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  • 1.
    Eklund, Anders
    et al.
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Bäcklund, Tomas
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Lindahl, Olof
    A resonator sensor for measurement of intraocular pressure: evaluation in an in vitro pig-eye model2000Inngår i: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 21, nr 3, s. 355-367Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Intraocular pressure (IOP) measurement is performed routinely at every eye clinic. High IOP, which can be a sign of glaucoma, can lead to degeneration of the retina and can cause blindness. In this study we developed a resonator sensor for IOP measurement based on an oscillator consisting of a piezoelectric element made of lead zirconate titanate, a flat contact piece of nylon and a feedback circuit. The aim of this study was to evaluate the new sensor's ability to determine lOP in an in vitro pig-eye model. Six eyes from four pigs were removed and fixed in agar. They were then pressurized by a saline column (10-35 cm H2O) through a cannula inserted into the vitreous chamber. The IOP was measured with the resonator sensor applied to cornea. An Alcon applanation pneumatonometer and a standard Viggo-Spectramed pressure sensor connected to the saline column were used as references. The IOP as measured with the resonator sensor correlated well with the pressure elicited by the saline column for individual eyes (r = 0.96-0.99, n = 60) and for all eyes (r = 0.92, n = 360). The correlation between the resonance sensor and the pneumatonometer was r = 0.92 (n = 360). The pneumatonometer also showed a good correlation with the saline column (r = 0.98, n = 360). We conclude that our in vitro pig-eye model made it possible to induce reproducible variation in IOP, and measurement of that pressure with the newly developed resonator sensor gave very promising results for development of a clinically applicable IOP tonometer with unique properties.

  • 2.
    Fröjse, Rolf
    et al.
    Umeå University Hospital, Department of Surgery.
    Amerlöv, Conny
    Umeå University Hospital, Department of Surgery.
    Hedberg, Bengt
    Umeå University Hospital, Department of Surgery.
    Häggström, Mats
    University Hospital of Umeå, Department of Biomedical Engineering.
    Bäcklund, Tomas
    University Hospital of Umeå, Department of Biomedical Engineering.
    Lindahl, Olof
    Ängquist, Karl-Axel
    Umeå University Hospital, Department of Surgery.
    A new method for continuous tonometric pCO2 measurement: in vitro studies1999Inngår i: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 20, nr 2, s. 129-36Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The available methods for tonometric pCO2 measurement only provide the possibility of performing intermittent registrations. A new method allowing continuous tonometric pCO2 measurement has been developed and tested in an in vitro model. A standard tonometer for intestinal pCO2 measurement was modified to allow continuous perfusion of the balloon with physiological saline solution in a closed system. The pCO2 in the system was determined in a specially sructed measurement chamber with a TCM20 percutaneous pCO2 monitor. In this in vitro model the tonometer balloon was placed in a saline bath with a constant pCO2 concentration and the measurements from the closed circulating system were compared with those obtained from a standard tonometer placed in the same bath. In 8 and 24 h experiments the circulating system measured the pCO2 value as accurately and reliably as traditional tonometry. This study indicates that the new method makes continuous monitoring of pCO2 possible

  • 3.
    Fröjse, Rolf
    et al.
    Department of Surgical and Perioperative Science, Umeå University.
    Hedberg, Bengt
    Department of Surgical and Perioperative Science, Umeå University.
    Bäcklund, Tomas
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Lindahl, Olof
    Häggström, Mats
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Ängquist, Karl-Axel
    Department of Surgical and Perioperative Science, Umeå University.
    Amerlöv, Conny
    Department of Surgical and Perioperative Science, Umeå University.
    Validation of a novel method for continuous saline tonometry in a porcine model2001Inngår i: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 22, nr 3, s. 453-60Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Only intermittent and semi-continuous tonometric measurement of gastric and intestinal pHi is possible with the equipment available today. Earlier we developed a system for continuous saline tonometry and tested it in vitro. To assess the in vivo reliability of this method for continuous gastrointestinal saline tonometry, a standard tonometer for measurement of intestinal pCO2 and corresponding pHi was modified to allow continuous perfusion of physiological saline in a closed system and tested in a porcine model. In 11 anaesthetized and haemodynamically stable pigs, two continuous tonometry balloons were inserted into the distal small bowel, and a standard tonometry balloon was used as reference. To test long-term function of the continuous tonometers the research protocol lasted for eight hours. The two continuous saline tonometers performed well, and after an equilibration time of three hours the mean pHi values were stable between 7.35 and 7.43 and between 7.32 and 7.39 respectively. The standard tonometer measured stable pHi values. These preliminary studies indicate that continuous saline tonometry performs well over eight hours with a small bias and a good precision

