| 1. |
- Andersson, Nina, et al.
(författare)
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Adaptive method for assessment of cerebrospinal fluid outflow conductance.
- 2007
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Ingår i: Medical and Biological Engineering and Computing. - : Springer Science and Business Media LLC. - 0140-0118 .- 1741-0444. ; 45:4, s. 337-343
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Tidskriftsartikel (refereegranskat)abstract
- Outflow conductance (C out) is important for predicting shunt responsiveness in patients with suspected idiopathic adult hydrocephalus syndrome (IAHS). C out is determined by performing an infusion test into the cerebrospinal fluid system, and the reliability of the test is dependent on the measurement time. The objective of this study was to develop an adaptive signal analysis method to reduce the investigation time, by taking the individual intracranial pressure variations of the patient into consideration. The method was evaluated on 28 patients with suspected IAHS. The results from full time investigations (60 min) were compared to the results of the new algorithm. Applying the new adaptive method resulted in a reduction of mean investigation time by 14.3 ± 5.9 min (mean ± SD), p < 0.01. The reduction of reliability in the C out estimation was found clinically negligible. We thus recommend this adaptive method to be used when performing constant pressure infusion tests.
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| 2. |
- Arildsson, Mikael, et al.
(författare)
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Spectral signature and heterodyne efficiency for different wavelengths in laser Doppler flowmetry
- 2002
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Ingår i: Medical and Biological Engineering and Computing. - 0140-0118 .- 1741-0444. ; 40:1, s. 85-89
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Tidskriftsartikel (refereegranskat)abstract
- Laser Doppler perfusion monitoring and imaging technologies generate time traces and two-dimensional flow maps of the microcirculation. With the goal of reaching different tissue depths, these technologies are equipped with lassers operating at different wavelengths λ. The fact that the average scattering angle, at a single scattering event, between a photon and a red blood cell increases with λ is compensated for by a 1/λ effect in the scattering vector, rendering the average frequency shift virtually independent of the choice of wavelength. Monte Carlo simulations showed that the corresponding spectral signature of the Doppler signals for λ=632.8nm and 780nm were close to identical. The theoretical predictions were verified by calculating the centre-of-gravity (COG) frequency of the laser Doppler power spectral density for the two wavelengths from forearm and finger skin, representing a low and high perfusion area, respectively (forearm COG=123 against 121Hz, finger COG=220 against 212 Hz). When the wavelength changes from 632.8nm to 780nm, the heterodyne efficiency of the detector and, thereby, the inherent system amplifcation increase. For tissues with identical microvascular flow conditions, the output signal therfore tends to increase in magnitude when shifting to longer wavelengths.
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| 3. |
- Bodén, Ida, 1977-, et al.
(författare)
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Characterization of healthy skin using near infrared spectroscopy and skin impedance
- 2008
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Ingår i: Medical and Biological Engineering and Computing. - : Springer Science and Business Media LLC. - 0140-0118 .- 1741-0444. ; 46:10, s. 985-995
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Tidskriftsartikel (refereegranskat)abstract
- Near infrared spectroscopy (NIR) and skin impedance (IMP) spectroscopy are two methods suggested for diagnoses of diseases inducing adverse effects in skin. The reproducibility of these methods and their potential value in non-invasive diagnostics were investigated. Measurements were performed in vivo on healthy skin at five anatomic body sites on eight young women. partial least squares discriminant analysis showed that both methods were useful for classification of the skin characteristics at the sites. Inter-individually the NIR model gave 100% correct classification while the IMP model provided 92%. Intra-individually the NIR model gave 88% correct classification whereas the IMP model did not provide any useful classification. The correct classification was increased to 93% when both datasets were combined, which demonstrates the value of adding information. Partial least squares discriminant analysis gave 72% correct predictions of skin sites while the combined model slightly improved to 73%.
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| 4. |
- Cacho, Fernando, et al.
