Risk factors for persistent abnormality on chest radiographs at 12-weeks post hospitalisation with PCR confirmed COVID-19.

BACKGROUND: The long-term consequences of COVID-19 remain unclear. There is concern a proportion of patients will progress to develop pulmonary fibrosis. We aimed to assess the temporal change in CXR infiltrates in a cohort of patients following hospitalisation for COVID-19. METHODS: We conducted a single-centre prospective cohort study of patients admitted to University Hospital Southampton with confirmed SARS-CoV2 infection between 20th March and 3rd June 2020. Patients were approached for standard-of-care follow-up 12-weeks after hospitalisation. Inpatient and follow-up CXRs were scored by the assessing clinician for extent of pulmonary infiltrates; 0-4 per lung (Nil = 0, < 25% = 1, 25-50% = 2, 51-75% = 3, > 75% = 4). RESULTS: 101 patients with paired CXRs were included. Demographics: 53% male with a median (IQR) age 53.0 (45-63) years and length of stay 9 (5-17.5) days. The median CXR follow-up interval was 82 (77-86) days with median baseline and follow-up CXR scores of 4.0 (3-5) and 0.0 (0-1) respectively. 32% of patients had persistent CXR abnormality at 12-weeks. In multivariate analysis length of stay (LOS), smoking-status and obesity were identified as independent risk factors for persistent CXR abnormality. Serum LDH was significantly higher at baseline and at follow-up in patients with CXR abnormalities compared to those with resolution. A 5-point composite risk score (1-point each; LOS ≥ 15 days, Level 2/3 admission, LDH > 750 U/L, obesity and smoking-status) strongly predicted risk of persistent radiograph abnormality (0.81). CONCLUSION: Persistent CXR abnormality 12-weeks post COVID-19 was common in this cohort. LOS, obesity, increased serum LDH, and smoking-status were risk factors for radiograph abnormality. These findings require further prospective validation.

Diffuse double-layer structure in mixed electrolytes considering ions as dielectric spheres.

The structure of the diffuse part of the electric double layer at solid-electrolyte solution interfaces is examined using a theoretical model that takes into account the finite ion size by modeling the solution as a suspension of polarizable insulating spheres in water. This formalism is applied to mixed electrolyte solutions using the "Boublik-Mansoori-Carnahan-Starling-Leland" (BMCSL) theory for the steric interactions among ions. It is shown that the ionic size differences have a strong bearing on the diffuse part of the electric double-layer structure of these systems. Moreover, for strong potential values, the different size-related effects become important even for binary electrolyte solutions due to the presence of H+ and OH- ions that are substantially smaller than hydrated ions originated from salt dissociation. The obtained results display some of the qualitative features observed in experiments on aqueous systems that are generally interpreted in terms of totally different mechanisms.

Excluded volume effect on the electrophoretic mobility of colloidal particles.

In a recent work [J. Colloid Interface Sci. 316 (2007) 196] we studied the influence of the excluded volume effect on spatial distributions of ionic species and electrostatic potential in the neighborhood of a suspended spherical particle. It was shown that the excluded volume effect considerably increases the surface potential (for a given value of the particle charge) as compared to the case when ideal ion behavior is assumed. In the present work we extend our previous equilibrium results to the perturbed/nonequilibrium problem and analyze the effect of ion size constraints on the electrophoretic mobility of a rigid spherical particle immersed in a general electrolyte solution. We find that the electrophoretic mobility always increases with the excluded volume effect, which might broaden the range of experimental data that can be interpreted, including those cases where the measured mobility exceeded the theoretical maximum value predicted by the standard model.

A new generalization of the standard electrokinetic model.

We present a new generalization of the standard electrokinetic model based on the assumption that there is a thin layer surrounding the suspended particle where the equilibrium ion density is not determined by the Gouy-Chapman distribution, while the standard model applies outside this layer. Our approach differs from existing models in that we consider that the surface layer is made both of free ions (mostly counterions) and of the fixed ions that constitute the charge of the particle. Furthermore, the free ion density is determined by appropriate boundary conditions without considering any adsorption isotherms. Finally, the fluid is allowed to freely flow inside the layer, only hindered by the presence of the fixed charges and the adhesion condition on the surface of the particle. We show that this generalization leads to results that qualitatively differ from those obtained using existing models: instead of always decreasing, the electrophoretic mobility can actually increase with the anomalous surface conductivity. This could make it possible to use our model for the interpretation of a broader set of experimental data, including those cases when the measured mobility is higher than predicted by the standard model.

