We study Lyapunov vectors (LVs) corresponding to the largest Lyapunov exponents in systems with s... more We study Lyapunov vectors (LVs) corresponding to the largest Lyapunov exponents in systems with spatiotemporal chaos. We focus on characteristic LVs and compare the results with backward LVs obtained via successive Gram-Schmidt orthonormalizations. Systems of a very different nature such as coupled-map lattices and the (continuous-time) Lorenz '96 model exhibit the same features in quantitative and qualitative terms. Additionally we propose a minimal stochastic model that reproduces the results for chaotic systems. Our work supports the claims about universality of our earlier results [I. G. Szendro et al., Phys. Rev. E 76, 025202(R) (2007)] for a specific coupled-map lattice.
Intact cardiac compensatory mechanisms are necessary to maintain adequate tissue oxygenation duri... more Intact cardiac compensatory mechanisms are necessary to maintain adequate tissue oxygenation during acute normovolemic hemodilution (ANH). Left ventricular (LV) perfusion, oxygenation and function were analyzed in an experimental whole-body model of profound ANH (Hct 9%) and effectiveness of a perfluorocarbon-based oxygen carrier in maintaining myocardial oxygenation and function was evaluated. A total of 22 anesthetized dogs were hemodiluted to Hct 20% followed by a simulated, controlled blood-loss phase in which dogs were randomized to either: (1) 1 : 1 exchange of lost blood with autologous red blood cells (RBC-group), (2) 1 : 1 exchange with a colloid (control-group) and (3) 1 : 1 exchange with a colloid after a single dose of 1.8 g/kg BW perflubron iv (PFC-group). Myocardial oxygen delivery and consumption as well as endocardial perfusion were determined using radioactive microspheres. LV myocardial contractility (LV MC) was assessed from: (1) the relationship between maximum rate of LV pressure increase (LVdp/dt max ) and LV enddiastolic volume (LVEDV) and (2) analysis of the LV endsystolic pressure volume relationship (ESPVR). LV diastolic properties were reflected by (1) minimum rate of LV pressure increase (LVdp/dt min ), (2) slope and intercept of the enddiastolic pressure-volume relationship (EDPVR) and (3) the time-constant of isovolumic LV pressure decline "τ 1 ⁄2". Full sets of LV MC data were obtained from 18 dogs (n = 6 per group). LV MC (LVdp/dt max -LVEDV relation) increased after perflubron administration. At the lowest Hct level, all parameters reflecting LV MC as well as LVdp/dt min were significantly higher in the PFC-group than in the control-group. After profound normovolemic hemodilution (Hct 9%) superiority of LV MC and LV diastolic Springer-Verlag 1996 properties was found, when myocardial oxygenation was supported by iv perflubron emulsion, a temporary O 2 carrier.
Speckle myocardial imaging modalities for http://heart.bmj.com/content/96/6/440.full.html Updated... more Speckle myocardial imaging modalities for http://heart.bmj.com/content/96/6/440.full.html Updated information and services can be found at:
The ventricular myocardium consists of a syncytium of myocytes organized into branching, transmur... more The ventricular myocardium consists of a syncytium of myocytes organized into branching, transmurally oriented laminar sheets approximately four cells thick. When systolic deformation is expressed in an axis system determined by the anatomy of the laminar architecture, laminar sheets of myocytes shear and laterally extend in an approximately radial direction. These deformations account for ~90% of normal systolic wall thickening in the left ventricular free wall. In the present study, we investigated whether the changes in systolic and diastolic function of the sheets were sensitive to alterations in systolic and diastolic load. Our results indicate that there is substantial reorientation of the laminar architecture during systole and diastole. Moreover, this reorientation is both site and load dependent. Thus as end-diastolic pressure is increased and the left ventricular wall thins, sheets shorten and rotate away from the radial direction due to transverse shearing, opposite of what occurs in systole. Both mechanisms of thickening contribute substantially to normal left ventricular wall function. Whereas the relative contributions of shear and extension are comparable at the base, sheet shear is the predominant factor at the apex. The magnitude of shortening/extension and shear increases with preload and decreases with afterload. These findings underscore the essential contribution of the laminar myocardial architecture for normal ventricular function throughout the cardiac cycle.
