Comparison of estimations of urinary bladder volume in different scanning positions using 2D linear dimension formula and 3D bladder circumference tracing in client-owned cats.

Urinary bladder volume (UBV) can be estimated using point-of-care ultrasound. The purpose of this study was to compare 2 UBV estimation methods, i.e., three-dimensional (3D) bladder circumference tracing and 2-dimensional (2D) linear bladder dimension formula, against actual bladder volumes in awake client-owned cats and identify the best scanning position for UBV estimations. Up to 3 paired sets of orthogonal longitudinal and transverse bladder ultrasound images were acquired by a trained clinician from 21 cats positioned in dorsal, right lateral, and left lateral recumbency. UBV estimation was performed with these images by 2 different observers using both methods. Actual bladder volumes were measured through urethral catheterization and compared to the estimated UBV using Lin's concordance correlation coefficient and Bland-Altman analyses. Considering all positions, both methods showed substantial strength-of-agreement with actual bladder volumes; the 3D bladder circumference method (ρc = 0.963, 95% CI: 0.952 to 0.974) with a significant median bias of -4.08 mL (P < 0.001, IQR -7.63 to -0.68 mL, LOA -48.55 to 21.75 mL) and the 2D linear dimension method (ρc = 0.974, 95% CI: 0.966 to 0.982) with a median bias of -0.82 mL (P = 0.686, IQR -3.89 to 4.05 mL, LOA -35.23 to 35.21 mL). Scanning in left lateral recumbency provided the strongest strengths-of-agreement and precision against actual bladder volumes for both methods. Regardless of scanning positions, the 2D linear dimension method is more accurate than the 3D bladder circumference method, although both methods are imprecise with increasing volumes and UBV assessment through urinary catheterization remains the gold standard.

Le volume vésical (UBV) peut être estimé à l'aide de l'échographie au point d'intervention. L'objectif de cette étude fut de comparer 2 méthodes d'estimation du UBV, i.e., le tracé tridimensionnel (3D) de la circonférence de la vessie et la formule de dimension linéaire en 2 dimensions (2D), aux volumes vésicaux réels chez des chats éveillés appartenant à des clients, ainsi que d'identifier la meilleure position de balayage pour l'estimation du UBV. Jusqu'à 3 séries appariées d'images ultrasonores longitudinales et transverses orthogonales ont été acquises par une clinicienne qualifiée sur 21 chats positionnés en décubitus dorsal, latéral droit et latéral gauche. L'estimation du UBV a été réalisée à partir de ces images par 2 observateurs différents utilisant les 2 méthodes. Les volumes vésicaux réels ont été mesurés par cathétérisme urétral et comparés aux UBV estimés à l'aide du coefficient de corrélation de concordance de Lin et d'analyses de Bland-Altman. Toutes positions confondues, les 2 méthodes ont montré une concordance considérable avec les volumes vésicaux réels; la méthode de la circonférence vésicale 3D (ρc = 0,963, 95 % CI : 0,952 à 0,974) avec un biais médian significatif de −4,08 mL (P < 0,001, IQR −7,63 à −0,68 mL, LOA −48,55 à 21,75 mL) et la méthode de la dimension linéaire 2D (ρc = 0,974, 95 % CI : 0,966 à 0,982) avec un biais médian de −0,82 mL (P = 0,686, IQR −3,89 à 4,05 mL, LOA −35,23 à 35,21 mL). Le balayage en décubitus latéral gauche a démontré les meilleures concordance et précision par rapport aux volumes vésicaux réels pour les 2 méthodes. Quelle que soit la position de balayage, la méthode de la dimension linéaire 2D est plus précise que la méthode de circonférence vésicale 3D, bien que les 2 méthodes deviennent imprécises avec des volumes vésicaux plus élevés et que l'évaluation du UBV par cathétérisme urinaire demeure l'étalon d'or.(Traduit par les auteurs).

Validation of 3-dimensional mathematical computation of feline bladder volume using orthogonal ultrasonographic bladder images.

