| 1. |
- Albano, Amanda, et al.
(författare)
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Echocardio-variability - Low and high frequency beat-to-beat variability in echocardiographic signals
- 2013
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Ingår i: Computing in Cardiology 2013. - 9781479908844 ; , s. 767-770
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Konferensbidrag (refereegranskat)abstract
- Measurement signals originating from the cardiovascular system are known to comprise oscillating components and beat-to-beat variability, e.g., heart-rate variability and blood pressure variability. In clinical echocardiographic procedures, typically only a few cardiac cycles are acquired. This pilot study analyses the beat-to-beat variability of echocardiographic variables (echocardio-variability) in minute long acquisitions.
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| 2. |
- Alenius Dahlqvist, Jenny, et al.
(författare)
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Handheld ECG in analysis of arrhythmia and heart rate variability in children with Fontan circulation
- 2014
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Ingår i: Journal of Electrocardiology. - : Elsevier BV. - 0022-0736 .- 1532-8430. ; 47:3, s. 374-382
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Tidskriftsartikel (refereegranskat)abstract
- Background: Our aim was to evaluate the intermittent use of a handheld ECG system for detecting silent arrhythmias and cardiac autonomic dysfunction in children with univentricular hearts. Methods: Twenty-seven patients performed intermittent ECG recordings with handheld devices during a 14-day period. A manual arrhythmia analysis was performed. We analyzed heart rate variability (HRV) using scatter plots of all interbeat intervals (Poincare plots) from the total observation period. Reference values of HRV indices were determined from Holter-ECGs in 41 healthy children. Results: One asymptomatic patient had frequent ventricular extra systoles. Another patient had episodes with supraventricular tachycardia (with concomitant palpitations). Seven patients showed reduced HRV. Conclusions: Asymptomatic arrhythmia was detected in one patient. The proposed method for pooling of intermittent recordings from handheld or similar devices may be used for detection of arrhythmias as well as for cardiac autonomic dysfunction.
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| 3. |
- Alenius Dahlqvist, Jenny, et al.
(författare)
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Heart rate variability in children with fontan circulation : lateral tunnel and extracardiac conduit
- 2012
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Ingår i: Pediatric Cardiology. - New York : Springer-Verlag New York. - 0172-0643 .- 1432-1971. ; 33:2, s. 307-315
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Tidskriftsartikel (refereegranskat)abstract
- The technique in Fontan surgery has developed from the lateral tunnel (LT) toward the extracardiac conduit (EC) used to reduce long-term complications such as atrial arrhythmia and sinus node dysfunction. Heart rate variability (HRV) examines cardiac nervous activity controlling the sinus node. This study aimed to investigate HRV in a cohort of children with univentricular hearts, focusing on the relation between HRV and surgical procedure. For 112 children with Fontan circulation, HRV was analyzed using power spectral analysis. Spectral power was determined in three regions: very-low-frequency (VLF), low-frequency (LF), and high-frequency (HF) regions. Patients were compared with 66 healthy controls subject. Patients with LT were compared with patients who had EC. The children with Fontan circulation showed a significantly reduced HRV including total power (P < 0.0001), VLF (P < 0.0001), LF (P < 0.0001), and HF (P = 0.001) compared with the control subjects. The LT and EC patients did not differ significantly. Reduced HRV was found in both the LT and EC patients. In terms of HRV reduction, EC was not superior to LT.
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| 4. |
- Andersson, Jonas, et al.
(författare)
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Dysregulation of subcutaneous adipose tissue blood flow in overweight postmenopausal women
- 2010
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Ingår i: Menopause. - : Ovid Technologies (Wolters Kluwer Health). - 1072-3714 .- 1530-0374. ; 17:2, s. 365-371
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: A putative link between abdominal obesity and metabolic-vascular complications after menopause may be due to a decreased adipose tissue blood flow (ATBF). The present work aimed to analyze possible changes in ATBF with being overweight and menopausal and its putative link to endothelial dysfunction and autonomic nervous system balance.METHODS: Forty-three healthy women were classified into four groups according to weight and menopause status. The ATBF was measured by xenon washout while fasting and after oral glucose intake. The nitric oxide synthase inhibitor asymmetric dimethylarginine was used as a marker of endothelial function and heart rate variability-estimated autonomic nervous system activity.RESULTS: Fasting ATBF was decreased in both overweight groups (P = 0.044 and P = 0.048) versus normal-weight premenopausal women. Normal-weight and overweight postmenopausal women exhibited lower maximum ATBF compared with normal-weight premenopausal women (P = 0.015 and P = 0.001, respectively), and overweight postmenopausal women exhibited lower maximum ATBF compared with normal-weight postmenopausal women (P = 0.003). A negative correlation was found between fasting ATBF and asymmetric dimethylarginine (P = 0.015), whereas maximum ATBF was negatively associated with sympathetic-parasympathetic nervous system balance (ratio of the power of the low frequency to the power of the high frequency; P = 0.002).CONCLUSIONS: Loss of ATBF flexibility in overweight postmenopausal women may contribute to the metabolic dysfunction seen in this group of women.
