not supplied

New instruments for dry eye diagnosis.

Several non-invasive techniques for dry eye diagnosis have been developed in the past decade. These include quantitative assessment of tear volume, tear film stability, tear dynamics, and integrity of ocular surface epithelium. A combination of meniscometry and interferometry is useful for proving focal dry eye, by confirming whether or not tears at the meniscus have an effect on the ocular surface. Interferometer is also useful to evaluate tear dynamics on soft contact lenses. Fluorophotometry is useful for assessing the severity of dry eye from the view point of corneal epithelial barrier function and measuring the tear turnover rate. Both video-meibography and meibometry are useful for screening meibomian gland dysfunction. The advances in these techniques accumulate knowledge regarding pathophysiology of dry eye and allow precise diagnosis of dry eye. More targeted treatment will become feasible based on the clearer pathophysiology.

Corneal Topography↗
PubMed1956

A comparison of nuclear dry weights determined by chemical and by interferometric methods.

1. The nuclei of cells from the thymus of the calf were isolated by three different techniques; the citric acid, the sucrose-calcium chloride, and the non-aqueous. 2. The mean dry weights of the nuclei were determined by chemical methods and by microscopic interferometry. There was a close correlation between the results from the interferometric and chemical methods. 3. The range of values about that mean was determined in each sample: the nuclei isolated in aqueous media contained approximately 45 per cent less material than those isolated in non-aqueous media. 4. The variations in dry weight with varying nuclear type are discussed. 5. The possible relationship between DNA content and dry weight is discussed.

Body Weight↗
PubMed1960

Studies in histochemistry. LVII. Determination of the total dry mass of human erythrocytes by interference microscopy and x-ray microradiography.

The total dry mass of human erythrocytes was determined by both interference microscopy and x-ray microradiography. The determination of mass per unit area, and calculation of total dry mass per cell were simplified by changing the shape of the cells to spheres which were then flattened to discs of constant thickness when smeared on glass slides for measurement of fixed cells by interferometry, and to oblate spheroids when smeared on parlodion-coated slides for measurement of fixed cells by x-ray absorption. From x-ray measurements of 100 smeared and alcohol-fixed cells a mean dry mass per cell of 33.7 x 10(-12) g was obtained. Interference measurements of 100 fresh cells suspended in isotonic saline gave a mean value of 32.4 x 10(-12)g while interference measurement of 100 smeared and alcohol-fixed cells gave a mean value of 30.8 x 10(-12)g. The first two values compare well with a mean corpuscular hemoglobin of 31.2 x 10(-12)g, obtained from determinations of erythrocyte count and hemoglobin, since 95 per cent of the dry mass of the cell is hemoglobin. The difference in interference values between the fixed and fresh cells is possibly due to a difference between the specific refractive increment of alcohol-denatured hemoglobin and that of the unmodified substance. The value for the latter was used since that of the former is unknown.

Erythrocyte Indices↗
PubMed1990

The value of the macerated skull as a model used in orthopaedic research.

In this study a method was developed to enable the measurement of initial bone displacement in vivo, post-mortem, and in vitro. Speckle interferometry was used as measuring technique. Through the construction of the centres of rotation, the different orthopaedic effects could easily be compared. Also the magnitude of the bone displacement could be calculated. The initial post-mortem displacement of the maxilla corresponds very well with the initial in vivo displacement. After maceration and drying of the skull, however, clear differences from the in vivo displacement were found. The orthopaedic effects on a macerated skull can be manipulated considerably by changing, for instance, the degree of humidity. Only a limited number of skulls was examined in these experiments and probably still other variables exert an influence on the bone displacement in the macerated skull. Nevertheless, it is certain now that the dry skull cannot reliably be used as a model to simulate the initial bone displacement in vivo. The experimental set-up of this study will be used in the future to evaluate the effect of environmental factors (humidity, temperature, etc.) in an attempt to improve the value of the skull as a model for orthopaedic research. Moreover, this technique permits investigation of the link between initial displacements in vivo and longitudinal changes.

Aging↗
PubMed1990

Effects of maxillary protraction determined by laser metrology.

In this work we studied some of the main effects of the maxillary protraction orthopedic device. The initial dento-craniofacial reactions induced by maxillary protraction similar to that commonly employed in clinical practice are reported. The fringe counting holographic interferometry technique is used to measure displacements. The experiments were performed on a dried human skull; traction application points were situated over the permanent lateral incisors or over the first permanent molars. The results fundamentally reveal an anterior rotation of the dentomaxillary complex, more intense when traction is applied to the lateral incisors, as shown by a more marked extrusion of the molars in this case. Moreover, major deformation patterns could be observed in inner hard structures of the skull base when applying orthopaedic forces.

