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  • 1
    Electronic Resource
    Electronic Resource
    Local Functional and Structural Changes in the Myocardium During Ventricular Pacing (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of interventional cardiology 9 (1996), S. 0 
    Details
    ISSN: 1540-8183
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: In patients with hypertrophic obstructive cardiomyopathy (HOCM), ventricular pacing improves the hemodynamic situation from the first paced beat, while a further improvement is obtained at continuation of pacing over months and years. The mechanisms responsible for the acute and chronic improvement are not yet completely understood. This article summarizes a number of experimental studies, the results of which may improve our insight into myocardial adaptations during ventricular pacing. Experiments in anesthetized dogs showed that abnormal, asynchronous electrical activation due to epicardial ventricular pacing results in specific and even more asynchronous sequences of onset of fiber shortening. Compared to sinus rhythm, fiber shortening during ejection (by ∼ 100%), mechanical load (by – 50%), and blood flow and oxygen consumption (by – 30%) were reduced in early activated regions of the ventricular wall. These variables were increased to a similar extent in late activated regions. Subsequent studies in dogs paced for 3 months at the epicardium of the left ventricular (LV) free wall showed a ∼ 20% decrease in free-wall thickness. In patients with left bundle branch block, the early activated septum was up to 10% thinner than the late activated free wall. These findings support the hypothesis that abnormal electrical activation causes regional differences in mechanical load, which, in the long run, may result in different local growth responses. These functional and structural adaptations may explain the progressive improvements observed during ventricular pacing in hypertrophic obstructive cardiomyopathy (HOCM) patients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-8183.1996.tb00637.x
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  • 2
    Electronic Resource
    Electronic Resource
    Ischemia And Reperfusion Induced Alterations In Membrane Phospholipids: An Overview (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 723 (1994), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1994.tb36712.x
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  • 3
    Electronic Resource
    Electronic Resource
    Optimization of Ventricular Function by Improving the Activation Sequence During Ventricular Pacing (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Pacing and clinical electrophysiology 21 (1998), S. 0 
    Details
    ISSN: 1540-8159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abnormal electrical activation occurring during ventricular pacing reduces left ventricular (LV) pump function. Two strategies were compared to optimize LV function using ventricular pacing, minimal asynchrony and optimal sequence of electrical activation. ECG and hemodynamics aortic flowpmbe, thermodilution cardiac output, LV pressure and its maximal rates of rise (LVdP/dtpos) and fall (LVdP/dtneg) were measured in anesthetized open-chest dogs (n = 7) with healthy hearts. The QRS duration (a measure of asynchrony of activation) was 47 ± 5 ms during sinus rhythm and increased to 110 ± 12 ms during DDD pacing at the right ventricular (RV) apex with a short AV interval. During pacing at the LV apex and LV base, the QRS duration was 8%± 7% and 15%± 7% (P 〈 0.05) longer than during RV apex pacing, respectively. Stroke volumes, LVdP/dtpos and LVdP/dtneg, however, were higher during LV apex(15%± 16%, 10%± 12% [P〈0.05], and 15%± 10%, respectively) and LV base pacing (11%± 12% [P〈0.05], 3%± 12%, and 3%± 11%, respectively) than during RV apex pacing. Systolic LV pressure was not influenced significantly by the site of pacing. Biventricular pacing (RV apex together with one or two LV sites) decreased the QRS duration by approximately 20% as compared with RV apex pacing, however, it did not improve stroke volumes, LVdP/dtpos and LVdP/dtneg beyond those during pacing at the LV apex alone. In conclusion, the sequence of electrical activation is a stronger determinant of ventricular function than the synchrony of activation. For optimal LV function the selection of an optimal single pacing site, like the LV apex, is more important than pacing from multiple sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-8159.1998.tb01163.x
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  • 4
    Electronic Resource
    Electronic Resource
    Windows for HSP 70 (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 793 (1996), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1996.tb33513.x
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of blood gases and pH on thromboembolic reactions in rabbit mesenteric microvessels (1989)
    Springer
    Pflügers Archiv 414 (1989), S. 324-330 