Urine output measurement is critical for the management of hospitalized cats and their underlying conditions. Ultrasound-guided estimation of urinary bladder volume (UBV) is a non-invasive surrogate measurement that can provide important clinical information. The purpose of this study was to validate the accuracy of a novel 3D computation method in estimating UBV using 2D point-of-care ultrasonographic images. Bladder volume estimation was performed using coordinates from bladder circumference tracings on paired longitudinal and transverse ultrasonographic images (n = 359) aligned in 3D space for mathematical algorithmic computation. Ultrasonographic images were obtained by 2 different observers at 18 different time points on 10 healthy, purpose-bred male cats under general anesthesia in sternal recumbency. Actual urine volumes were measured via urinary catheterization and compared to UBV estimations using Lin's concordance correlation coefficient and Bland-Altman analysis. Estimation of UBV using the 3D computational bladder circumference tracing method showed moderate strength-of-agreement with actual bladder volume (ρc = 0.94 to 0.95) with clinically insignificant bias (3D computation-derived minus actual volume) of -1.96 mL (IQR = -3.89 to -0.57 mL, P < 0.001) and -2.42 mL (IQR = -4.64 to -0.66 mL, P < 0.001) for the 2 observers, respectively. Our study demonstrated acceptable accuracy of 3D computation method for UBV estimation in healthy cats. This method may provide a bridging alternative until 3D ultrasound becomes more readily accessible.

La mesure de la diurèse est critique pour la gestion de chats hospitalisés ainsi que de leurs conditions sous-jacentes. L'estimation échoguidée du volume vésical (UBV) est une mesure de substitution non-invasive qui peut fournir d'importantes informations cliniques. L'objectif de cette étude fut de valider la précision d'une nouvelle méthode de calcul 3D dans l'estimation du volume vésical à l'aide d'images 2D obtenues par échographie au point d'intervention. L'estimation du volume vésical a été réalisée à l'aide de coordonnées des tracés de la circonférence de la vessie sur des images échographiques longitudinales et transversales appariées (n = 359), alignées dans l'espace 3D pour le calcul algorithmique mathématique. Des images échographiques ont été obtenues par deux observateurs différents à 18 moments différents sur 10 chats mâles sains et élevés à cette fin, sous anesthésie générale en décubitus sternal. Les volumes d'urine réels ont été mesurés par cathétérisme urinaire et comparés aux estimations de volume vésical à l'aide du coefficient de corrélation de concordance de Lin et de l'analyse de Bland-Altman. L'estimation du volume vésical à l'aide de la méthode 3D de traçage de la circonférence de la vessie a démontré un degré d'accord modérée avec le volume réel de la vessie (ρc = 0,94 to 0,95) avec un biais cliniquement insignifiant (calcul 3D moins volume réel) de −1,96 mL (écart interquartile = −3,89 à −0,57 mL, P < 0,001) et de −2,42 mL (écart interquartile = −4,64 à −0,66 mL, P < 0,001) pour les deux observateurs respectivement. Notre étude a démontré une précision acceptable de la méthode de calcul 3D pour l'estimation du volume vésical chez des chats en bonne santé. Cette méthode peut fournir une alternative de transition jusqu'à ce que l'échographie 3D devienne plus facilement accessible.(Traduit par Docteur Sabrina Ayoub).

A physiologically-structured fish population model with size-dependent foraging.

A previous physiologically-structured model for a fish population based on individual-level characteristics is studied. The foraging rate is generalized to include a size-dependent functional response and the energy distribution of adults is generalized to permit both reproduction and growth. Equilibria are determined and their stability studied along with a discussion of harvesting strategies. The model with these generalizations is shown to give different predictions than the original model regarding age distribution of fish and harvesting strategies.

Probability of Escherichia coli contamination spread in ground beef production.

