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  • 1
    Electronic Resource
    Electronic Resource
    Repolarization abnormalities in cardiomyocytes of dogs with chronic heart failure: role of sustained inward current (1999)
    Springer
    Cellular and molecular life sciences 55 (1999), S. 494-505 
    Details
    ISSN: 1420-9071
    Keywords: Key words. Cardiomyocyte; action potential; saxitoxin; lidocaine; nifedipine; patch clamp; sodium channel; calcium channel.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. We previously showed that a canine model of chronic heart failure (HF) produced by multiple coronary microembolizations manifests ventricular arrhythmias similar to those observed in patients with chronic HF. In the present study, we used single canine cardiomyocytes isolated from the left ventricle (LV) of normal dogs (n = 13) and dogs with HF (n = 15) to examine the cellular substrate of these arrhythmias. Action potentials (APs) and ion currents were measured by perforated and whole cell patch clamp, respectively. We found prolonged APs and alterations of AP duration resulting in early afterdepolarizations (EADs) at the low pacing rates of 0.5 Hz and 0.2 Hz. Na+ channel blockers saxitoxin (STX, 100 nM) and lidocaine (90 μM) reduced AP duration dispersion and abolished EADs in HF cardiomyocytes. The steady-state current (Iss)-voltage relation, in the voltage range from −25 mV to 25 mV analogous to the AP plateau level, was significantly shifted inward in HF cardiomyocytes. STX and lidocaine shifted the Iss-voltage relationship in an outward direction. The shifts produced by both drugs was significantly greater in cardiomyocytes of dogs with HF, indicating an increase in inward current. In the experimental configuration in which K+ currents were blocked, the density of the steady-state Ca2+ current (ICa) was found to decrease in HF cardiomyocytes by approximately 33%. In contrast, the density of the steady-state Na+ current (INa) significantly (P 〈 0.01) increased in HF cardiomyocytes (0.17 ± 0.06 pA/pF) compared with normal cells (0.08 ± 0.02 pA/pF). The relative contribution of INa to the net inward current was greater in HF cardiomyocytes, as evident from the increased ratio of INa/ICa (from 0.22 to 0.68). These observations support a hypothesis that anomalous repolarization of HF cardiomyocytes is due, at least in part, to an increased steady-state inward Na+ current.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000180050306
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  • 2
    Electronic Resource
    Electronic Resource
    Relationship between action potential, contraction-relaxation pattern, and intracellular Ca2+ transient in cardiomyocytes of dogs with chronic heart failure (1998)
    Springer
    Cellular and molecular life sciences 54 (1998), S. 597-605 
    Details
    ISSN: 1420-9071
    Keywords: Key words. Heart failure; single cardiomyocytes; action potential; calcium transient; contraction; relaxation; saxitoxin; lidocaine; perforated patch clamp.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. Abnormalities of contractile function have been identified in cardiomyocytes isolated from failed human hearts and from hearts of animals with experimentally induced heart failure (HF). The mechanism(s) responsible for these functional abnormalities are not fully understood. In the present study, we examined the relationship between action potential duration, pattern of contraction and relaxation, and associated intracellular Ca2+ transients in single cardiomyocytes isolated from the left ventricle (LV) of dogs (n = 7) with HF produced by multiple sequential intracoronary microembolizations. Comparisons were made with LV cardiomyocytes isolated from normal dogs. Action potentials were measured in isolated LV cardiomyocytes by perforated patch clamp, Ca2+ transients by fluo 3 probe fluorescence, and cardiomyocyte contraction and relaxation by edge movement detector. HF cardiomyocytes exhibited an abnormal pattern of contraction and relaxation characterized by an attenuated initial twitch (spike) followed by a sustained contracture ('dome') of 1 to 8 s in duration and subsequent delayed relaxation. This pattern was more prominent at low stimulation rates (58% at 0.2 Hz, n = 211, 21% at 0.5 Hz, n = 185). Measurements of Ca2+ transients in HF cardiomyocytes at 0.2 Hz manifested a similar spike and dome configuration. The dome phase of both the contraction/relaxation pattern and Ca2+ transients seen in HF cardiomyocytes coincided with a sustained plateau of the action potential. Shortening of the action potential duration by administration of saxitoxin (100 nM) or lidocaine (30 μM) reduced the duration of the dome phase of both the contraction/relaxation profile as well as that of the Ca2+ transient profile. An increase of stimulation rate up to 1 Hz caused shortening of the action potential and disappearance of the spike-dome profile in the majority of HF cardiomyocytes. In HF cardiomyocytes, the action potential and Ca2+ transient duration were not significantly different from those measured in normal cells. However, the contraction-relaxation cycle was significantly longer in HF cells (314 ± 67 ms, n = 21, vs. 221 ± 38 ms, n = 46, mean ± SD), indicating impaired excitation-contraction uncou pling in HF cardiomyocytes. The results show that, in cardiomyocytes isolated from dogs with HF, contractile abnormalities and abnormalities of intracellular Ca2+ transients at low stimulation rates are characterized by a spike-dome configuration. This abnormal pattern appears to result from prolongation of the action potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000180050187