(författare)
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A procedure to simulate coronary artery bypass graft surgery
- 2007
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Ingår i: Medical and Biological Engineering and Computing. - : Springer Science and Business Media LLC. - 0140-0118 .- 1741-0444. ; 45:9, s. 819-827
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Tidskriftsartikel (refereegranskat)abstract
- In coronary artery bypass graft (CABG) surgery the involved tissues are overstretched, which may lead to intimal hyperplasia and graft failure. We propose a computational methodology for the simulation of traditional CABG surgery, and analyze the effect of two clinically relevant parameters on the artery and graft responses, i.e., incision length and insertion angle for a given graft diameter. The computational structural analyses are based on actual three-dimensional vessel dimensions of a human coronary artery and a human saphenous vein. The analyses consider the structure of the end-to-side anastomosis, the residual stresses and the typical anisotropic and nonlinear vessel behaviors. The coronary artery is modeled as a three-layer thick-walled tube. The finite element method is employed to predict deformation and stress distribution at various stages of CABG surgery. Small variations of the arterial incision have relatively big effects on the size of the arterial opening, which depends solely on the residual stress state. The incision length has a critical influence on the graft shape and the stress in the graft wall. Stresses at the heel region are higher than those at the toe region. The changes in the mechanical environment are severe along all transitions between the venous tissue and the host artery. Particular stress concentrations occur at the incision ends. The proposed computational methodology may be useful in designing a coronary anastomotic device for reducing surgical trauma. It may improve the quantitative knowledge of vessel diseases and serve as a tool for virtual planning of vascular surgery.
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| 5. |
- Carlqvist, Håkan, et al.
(författare)
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Amplitude and phase relationship between alpha and beta oscillations in the human electroencephalogram
- 2005
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Ingår i: Medical and Biological Engineering and Computing. - 0140-0118 .- 1741-0444. ; 43:5, s. 599-607
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Tidskriftsartikel (refereegranskat)abstract
- The relationship between the electro-encephalographic (EEG) alpha and beta oscillations in the resting condition was investigated in the study. EEGs were recorded in 33 subjects, and alpha (7.5-12.5Hz) and beta (15-25Hz) oscillations were extracted with the use of a modified wavelet transform. Power, peak frequency and phase synchronisation were evaluated for both types of oscillation. The average beta-alpha peak frequency ratio was about 1.9-2.0 for all electrode derivations. The peak frequency of beta activity was within 70-90 % of the 95 % confidence interval of twice the alpha frequency. A significant (p < 0.05) linear regression was found between beta and alpha power in all derivations in 32 subjects, with the slope of the regression line being approximate to 0.3. There was no significant difference in the slope of the line in different electrode locations, although the power correlation was strongest in the occipital locations where alpha and beta oscillations had the largest power. A significant 1:2 phase synchronisation was present between the alpha and beta oscillations, with a phase lag of about pi/2 in all electrode derivations. The strong frequency relationship between the resting beta and alpha oscillations suggests that they are generated by a common mechanism. Power and phase relationships were weaker suggesting that these properties can be modulated by additional mechanisms as well as be influenced by noise. A careful distinction between alpha-dependent and alpha-independent beta activity should be considered when making statements about the possible significance of genuine beta activity in different neurophysiological mechanisms.
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| 6. |
- Eklund, Anders, et al.
(författare)
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Assessment of cerebrospinal fluid outflow resistance.
- 2007
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Ingår i: Medical and Biological Engineering and Computing. - : Springer Science and Business Media LLC. - 0140-0118 .- 1741-0444. ; 45:8, s. 719-735
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Tidskriftsartikel (refereegranskat)
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| 7. |
- Eklund, Anders, et al.
(författare)
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Evaluation of applanation resonator sensors for intra-ocular pressure measurement : results from clinical and in vitro studies.