The spatiotemporal dynamics of Lyapunov vectors (LVs) in spatially extended chaotic systems is st... more The spatiotemporal dynamics of Lyapunov vectors (LVs) in spatially extended chaotic systems is studied by means of coupled-map lattices. We determine intrinsic length scales and spatiotemporal correlations of LVs corresponding to the leading unstable directions by translating the problem to the language of scale-invariant growing surfaces. We find that the so-called characteristic LVs exhibit spatial localization, strong clustering around given spatiotemporal loci, and remarkable dynamic scaling properties of the corresponding surfaces. In contrast, the commonly used backward LVs (obtained through Gram-Schmidt orthogonalization) spread all over the system and do not exhibit dynamic scaling due to artifacts in the dynamical correlations by construction.
We compute Lyapunov vectors (LVs) corresponding to the largest Lyapunov exponents in delay-differ... more We compute Lyapunov vectors (LVs) corresponding to the largest Lyapunov exponents in delay-differential equations with large time delay. We find that characteristic LVs, and backward (Gram-Schmidt) LVs, exhibit long-range correlations, identical to those already observed in dissipative extended systems. In addition we give numerical and theoretical support to the hypothesis that the main LV belongs, under a suitable transformation, to the universality class of the Kardar-Parisi-Zhang equation. These facts indicate that in the large delay limit (an important class of) delayed equations behave exactly as dissipative systems with spatiotemporal chaos.
Increased mortality from cardiovascular diseases has been reported in acromegaly. Our objective w... more Increased mortality from cardiovascular diseases has been reported in acromegaly. Our objective was to evaluate the impact of glucose tolerance abnormalities and/or systemic hypertension in further worsening the acromegalic cardiomyopathy. The study design was open transversal. The subjects studied were 130 consecutive naive acromegalic patients (74 women and 56 men; age, 17-80 yr). Interventricular septum (IST) and left ventricular (LV) posterior wall thickness (PWT), LV mass index (LVMi), maximal early to late diastolic flow velocity ratio (E/A), isovolumic relaxation time (IRT), and LV ejection fraction (EF) were measured by echocardiography. The results were analyzed in line with the presence of glucose tolerance abnormalities (normal in 60, impaired in 38, diabetes mellitus in 32) and the presence (in 46) or absence (in 84) of hypertension. Patients with impaired glucose tolerance and diabetes mellitus had significantly higher age (P ϭ 0.01), and systolic (P ϭ 0.01) and diastolic (P ϭ 0.01) blood pressures and lower E/A (P ϭ 0.01) and EF (P ϭ 0.01) than those with normal glucose tolerance. Disease duration, circulating GH and insulin-like growth factor I (IGF-I) levels, IST, LVPWT, LVMi, and IRT were similar in the 3 groups. Normotensive patients had significantly lower age (P Ͻ 0.001), LVPWT (P Ͻ 0.001), IST (P ϭ 0.003), LVMi (P Ͻ 0.001), and IRT (P ϭ 0.02) and significantly higher E/A (P Ͻ 0.001) and EF (P Ͻ 0.001) than hypertensive subjects.