  • 4.
    Hallberg, Per
    et al.
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Lindén, Christina
    Umeå University, Department of Clinical Science, Ophthalmology.
    Lindahl, Olof
    Bäcklund, Tomas
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Eklund, Anders
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Applanation resonance tonometry for intraocular pressure in humans2004Inngår i: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 25, nr 4, s. 1053-65Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Glaucoma is a group of diseases associated with optic nerve damage and loss of visual field. The aetiology is not completely understood, but one of the major risk factors is elevated intraocular pressure (IOP). Reliable methods for measuring the IOP are therefore important. The aim of the study was to investigate the ability of the applanation resonance tonometry (ART) system, based on continuous force and area recording, to measure IOP in humans. Both the phase of initial indentation (IOPIndentation) and the phase when the sensor was removed (IOPRemoval) from the cornea were analysed. The Goldmann applanation tonometry (GAT) was used as reference method. The study included 24 healthy volunteers with normal IOP and 24 patients with elevated IOP. The correlation and standard deviation (SD) between IOPIndentation and IOPGAT was R = 0.92 (p < 0.001), SD = 3.6 mmHg, n = 104, and between IOPRemoval and IOPGAT R = 0.94 (p < 0.001), SD = 3.1 mmHg, n = 104. In conclusion, resonance sensor technology has made it possible to introduce a new multi-point method for measuring IOP, and the method is relevant for measuring IOP in humans. The study indicates that with further development towards elimination of position dependence, the ART has the potential to become a useful clinical instrument for IOP measurement.

  • 5.
    Jalkanen, Ville
    et al.
    Umeå University. Department of Applied Physics and Electronics.
    Andersson, Britt M.
    Umeå University. Department of Applied Physics and Electronics.
    Bergh, Anders
    Department of Medical Biosciences Pathology, Umeå University.
    Ljundberg, Börje
    Umeå University, Department of Surgical and Perioperative Science, Urology and Andrology.
    Lindahl, Olof
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Explanatory models for a tactile resonance sensor system: elastic and density-related variations of prostate tissue in vitro2008Inngår i: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 29, nr 7, s. 729-745Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Tactile sensors based on piezoelectric resonance have been adopted for medical applications. The sensor consists of an oscillating piezoelectric sensor-circuit system, and a change in resonance frequency is observed when the sensor tip contacts a measured object such as tissue. The frequency change at a constant applied force or mass load is used as a stiffness-sensitive parameter in many applications. Differential relations between force and frequency have also been used for monitoring intraocular pressure and stiffness variations in prostate tissue in vitro. The aim of this study was to relate the frequency change (Δf), measured force (F) and the material properties, density and elasticity to an explanatory model for the resonance sensor measurement principle and thereby to give explanatory models for the stiffness parameters used previously. Simulations of theoretical equations were performed to investigate the relation between frequency change and contact impedance. Measurements with a resonance sensor system on prostate tissue in vitro were used for experimental validation of the theory. Tissue content was quantified with a microscopic-based morphometrical method. Simulation results showed that the frequency change was dependent upon density (ρ) and contact area (S) according to Δf ∝ ρS3/2. The experiments followed the simulated theory at small impression depths. The measured contact force followed a theoretical model with the dependence of the elastic modulus (E) and contact area, F ∝ ES3/2. Measured density variations related to histological variations were statistically weak or non-significant. Elastic variations were statistically significant with contributions from stroma and cancer relative to normal glandular tissue. The theoretical models of frequency change and force were related through the contact area, and a material-dependent explanatory model was found as Δf ∝ ρE-1F. It explains the measurement principle and the previously established stiffness parameters from the material properties point of view.

