Twist Dynamics Research Articles

PP-169 Left Ventricular Torsion in Our First Four Heart Transplant Recipients: A Preliminary Report

Left ventricular (LV) rotation is the dominant deformation during relaxation and links systole with early diastolic recoil. In adult heart transplant recipients,LV twist dynamics are significantly impaired. This study aimed at exploring LV twist in our first four child heart transplant (HT) recipients.

Noise-driven signal transmission device using molecular dynamics of organic polymers

Stochastic threshold devices using a trap-filling transition (TFT) coupled with molecular dynamics in poly(3-alkylthiophene)s were fabricated as potential key devices for noise-driven bioinspired sensors and information processors. This article deals with variable-temperature direct current conductivity and alternating current impedance measurements for vertical-type device elements of Au/regioregular poly(3-decylthiophene) ((RR−P3DT) (thickness: 100 nm)/Au, which show multiple conducting states and quasi-stochastic transitions between these states. Noise measurements indicate the ω−2-type (if V VTFT) power spectral densities, where V and VTFT are an applied voltage and the voltage for TFT, respectively. The noise generation is due to the TFT associated with twist dynamics of π-conjugated polymers near the order-disorder phase transition (ODT). At 298 K, the quasi-stochastic behavior is more noticeable for RR-P3DT than poly(3-hexylthiophene). The quasi-stochastic property is employed to a stochastic one-directional signal transmitting device using optical-electric conversion. The dynamics of ODT for powder samples were also investigated by differential scanning calorimetry measurements and high-resolution solid-state C13 nuclear magnetic resonance spectroscopy, and the correlation of the molecular structure and dynamics with electric properties was discussed.

Torque correlation length and stochastic twist dynamics of DNA.

We introduce a short correlation length for torque in twisting-stiff biomolecules, which is necessary for the physical property that torque fluctuations be finite in amplitude. We develop a nonequilibrium theory of dynamics of DNA twisting which predicts two crossover time scales for temporal torque correlations in single-molecule experiments. Bending fluctuations can be included, and at linear order we find that they do not affect the twist dynamics. However, twist fluctuations affect bending, and we predict the spatial inhomogeneity of twist, torque, and buckling arising in nonequilibrium "rotor-bead" experiments.

Elastic Twist Dynamics of DNA

Single-molecule DNA experiments have revealed a number of observations about the mechanical properties of DNA, but little is known about the dynamics of twist and bend in these experiments. To understand these experiments, we develop and solve a stochastic and elastic model for twist dynamics in a DNA molecule that is driven at one end and dissipates torsional energy through viscous drag at the other end. To ensure that torque fluctuations remain finite in our model, we include a term depending on the gradient-squared of twist strain. We find that the boundary conditions of our system quantize the spectrum of DNA twisting modes and modulate the dynamics in a striking way. To see this, we derive a nonequilibrium fluctuation relation for twist and construct the spatiotemporal correlation function. We find that a novel elastic correlation length controls spatial correlations between twist fluctuations. In the middle of a long DNA molecule, twist correlations initially decay as t−1/4 and crossover to t−1/2 decay at longer times. In contrast, in a shorter molecule, correlations decay exponentially with a decay time that depends on the magnitude of the viscous drag. For nearly straight DNA molecules, twist dynamics are unaffected by bending fluctuations at linear order, even though writhing dynamics are modulated by twist at this order. Our model for twist dynamics suggests several new single-molecule experiments, which could shed further light on DNA mechanics and dynamics.

Theoretical study on the intramolecular charge transfer induced twisting of the nitro and dimethylamino groups

The ground-state and excited-state electronic structures, relaxation dynamics as well as photophysical properties of the donor–π–acceptor compound 2-dimethylamino-7-nitrofluorene (DMANF) have been theoretically investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The calculated absorption and fluorescence spectrum agree well with the experimental results. The qualitative potential energy curves of twisting either donor or acceptor group favor the excited state intramolecular charge-transfer (ICT) relaxation process. However, the frontier molecular orbital picture supports that the twisting along the donor part is responsible for the fluorescence of the excited state. Further investigation of the strong dipolar stabilization with different structures indicates that two processes are involved in the whole twist and charge transfer dynamics: first, charge transfer is rapidly caused by the excitation to the first singlet state; second, charge transfer goes on slowly together with the twist motion. For strong dipolar stabilization, induced by twisting of the dimethylamino group, the charge transfer excited state corresponds to a more stable state with the twisted structure. Which results in these kinds of D–π–A compounds do not twist in nonpolar solvent. In the twisting charge transfer process, the nitrogen lone pair electrons play an important role.