Objective: The effects of different annuloplasty rings on mitral annulus dynamics and left-ventri... more Objective: The effects of different annuloplasty rings on mitral annulus dynamics and left-ventricular (LV) function after mitral-valve repair (MVR) are still controversial. This study sought to compare biological versus prosthetic rigid rings for annular remodelling in MVR at long term. Methods: Forty-four consecutive patients were retrospectively enrolled. All patients had isolated posterior-lea¯et prolapse and underwent identical surgical mitral-valve reconstruction (quadrangular resection of the posterior lea¯et associated with annuloplasty). Twenty-three patients underwent mitral annuloplasty with an autologous pericardial ring (group I), whereas 21 patients had MVR with a Carpentier±Edwards rigid ring (group II). No differences existed between the groups in terms of pre-operative patient pro®le. Post-operative LV systolic indices have been assessed by two-dimensional echocardiography at rest and during supine bicycle exercise. Mitral annular motion has been examined by means of the extent of mitral annulus systolic excursion (MASE), as measured in four longitudinal LV segments (anterior, inferior, septal and lateral). Mean and peak trans-mitral¯ow velocities (TMFV) have been also evaluated by continuouswave Doppler. Results: The mean follow-up did not differ between the groups, those being 41^12 months in group I (range17±65 months) and 46^15 months in group II (range 23±83 months), respectively. Post-operative echocardiographic study did not show signi®cant mitral regurgitation at rest or at peak exercise in any patient. ANOVA analysis for repeated measures showed a signi®cant interaction in peak TMFV (F 1;42 5:23; P 0:03), and in left-ventricular ejection fraction (LVEF; F 1;42 7:61, P 0:01). The analysis of contrasts showed a signi®cant increase in TMFV in both groups (group I from 1.22^0.22 to 1.79^0.32 m/s, t 28:8, P , 0:0001; and group II from 1.19^0.17 to 1.96^0.33 m/s, t 212:8, P , 0:0001). Recruitment of LVEF reserve during exercise was observed only in group I (from 59.5^6 to 65.8^6%, t 23:95, P , 0:005), whereas no substantial change occurred in LV performance in group II. A trend towards better MASE at all the studied longitudinal segments at rest and during exercise was observed in group I. No minor or major calci®cations have been observed on pericardial rings. Conclusions: The autologous pericardium seems to be superior to rigid prosthetic rings for annuloplasty in MVR since it provides more favourable mitral annulus dynamics and preserves LV function during stress conditions. Effective and durable annular remodelling with the autologous pericardium is achieved up to 6 years from surgery, with no echocardiographic sign of degeneration in the long term. Further studies are required to compare biological versus¯exible prosthetic rings in MVR. q
We study Lyapunov vectors (LVs) corresponding to the largest Lyapunov exponents in systems with s... more We study Lyapunov vectors (LVs) corresponding to the largest Lyapunov exponents in systems with spatiotemporal chaos. We focus on characteristic LVs and compare the results with backward LVs obtained via successive Gram-Schmidt orthonormalizations. Systems of a very different nature such as coupled-map lattices and the (continuous-time) Lorenz '96 model exhibit the same features in quantitative and qualitative terms. Additionally we propose a minimal stochastic model that reproduces the results for chaotic systems. Our work supports the claims about universality of our earlier results [I. G. Szendro et al., Phys. Rev. E 76, 025202(R) (2007)] for a specific coupled-map lattice.
Intact cardiac compensatory mechanisms are necessary to maintain adequate tissue oxygenation duri... more Intact cardiac compensatory mechanisms are necessary to maintain adequate tissue oxygenation during acute normovolemic hemodilution (ANH). Left ventricular (LV) perfusion, oxygenation and function were analyzed in an experimental whole-body model of profound ANH (Hct 9%) and effectiveness of a perfluorocarbon-based oxygen carrier in maintaining myocardial oxygenation and function was evaluated. A total of 22 anesthetized dogs were hemodiluted to Hct 20% followed by a simulated, controlled blood-loss phase in which dogs were randomized to either: (1) 1 : 1 exchange of lost blood with autologous red blood cells (RBC-group), (2) 1 : 1 exchange with a colloid (control-group) and (3) 1 : 1 exchange with a colloid after a single dose of 1.8 g/kg BW perflubron iv (PFC-group). Myocardial oxygen delivery and consumption as well as endocardial perfusion were determined using radioactive microspheres. LV myocardial contractility (LV MC) was assessed from: (1) the relationship between maximum rate of LV pressure increase (LVdp/dt max ) and LV enddiastolic volume (LVEDV) and (2) analysis of the LV endsystolic pressure volume relationship (ESPVR). LV diastolic properties were reflected by (1) minimum rate of LV pressure increase (LVdp/dt min ), (2) slope and intercept of the enddiastolic pressure-volume relationship (EDPVR) and (3) the time-constant of isovolumic LV pressure decline "τ 1 ⁄2". Full sets of LV MC data were obtained from 18 dogs (n = 6 per group). LV MC (LVdp/dt max -LVEDV relation) increased after perflubron administration. At the lowest Hct level, all parameters reflecting LV MC as well as LVdp/dt min were significantly higher in the PFC-group than in the control-group. After profound normovolemic hemodilution (Hct 9%) superiority of LV MC and LV diastolic Springer-Verlag 1996 properties was found, when myocardial oxygenation was supported by iv perflubron emulsion, a temporary O 2 carrier.