Human illness due to contamination of food by pathogenic strains of Escherichia coli is a serious public health concern and can cause significant economic losses in the food industry. Recent outbreaks of such illness sourced from ground beef production motivates the work in this paper. Most ground beef is produced in large facilities where many carcasses are butchered and various pieces of them are ground together in sequential batches. Assuming that the source of contamination is a single carcass and that downstream from the production facility ground beef from a particular batch has been identified as contaminated by E. coli, the probability that previous and subsequent batches are also contaminated is modelled. This model may help the beef industry to identify the likelihood of contamination in other batches and potentially save money by not needing to cook or recall unaffected batches of ground beef.

Huygens' clocks revisited.

In 1665, Huygens observed that two identical pendulum clocks, weakly coupled through a heavy beam, soon synchronized with the same period and amplitude but with the two pendula swinging in opposite directions. This behaviour is now called anti-phase synchronization. This paper presents an analysis of the behaviour of a large class of coupled identical oscillators, including Huygens' clocks, using methods of equivariant bifurcation theory. The equivariant normal form for such systems is developed and the possible solutions are characterized. The transformation of the physical system parameters to the normal form parameters is given explicitly and applied to the physical values appropriate for Huygens' clocks, and to those of more recent studies. It is shown that Huygens' physical system could only exhibit anti-phase motion, explaining why Huygens observed exclusively this. By contrast, some more recent researchers have observed in-phase or other more complicated motion in their own experimental systems. Here, it is explained which physical characteristics of these systems allow for the existence of these other types of stable solutions. The present analysis not only accounts for these previously observed solutions in a unified framework, but also introduces behaviour not classified by other authors, such as a synchronized toroidal breather and a chaotic toroidal breather.

A model of the effects of fluid variation due to body position on Cheyne-Stokes respiration.

Cheyne-Stokes respiration is a distinct breathing pattern consisting of periods of hyperpnea followed by apnoeas, with unknown aetiology. One in two patients with congestive heart failure suffers from this condition. Researchers hypothesize that key factors in CSR are the fluid shift from the standing to supine position and the differences between genders. A mathematical model of the cardiorespiratory system was constructed using parameter values from real data. Hopf bifurcation analysis was used to determine regions of steady versus oscillatory breathing patterns. In the model, Cheyne-Stokes respiration is more likely to occur while in the supine position and males are more likely to develop Cheyne-Stokes than females. These findings, which are in agreement with clinical experience, suggest that both gender and fluid shift contribute to the pathogenesis of Cheyne-Stokes respiration and that physical quantities such as blood volumes and neural feedback may be sufficient to explain the observations of CSR.

Clusters of reaction rates and concentrations in protein networks such as the phosphotransferase system.

To understand the functioning of living cells, it is often helpful or even necessary to exploit inherent timescale disparities and focus on long-term dynamic behaviour. In the present study, we explore this type of behaviour for the biochemical network of the phosphotransferase system. We show that, during the slow phase that follows a fast initial transient, the network reaction rates are partitioned into clusters corresponding to connected parts of the reaction network. Rates within any of these clusters assume essentially the same value: differences within each cluster are vastly smaller than that from one cluster to another. This rate clustering induces an analogous clustering of the reactive compounds: only the molecular concentrations on the interface between these clusters are produced and consumed at substantially different rates and hence change considerably during the slow phase. The remaining concentrations essentially assume their steady-state values already by the end of the transient phase. Further, we find that this clustering phenomenon occurs for a large number of parameter values and also for models with different topologies; to each of these models, there corresponds a particular network partitioning. Our results show that, in spite of its complexity, the phosphotransferase system tends to behave in a rather simple (yet versatile) way. The persistence of clustering for the perturbed models we examined suggests that it is likely to be encountered in various environmental conditions, as well as in other signal transduction pathways with network structures similar to that of the phosphotransferase system.

Real-time robot path planning based on a modified pulse-coupled neural network model.