Electrical double layer around a spherical colloid particle: the excluded volume effect.

The influence of the excluded volume effect on both the spatial distribution of ionic species and the electrostatic potential distribution in the neighborhood of a suspended spherical particle is examined on the basis of a modified Poisson-Boltzmann equation, which takes into account the finite ion size by means of a Langmuir-type correction. We find that kappaa (kappa and a being the reciprocal Debye length and the particle radius, respectively) ceases to be a valid parameter for the characterization of the electrical double layer, and that it is necessary to use both parameters kappa and a to characterize adequately the system. We also find that the excluded volume effect considerably increases the surface potential (for a given value of the surface charge density) as compared to the case when ideal ion behavior is assumed. This suggests the use of the particle charge rather than the surface potential in order to characterize the system. Because of this, an approximate equation for the surface charge density of spherical colloid particles, valid for a wide range of system parameter values, is also reported.

Differential capacitance of the diffuse double layer at electrode-electrolyte interfaces considering ions as dielectric spheres: Part I. Binary electrolyte solutions.

A full theoretical account of the differential capacitance of the diffuse part of the electric double layer at electrode-electrolyte solution interfaces is presented. It builds upon the standard electrokinetic model adding all the additional effects related to the finite ionic size. This includes steric interactions among ions by means of either the Bikerman or Carnahan-Starling expressions and all the permittivity related effects that arise when ions are represented as dielectric spheres. These include the solution permittivity dependence on the local ionic concentration, calculated by means of the Maxwell mixture formula, and two additional forces acting on the ions, namely the Born and the dielectrophoretic forces that depend on the permittivity and the electric field gradients, respectively. The obtained results show that the diffuse double layer behavior is sufficient to qualitatively account for the observed differential capacitance dependence on the electrode voltage. Moreover, when combined with an inner layer capacitance and using the Carnahan-Starling expression, a remarkably good quantitative agreement is achieved.

Numerical calculation of the electrophoretic mobility of concentrated suspensions of soft particles.

The electrophoretic mobility of spherical soft particles in concentrated colloidal suspensions is numerically calculated. The particle is modeled as a hard core coated with an ion-penetrable membrane bearing a uniform distribution of fixed charges, while the high particle concentration is taken into account by means of a cell model. The network simulation method used makes it possible to solve the problem without any restrictions on the values of the parameters such as particle concentration, membrane thickness, fixed charge density in the membrane, viscous drag in the membrane, number and valence of ionic species, electrolyte concentration, etc. The theoretical model used is similar to the one presented by Ohshima [H. Ohshima, J. Colloid Interface Sci. 225 (2000) 233], except for the use of the Shilov-Zharkikh, rather than the Levine-Neale, boundary condition for the electric potential, and the inclusion in the force balance equation of an additional term corresponding to the force exerted by the liquid on the core of the moving particle [J.J. López-García, C. Grosse, J. Horno, J. Colloid Interface Sci. 265 (2003) 327]. The obtained results only coincide with existing analytical expressions for low particle concentrations, low particle charge, and when the electrolyte concentration is high, the membrane is thick, and its resistance to the fluid flow is high. This suggests that most interpretations of the electrophoretic mobility of soft particles in concentrated suspensions require numerical calculations.

Comment on "The surface potential of a spherical colloid particle: functional theoretical approach".

In a work published in this journal by Z.W. Wang, G.Z. Li, D.R. Guan, X.Z. Yi, and A.J. Lou [J. Colloid Interface Sci. 246 (2002) 302], an iterative method for the determination of the potential around a colloidal particle is presented. It is claimed that successive terms of the iteration series converge to the exact solution of the Poisson-Boltzmann equation. This claim seems to be unfounded when the analytical expressions of the iteration terms are compared with well established numerical data.

On the use of the hypothesis of local electroneutrality in colloidal suspensions for the calculation of their dielectric properties.