Speckle myocardial imaging modalities for http://heart.bmj.com/content/96/6/440.full.html Updated... more Speckle myocardial imaging modalities for http://heart.bmj.com/content/96/6/440.full.html Updated information and services can be found at:
The ventricular myocardium consists of a syncytium of myocytes organized into branching, transmur... more The ventricular myocardium consists of a syncytium of myocytes organized into branching, transmurally oriented laminar sheets approximately four cells thick. When systolic deformation is expressed in an axis system determined by the anatomy of the laminar architecture, laminar sheets of myocytes shear and laterally extend in an approximately radial direction. These deformations account for ~90% of normal systolic wall thickening in the left ventricular free wall. In the present study, we investigated whether the changes in systolic and diastolic function of the sheets were sensitive to alterations in systolic and diastolic load. Our results indicate that there is substantial reorientation of the laminar architecture during systole and diastole. Moreover, this reorientation is both site and load dependent. Thus as end-diastolic pressure is increased and the left ventricular wall thins, sheets shorten and rotate away from the radial direction due to transverse shearing, opposite of what occurs in systole. Both mechanisms of thickening contribute substantially to normal left ventricular wall function. Whereas the relative contributions of shear and extension are comparable at the base, sheet shear is the predominant factor at the apex. The magnitude of shortening/extension and shear increases with preload and decreases with afterload. These findings underscore the essential contribution of the laminar myocardial architecture for normal ventricular function throughout the cardiac cycle.
The spatiotemporal dynamics of Lyapunov vectors (LVs) in spatially extended chaotic systems is st... more The spatiotemporal dynamics of Lyapunov vectors (LVs) in spatially extended chaotic systems is studied by means of coupled-map lattices. We determine intrinsic length scales and spatiotemporal correlations of LVs corresponding to the leading unstable directions by translating the problem to the language of scale-invariant growing surfaces. We find that the so-called characteristic LVs exhibit spatial localization, strong clustering around given spatiotemporal loci, and remarkable dynamic scaling properties of the corresponding surfaces. In contrast, the commonly used backward LVs (obtained through Gram-Schmidt orthogonalization) spread all over the system and do not exhibit dynamic scaling due to artifacts in the dynamical correlations by construction.
We compute Lyapunov vectors (LVs) corresponding to the largest Lyapunov exponents in delay-differ... more We compute Lyapunov vectors (LVs) corresponding to the largest Lyapunov exponents in delay-differential equations with large time delay. We find that characteristic LVs, and backward (Gram-Schmidt) LVs, exhibit long-range correlations, identical to those already observed in dissipative extended systems. In addition we give numerical and theoretical support to the hypothesis that the main LV belongs, under a suitable transformation, to the universality class of the Kardar-Parisi-Zhang equation. These facts indicate that in the large delay limit (an important class of) delayed equations behave exactly as dissipative systems with spatiotemporal chaos.