  • 6.
    Jalkanen, Ville
    et al.
    Umeå University. Department of Applied Physics and Electronics.
    Andersson, Britt M.
    Umeå University. Department of Applied Physics and Electronics.
    Bergh, Anders
    Umeå University, Department of Medical Biosciences, Pathology.
    Ljungberg, Börje
    Umeå University, Department of Surgical and Perioperative Science, Urology and Andrology.
    Lindahl, Olof
    Resonance sensor measurements of stiffness variations in prostate tissue in vitro: a weighted tissue proportion model2006Inngår i: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 27, nr 12, s. 1373-86Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Prostate cancer is the most common type of cancer in men in Europe and the US. The methods to detect prostate cancer are still precarious and new techniques are needed. A piezoelectric transducer element in a feedback system is set to vibrate with its resonance frequency. When the sensor element contacts an object a change in the resonance frequency is observed, and this feature has been utilized in sensor systems to describe physical properties of different objects. For medical applications it has been used to measure stiffness variations due to various patho-physiological conditions. In this study the sensor's ability to measure the stiffness of prostate tissue, from two excised prostatectomy specimens in vitro, was analysed. The specimens were also subjected to morphometric measurements, and the sensor parameter was compared with the morphology of the tissue with linear regression. In the probe impression interval 0.5-1.7 mm, the maximum R(2) > or = 0.60 (p < 0.05, n = 75). An increase in the proportion of prostate stones (corpora amylacea), stroma, or cancer in relation to healthy glandular tissue increased the measured stiffness. Cancer and stroma had the greatest effect on the measured stiffness. The deeper the sensor was pressed, the greater, i.e., deeper, volume it sensed. Tissue sections deeper in the tissue were assigned a lower mathematical weighting than sections closer to the sensor probe. It is concluded that cancer increases the measured stiffness as compared with healthy glandular tissue, but areas with predominantly stroma or many stones could be more difficult to differ from cancer

  • 7.
    Karvelis, Petros
    et al.
    Laboratory of Knowledge and Intelligent Computing, Department of Computer Engineering, Technological Educational Institute of Epirus.
    Spilka, Jiří
    Department of Cybernetics, FEE, Czech Technical University in Prague.
    Georgoulas, Georgios
    Laboratory of Knowledge and Intelligent Computing, Department of Computer Engineering, Technological Educational Institute of Epirus.
    Chudáček, Václav
    Department of Cybernetics, FEE, Czech Technical University in Prague.
    Stylios, Chrysostomos D.
    Laboratory of Knowledge and Intelligent Computing, Department of Computer Engineering, TEI of Epirus, Artas, Kostakioi.
    Lhotská, Lenka
    Department of Cybernetics, FEE, Czech Technical University in Prague.
    Combining latent class analysis labeling with multiclass approach for fetal heart rate categorization2015Inngår i: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 36, nr 5, s. 1001-1024, artikkel-id 1001Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The most common approach to assess fetal well-being during delivery is monitoring of fetal heart rate and uterine contractions - the cardiotocogram (CTG). Nevertheless, 40 years since the introduction of CTG to clinical practice, its evaluation is still challenging with high inter- and intra-observer variability. Therefore the development of more objective methods has become an issue of major importance in the field. Unlike the usually proposed approaches to assign classes for classification methods that rely either on biochemical parameters (e.g. pH value) or a simple aggregation of expert judgment, this work investigates the use of an alternative labeling system using latent class analysis (LCA) along with an ordinal classification scheme. The study is performed on a well-documented open-access database, where nine expert obstetricians provided CTG annotations. The LCA is proposed here to produce more objective class labels while the ordinal classification aims to explore the natural ordering, and representation of increased severity, for obtaining the final results. The results are promising suggesting that more effort should be put into this proposed approach.