Left ventricular twist dynamics: principles and applications

### Left ventricular anatomy The normal left ventricular (LV) shape has been assimilated to a thick walled prolate ellipsoid with its long axis directed from apex to base.1 w1 The...

Left ventricular twist in clinically stable heart transplantation recipients: A speckle tracking echocardiography study

Background and aimCavity twist is an integral part of LV function and its pattern in transplanted hearts is not well known. This study aimed at exploring LV twist in clinically stable heart transplant (HT) recipients with no evidence for rejection. MethodsWe studied 32 HT patients (54±24months after HT), 34 other cardiac surgery (CS) patients and compared them with 35 health controls using speckle tracking echocardiography, measuring peak twist angle, time-to-peak twist, and untwist rate. ResultsLV twist angle was smaller in the HT group (6.2±3.3°) in comparison with the CS group and controls (13.2±3.5° and 13.1±4.5°, respectively; p<0.0001 for all) and untwist rate was reduced (HT group: −74±30°/s; CS group: −118±43°/s; controls: −116±39°/s; p<0.0001 for all). Time-to-peak twist was not different between groups. Time after HT was the main independent predictor of both LV twist angle and untwist rate (β=0.8, p<0.0001). ConclusionThough clinically stable, LV twist dynamics are significantly impaired in HT recipients, even in comparison with patients who underwent other cardiac surgery.

Time to twist: marker of systolic dysfunction in Africans with hypertension

Speckle-tracking echocardiography (STE) has emerged as a quantitative technique to assess left ventricular (LV) function via twist mechanics. Hypertension-associated changes in LV twist have not been previously evaluated in African patients with LV systolic dysfunction. This study evaluates LV twist dynamics in hypertensive patients with a low ejection fraction (EF). Forty-one hypertensive patients with EF <45% and normal coronary angiography (HTLEF group) were compared with 41 control subjects using STE. Peak apical rotation (AR) and isochronous basal rotation (BR) were measured, as was net twist (maximal value of simultaneous AR-BR). Rigid body rotation (RBR) was defined as AR and BR occurring in the same direction. Of 41 HTLEF patients, 28 (68%) had normal twist pattern, whereas 13 (32%) exhibited RBR; 11 of those 13 exhibited clockwise rotation. AR (1.89° ± 0.99 vs. 7.15° ± 2.26; P < 0.0001), BR (1.44° ± 0.78 vs. -3.75° ± 1.61; P < 0.0001), and net twist (3.3° ± 1.17 vs. 10.9° ± 2.7; P < 0.0001) were lower in HTLEF patients. The subgroup with clockwise RBR showed greater LV dysfunction (EF: 27.9 ± 5.8 vs. 35 ± 7.5%; P = 0.005) and more spherical LV geometry in both diastole and systole (P = 0.0009 and P = 0.0002, respectively) compared with those who had a normal pattern of twist. In the HTLEF subgroup with normal twist pattern, AR (r = 0.57; P = 0.002) and net twist (r = 0.57; P = 0.002) correlated with EF. LV twist in patients with hypertension and EF <45% is diminished. Apical rotation and net twist are good correlates for EF in hypertensive patients with EF <45%.

Prolonged left ventricular twist in cardiomyopathies: a potential link between systolic and diastolic dysfunction

Left ventricular (LV) twist and untwist play a major role in LV mechanics. We sought to acquire new pathophysiological insights in cardiomyopathies (CM) studying LV twist dynamics by speckle tracking imaging (STI). Standard echo-Doppler and STI study were performed in 67 CM patients divided in four age- and sex-matched subgroups: 18 with apical hypertrophic cardiomyopathy (Group A); 20 with asymmetrical hypertrophic cardiomyopathy (Group B); 15 with dilated cardiomyopathy (Group C); 14 with LV non-compaction (Group D). As controls, 34 age- and sex-matched normal subjects were studied. Compared with control group, all CM Groups showed significantly lower longitudinal, circumferential, and radial myocardial deformations (P < 0.05). LV twist was correlated with ejection fraction (EF; r = 0.62; P < 0.0001). Furthermore, all CM patients had a significantly lower twist rate (P < 0.05) and delayed onset of untwist (P < 0.01). Of interest a significant correlation was found between isovolumic relaxation time and untwist onset (r= 0.485, P < 0.0001). In addition, a significant correlation was found between longitudinal deformations and the onset of untwist (strain: r = 0.46, P = 0.0001; strain rate: r = 0.33, P = 0.0056) and between longitudinal strain rate and twisting rate (r= -0.38; P = 0.0015). (i) All CM patients show an impairment of longitudinal, circumferential, and radial myocardial deformations; (ii) LV peak twist is impaired only in CM with reduced EF but preserved in those with normal or increased EF; (iii) LV twist is prolonged and untwisting onset is delayed in all CM, suggesting that a mechanical adaptation to subclinical systolic abnormalities might induce, by a prolonged LV twist, the early onset of diastolic dysfunction.