- 2003
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Ingår i: Medical and Biological Engineering and Computing. - 0140-0118 .- 1741-0444. ; 41:2, s. 190-197
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Tidskriftsartikel (refereegranskat)abstract
- Glaucoma is an eye disease that, in its most common form, is characterised by high intra-ocular pressure (IOP), reduced visual field and optic nerve damage. For diagnostic purposes and for follow-up after treatment, it is important to have simple and reliable methods for measuring IOP. Recently, an applanation resonator sensor (ARS) for measuring IOP was introduced and evaluated using an in vitro pig-eye model. In the present study, the first clinical evaluation of the same probe has been carried out, with experiments in vivo on human eyes. There was a low but significant correlation between IOP(ARS) and the IOP measured with a Goldmann applanation tonometer (r = 0.40, p = 0.001, n = 72). However, off-centre positioning of the sensor against the cornea caused a non-negligible source of error. The sensor probe was redesigned to have a spherical, instead of flat, contact surface against the eye and was evaluated in the in vitro model. The new probe showed reduced sensitivity to off-centre positioning, with a decrease in relative deviation from 89% to 11% (1 mm radius). For normalised data, linear regression between IOP(ARS) and direct IOP measurement in the vitreous chamber showed a correlation of r = 0.97 (p < 0.001, n = 108) and a standard deviation for the residuals of SD < or = 2.18 mm Hg (n = 108). It was concluded that a spherical contact surface should be preferred and that further development towards a clinical instrument should focus on probe design and signal analysis.
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| 8. |
- Eklund, Anders, et al.
(författare)
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Infusion technique can be used to distinguish between dysfunction of a hydrocephalus shunt system and a progressive dementia
- 2004
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Ingår i: Medical and Biological Engineering and Computing. - : Springer. - 0140-0118 .- 1741-0444. ; 42:5, s. 644-649
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Tidskriftsartikel (refereegranskat)abstract
- In a deteriorating shunted patient with hydrocephalus, an investigation of shunt function is often performed to distinguish a dysfunctioning shunt from an aggravated condition of the disease. The paper illustrates how a lumbar cerebrospinal fluid (CSF) infusion method can be used to evaluate post-operative deterioration in a shunted patient in order to give the physician valuable support in the shunt revision decision. A 77-year-old man with hydrocephalus was treated operatively by the insertion of a CSF shunt. Owing to shunt failure, the shunt was revised twice during a 5 year period. Using a computerised infusion technique method, with two needles placed in the lumbar subarachnoid space, the CSF dynamic system was determined pre- and post-operatively with the functioning as well as the dysfunctioning shunts. The data were verified with a bench-test of the extirpated CSF shunt. There was a significant difference in conductance G between CSF systems with an open shunt and CSF systems with no shunt or an occluded shunt (ΔG=38mm3 s−1 kPa−1, p=0.014, n=7, ANOVA). CSF dynamics investigations, with and without a shunt, can give valuable clinical support in the management of a deteriorating hydrocephalus patient. With further development of the lumbar infusion method moving towards easy-to-use equipment, there is potential for widespread clinical use.
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| 9. |
- El-Segaier, Milad, et al.
(författare)
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Atrial septal defect: a diagnostic approach
- 2006
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Ingår i: Medical & Biological Engineering & Computing. - : Springer Science and Business Media LLC. - 0140-0118 .- 1741-0444. ; 44:9, s. 739-745
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Tidskriftsartikel (refereegranskat)
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| 10. |
- Folke, Mia, et al.
(författare)
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A new capnograph based on an electro acoustic sensor
- 2008
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Ingår i: Medical and Biological Engineering and Computing. - : Springer Science and Business Media LLC. - 0140-0118 .- 1741-0444. ; 46, s. 55-59
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Tidskriftsartikel (refereegranskat)abstract
- End tidal carbon dioxide measurements with an electro acoustic capnograph prototype have been demonstrated. The aim of this study was to verify that it is possible to obtain an adequate capnogram using the prototype and to investigate the influence of ambient temperature and humidity variations. By simultaneous measurements with a reference capnograph, on subjects performing exercise, hypo- and hyperventilation, PETCO2 readings from the reference were compared with the output signal from the prototype. The capnogram from the prototype correlated well with the reference in terms of breath time. The first parts of the expiration and inspiration phases were steeper for the reference than the prototype. The output signal from the prototype correlated well with the reference PETCO2 readings with a correlation coefficient of 0.93 at varied temperature and relative humidity.
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