    Details
    ISSN: 1432-2013
    Keywords: Blood gases ; pH ; Vessel wall injury ; Thromboembolic reaction ; Arterioles ; Venules
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The influence of changes in systemic blood gas and pH values on the thromboembolic reaction following wall puncture was studied in rabbit mesenteric arterioles and venules (diameter 20–40 μm), using intravital videomicroscopy. Under normal circumstances the number of emboli produced was higher in arterioles than in venules (6 and 1, respectively). The initial thrombus growth, the number of emboli produced per vessel and the total duration of the embolisation period were not significantly influenced by changes in blood gas and pH values in both arterioles and venules. Therefore, the observed difference in thromboembolic reaction between arterioles and venules cannot be explained by differences in blood gas and pH values in these microvessels. Since reduced velocity, as a measure of wall shear rate, did not correlate with the thromboembolic reaction in arterioles or venules, fluid dynamics can also not explain the difference, indicating that the thrombogenic or anuthrombogenic activity of arteriolar and venular walls differs following injury. A combination of hypercapnia and hypoxia was found to result in a prolongation of the average time period needed to produce a new embolus in both vessel types. This prolongation in embolus production time was largely due to the occurrence of periods, in which the thrombus did not grow, reflecting hampering of the adhesion and aggregation of blood platelets to a growing thrombus under hypereapnic/hypoxic conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00584634
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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Mapping the sequence of contraction of the canine left ventricle (1991)
    Springer
    Pflügers Archiv 419 (1991), S. 529-533 
    Details
    ISSN: 1432-2013
    Keywords: Myocardial contraction ; Computer assisted image processing ; Video ; Cardiac pacing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A method has been developed to map the sequence of contraction as measured at the epicardial surface of the anterior free wall of the canine left ventricle during sinus rhythm and electrical stimulation of the ventricle. In an area of 35×45 mm, 40–60 white markers were attached to the epicardial surface. The motion of the markers was recorded on video and analysed off-line by computer. In an array of 35 regions, regional surface deformation and epicardial fibre strain were calculated from the motion of the markers. Between all adjacent regions, the differences in timing of contraction were determined by cross-correlation of the related fibre strain signals. A map of the time sequence of contraction has been calculated so that the sum of the squares of the deviations between time intervals of the map and the measurements was minimised. If individual correlation coefficients were found to be less than 0.85, the related time difference was discarded from the analysis. If more than 25% of the time differences were discarded because of this reason, the whole map was obtained by determining time of the negative peak of the second time derivative in the early phase of contraction. The accuracy in time marking was sufficient (±7 ms), as compared to the time differences over the epicardial surface, which were found to be on the average between 10 and 80 ms in case of sinus rhythm and electrical stimulation of the right ventricular outflow tract, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00370800
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  • 8
    Electronic Resource
    Electronic Resource
    The role of mast cells and histamine in leukocyte-endothelium interactions in four rat strains (1998)
    Springer
    Pflügers Archiv 436 (1998), S. 255-261 
    Details
    ISSN: 1432-2013
    Keywords: Key words Mast cell degranulation ; Mast cell stabilization ; Cromoglycate ; Leukocyte rolling ; Mesentery ; Strain specificity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The objective of the present study was to determine the role of mast cells and histamine in leukocyte-endothelium interactions in mesenteric venules of four rat strains: Brown Norway, Lewis, Sprague-Dawley and Wistar. Intravital microscopy showed that the mast cell stabilizer cromoglycate (5 mg/kg i.v. just before exteriorization of the mesentery) did not affect the baseline level and velocity of leukocyte rolling in any of the four strains. This finding is in agreement with the observation that cromoglycate pretreatment only slightly influenced mast cell degranulation in all strains except the Brown Norway. After mast cell stabilization, only in Sprague-Dawley did topical administration of histamine (10–4 M) result in a significant increase in the level of leukocyte rolling and a decrease in the rolling velocity compared with the time control. Histamine induced leukocyte adhesion only in the Brown Norway strain. In conclusion, the hypothesis presented in other studies, that degranulation of mast cells, and more specifically the release of histamine, is of major importance for the induction of leukocyte-endothelium interactions in rat mesenteric venules is not generally applicable; the present study shows a clear strain dependency.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050630