Ultrafast Twisting Dynamics in the Excited State of Auramine

Relaxation dynamics of the excited state of bis-[4-(dimethylamino)-phenyl] methaniminium chloride (Auramine) has been investigated using subpicosecond time-resolved absorption spectroscopic technique in both aprotic and alcoholic solvents. The locally excited (LE) state, formed following photoexcitation of Auramine using 400 nm light, undergoes intramolecular charge transfer (ICT) process, which is accompanied by the twisting of the dimethylanilino groups. Time evolution of the transient absorption-stimulated emission spectra as well as the wavelength dependence of the temporal dynamics investigated in each kind of solvents suggest that the relaxation process proceeds via the formation of at least two transient states (TS I and TS II), which are geometrical conformers and consecutively formed following the decay of the LE state. Twisting of the dimethylaniline groups are nearly barrierless processes, the rates of which show linear correlation both with the macroscopic or shear viscosities as well as the solvation times of the solvents. Time-dependent and fractional viscosity dependence of the relaxation rates of the LE and the TS I states in aprotic solvents suggest the multidimensionality of the reaction coordinate as well as reveal the viscoelastic property of the solvents. However, in normal alcohols, in addition to these two factors, activation energy of the solvent viscosity may be another important factor for the slower twisting dynamics of Auramine in alcohols. To explain the viscosity dependence of the decay time of the TS II state, which undergoes an efficient internal conversion process to the ground state, the possibility of occurrence of different mechanisms, such as, energy gap law, involvement of intramolecular high frequency modes, as well as the phenyl group twisting motion on a potential energy surface having a photochemical funnel, have been discussed. TDDFT method has been applied to obtain the optimized electronic structures of the transient states but it has been possible to obtain only that for the TS II state.

A dynamic double helical band as a model for cardiac pumping

We address here, by means of finite-element computational modeling, two features of heart mechanics and, most importantly, their timing relationship: one of them is the ejected volume and the other is the twist of the heart. The corner stone of our approach is to take the double helical muscle fiber band as the dominant active macrostructure behind the pumping function. We show that this double helical model easily reproduces a physiological maximal ejection fraction of up to 60% without exceeding the limit on local muscle fiber contraction of 15%. Moreover, a physiological ejection fraction can be achieved independently of the excitation pattern. The left ventricular twist is also largely independent of the type of excitation. However, the physiological relationship between the ejection fraction and twist can only be reproduced with Purkinje-type excitation schemes. Our results indicate that the proper timing coordination between twist and ejection dynamics can be reproduced only if the excitation front originates in the septum region near the apex. This shows that the timing of the excitation is directly related to the productive pumping operation of the heart and illustrates the direction for possible bioinspired pump design.

Left Ventricular Twist Mechanics in a Canine Model of Reversible Congestive Heart Failure: A Pilot Study

Left ventricular (LV) twist dynamics play an important role in LV systolic and diastolic function. The aim of this preliminary study was to investigate LV twist dynamics in a canine model of reversible congestive heart failure (CHF). Pacing systems were implanted in adult dogs, and continuous chronic right ventricular pacing (230-250 beats/min) was applied until CHF induction. Pacing was then stopped to allow the heart to recover. Echocardiography and LV catheterization were performed at baseline, during CHF while pacing was temporarily switched off, and during recovery. LV twist was computed as the difference between apical and basal rotation measured using 2-dimensional speckle tracking. Torsion was further calculated as LV twist divided by the LV long axis. The untwisting rate was computed as the peak diastolic time derivative of twist. In 6 dogs that completed the study, we found that CHF developed after 2 to 4 weeks of pacing, with LV end-diastolic volume, end-systolic volume, end-diastolic pressure, and the time constant of relaxation during isovolumic relaxation period (tau) all increasing significantly compared with baseline and recovering to normal levels 2 to 4 weeks after pacing was stopped. LV twist, torsion, and untwisting rate decreased significantly with CHF compared with baseline and improved during recovery from CHF. LV twist dynamics reflect pacing-induced CHF and its reversal as assessed by echocardiographic speckle tracking.

