Mismatch of arterial and central venous blood gas analysis during haemorrhage.

BACKGROUND AND OBJECTIVE: Arterial base excess and lactate levels are key parameters in the assessment of critically ill patients. The use of venous blood gas analysis may be of clinical interest when no arterial blood is available initially. METHODS: Twenty-four pigs underwent progressive normovolaemic haemodilution and subsequent progressive haemorrhage until the death of the animal. Base excess and lactate levels were determined from arterial and central venous blood after each step. In addition, base excess was calculated by the Van Slyke equation modified by Zander (BE(z)). Continuous variables were summarized as mean +/- SD and represent all measurements (n = 195). RESULTS: Base excess according to National Committee for Clinical Laboratory Standards for arterial blood was 2.27 +/- 4.12 versus 2.48 +/- 4.33 mmol(-l) for central venous blood (P = 0.099) with a strong correlation (r(2) = 0.960, P < 0.001). Standard deviation of the differences between these parameters (SD-DIFBE) did not increase (P = 0.355) during haemorrhage as compared with haemodilution. Arterial lactate was 2.66 +/- 3.23 versus 2.71 +/- 2.80 mmol(-l) in central venous blood (P = 0.330) with a strong correlation (r(2) = 0.983, P < 0.001). SD-DIFLAC increased (P < 0.001) during haemorrhage. BE(z) for central venous blood was 2.22 +/- 4.62 mmol(-l) (P = 0.006 versus arterial base excess according to National Committee for Clinical Laboratory Standards) with strong correlation (r(2) = 0.942, P < 0.001). SD-DIFBE(z)/base excess increased (P < 0.024) during haemorrhage. CONCLUSION: Central venous blood gas analysis is a good predictor for base excess and lactate in arterial blood in steady-state conditions. However, the variation between arterial and central venous lactate increases during haemorrhage. The modification of the Van Slyke equation by Zander did not improve the agreement between central venous and arterial base excess.

Closure of the Monte Carlo dynamical equation in the spherical Sherrington-Kirkpatrick model

We study the analytical solution of the Monte Carlo dynamics in the spherical Sherrington-Kirkpatrick model using the technique of the generating function. Explicit solutions for one-time observables (like the energy) and two-time observables (like the correlation and response function) are obtained. We show that the crucial quantity which governs the dynamics is the acceptance rate. At zero temperature, an adiabatic approximation reveals that the relaxational behavior of the model corresponds to that of a single harmonic oscillator with an effective renormalized mass.

Single-hole GPR reflection imaging of solute transport in a granitic aquifer

Identifying transport pathways in fractured rock is extremely challenging as flow is often organized in a few fractures that occupy a very small portion of the rock volume. We demonstrate that saline tracer experiments combined with single-hole ground penetrating radar (GPR) reflection imaging can be used to monitor saline tracer movement within mm-aperture fractures. A dipole tracer test was performed in a granitic aquifer by injecting a saline solution in a known fracture, while repeatedly acquiring single-hole GPR sections in the pumping borehole located 6 m away. The final depth-migrated difference sections make it possible to identify consistent temporal changes over a 30 m depth interval at locations corresponding to fractures previously imaged in GPR sections acquired under natural flow and tracer-free conditions. The experiment allows determining the dominant flow paths of the injected tracer and the velocity (0.4-0.7 m/min) of the tracer front. Citation: Dorn, C., N. Linde, T. Le Borgne, O. Bour, and L. Baron (2011), Single-hole GPR reflection imaging of solute transport in a granitic aquifer, Geophys. Res. Lett., 38, L08401, doi: 10.1029/2011GL047152.

From Galilean-invariant to relativistic wave equations

Through an imaginary change of coordinates in the Galilei algebra in 4 space dimensions and making use of an original idea of Dirac and Lvy-Leblond, we are able to obtain the relativistic equations of Dirac and of Bargmann and Wigner starting with the (Galilean-invariant) Schrdinger equation.

Dark energy equation of state and anthropic selection

We explore the possibility that the dark energy is due to a potential of a scalar field and that the magnitude and the slope of this potential in our part of the Universe are largely determined by anthropic selection effects. We find that, in some models, the most probable values of the slope are very small, implying that the dark energy density stays constant to very high accuracy throughout cosmological evolution. In other models, however, the most probable values of the slope are such that the slow roll condition is only marginally satisfied, leading to a recollapse of the local universe on a time scale comparable to the lifetime of the Sun. In the latter case, the effective equation of state varies appreciably with the redshift, leading to a number of testable predictions.

Spatiotemporal stochastic resonance in the Swift-Hohenberg equation

We show the appearance of spatiotemporal stochastic resonance in the Swift-Hohenberg equation. This phenomenon emerges when a control parameter varies periodically in time around the bifurcation point. By using general scaling arguments and by taking into account the common features occurring in a bifurcation, we outline possible manifestations of the phenomenon in other pattern-forming systems.

Solutions of the telegrapher's equation in the presence of traps

Several problems in the theory of photon migration in a turbid medium suggest the utility of calculating solutions of the telegrapher¿s equation in the presence of traps. This paper contains two such solutions for the one-dimensional problem, the first being for a semi-infinite line terminated by a trap, and the second being for a finite line terminated by two traps. Because solutions to the telegrapher¿s equation represent an interpolation between wavelike and diffusive phenomena, they will exhibit discontinuities even in the presence of traps.