Increased mortality from cardiovascular diseases has been reported in acromegaly. Our objective w... more Increased mortality from cardiovascular diseases has been reported in acromegaly. Our objective was to evaluate the impact of glucose tolerance abnormalities and/or systemic hypertension in further worsening the acromegalic cardiomyopathy. The study design was open transversal. The subjects studied were 130 consecutive naive acromegalic patients (74 women and 56 men; age, 17-80 yr). Interventricular septum (IST) and left ventricular (LV) posterior wall thickness (PWT), LV mass index (LVMi), maximal early to late diastolic flow velocity ratio (E/A), isovolumic relaxation time (IRT), and LV ejection fraction (EF) were measured by echocardiography. The results were analyzed in line with the presence of glucose tolerance abnormalities (normal in 60, impaired in 38, diabetes mellitus in 32) and the presence (in 46) or absence (in 84) of hypertension. Patients with impaired glucose tolerance and diabetes mellitus had significantly higher age (P ϭ 0.01), and systolic (P ϭ 0.01) and diastolic (P ϭ 0.01) blood pressures and lower E/A (P ϭ 0.01) and EF (P ϭ 0.01) than those with normal glucose tolerance. Disease duration, circulating GH and insulin-like growth factor I (IGF-I) levels, IST, LVPWT, LVMi, and IRT were similar in the 3 groups. Normotensive patients had significantly lower age (P Ͻ 0.001), LVPWT (P Ͻ 0.001), IST (P ϭ 0.003), LVMi (P Ͻ 0.001), and IRT (P ϭ 0.02) and significantly higher E/A (P Ͻ 0.001) and EF (P Ͻ 0.001) than hypertensive subjects.
Objective: The effects of different annuloplasty rings on mitral annulus dynamics and left-ventri... more Objective: The effects of different annuloplasty rings on mitral annulus dynamics and left-ventricular (LV) function after mitral-valve repair (MVR) are still controversial. This study sought to compare biological versus prosthetic rigid rings for annular remodelling in MVR at long term. Methods: Forty-four consecutive patients were retrospectively enrolled. All patients had isolated posterior-lea¯et prolapse and underwent identical surgical mitral-valve reconstruction (quadrangular resection of the posterior lea¯et associated with annuloplasty). Twenty-three patients underwent mitral annuloplasty with an autologous pericardial ring (group I), whereas 21 patients had MVR with a Carpentier±Edwards rigid ring (group II). No differences existed between the groups in terms of pre-operative patient pro®le. Post-operative LV systolic indices have been assessed by two-dimensional echocardiography at rest and during supine bicycle exercise. Mitral annular motion has been examined by means of the extent of mitral annulus systolic excursion (MASE), as measured in four longitudinal LV segments (anterior, inferior, septal and lateral). Mean and peak trans-mitral¯ow velocities (TMFV) have been also evaluated by continuouswave Doppler. Results: The mean follow-up did not differ between the groups, those being 41^12 months in group I (range17±65 months) and 46^15 months in group II (range 23±83 months), respectively. Post-operative echocardiographic study did not show signi®cant mitral regurgitation at rest or at peak exercise in any patient. ANOVA analysis for repeated measures showed a signi®cant interaction in peak TMFV (F 1;42 5:23; P 0:03), and in left-ventricular ejection fraction (LVEF; F 1;42 7:61, P 0:01). The analysis of contrasts showed a signi®cant increase in TMFV in both groups (group I from 1.22^0.22 to 1.79^0.32 m/s, t 28:8, P , 0:0001; and group II from 1.19^0.17 to 1.96^0.33 m/s, t 212:8, P , 0:0001). Recruitment of LVEF reserve during exercise was observed only in group I (from 59.5^6 to 65.8^6%, t 23:95, P , 0:005), whereas no substantial change occurred in LV performance in group II. A trend towards better MASE at all the studied longitudinal segments at rest and during exercise was observed in group I. No minor or major calci®cations have been observed on pericardial rings. Conclusions: The autologous pericardium seems to be superior to rigid prosthetic rings for annuloplasty in MVR since it provides more favourable mitral annulus dynamics and preserves LV function during stress conditions. Effective and durable annular remodelling with the autologous pericardium is achieved up to 6 years from surgery, with no echocardiographic sign of degeneration in the long term. Further studies are required to compare biological versus¯exible prosthetic rings in MVR. q
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