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  • 9
    Electronic Resource
    Electronic Resource
    Red blood cell flow cessation and diameter reductions in skeletal muscle capillaries in vivo — the role of oxygen (1995)
    Springer
    Pflügers Archiv 430 (1995), S. 852-861 
    Details
    ISSN: 1432-2013
    Keywords: Capillary diameter ; Oxygen tension ; Reduction of perfusion pressure ; Intravital microscopy ; Recoil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract When perfusion pressure is reduced, red blood cell flow in the capillaries of skeletal muscle ceases at a positive pressure difference across the vascular bed, while arterioles dilate and venules are not constricted. This flow cessation (i.e., cessation of red blood cell flow) and luminal diameter changes in capillaries following femoral arterial pressure reduction were investigated in the rabbit tenuissimus muscle in situ (n=42) using intravital video microscopy. Arterial pressure was reduced by occlusion of the aorta distal to the renal arteries. During the experiments, leg and muscle were placed in a sealed box. The muscle was exposed to low PO2 by leading a gas mixture deprived of O2 through the box. Locally at the muscle surface, i.e., under the microscope objective, PO2 was varied by varying the PO2 in the superfusion solution. In all experiments, the remainder of the muscle was kept at low (〈 20 mm Hg) PO2. The incidence of flow cessation was virtually zero at low local (〈 20 mm Hg) PO2 and became almost 100% at local values above 70 mm Hg. Initial equivalent capillary diameters were 3.1–5.8 μm (median 4.0 μm) and did not correlate with local O2 tension. During aorta occlusion, capillary diameters significantly (P 〈 0.0001) decreased by a median value of 8% at all local PO2 values; in 14 out of 54 capillaries local diameter became less than 2.8 μm. The extent of diameter reduction did not correlate with PO2. In the 14 capillaries in which the diameter became less than 2.8 μm flow cessation occurred in only four cases. The minimal diameter reached was always at the site of an endothelial nucleus. The capillary diameter reductions are probably due to passive recoil. In the 48 capillaries in which flow ceased, only in four cases did a red blood cell stop at the site of the nucleus. We conclude that capillary diameter reductions (local and generalized) lead to a considerable increase in capillary resistance which contributes to the occurrence of flow cessation but cannot solely explain it.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00386186
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  • 10
    Electronic Resource
    Electronic Resource
    Performance of the isolated, ejecting heart: effects of aortic impedance and exogenous substrates (1991)
    Springer
    Pflügers Archiv 419 (1991), S. 7-12 
    Details
    ISSN: 1432-2013
    Keywords: Ejecting heart ; Aortic impedance ; Pyruvate ; Assisted-Mode perfusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The workload of the isolated, left-ventricular ejecting heart (i.e. working heart) is determined by the left atrial filling pressure and the afterload imposed on the left ventricular outflow tract. In addition to the level of end-diastolic aortic pressure, afterload is highly determined by the aortic impedance. For the isolated, ejecting heart optimum matching of the left ventricle to its afterload requires the highest possible similarity between the impedance of the artificial aortic conduit and the natural aortic impedance. The present study shows that the haemodynamic performance of the ejecting rat heart preparation can be affected by the impedance of the aortic conduit. A proper choice of substrates in the perfusion fluid further improves the performance of the heart in the artificial set-up. The present paper also provides guidelines with respect to the design of the aortic cannula and compliance chamber. The occurrence of turbulence, which is related to the Bernoulli pressure drop, is a major determinant of the impedance of the aortic conduit. This effect is used to simulate the natural resistance component of the aortic impedance. Further, the applicability of the perfusion model can be extended by the so-called assisted-mode perfusion, which allows automatic adjustment from antegrade to retrograde perfusion if the heart is not able to generate sufficient pumping power to provide its own coronary perfusion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00373740
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