The validity of the hypothesis of electroneutrality outside the double layer of a suspended particle with an applied ac electric field is analyzed. It is shown that the electrolyte solution remains electroneutral for distances greater than a few Debye lengths from the particle surface only when the diffusion coefficients of the two ion species are identical. On the contrary, in the general case, a volume charge density around the particle builds up, which extends to distances that are proportional to the square root of the effective diffusion coefficient value divided by the frequency. These distances can easily attain many particle radii. Numerical results for both uncharged and charged suspended particles are presented, and a correction to existing analytical expressions for the field-induced ion distributions around uncharged particles (J. Phys. Chem. 2004, 108, 8397) is given. While the charge densities far from the particle are usually very weak, it is shown that they strongly contribute to the dipole coefficient value and, therefore, to the calculated values of the permittivity and conductivity increments. The errors that would be committed if these charge densities were ignored, assuming local electroneutrality and determining the dipole coefficient at a few Debye lengths from the particle surface, are analyzed and shown to be substantial.

Influence of the counterion and co-ion diffusion coefficient values on some dielectric and electrokinetic properties of colloidal suspensions.

The dependences of the conductivity increment, the electrophoretic mobility, and the permittivity increment on the counterion diffusion coefficient value were numerically determined. The use of the network simulation method made it possible to solve the governing equations for the whole range of counterion and co-ion diffusion coefficients and for very low frequencies, despite the far-reaching field-induced charge density outside the double layer. Calculations performed for different zeta potential and electrolyte concentration values show that increasing the counterion mobility, while keeping constant the electrolyte solution conductivity and the kappa a values, strongly increases the conductivity increment, barely affects the electrophoretic mobility, and strongly decreases the permittivity increment. The numerical results are discussed and compared to analytical predictions derived from the Shilov-Dukhin model, which generally leads to a good agreement, at least for high kappa a and moderate zeta.

Analysis of the response of suspended colloidal soft particles to a constant electric field.

A network model, originally designed for an electrokinetic study of soft particle suspensions, has been used for an in-depth analysis of the physical behavior of these systems under the action of an externally applied DC electric field. The versatility of the network simulation method used makes it possible to obtain information readily not only about the electrophoretic mobility, but also about any physical variable of interest at all points around the suspended particle: electric potential, ion concentrations, fluid velocity. The field-induced polarization of the double layer is described in terms of the dependence of these and other derived variables (volume charge density, electric field components, ion flux components) on the distance to the membrane-solution interface. In contrast to colloidal suspensions of hard particles, which basically depend on just two parameters (the reciprocal Debye length multiplied by the particle radius, kappaa, and the zeta potential, zeta), soft particle suspensions require a wider parameter set. First, there are two characteristic diffusion lengths in the system (one inside the membrane and the other in the solution) and two geometrical lengths (the core radius a and the membrane thickness (b-a)). Furthermore, there is the fixed charge density inside the membrane (and possibly a surface charge density over the core) that cannot be represented by a zeta potential. Finally, the parameter that characterizes the interaction between the fluid and the permeable membrane, gamma, strongly influences the behavior of the system. Dependences on all these parameters (except the geometrical ones) are included in this study.

Numerical study of colloidal suspensions of soft spherical particles using the network method. 1. DC electrophoretic mobility.

The electrophoretic mobility of a spherical particle coated with a uniformly charged permeable membrane and suspended in a general electrolyte solution is calculated numerically. The network simulation method used makes it possible to solve the problem without any restrictions on the values of the parameters such as the membrane thickness, fixed charge density in the membrane, viscous drag in the membrane, number and valence of the ionic species, and electrolyte concentration. The theoretical model used is similar to the one presented by Ohshima (H. Ohshima, J. Colloid Interface Sci. 228 (2000) 190), except for the inclusion in the force balance equation of an additional term corresponding to the force exerted by the liquid on the core of the moving particle. This inclusion is theoretically proven in the limiting case of a nonconducting suspending medium, in which the equation system can be analytically solved. The results obtained coincide with existing analytical expressions when the electrolyte concentration is high, the membrane is thick, and its resistance to the fluid flow is high.

