Ineffectiveness of probiotics in preventing recurrence after curative resection for Crohn's disease: a randomised controlled trial with Lactobacillus GG

BACKGROUND AND AIMS

Experimental studies have shown that luminal bacteria may be involved in Crohn's disease. Probiotics are a possible alternative to antibiotics. The aim of this randomised placebo controlled study was to determine if Lactobacillus GG, given by mouth for one year, could prevent Crohn's recurrent lesions after surgery or to reduce their severity.

METHODS

Patients operated on for Crohn's disease in whom all of the diseased gut had been removed were randomly allocated to receive 12 billion colony forming units of Lactobacillus or identical placebo for one year. Ileocolonoscopy was performed at the end of the trial or at the onset of symptoms. Endoscopic recurrence was defined as grade 2 or higher of Rutgeerts scoring system.

RESULTS

Eight of 45 patients were excluded from the trial (three for non-compliance and five for protocol violations). Clinical recurrence was ascertained in three (16.6%) patients who received Lactobacillus and in two (10.5%) who received placebo. Nine of 15 patients in clinical remission on Lactobacillus (60%) had endoscopic recurrence compared with six of 17 (35.3%) on placebo (p=0.297). There were no significant differences in the severity of the lesions between the two groups.

CONCLUSIONS

Lactobacillus GG seems neither to prevent endoscopic recurrence at one year nor reduce the severity of recurrent lesions.

Role of ultrasonography in the diagnosis of postsurgical recurrence of Crohn's disease

OBJECTIVE

Ultrasonography is a valid tool in the diagnosis of Crohn's disease, but its sensitivity, specificity, and overall accuracy in the diagnosis of postoperative recurrence are still not well established. The aim of this study was to evaluate the accuracy of ultrasonography compared with endoscopy in the diagnosis of postoperative recurrence of Crohn's disease.

METHODS

Forty-seven patients resected for Crohn's ileitis were studied by ultrasonography and colonoscopy to detect possible recurrence of the disease; 10 patients operated on for cancer of the right colon were used as controls. Six patients with Crohn's disease were excluded from the study because of failure to endoscopically reach the anastomosis; the remaining 41 patients had both ultrasonography and colonoscopy over a period of 14 days. Sonographic recurrence was defined as the presence of >5 mm thickness of the ileal wall.

RESULTS

Sensitivity, specificity, and overall accuracy of ultrasonography in diagnosis of postoperative recurrence were 81%, 86%, and 83% respectively. Positive predictive value was 96% and negative predictive value was 57%.

CONCLUSION

This study is the first to assess the role of ultrasonography in comparison with endoscopy in detecting Crohn's disease recurrence after surgery. Our data suggest that ultrasonography should be used first in the case of clinical suspicion of Crohn's disease recurrence, reserving ileocolonoscopy for negative or uncertain cases.

Information Thermodynamics of Turing Patterns

We set up a rigorous thermodynamic description of reaction-diffusion systems driven out of equilibrium by time-dependent space-distributed chemostats. Building on the assumption of local equilibrium, nonequilibrium thermodynamic potentials are constructed exploiting the symmetries of the chemical network topology. It is shown that the canonical (resp. semigrand canonical) nonequilibrium free energy works as a Lyapunov function in the relaxation to equilibrium of a closed (resp. open) system, and its variation provides the minimum amount of work needed to manipulate the species concentrations. The theory is used to study analytically the Turing pattern formation in a prototypical reaction-diffusion system, the one-dimensional Brusselator model, and to classify it as a genuine thermodynamic nonequilibrium phase transition.

Dissipation-Time Uncertainty Relation

We show that the entropy production rate bounds the rate at which physical processes can be performed in stochastic systems far from equilibrium. In particular, we prove the fundamental tradeoff ⟨S[over ˙]_{e}⟩T≥k_{B} between the entropy flow ⟨S[over ˙]_{e}⟩ into the reservoirs and the mean time T to complete any process whose time-reversed is exponentially rarer. This dissipation-time uncertainty relation is a novel form of speed limit: the smaller the dissipation, the larger the time to perform a process.

Exact symmetries in the velocity fluctuations of a hot Brownian swimmer

Symmetries constrain dynamics. We test this fundamental physical principle, experimentally and by molecular dynamics simulations, for a hot Janus swimmer operating far from thermal equilibrium. Our results establish scalar and vectorial steady-state fluctuation theorems and a thermodynamic uncertainty relation that link the fluctuating particle current to its entropy production at an effective temperature. A Markovian minimal model elucidates the underlying nonequilibrium physics.