  • 8. Lindahl, Olof
    The evaluation of a biexponential model for description of intercompartmental fluid shifts in compressed oedematous tissue1995Inngår i: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 16, nr 1, s. 17-28Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A parametric model was fitted to force curve data gained by a non-invasive impression method that measures force and fluid translocation during mechanical compression of the skin. The ability of the model parameters to estimate high- and low-viscosity fluid flow in compressed areas were evaluated in a silicone rubber model and in six patients with chronic pitting oedema. Different softnesses of silicone rubber gave significantly different parameter values. The flow properties of the silicone model could be analysed in detail with the suggested model. Parameter analysis showed a higher fraction of low-viscosity fluid for oedema than for reference sites. The model parameters could be interpreted in softness value according to an international standard for consistency (ISO 2137). The suggested parametric model gave reliable and detailed information about high- and low-viscosity fluid flow and can be used to estimate intercompartmental fluid shifts in oedematous tissue

  • 9. Lindahl, Olof
    et al.
    Bäcklund, Tomas
    Umeå University Hospital, Department of Biomedical Engineering.
    Sjödin, Jan-Gunnar
    Umeå University Hospital, Department of Urology and Andrology.
    Monitoring of renal pelvic pressure in patients with hydronephrosis1995Inngår i: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 16, nr 3, s. 169-79Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A diagnostic method for the determination of obstructions in the pelvoureteral junction in patients with suspected idiopathic hydronephrosis is described and discussed. Two microtransducer catheters (MTCs) with infusion lumens are inserted under fluoroscopic control, one into the renal pelvis and the other in the perirenal space as a reference. The pressure values obtained are stored on a portable microcomputer system, carried by the ambulatory patients. Renal pelvic pressure, intra-abdominal pressure and differential pressure are calculated and displayed as time-pressure diagrams on a plotter. The pressures can be measured for long periods (3-24 h). Furthermore, steady state conditions can be evaluated during pelvic infusion of saline. The results from the pressure measurements are compared with clinical and radiological evaluations. Our results show that this method of long-term monitoring of intrapelvic pressure together with intra-abdominal pressure contributes to the evaluation of patients with suspected pelvoureteral obstructions and complements other methods in the preoperative investigation. However, this study reveals difficulties with measurements of intra-abdominal pressure. Carrying the equipment was not inconvenient for the patients

  • 10.
    Zdolsek, Hans-Joachim
    et al.
    Linköping University Hospital, Department of Anaesthesiology and Intensive Care.
    Lindahl, Olof
    Sjöberg, Folke
    Linköping University Hospital, Department of Anaesthesiology and Intensive Care.
    Non-invasive assessment of fluid volume status in the interstitium after haemodialysis2000Inngår i: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 21, nr 2, s. 211-20Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During dialysis excess fluid is removed from uraemic patients. The excess fluid is mainly located in the skin and subcutaneous tissues. In this study we wished, with two noninvasive techniques, the IM (impression method) and BIA (bioimpedance analysis), to study what mechanical (IM) and electrical cellular membrane (BIA) effects the fluid withdrawal has on these tissues. The IM measures the resistive force of the tissues when mechanically compressed. From the force curve two parameters are calculated, the F(0), indicative of interstitial tissue pressure and the FT corresponding to the translocation of tissue fluid (interstitial movable water). The BIA phase angle shift (phi), i.e. geometrical angular transformation of the ratio between reactance and resistance, which has been associated with cellular membrane function, was used as a measurement of electrical cellular membrane effects. Twenty patients were studied before and after haemodialysis measuring the F(0), FT and phi. Theresults showed that the patients lost a median of 3.7 kg during the haemodialysis. F(0) increased until after dialysis, but did not reach significant values, whereas FT increased significantly after dialysis, p < 0.001, as compared with before. After a peak at one hour postdialysis the FT value returned to predialysis values at four hours after termination of dialysis. Also phi increased from before to after dialysis, p < 0.001, but already after one hour it returned to predialysis values. It is common knowledge that dialysis alters the dynamics of fluid in the interstitium of the skin and subcutis. We conclude that the impression method is sensitive enough to detect and chronicle these changes. Furthermore, with the BIA, (phase angle) signs of changes in the electrical properties of the tissues, possibly reflecting cellular membrane function, could be detected

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