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  • 1
    Electronic Resource
    Electronic Resource
    Discrepancies between myocardial blood flow and fiber shortening in the ischemic border zone as assessed with video mapping of epicardial deformation (1989)
    Springer
    Pflügers Archiv 415 (1989), S. 220-229 
    Details
    ISSN: 1432-2013
    Keywords: Myocardial function ; Myocardial blood flow ; Epicardial deformation ; Area at risk ; Functional border zone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Myocardial function around the border of ischemia was investigated in eight open-chest dogs using video mapping of epicardial deformation. With this method, 40–60 white markers attached to the left ventricular epicardium were traced in time automatically. Before and 5–10 min after coronary artery occlusion, blood flow and epicardial deformation were determined in 30–40 regions with a spatial resolution of about 5 mm. Epicardial deformation was expressed as subepicardial fiber shortening and surface area decrease during the ejection phase. The latter indicates local contribution to stroke volume. The absolute values of these variables were normalized relative to the central ischemic (= 0%) and remote non-ischemic area (= 100%). The 50% contour line of a variable was defined as its border. The average distance between the borders of perfusion and function was not significantly different from zero, due to considerable variation in this distance both within one heart (± 5.7 mm) and between mean distances for different hearts (± 4.4 mm). The width of the transition zone (distance between the 20% and 80% contour lines) of surface area decrease and subepicardial fiber shortening was significantly larger (20.5 and 15.0 mm, respectively) than those of transmural and subepicardial blood flow (8.5 and 9.5 mm, respectively). The present results demonstrate that in a 20-mm zone around the border of ischemia, major discrepancies are present between perfusion and deformation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00370596
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of age on arterial distensibility in healthy subjects and in patients with end-stage renal failure (1995)
    Springer
    The international journal of angiology 4 (1995), S. 103-105 
    Details
    ISSN: 1615-5939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Noninvasive studies have shown that arterial compliance decreases with age before leveling out at about 60 years. To investigate the effect of age on arterial compliance in patients with end-stage renal failure, arterial compliance of the common carotid artery was determined in 25 normotensive, renal transplanted patients (22–60 years) 6–12 weeks after transplantation and in 25 healthy controls (21–64 years). A multigate Doppler system was used to measure the vessel wall movements of the common carotid artery and blood pressure was recorded by finger-plethysmography. The distensibility and the cross-sectional compliance of the common carotid artery was significantly lower in the renal transplant group than in the healthy controls (p〈0.01). In both groups there was a significant decrease of arterial distensibility with increasing age (p〈0.01). The decrease of distensibility with increasing age was more pronounced in the renal transplant group when compared with the healthy controls. Normal arterial aging processes may be accelerated in end-stage renal failure and could contribute to the high cardiovascular morbidity and mortality of patients with end-stage renal failure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02043627
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Conductance Method for the Measurement of Cross-Sectional Areas of the Aorta (1999)
    Springer
    Annals of biomedical engineering 27 (1999), S. 141-150 
    Details
    ISSN: 1573-9686
    Keywords: Conductivity ; Erythrocytes ; Ultrasound ; Shear stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract A modified conductance method to determine the cross-sectional areas (CSAs) of arteries in piglets was evaluated in vivo. The method utilized a conductance catheter having four electrodes. Between the outer electrodes an alternating current was applied and between the inner electrodes the induced voltage difference was measured and converted into a conductance. CSA was determined from measured conductance minus parallel conductance, which is the conductance of the tissues surrounding the vessel times the length between the measuring electrodes of the conductance catheter divided by the conductivity of blood. The parallel conductance was determined by injecting hypertonic saline to change blood conductivity. The conductivity of blood was calculated from temperature and hematocrit and corrected for maximal deformation and changes in orientation of the erythrocytes under shear stress conditions. The equations to calculate the conductivity of blood were obtained from in vitro experiments. In vivo average aortic CSAs, determined with the conductance method CSA (G) in five piglets, were compared to those determined with the intravascular ultrasound method CSA(IVUS). The regression equation between both values was CSA (G) =−0.09+1.00·CSA(IVUS) r=0.97, n=53. The mean difference between the values was −0.29% · 5.57% (2 standard deviations). We conclude that the modified conductance method is a reliable technique to estimate the average cross-sectional areas of the aorta in piglets. © 1999 Biomedical Engineering Society. PAC99: 8780-y, 8437+q, 8719Nn
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.219
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  • 4
    Electronic Resource
    Electronic Resource
    Measurement of the Contrast Agent Intrinsic and Native Harmonic Response with Single Transducer Pulse Waved Ultrasound Systems (1999)
    Springer
    Annals of biomedical engineering 27 (1999), S. 670-681 
    Details
    ISSN: 1573-9686
    Keywords: Ultrasound contrast agents ; Nonlinear distortion ; Native harmonics ; Contaminating harmonics ; Harmonic imaging ; rf-signal processing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Ultrasound contrast agents, i.e., small gas filled microbubbles, enhance the echogenicity of blood and have the potential to be used for tissue perfusion assessment. The contrast agents scatter ultrasound in a nonlinear manner and thereby introduce harmonics in the ultrasound signal. This property is exploited in new ultrasound techniques like harmonic imaging, which aims to display only the contrast agent presence. Much attention has already been given to the physical properties of the contrast agent. The present study focuses on practical aspects of the measurement of the intrinsic harmonic response of ultrasound contrast agents with single transducer pulse waved ultrasound systems. Furthermore, the consequences of two other sources of harmonics are discussed. These sources are the nonlinear distortion of ultrasound in a medium generating native harmonics, and the emitted signal itself which might contain contaminating harmonics. It is demonstrated conceptually and by experiments that optimization of the contrast agent harmonic response measured with a single transducer is governed by the transducer spectral sensitivity distribution rather than the resonance properties of the contrast agent. Both native and contaminating harmonics may be of considerable strength and can be misinterpreted as intrinsic harmonics of the contrast agent. Practical difficulties to filter out the harmonic component selectively, without deteriorating the image, may cause misinterpretation of the fundamental as a harmonic. © 1999 Biomedical Engineering Society. PAC99: 8763Df, 4380Qf
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.209
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    Paper (German National Licenses)
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