Review article: Immunosuppressants in distal ulcerative colitis

BACKGROUND

Distal ulcerative colitis may prove to be resistant to steroids and aminosalicylates, but total colectomy is more difficult to justify than in severe extensive colitis. Immunosuppression is of established benefit in generalized colitis, but there are no data available specific to distal disease.

AIM

To determine whether the protocol-driven use of immunosuppressants in resistant distal ulcerative colitis is of similar efficacy and safety to that in extensive disease.

METHODS

Two hundred and twenty-eight patients with distal ulcerative colitis seen in a 5-year period were identified from a prospective database. Details of 52 who had received immunosuppression were analysed.

RESULTS

The 52 patients received 68 courses of therapy (53 azathioprine, five mercaptopurine, 10 ciclosporin). The thiopurines yielded clinically valuable responses in only 43% of courses, with failure of response in 16% and toxicity in 34%. Ciclosporin was helpful on only two of 10 occasions. Eight patients required total colectomy. Adverse events were typical of those normally associated with immunosuppressants, with potential risk to life in seven patients; treatment was discontinued because of toxicity on a total of 31% of occasions.

CONCLUSIONS

Immunosuppression appears to be of lower efficacy and higher toxicity in resistant distal colitis than when used in more extensive colitis.

Microscopic derivation of the hydrodynamics of active-Brownian-particle suspensions

We derive the hydrodynamic equations of motion for a fluid of active particles described by underdamped Langevin equations that reduce to the active-Brownian-particle model, in the overdamped limit. The contraction into the hydrodynamic description is performed by locally averaging the particle dynamics with the nonequilibrium many-particle probability density, whose formal expression is found in the physically relevant limit of high friction through a multiple-time-scale analysis. This approach permits us to identify the conditions under which self-propulsion can be subsumed into the fluid stress tensor and thus to define systematically and unambiguously the local pressure of the active fluid.

Nonisothermal fluctuating hydrodynamics and Brownian motion

The classical theory of Brownian dynamics follows from coarse graining the underlying linearized fluctuating hydrodynamics of the solvent. We extend this procedure to globally nonisothermal conditions, requiring only a local thermal equilibration of the solvent. Starting from the conservation laws, we establish the stochastic equations of motion for the fluid momentum fluctuations in the presence of a suspended Brownian particle. These are then contracted to the nonisothermal generalized Langevin description of the suspended particle alone, for which the coupling to stochastic temperature fluctuations is found to be negligible under typical experimental conditions.

Effective temperatures of hot Brownian motion

We derive generalized Langevin equations for the translational and rotational motion of a heated Brownian particle from the fluctuating hydrodynamics of its nonisothermal solvent. The temperature gradient around the particle couples to the hydrodynamic modes excited by the particle itself so that the resulting noise spectrum is governed by a frequency-dependent temperature. We show how the effective temperatures at which the particle coordinates and (angular) velocities appear to be thermalized emerge from this central quantity.

Interacting Brownian dynamics in a nonequilibrium particle bath

We set up a mesoscopic theory for interacting Brownian particles embedded in a nonequilibrium environment, starting from the microscopic interacting many-body theory. Using nonequilibrium linear-response theory, we characterize the effective dynamical interactions on the mesoscopic scale and the statistics of the nonequilibrium environmental noise, arising upon integrating out the fast degrees of freedom. As hallmarks of nonequilibrium, the breakdown of the fluctuation-dissipation and action-reaction relations for Brownian degrees of freedom is exemplified with two prototypical models for the environment, namely active Brownian particles and stirred colloids.

Nonequilibrium thermodynamics of non-ideal chemical reaction networks

All current formulations of nonequilibrium thermodynamics of open chemical reaction networks rely on the assumption of non-interacting species. We develop a general theory that accounts for interactions between chemical species within a mean-field approach using activity coefficients. Thermodynamic consistency requires that rate equations do not obey standard mass-action kinetics but account for the interactions with concentration dependent kinetic constants. Many features of the ideal formulations are recovered. Crucially, the thermodynamic potential and the forces driving non-ideal chemical systems out of equilibrium are identified. Our theory is general and holds for any mean-field expression of the interactions leading to lower bounded free energies.