This paper presents a modified pulse-coupled neural network (MPCNN) model for real-time collision-free path planning of mobile robots in nonstationary environments. The proposed neural network for robots is topologically organized with only local lateral connections among neurons. It works in dynamic environments and requires no prior knowledge of target or barrier movements. The target neuron fires first, and then the firing event spreads out, through the lateral connections among the neurons, like the propagation of a wave. Obstacles have no connections to their neighbors. Each neuron records its parent, that is, the neighbor that caused it to fire. The real-time optimal path is then the sequence of parents from the robot to the target. In a static case where the barriers and targets are stationary, this paper proves that the generated wave in the network spreads outward with travel times proportional to the linking strength among neurons. Thus, the generated path is always the global shortest path from the robot to the target. In addition, each neuron in the proposed model can propagate a firing event to its neighboring neuron without any comparing computations. The proposed model is applied to generate collision-free paths for a mobile robot to solve a maze-type problem, to circumvent concave U-shaped obstacles, and to track a moving target in an environment with varying obstacles. The effectiveness and efficiency of the proposed approach is demonstrated through simulation and comparison studies.

Real-time robot path planning via a distance-propagating dynamic system with obstacle clearance.

An efficient grid-based distance-propagating dynamic system is proposed for real-time robot path planning in dynamic environments, which incorporates safety margins around obstacles using local penalty functions. The path through which the robot travels minimizes the sum of the current known distance to a target and the cumulative local penalty functions along the path. The algorithm is similar to D* but does not maintain a sorted queue of points to update. The resulting gain in computational speed is offset by the need to update all points in turn. Consequently, in situations where many obstacles and targets are moving at substantial distances from the current robot location, this algorithm is more efficient than D*. The properties of the algorithm are demonstrated through a number of simulations. A sufficient condition for capture of a target is provided.

A geometric comparison of single chain multi-state models of ion channel gating.

Multi-state models of ion channel gating have been used extensively, but choosing optimally small yet sufficiently complex models to describe particular experimental data remains a difficult task. In order to provide some insight into appropriate model selection, this paper presents some basic results about the behavior of solutions of multi-state models, particularly those arranged in a chain formation. Some properties of the eigenvalues and eigenvectors of constant-rate multi-state models are presented. A geometric description of a three-state chain is given and, in particular, differences between a chain equivalent to an Hodgkin-Huxley model and a chain with identical rates are analyzed. One distinguishing feature between these two types of systems is that decay from the open state in the Hodgkin-Huxley model is dominated by the most negative eigenvalue while the identical rate chain displays a mix of modes over all eigenvalues.

The United States and Canada as a coupled epidemiological system: an example from hepatitis A.

BACKGROUND: Hepatitis A (HA) is a low-incidence, non-endemic disease in Canada and the United States (US). However, a large difference in HA incidence between Canada and HA-endemic countries has made travel an important contributor to hepatitis A prevalence in Canada. There is also a (smaller) incidence differential between Canada and the US. Although the US has only moderately higher HA incidence, the volume of travel by Canadians to the US is many times higher than travel volume to endemic countries. Hence, travel to the US may constitute a source of low to moderate risk for Canadian travelers. To our knowledge, travel to the US has never been included as a potential risk factor for HA infection in Canadian epidemiologic analyses. The objective of this study was to use dynamic models to investigate the possible effects on hepatitis A incidence in Canada due to (1) implementing vaccination in the US, and (2) varying the volume of travel by Canadians to the US. METHODS: We developed and analyzed age-structured compartmental models for the transmission and vaccination of hepatitis A, for both Canada and the US. Models were parameterized using data on seroprevalence, case reporting, and travel patterns. The potential effect of hepatitis A prevalence in the US on hepatitis A prevalence in Canada was captured through a term representing infection of Canadians due to travel in the US. RESULTS: The model suggests that approximately 22% of HA cases in Canada in the mid 1990s may have been attributable to travel to the US. A universal vaccination programme that attained 70% coverage in young children in the US in the mid 1990s could have reduced Canadian incidence by 21% within 5 years. CONCLUSION: Since not all necessary data were available to parameterize the model, the results should be considered exploratory. However, the analysis shows that, under plausible assumptions, the US may be more important for determining HA prevalence in Canada than is currently supposed. As international travel continues to grow, making vaccination policies ever more relevant to populations beyond a country's borders, such multi-country models will most likely come into wider use as predictive aids for policy development.