Child↗
PubMed1990

The interaction between reaction forces and stabilization systems during intrusion of the anterior teeth and its effect on the posterior unit.

The aim of this research is to attain a better understanding of the initial reaction forces induced by an intrusion mechanism (acting on the anterior teeth) on the posterior unit and to examine how these forces can be neutralized. The experiments were performed on the dentition of a dry human skull and initial tooth displacements were registered by means of two laser measuring techniques, namely holographic interferometry and the laser reflection technique. It was established that of all reaction forces induced by the intrusion arch, distal tipping of the first molars is the most pronounced. A transpalatal bar connecting the teeth does not counteract this movement. The stabilization of the posterior unit with a transpalatal bar, buccal sectionals, and high-pull headgear proved to be the most effective technique.

Bicuspid↗
PubMed1999

Initial orthopaedic displacement compared with longitudinal displacement of the maxilla after a forward force application. An experimental study in dogs.

The aim of this study was to compare the initial orthopaedic displacement of the maxilla in vivo and the longitudinal changes after a forward force application. The sample consisted of five 1-year-old dogs. An anterior force of 5 N on the maxilla was applied by a coil spring system pushing between Brånemark implants and a maxillary splint. The initial displacement of the maxilla after force application was measured by means of speckle interferometry. The longitudinal displacement of the maxilla after a force application during 8 weeks was measured by superimposing standardized lateral cephalograms. The initial, as well as the longitudinal, displacement of the maxilla of the dogs was in a forward direction with some counterclockwise rotation. There was no statistical difference between the initial and longitudinal displacement. The biological response after force application during 8 weeks can be predicted by the initial orthopaedic displacement.

Animals↗
PubMed2001

Three-dimensional finite element modelling of a dog skull for the simulation of initial orthopaedic displacements.

From 55 frontal tomograms (CT-scans) using the 'Patran' finite element processor, a three-dimensional finite element model (FEM) of a dog skull was constructed. The model was used to calculate bone displacements under orthopaedic loads. This required good representation of the complex anatomy of the skull. Five different entities were distinguished: cortical and cancellous bone, teeth, acrylic and sutures. The first model consisted of 3007 elements and 5323 nodes, including three sutures, and the second model 3579 elements and 6859 nodes, including 18 sutures. Prior to construction of the FEM, an in vivo study was undertaken using the same dog. The initial orthopaedic displacements of the maxilla were measured using laser speckle interferometry. Under the same loading conditions, using the second FEM, bone displacements of the maxilla were calculated and the results were compared with the in vivo measurements. Compared with the initial displacement measured in vivo, the value of the constructed FEM to simulate the orthopaedic effect of extra-oral force application was high for cervical traction and acceptable for anterior traction.

Acrylic Resins↗
PubMedDate not supplied

Fiber optic pressure sensor for biomedical applications.

In vivo measurement of blood pressure is critical in many settings, including patient care, medical research, and control of cardiovascular assist and replacement devices. This article describes a pressure sensor based on fiber optic, white light interferometry. An optical interference filter formed between the end face of an optical fiber and the sensing diaphragm selectively reflects a wavelength component. A low cost, thin film optical wedge interferometer placed at the output end detects the wavelength of the reflected signal, which represents a unique cavity length of the interference filter directly related to the diaphragm deflection and, therefore, pressure. Several key features of this sensing scheme include low drift, high accuracy, and insensitivity to light loss factors along the length of the optical fiber. This fiber optic pressure sensor promises significant advances as a medical monitoring tool, a research instrument, and a component of cardiovascular assist and replacement devices. A prototype pressure gauge has been built, and the feasibility of the optical approach verified. Experimental results of the prototype gauge for resolution, repeatability, and drift and a preliminary design for a high resolution, low drift, miniature fiber optic pressure probe are presented herein.

Biomechanical Phenomena↗
PubMedDate not supplied

Surface analysis of bileaflet prosthetic heart valve leaflet leading edge.

In 1991 and 1992, two patients presented with persistent clinical hemolysis after mitral valve replacement with bileaflet valves, in the absence of paravalvular leaks. When each valve was replaced, the hemolysis disappeared. The first valve was not examined in the laboratory owing to its loss, but it looked normal. The second valve was tested and found to have normal hemodynamics and a normal appearance by light microscopy (LM) and scanning electron microscopy (SEM), but fringe pattern interferometry (FPI) showed its leading leaflet edges to be flatter and rougher than another St. Jude Medical valves (SJMV). This led the authors to collect 17 bileaflet valves (14 SJMV and 3 Carbomedics) for examination of their surface characteristics to see if there was any correlation with hemolysis. All valves were examined by LM, SEM, and FPI. However, only FPI indicated the presence of notable differences in surface roughness and convexity of the leading leaflet edges. Further, convexity of an edge tended to vary inversely with its roughness, and the flat inlet surfaces of most leaflets were consistently less rough than the adjacent edge. The authors' hemolytic valve had one of the flattest and roughest edges of the series. Roughness of the leading edge may contribute to hemolysis by presenting an abrasive surface to the antegrade flow of blood, and by forming the sides of the gap between the leaflets, through which blood is squeezed during closed regurgitation, generating substantial shear forces and causing hemolysis. FPI is a noncontact, sensitive modality, useful in screening pyrolytic carbon surfaces but, unlike other current methods, it is reproducible, does not require modification of the surface, and causes no alteration of the surface texture.