Ventriculo-arterial coupling and mechanical efficiency with remifentanil in patients with coronary artery disease

BACKGROUND

Optimum transfer of energy from the left ventricle to the arterial circulation requires appropriate matching of these mechanical systems. Left ventricular-arterial coupling describes this relationship between the ventricular elastance (Ees) and arterial elastance (Ea). The ratio of these elastances defines the efficiency of myocardium and provides in our study a useful technique for assessment of the actions of remifentanil. The purpose of this study was to evaluate the effects of remifentanil on ventriculo-arterial coupling in cardiac surgery in patients with coronary artery disease.

METHODS

Fourteen patients with coronary artery disease, submitted intraoperatively to cardiac anesthesia for myocardial revascularization, were examined prospectively. With the use of transesophageal echocardiography (TEE) and different dicrotic arterial pressures, we determined the ventricle elastance (Ees), the arterial elastance (Ea) and myocardial efficiency before and after administration of a slow-bolus of remifentanil (1 micro kg(-1)).

RESULTS

Remifentanil decreases significantly the ventricular elastance (from 6.09 mmHg ml-1 m(-2) to 4.88) (P < 0.05), with a less, but however, significant decrease of arterial elastance (from 3.68 mmHg ml(-1) m(-2) to 3.13) (P < 0.05). Despite causing simultaneous declines, maintains a good myocardial efficiency (0.64-0.68) with no significant difference.

CONCLUSION

Although remifentanil depresses ventricular and arterial elastance, preserves a good left ventricular-arterial coupling and mechanical efficiency, despite a little increase of coupling. However, these effects are maintained only during a slow intravenous infusion and are dose-dependent with impairment of coupling, that may contribute to decline in overall cardiovascular performance, at higher anesthetic dose and rapid infusion in patients with a severe myocardial dysfunction.

Energy repartition for a harmonic chain with local reservoirs

We exactly analyze the vibrational properties of a chain of harmonic oscillators in contact with local Langevin heat baths. Nonequilibrium steady-state fluctuations are found to be described by a set of mode temperatures, independent of the strengths of both the harmonic interaction and the viscous damping. Energy is equally distributed between the conjugate variables of a given mode but differently among different modes, in a manner which depends exclusively on the bath temperatures and on the boundary conditions. We outline how bath-temperature profiles can be designed to enhance or reduce fluctuations at specific frequencies in the power spectrum of the chain length.

Local detailed balance across scales: From diffusions to jump processes and beyond

Diffusive dynamics in presence of deep energy minima and weak nongradient forces can be coarse grained into a mesoscopic jump process over the various basins of attraction. Combining standard weak-noise results with a path integral expansion around equilibrium, we show that the emerging transition rates satisfy local detailed balance (LDB). Namely, the log ratio of the transition rates between nearby basins of attractions equals the free-energy variation appearing at equilibrium, supplemented by the work done by the nonconservative forces along the typical transition path. When the mesoscopic dynamics possesses a large-size deterministic limit, it can be further reduced to a jump process over macroscopic states satisfying LDB. The persistence of LDB under coarse graining of weakly nonequilibrium states is a generic consequence of the fact that only dissipative effects matter close to equilibrium.

Chemical cloaking

Hiding an object in a chemical gradient requires one to suppress the distortions it would naturally cause on it. To do so, we propose a strategy based on coating the object with a chemical reaction-diffusion network which can act as an active cloaking device. By controlling the concentration of some species in its immediate surrounding, the chemical reactions redirect the gradient as if the object was not there. We also show that a substantial fraction of the energy required to cloak can be extracted from the chemical gradient itself.

Inflow rate, a time-symmetric observable obeying fluctuation relations

While entropy changes are the usual subject of fluctuation theorems, we seek fluctuation relations involving time-symmetric quantities, namely observables that do not change sign if the trajectories are observed backward in time. We find detailed and integral fluctuation relations for the (time-integrated) difference between entrance rate and escape rate in mesoscopic jump systems. Such inflow rate, which is even under time reversal, represents the discrete-state equivalent of the phase-space contraction rate. Indeed, it becomes minus the divergence of forces in the continuum limit to overdamped diffusion. This establishes a formal connection between reversible deterministic systems and irreversible stochastic ones, confirming that fluctuation theorems are largely independent of the details of the underling dynamics.