Quantitative Distinction between Competing Intramolecular Bond Twisting and Solvent Relaxation Dynamics: An Ultrafast Study

Often an intramolecular relaxation process takes place in a time scale similar to that of the solvent relaxation process. Under these circumstances the dynamic Stokes' shift of the probe can be modulated by the combined effect of these two relaxation processes. In the present article we have studied ultrafast solvent relaxation using three different coumarin dyes and proposed a methodology for the quantitative separation of the dynamics of two competing processes, namely, solvent relaxation and bond twisting, that take place simultaneously in the present systems.

Abstract 2474: Dynamic Change in LV Twist Mechanics in a Canine Model of Pacing-Induced Heart Failure

Background : LV twist may reflect LV contractility under different conditions. This study investigated LV twist dynamics and its determinants in a canine model of congestive heart failure (CHF). Methods : Pacemakers and percutaneous leads were implanted in 8 adult hound dogs (mean weight, 38 kg), and continuous chronic RV pacing was applied at 230–250 bpm until CHF induction. Subsequently, pacing was turned off to allow the heart to recover. Echocardiography and LV catheterization were performed simultaneously at baseline, during CHF while pacing was temporarily switched off, and during recovery from CHF after pacing was stopped. CHF induction by pacing was repeated in 4 dogs. Apical and basal rotations were measured using 2D speckle tracking, and LV twist was calculated as the difference between apical and basal rotations. Untwisting rate was calculated as the peak diastolic time derivative of LV twist. Results : CHF developed after 2–4 wks of pacing with LV end-diastolic volume (LVEDV), end-systolic volume (LVESV), end-diastolic pressure (LVEDP), and time constant of LV relaxation during isovolumic relaxation period (tau) all increasing significantly compared to baseline (Table ), and recovering to baseline levels 2–4 wks after pacing was stopped. LV twist and untwisting rate decreased with CHF compared to baseline, and improved during recovery from CHF although the change in untwisting rate between CHF and baseline was not significant. In pooled data, LV twist was significantly related to LVEDV (r=-0.60, P&lt;0.001), LVESV (r=-0.59, P=0.001), LVEF (r=0.81, P&lt;0.001), LVEDP (r=0.41, P=0.03) and +dp/dt (r=0.71, P&lt;0.001), but not with end-systolic pressure (r=0.06, P=0.77). In multiple analysis, +dp/dt was the only independent predictor of twist (P &lt; 0.001). Conclusions : LV twist dynamics can reflect the presence of pacing-induced CHF and its recovery. LV contractility appears to be the only determinant of LV twist in CHF.

Feedback based simultaneous correction of imaging artifacts due to geometrical and mechanical cross-talk and tip-sample stick in atomic force microscopy

This paper presents a feedback scheme that simultaneously corrects, in real time, for the imaging artifacts caused by cantilever and photosensor misalignments as well as misinterpretations in relative lateral position of the tip with respect to the sample due to the tip-sample stick in atomic force microscopy (AFM). The optical beam bounce method, typically used in AFM for imaging, is sensitive to inaccuracies of cantilever geometry and the relative misalignment of the laser source, cantilever, and the laser sensitive diode from the intended design. These inaccuracies, which contribute to the geometrical cross-talk between the normal and the lateral signals, become prominent at the atomic and subnanometer scales, and thereby impede high resolution imaging studies. The feedback scheme accounts for these artifacts and makes imaging insensitive to, in fact, practically independent of these inaccuracies. This scheme counteracts the lateral twisting dynamics of the cantilever, and as a result, it avoids the misinterpretation problem of the relative lateral position of the cantilever tip from the sample and thereby avoids the corresponding imaging artifacts that are typically prominent in contact mode friction force microscopy (FFM). The feedback scheme consists of simultaneously regulating the normal as well as the lateral cantilever deflection signal at their respective set points. This not only removes the imaging artifacts due to geometrical misalignments, mechanical cross-talk, and irregular sliding but also the corresponding compensatory control signal gives a more accurate real time measure of the lateral interaction force between the sample and the cantilever as compared to the lateral deflection signal used in FFM. Experimental results show significant improvement, and in some cases, practical elimination of the artifacts. The design and implementation of a split piezoassembly needed for the lateral actuation for the feedback scheme are also presented.