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| 5. |
- Andersson, Kennet, et al.
(författare)
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Directed coherence analysis in patients with severe autonomic dysfunction
- 2014
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Ingår i: 2014 8th conference of the European Study Group on Cardiovascular Oscillations (ESGCO). - : IEEE conference proceedings. ; , s. 167-168
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Konferensbidrag (refereegranskat)abstract
- Many different approaches have been applied to analyse the coupling between cardiovascular signals. This study evaluated the use of directed coherence, based on multivariate autoregressive modelling, for analysis of cardiovascular signals in patients with transthyretin amyloidosis, a rare disease where severe autonomic dysfunction is common.
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| 6. |
- André, Benny, et al.
(författare)
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Friction and contact resistance of nanocomposite Ti-Ni-C coatings
- 2011
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 270:9-10, s. 555-566
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Tidskriftsartikel (refereegranskat)abstract
- Ceramic nanocomposite coatings in the Ti-Ni-C were deposited using PVD and studied with respect to tribological properties and contact resistance. It was shown that coatings could be deposited combining of a low contact resistance and a low friction coefficient against silver, making them suitable for use in high performance electrical contacts.Nine coatings with different amounts of C and Ni were deposited. Coatings on flat Ni plated copper substrates were tested in a tribological ball-on-disc setup against ball bearing steel balls. Depending on primarily the amount of carbon the coatings showed very different friction coefficient and wear rate. The coatings were also deposited on cylindrical Ni plated copper substrates. Using geometrically identical silver plated cylinders as counter surface these were evaluated in a test setup better resembling a real life electrical contact. For most coatings a low electrical contact resistance was measured. The evolution of friction coefficient and contact resistance was correlated to wear marks and contact tracks, with their generated tribofilms, as examined after testing using electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy.
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| 7. |
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| 8. |
- André, Benny
(författare)
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Nanocomposites for Use in Sliding Electrical Contacts
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis nanocomposite materials for use in high performance electrical contacts are tested. Self mating silver as coatings on cupper substrates are the most used material combination in power connectors today. In this work two new concepts were tested. The first one was to change one of the mating surfaces to a hard thin coating and keep the other surface made of silver. Tested coatings were nanocomposites with hard carbides in a matrix of amorphous carbon. TiC/a-C and Ti-Ni-C/a-C were tested both electrically and tribologically. The total amount of carbon and the amount of carbon matrix was important, both for the electrical and the tribological properties. The Ti-Ni-C coating also showed that substituting Ti in TiC with the weak carbide former Ni changed the stability of the carbides. The substitution resulted in more a-C matrix and less C in the carbides. Thin coatings of nc-TiC/a-C and Ti-Ni-C/a-C showed high potential as material candidates for use in electrical contacts. The other tested concept was to modify the used silver instead of replacing it. This was done by embedding nanoparticles of solid lubricant IF-WS2 in the silver. The results from reciprocating sliding displayed low friction and high wear resistance. The modified silver surfaces lasted for 8000 strokes with a friction of about 0.3 while at the same time allowing for a low contact resistance. The results for surfaces of pure silver coating displayed a friction of 0.8-1.2 and that the silver was worn through already after 300 strokes. A new method to investigate inherent hardness and residual stress of thin coatings, on complex geometries or in small areas, was also developed. An ion beam was used to create stress free coating as free standing micro pillars. Hardness measured on the pillars and on as-deposited coating were then used to calculate the residual stress in the coatings.
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| 9. |
- Andre, Benny, et al.
(författare)
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Nanoindentation on micro pillars for determination of intrinsic hardness and residual stress in coatings deposited on complex geometries
- 2012
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Ingår i: Tribologia. - 0780-2285. ; 31:1-2, s. 22-31
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Tidskriftsartikel (refereegranskat)abstract
- In this work a procedure to assess the local residual stress in coatings deposited on complex substrate geometries is described. A focused ion beam (FIB) is used to mill structures small enough to relax from residual stress. Nanoindentation is used to measure the change in mechanical properties, most importantly the hardness, in relaxed coating and in as-deposited coating. This change is then related to the residual stress in the coating. This relationship can then be used to calculate the residual stresses, at other positions or at other components, from changes in hardness as measured as before. The procedure is demonstrated on two different PVD coatings; one TiN coating and one nanocomposite TiNiC coating. On a large high speed steel substrate the TiN was measured to a hardness of 28 GPa using conventional techniques. Using this procedure, this could be divided into 23 GPa of intrinsic hardness and an extra 5 GPa induced by the known compressive residual stress of 3.9 GPa. When the same coating was deposited on a thin wire the full procedure allowed the residual stress to be determined to 3.5 GPa in compression.
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| 10. |
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