Numerical study of colloidal suspensions of soft spherical particles using the network method. 2. AC electrokinetic and dielectric properties.

The network simulation method is used to solve numerically the equation system that determines the dynamic electrophoretic mobility and the dielectric response of dilute suspensions of soft particles. This system was extensively studied theoretically by Ohshima (H. Ohshima, J. Colloid Interface Sci. 233 (2001) 142-152), who obtained analytical expressions for the static and dynamic electrophoretic mobility. However, the validity of his analytical result is restricted to relatively thick membranes with high drag coefficient and to relatively high electrolyte concentrations. As for the dielectric properties, there are only a few works dealing with particles without a core (ion exchange resins) and, to our knowledge, no numerical studies. Our theoretical model is basically similar to Ohshima's, except that we take into account the mechanical force acting on the surface of the core, which he neglects. The inclusion of this term is crucial when the general problem including arbitrary values of the parameters is analyzed. However, it has little bearing when the membrane is thick and the drag coefficient is high, so that our results for the electrophoretic mobility generally confirm Ohshima's equation when all the required conditions are met.

Electrokinetics of charged spherical colloidal particles taking into account the effect of ion size constraints.

The electrokinetic properties of suspended spherical particles are examined using a modified standard electrokinetic model, which takes into account the finite ion size and considers that the minimum approach distance of ions to the particle surface need not be equal to their effective radius in the bulk solution. We calculate the conductivity increment and the electrophoretic mobility and present a detailed interpretation of the obtained results, based on the analysis of the equilibrium and field-induced ion concentrations, as well as the convective fluid flow in the neighborhood of the particle surface. We show that when charge reversal takes place, the sign of the concentration polarization remains unchanged while the sign of the electrophoretic mobility only changes under favorable circumstances.

Equilibrium electric double layer of charged spherical colloidal particles: effect of different distances of minimum ion approach to the particle surface.

A study of the equilibrium double layer surrounding charged spherical particles is presented, considering that ions in the suspending medium have a finite size. It is assumed that each ionic species has a different minimum approach distance to the particle surface, while the distance of minimum approach between ions in the bulk has the same value for all ion species. Numerical calculations made using the network simulation method and including all the features of the considered model are presented, together with rigorous analytical results valid for a flat interface and point ions in the bulk electrolyte solution. It is shown that the double-layer parameters are very sensitive to the difference between the minimum approach distances of co-ions and counterions. For negative particles and greater approach distances for co-ions than for counterions, the potential always increases with this difference and, under appropriate circumstances, attains positive values leading to charge reversal. This phenomenon is favored by a high electrolyte concentration, high counterion valences, and low surface charge (in modulus). An analytical expression relating these parameters to the threshold value of the difference between the minimum approach distances of co-ions and counterions to the particle surface is presented.

Electrokinetic characterization of magnetite nanoparticles functionalized with amino acids.

The synthesis of nanoparticles consisting of a magnetite core coated with one or more layers of amino acid (L-arginine, L-lysine, glycine, and L-glutamine) is described in this paper. For all the amino acids it is found that adsorption increases with concentration in solution in the range 0.5-10 mg/mL. The adsorption, however, differs substantially from one amino acid to another, depending on the length of the hydrocarbon chain and the polarity and charge of the side group. Thus, for given concentration and pH, adsorption is found to increase in the order L-arginine < L-lysine < L-glutamine < glycine. This order corresponds roughly to amino acids with decreasing chain length; in addition, the presence of the less polarizable guanidine group in the arginine molecule may explain why this amino acid is slightly less adsorbed than lysine. The pH dependence of the adsorption of each amino acid is reasonably explained considering the surface charge of magnetite and the charge of the amino acid molecules for different pHs, indicating a significant role of electrostatics in adsorption. This is further checked by means of determinations of the electrophoretic mobility of amino acid-coated magnetite as a function of pH: the results indicate a shift of the isoelectric point of the raw magnetite toward more basic pHs, an indication of adsorption of positive species, as confirmed by the tendency of the mobility of amino acid-coated magnetite toward more positive values below neutral pH. The electrophoretic mobility of coated particles was also measured as a function of the concentration of amino acid, and it was found that for low concentrations the four amino acids provoke charge inversion and overcharging of the magnetite surface at pH 6. Finally, the dependence of the electrophoretic mobility on the ionic strength indicated that from an electrophoretic point of view, the functionalized magnetite-amino acid particles do not behave as soft particles, and that the amino acid coating should be very compact.