Fixed twist dynamics of SO(3) gauge theory

We perform a throughout study of 3+1 dim. SO(3) LGT for any fixed-twist background. We concentrate in particular on the physically significant trivial and 1-twist sectors. Introducing a Z(2) monopole chemical potential the 1st order bulk transition is moved down in the strong coupling region and weakened to 2nd order in the 4-dim Ising model universality class. In this extended phase diagram we gain access to a confined phase in every fixed twist sector of the theory. The Pisa disorder operator is employed together with the Polyakov loop to study the confinement-deconfinement transition in each sector. Due to the specific properties of both operators, most results can be used to gain insight in the ergodic theory, where all twist sectors should be summed upon. An explicit mapping of each fixed twist theory to effective positive plaquette models with fixed twisted boundary conditions is applied to better establish their properties in the different phases.

Monitoring of the Heterogroup Twisting Dynamics in Phenol Type Molecules via Different Characteristic Free-Electron-Transfer Products

Phenol radical cations as well as phenoxyl radicals were observed as direct products of free electron transfer from phenol type solute molecules to solvent parent radical cations generated by ionizing irradiation. It is shown that the finding of the two species in comparable amounts can be explained by a nuclear-structure dependent solute cation dissociation behavior: Quantum-chemical calculations indicate that for phenol as solute primarily its conformers with perpendicular C−OH axis orientation to the aromatic ring tend to prompt deprotonation after ionization. A quite similar behavior could be predicted also for the heteroanalogous thiophenols and selenophenols. Quite generally considerable changes in the electron distribution of the ground-state molecules with the twisting angle of the −OH, −SH and −SeH groups could be calculated, with the greatest differences between “parallel” and “perpendicular” conformations. On the assumption that the fast electron-transfer projects the equilibrium solute conformer distribution onto the solute cation conformer one it is demonstrated that the experimental findings are compatible with a simple solute-cation internal relaxation model. By applying the quantum-chemically calculated conformer interconversion barrier heights it can be understood that radical fraction among the direct products increases if phenols are substituted by thiophenols or those by selenophenols, as observed in experiment.

Twist and writhe dynamics of stiff polymers.

I consider the dynamics of a stiff filament, in particular the coupling of twist and bend via writhe. The time dependence of the writhe of a filament of length L is ([Wr(t) - Wr(0)]2) > approximately Lt(1/4). Simulations, on a simple model of a stiff polymer, are used to confirm scaling arguments. Fuller's theorem, and its relation with geometric phases, is reconsidered for open filaments.

Ultrafast Twisting Dynamics of Photoexcited Auramine in Solution

Subpicosecond fluorescence up-conversion and transient absorption spectroscopy is applied to study the excited-state dynamics of auramine, a diphenylmethane dye, in liquid solutions. The fluorescence decays, on a time scale of a few picoseconds to a few tens of picoseconds, are found to be nonexponential and solvent viscosity dependent. They can be fitted as a sum of two exponentials in ethanol and three exponentials in decanol with a larger average lifetime in the more viscous solvent. The decays exhibit wavelength-dependent time constants, whereas the fluorescence rise time is instrument limited (150 fs) at all wavelengths. The average decay time increases with the wavelength across the steady-state emission spectrum. The spectral reconstruction indicates a few hundred wavenumbers dynamic Stokes shift accompanied by a drop in the intensity in both solvents. From transient absorption experiments, the fluorescent state population is shown to decay to an intermediate dark state and then to the ground state, with a viscosity-dependent rate. A barrierless or quasi-barrierless photoreaction involving the rotational diffusion of the phenyl rings, with a change in the radiative transition rate along the reaction path, is proposed to explain the wavelength-dependent nonexponential fluorescence decays. Both fluorescence and transient absorption data are discussed in support of an adiabatic photoreaction involving internal twisting and charge shift.

Viscous Nonlinear Dynamics of Twist and Writhe

Exploiting the "natural" frame of space curves, we formulate an intrinsic dynamics of twisted elastic filaments in viscous fluids. A pair of coupled nonlinear equations describing the temporal evolution of the filament's complex curvature and twist density embodies the dynamic interplay of twist and writhe. These are used to illustrate a novel nonlinear phenomenon: ``geometric untwisting" of open filaments, whereby twisting strains relax through a transient writhing instability without performing axial rotation. This may explain certain experimentally observed motions of fibers of the bacterium B. subtilis [N.H. Mendelson, et al., J. Bacteriol. 177, 7060 (1995)].