Continued fraction solution for the radiative transfer equation in three dimensions

Starting from the radiative transfer equation, we obtain an analytical solution for both the free propagator along one of the axes and an arbitrary phase function in the Fourier-Laplace domain. We also find the effective absorption parameter, which turns out to be very different from the one provided by the diffusion approximation. We finally present an analytical approximation procedure and obtain a differential equation that accurately reproduces the transport process. We test our approximations by means of simulations that use the Henyey-Greenstein phase function with very satisfactory results.

Solution to telegrapher's equation in the presence of reflecting and partly reflecting broundaries

We show that the reflecting boundary condition for a one-dimensional telegraphers equation is the same as that for the diffusion equation, in contrast to what is found for the absorbing boundary condition. The radiation boundary condition is found to have a quite complicated form. We also obtain exact solutions of the telegraphers equation in the presence of these boundaries.

Telegrapher's equation with variable propagation speeds

All derivations of the one-dimensional telegraphers equation, based on the persistent random walk model, assume a constant speed of signal propagation. We generalize here the model to allow for a variable propagation speed and study several limiting cases in detail. We also show the connections of this model with anomalous diffusion behavior and with inertial dichotomous processes.

Modified Blalock Taussig shunt: a not-so-simple palliative procedure.

OBJECTIVES: Thirty-two consecutive isolated modified Blalock Taussig (BT) shunts performed in infancy since 2004 were reviewed and analysed to identify the risk factors for shunt intervention and mortality. METHODS: Sternotomy was the only approach used. Median age and weight were 10.5 (range 1-74) days and 2.9 (1.9-4.4) kg, respectively. Shunt palliation was performed for biventricular hearts (Tetralogy of Fallot/double outlet right ventricle/transposition of great arteries_ventricular septal defect_pulmonary stenosis/pulmonary atresia_ventricular septal defect/others) in 21, and univentricular hearts in 11, patients. Hypoplastic left heart syndrome patients were excluded. Two procedures required cardiopulmonary bypass. Median shunt size was 3.5 (3-4) mm and median shunt size/kg body weight was 1.2 (0.9-1.7) mm/kg. Reduction in shunt size was necessary in 5 of 32 (16%) patients. RESULTS: Three of 32 (9%) patients died after 3 (1-15) days due to cardiorespiratory decompensation. Lower body weight (P = 0.04) and bigger shunt size/kg of body weight (P = 0.004) were significant risk factors for mortality. Acute shunt thrombosis was observed in 3 of 32 (9%), none leading to death. Need for cardiac decongestive therapy was associated with univentricular hearts (P < 0.001), bigger shunt size (P = 0.054) and longer hospital stay (P = 0.005). Twenty-eight patients have undergone a successful shunt takedown at a median age of 5.5 (0.5-11.9) months, without late mortality. CONCLUSIONS: Palliation with a modified BT shunt continues to be indicated despite increased thrust on primary corrective surgery. Though seemingly simple, it is associated with significant morbidity and mortality. Effective over-shunting and acute shunt thrombosis are the lingering problems of shunt therapy.

Liquid-liquid phase transition for soft-core attractive potential

Using event-driven molecular dynamics simulations, we study a three-dimensional one-component system of spherical particles interacting via a discontinuous potential combining a repulsive square soft core and an attractive square well. In the case of a narrow attractive well, it has been shown that this potential has two metastable gas-liquid critical points. Here we systematically investigate how the changes of the parameters of this potential affect the phase diagram of the system. We find a broad range of potential parameters for which the system has both a gas-liquid critical point C1 and a liquid-liquid critical point C2. For the liquid-gas critical point we find that the derivatives of the critical temperature and pressure, with respect to the parameters of the potential, have the same signs: they are positive for increasing width of the attractive well and negative for increasing width and repulsive energy of the soft core. This result resembles the behavior of the liquid-gas critical point for standard liquids. In contrast, for the liquid-liquid critical point the critical pressure decreases as the critical temperature increases. As a consequence, the liquid-liquid critical point exists at positive pressures only in a finite range of parameters. We present a modified van der Waals equation which qualitatively reproduces the behavior of both critical points within some range of parameters, and gives us insight on the mechanisms ruling the dependence of the two critical points on the potential¿s parameters. The soft-core potential studied here resembles model potentials used for colloids, proteins, and potentials that have been related to liquid metals, raising an interesting possibility that a liquid-liquid phase transition may be present in some systems where it has not yet been observed.

Reply to "Comment on 'Solutions of the telegrapher's equation in the presence of traps'"

This reply adds a number of details to remarks by Foong and Kanno [preceding Comment, Phys. Rev. A 46, 5296 (1992)] on our paper [Phys. Rev. A 45, 2222 (1992)] regarding the discontinuities observed in the curves generated in that paper.

When telegrapher's equation furnishes a better approximation to transport equation than the difussion approximation

It has been suggested that a solution to the transport equation which includes anisotropic scattering can be approximated by the solution to a telegrapher's equation [A.J. Ishimaru, Appl. Opt. 28, 2210 (1989)]. We show that in one dimension the telegrapher's equation furnishes an exact solution to the transport equation. In two dimensions, we show that, since the solution can become negative, the telegrapher's equation will not furnish a usable approximation. A comparison between simulated data in three dimensions indicates that the solution to the telegrapher's equation is a good approximation to that of the full transport equation at the times at which the diffusion equation furnishes an equally good approximation.

Strong coupling solution to Schrödinger Equation: the mixing of states

In this paper we give some ideas that can be useful to solve Schrödinger equations in the case when the Hamiltonian contains a large term. We obtain an expansion of the solution in reciprocal powers of the large coupling constant. The procedure followed consists in considering that the small part of the Hamiltonian engenders a motion adiabatic to the motion generated by the large part of the same.