On the use of the Stern-layer and the charged-layer formalisms for the interpretation of dielectric and electrokinetic properties of colloidal suspensions.

The classical description of colloidal suspensions is based on a series of assumptions that constitute the standard electrokinetic model: suspended particles are surrounded by a uniform surface density of fixed charge, the equilibrium ion density coincides with the Gouy-Chapman distribution, and the surface conductivity coincides with the conductivity of the diffuse double layer. Although highly versatile and relatively simple to compute, the classical model often fails to predict crucial experimental trends. Consequently, various attempts have been made to generalize the standard electrokinetic model in order to encompass a broader set of experimental data. Numerical results show that the Stern-layer formalism increases the conductivity and dielectric response but decreases the electrophoretic mobility, while the charged-layer approach leads to electrophoretic mobility values that can actually increase with the surface layer conductivity. Here we compare the predictions of these two surface layer models regarding the conductivity increment, the electrophoretic mobility, and the dielectric increment. We show that for high kappaa (kappa and a being the reciprocal Debye length and the particle radius, respectively) and intermediate electrophoretic mobility values as well as cases when the measured mobility is higher than the maximum value predicted by the standard electrokinetic model, the experimental data can only be interpreted using the charged-layer model.

Electrokinetics of suspended charged particles taking into account the excluded volume effect.

In two recent works [López-García et al., J. Colloid Interface Sci. 316 (2007) 196; López-García et al., J. Colloid Interface Sci. 323 (2008) 146] we presented a simple modification of the standard electrokinetic model that takes into account the finite size of ions in the electrolyte solution. In the first we presented numerical results for the equilibrium properties while, in the second, we calculated the effect of the excluded ion volume on the electrophoretic mobility. In the present work we first extend our previous results incorporating a distance of closest approach of the ions to the particle surface. We then calculate the conductivity increment and present a detailed interpretation of the mobility and conductivity increment results, based on the analysis of the equilibrium and field-induced ion concentrations and of the convective fluid flow in the neighborhood of the particle surface. We show that the inclusion of the ion size effect generally improves the predictions of the standard electrokinetic model: both the electrophoretic mobility and the conductivity increment increase. We also show that, largely due to the above-noted extension of considering a minimum approach distance between the ions and the particle surface, the excluded volume effect is not negligible even for weakly charged particles.

Influence of the finite ion size on the predictions of the standard electrokinetic model: frequency response.

An extension into the frequency domain of our previous static and stationary works that modify the standard electrokinetic model taking into account the finite size of ions in the electrolyte solution [J.J. López-García, M.J. Aranda-Rascón, J. Horno, J. Colloid Interface Sci. 316 (2007) 196; J.J. López-García, M.J. Aranda-Rascón, J. Horno, J. Colloid Interface Sci. 323 (2008) 146; M.J. Aranda-Rascón, C. Grosse, J.J. López-García, J. Horno, J. Colloid Interface Sci., in press] is presented. It is shown that the excluded volume effect can be quite substantial in some cases and is not negligible even for weakly charged particles. Furthermore, it generally improves on the predictions of the standard electrokinetic model since the low-frequency dielectric and conductivity increments as well as the electrophoretic mobility increase with the ion size.

Distribution of GC, PI and TF polymorphisms in a Spanish population sample from central Pyrenees.

GC-, PI-, and TF-subtype determinations have been performed in a population from Central Pyrenees. The observed allele frequencies are as follows: GC*1F = 0.0582, GC*1S = 0.6199, GC*2 = 0.3219; PI*M1 = 0.6164, PI*M2 = 0.1884, PI*M3 = 0.0308, PI*M4 = 0.0171, PI*S = 0.1473 and TF*C1 = 0.7740, TF*C2 = 0.1712, TF*C3 = 0.0479, TF*B = 0.0069. In spite of the extreme values found for some alleles of the GC and PI systems, the data of the sample analyzed can be considered similar to those described in other populations of the Iberian Peninsula.