Strong current response to slow modulation: A metabolic case-study

We study the current response to periodic driving of a crucial biochemical reaction network, namely, substrate inhibition. We focus on the conversion rate of substrate into product under time-varying metabolic conditions, modeled by a periodic modulation of the product concentration. We find that the system exhibits a strong nonlinear response to small driving frequencies both for the mean time-averaged current and for the fluctuations. For the first, we obtain an analytic formula by coarse-graining the original model to a solvable one. The result is nonperturbative in the modulation amplitude and frequency. We then refine the picture by studying the stochastic dynamics of the full system using a large deviation approach that allows us to show the resonant effect at the level of the time-averaged variance and signal-to-noise ratio. Finally, we discuss how this nonequilibrium effect may play a role in metabolic and synthetic networks.

Tight uncertainty relations for cycle currents

Several recent inequalities bound the precision of a current, i.e., a counter of the net number of transitions in a system, by a thermodynamic measure of dissipation. However, while currents may be defined locally, dissipation is a global property. Inspired by the fact that, ever since Carnot, cycles are the unit elements of thermodynamic processes, we prove similar bounds tailored to cycle currents, counting net cycle completions, in terms of their conjugate affinities. We show that these inequalities are stricter than previous ones, even far from equilibrium, and that they allow us to tighten those on transition currents. We illustrate our results with a simple model and discuss some technical and conceptual issues related to shifting attention from transition to cycle observables.

Thermal response of nonequilibrium RC circuits

We analyze experimental data obtained from an electrical circuit having components at different temperatures, showing how to predict its response to temperature variations. This illustrates in detail how to utilize a recent linear response theory for nonequilibrium overdamped stochastic systems. To validate these results, we introduce a reweighting procedure that mimics the actual realization of the perturbation and allows extracting the susceptibility of the system from steady-state data. This procedure is closely related to other fluctuation-response relations based on the knowledge of the steady-state probability distribution. As an example, we show that the nonequilibrium heat capacity in general does not correspond to the correlation between the energy of the system and the heat flowing into it. Rather, also nondissipative aspects are relevant in the nonequilibrium fluctuation-response relations.

Thermokinetic relations

Thermokinetic relations bound thermodynamic quantities, such as entropy production of a physical system over a certain time interval, with statistics of kinetic (or dynamical) observables, such as mean total variation of the observable over the time interval. We introduce a thermokinetic relation to bound the entropy production or the nonadiabatic (or excess) entropy production for overdamped Markov jump processes, possibly with time-varying rates and nonstationary distributions. For stationary cases, this bound is akin to a thermodynamic uncertainty relation, only involving absolute fluctuations rather than the mean square, thereby offering a better lower bound far from equilibrium. For nonstationary cases, this bound generalizes (classical) speed limits, where the kinetic term is not necessarily the activity (number of jumps) but any trajectory observable of interest. As a consequence, in the task of driving a system from a given probability distribution to another, we find a tradeoff between nonadiabatic entropy production and housekeeping entropy production: the latter can be increased to decrease the former, although to a limited extent. We also find constraints specific to constant-rate Markov processes. We illustrate our thermokinetic relations on simple examples from biophysics and computing devices.

Bridging Freidlin-Wentzell large deviations theory and stochastic thermodynamics

For overdamped Langevin systems subjected to weak thermal noise and nonconservative forces, we establish a connection between Freidlin-Wentzell large deviations theory and stochastic thermodynamics. First, we derive a series expansion of the quasipotential around the detailed-balance solution, that is, the system's free energy, and identify the conditions for the linear response regime to hold, even far from equilibrium. Second, we prove that the escape rate from dissipative fixed points of the macroscopic dynamics is bounded by the entropy production of trajectories that relax into and escape from the attractors. These results provide the foundation to study the nonequilibrium thermodynamics of dissipative metastable states.

Generalized virial equation for nonlinear multiplicative Langevin dynamics: Application to laser-cooled atoms

The virial theorem, and the equipartition theorem in the case of quadratic degrees of freedom, are handy constraints on the statistics of equilibrium systems. Their violation is instrumental in determining how far from equilibrium a driven system might be. We extend the virial theorem to nonequilibrium conditions for Langevin dynamics with nonlinear friction and multiplicative noise. In particular, we generalize it for confined laser-cooled atoms in the semiclassical regime. The resulting relation between the lowest moments of the atom position and velocity allows to measure in experiments how dissipative the cooling mechanism is. Moreover, its violation can reveal the departure from a strictly harmonic confinement or from the semiclassical regime.