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  • 3
    Electronic Resource
    Electronic Resource
    A streaming birefringence study of the flow at the junction of the aorta and the renal arteries (1989)
    Springer
    Experiments in fluids 7 (1989), S. 73-80 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Streaming birefringence with an organic dye (Milling Yellow) was used to investigate the flow near the junction of the renal arteries and the descending aorta in a model of human vessels. The dye concentration was adjusted to give fluid rheological properties, typical of blood. Steady and pulsatile flow were investigated at branch-to-trunk flow ratios of 0.050–0.350. The flow ratio range over which flow separation and simple secondary flows were identified during systole near the renal ostia are reported. Streaming birefringence has the advantage of allowing visualization of the entire flow field. Also, the fluid rather than suspended particles are observed. An important disadvantage, however, is that three-dimensional flows make interpretation difficult.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00207298
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  • 4
    Electronic Resource
    Electronic Resource
    An experimental evaluation of the use of an ensemble average for the calculation of turbulence in pulsatile flow (1983)
    Springer
    Annals of biomedical engineering 11 (1983), S. 385-399 
    Details
    ISSN: 1573-9686
    Keywords: Ensemble average ; Digital filter ; Turbulence intensity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract A comparison was made between turbulence calculated by subtracting an ensemble average from the instantaneous velocity and calculations made with a high pass digital filter. Velocity was measured with a laser Doppler anemometèr in vitro in the region of a normal porcine aortic valve and in patients with a hot film anemometer in the region of normal aortic valves. From the velocity obtained in patients, the absolute turbulence intensity calculated using an ensemble average of 50 beats was nearly twice the turbulence intensity calculated dusing a digital filter. Individual beats sometimes showed differences of 150% compared to calculations based upon the use of a digital filter. Inspection showed that the ensemble average varied widely from the actual nonfluctuating velocity. Studies in vitro showed less beat to beat variation than occurred in patients. The absolute turbulence intensity measured in vitro, when calculated using an ensemble average, was only 20% greater than calculations using a digital filter. The differences were due primarily to beat-to-beat variations of the nonfluctuating velocity, but these beat-to-beat variations were less prominent than occurred in patients. These observations suggest that ensemble averaging may not be appropriate for the calculation of turbulence, particularly in patients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00000002
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  • 5
    Electronic Resource
    Electronic Resource
    Comparison of spectral techniques for computer-assisted classification of spectra of heart sounds in patients with porcine bioprosthetic valves (1993)
    Springer
    Medical & biological engineering & computing 31 (1993), S. 229-236 
    Details
    ISSN: 1741-0444
    Keywords: Bioprosthetic heart valve ; Feature extraction ; Heart sounds ; Pattern recognition ; Spectral techniques
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The diagnositic performance of two spectral techniques (the fast Fourier transform, FFT, and autoregressive modelling, ARM) combined with four windowing functions (rectangular, Hanning, Hamming, and sine-cosine) and two classifiers (Bayes and nearest neighbour) to detect valvular degeneration was evaluated in a group of 95 patients. Forth-seven patients had a porcine bioprosthetic valve inserted in the aortic position and 48 patients had a porcine bioprosthetic valve inserted in the mitral position. Among the aortic valves, 24 were normal and 23 were degenerated whereas among the mitral valves, 19 were normal and 29 were degenerated. The aortic and mitral valves were analysed separately. For each type of valve, 21 features were extracted from the spectra of the valve closure sounds to train and test the performance of four pattern recognition systems by using the leave-one-out method. The discriminant properties of all feature combinations between two and five among the 21 features selected were evaluated. Results show that the FFT combined to the nearest neighbour classifier provided the best performances: 87 per cent of correct classifications (CCs) for aortic valves when using the Hanning or the Hamming window and 94 per cent of CCs for mitral valves when using the rectangular window. The best performances obtained with the ARM were 81 per cent of CCs for the aortic valves (nearest neighbour classifier and the Hanning or the Hamming window) and 92 per cent of CCs for the mitral valves (nearest neighbour classifier and the Hamming window or the Bayes classifier and the Hanning or the Hamming window).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458041
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