Anemia, Hemolytic↗
PubMed1996

The effect of tympanic membrane perforation size on umbo velocity in the rat.

The tympanic membrane (TM) in adult rats was surgically exposed and laser interferometry was used to measure TM velocity at the umbo for frequencies between 1.0 and 40.0 kHz. Velocity measures were obtained for five conditions: TM intact, and four progressively larger holes cut into the posterior region of the membrane. Photomicrographs of each condition were used to calculate the percentage of pars tensa lost to the perforation. The relation between TM velocity and stimulus sound pressure level (SPL) was also examined for each of the conditions. The results revealed a systematic loss in low-frequency velocity as perforation size increased. These observations were consistent with clinical reports of low-frequency hearing loss in the perforated human TM. The rat appears to be a successful model for studying this form of conductive pathology.

Animals↗
PubMed1996

Advances in the development of the interferometric otoscope.

Present measurement techniques for middle ear function have inherent limitations because they are either spatially insensitive (acoustic immittance) or descriptive and qualitative in nature (otoscopy). By integrating advances in electrooptic technology (fiber optics, miniature diode lasers, solid-state detector arrays) and digital processing, further advances are possible. On the basis of measurements taken with electronic speckle-pattern interferometry on human temporal bones and models, we demonstrate quantitative static and dynamic vibration/displacement characteristics of the tympanic membrane with high spatial resolution. Our presentation emphasizes advantages of optically based methods and demonstrates computerized signal processing capable of fringe localization, enhancement, and counting. Miniaturization and real-time digital image processing in the clinical setting is the goal of this research.

Humans↗
PubMed2004

Ocular component measurement using the Zeiss IOLMaster.

PURPOSE: Axial length is traditionally measured using A-scan ultrasound. The IOLMaster is a new instrument that uses partial coherence interferometry to measure axial length. We compared the repeatability of these techniques for both an experienced and an inexperienced observer, the agreement between the two techniques, and the effect of cycloplegia on IOLMaster measurements. METHODS: Five measurements of axial length and three measurements of anterior chamber depth were taken with the IOLMaster in two sessions separated by 1 to 12 days in 20 young adults. The two examiners each took measurements, and the subject was then cyclopleged with 1% tropicamide. The IOLMaster readings were then repeated by both examiners, followed by five ultrasound readings. Repeatability was evaluated by calculating the difference between measurements from the two sessions. The mean and standard deviation of these differences was then used to determine the 95% limits of agreement (LoA) for each technique. In addition, the agreement between the IOLMaster and ultrasound was assessed, along with the effect of cycloplegia on IOLMaster readings. RESULTS: The IOLMaster was more repeatable than ultrasound. For axial length, the 95% LoA were -0.11 to +0.07 mm, -0.06 to +0.05 mm, and -0.25 to +0.35 mm, for noncycloplegic IOLMaster, cycloplegic IOLMaster, and ultrasound, respectively. The two instruments showed modest agreement with each other (mean difference, +0.12 mm; 95% LoA, -0.39 to +0.64 mm; p > 0.0125). Cycloplegia had no significant effect on IOLMaster axial length measurements. The 95% LoA for anterior chamber depth measurement were -0.11 to +0.18 mm, -0.06 to +0.04 mm, and -0.19 to +0.21 mm, for noncycloplegic IOLMaster, cycloplegic IOLMaster, and ultrasound, respectively. The IOLMaster gave significantly longer anterior chamber depths than ultrasound (mean, +0.18 mm; 95% LoA, -0.02 to +0.37 mm; p < 0.0125), and cycloplegia produced significantly deeper anterior chamber depths using the IOLMaster (mean, +0.12 +/- 0.09 mm; 95% LoA, -0.05 to +0.29 mm; t = 6.17; p < 0.001). The experienced observer's measurements were more repeatable than the inexperienced observer's for ultrasound, but not for the IOLMaster. CONCLUSIONS: The superior repeatability of the IOLMaster suggests that it should become the standard for axial length measurement. The 95% limits of agreement for the cycloplegic measurements correspond to a change in refractive error of +/-0.12 D.

Adult↗