Reconstruction of walleye exploitation based on angler diary records and a model of predicted catches.

The walleye population in Canadarago Lake, New York, was 81-95% exploited in the 1988 fishing season, the year in which a previous restriction on the length and number of legally harvestable fish was liberalized. Using diary records from a subset of fishermen, growth estimates, and an estimate of the walleye population in the following year, a method is developed to reconstruct the fish population back to the spring of 1988 and thus determine the exploitation rate. The method is based on a model of diary catches that partitions time and fish length into a set of cells and relates predicted catches and population sizes in these cells. The method's sensitivity to the partitioning scheme, the growth estimates, and the diary data is analyzed. The method could be employed in other fish exploitation analyses and demonstrates the use of inexpensive angler-collected data in fisheries management.

An efficient dynamic system for real-time robot-path planning.

This paper presents a simple yet efficient dynamic-programming (DP) shortest path algorithm for real-time collision-free robot-path planning applicable to situations in which targets and barriers are permitted to move. The algorithm works in real time and requires no prior knowledge of target or barrier movements. In the case that the barriers are stationary, this paper proves that this algorithm always results in the robot catching the target, provided it moves at a greater speed than the target, and the dynamic-system update frequency is sufficiently large. Like most robot-path-planning approaches, the environment is represented by a topologically organized map. Each grid point on the map has only local connections to its neighboring grid points from which it receives information in real time. The information stored at each point is a current estimate of the distance to the nearest target and the neighbor from which this distance was determined. Updating the distance estimate at each grid point is done using only the information gathered from the point's neighbors, that is, each point can be considered an independent processor, and the order in which grid points are updated is not determined based on global knowledge of the current distances at each point or the previous history of each point. The robot path is determined in real time completely from the information at the robot's current grid-point location. The computational effort to update each point is minimal, allowing for rapid propagation of the distance information outward along the grid from the target locations. In the static situation, where both the targets and the barriers do not move, this algorithm is a DP solution to the shortest path problem, but is restricted by lack of global knowledge. In this case, this paper proves that the dynamic system converges in a small number of iterations to a state where the minimal distance to a target is recorded at each grid point and shows that this robot-path-planning algorithm can be made to always choose an optimal path. The effectiveness of this algorithm is demonstrated through a number of simulations.

Static recipient cells as reservoirs of antibiotic resistance during antibiotic therapy.

How does taking the full course of antibiotics prevent antibiotic resistant bacteria establishing in patients? We address this question by testing the possibility that horizontal/lateral gene transfer (HGT) is critical for the accumulation of the antibiotic-resistance phenotype while bacteria are under antibiotic stress. Most antibiotics prevent bacterial reproduction, some by preventing de novo gene expression. Nevertheless, in some cases and at some concentrations, the effects of most antibiotics on gene expression may not be irreversible. If the stress is removed before the bacteria are cleared from the patients by normal turnover, gene expression restarts, converting the residual population to phenotypic resistance. Using mathematical models we investigate how static recipients of resistance genes carried by plasmids accumulate resistance genes, and how specifically an environment cycling between presence and absence of the antibiotic uniquely favors the evolution of horizontally mobile resistance genes. We found that the presence of static recipients can substantially increase the persistence of the plasmid and that this effect is most pronounced when the cost of carriage of the plasmid decreases the cell's growth rate by as much as a half or more. In addition, plasmid persistence can be enhanced even when conjugation rates are as low as half the rate required for the plasmid to persist as a parasite on its own.

NEUROFIT: software for fitting Hodgkin-Huxley models to voltage-clamp data.

I introduce publicly available software for accurate fitting of Hodgkin-Huxley models to voltage-clamp data. I describe the model and non-linear fitting procedure employed by the software and compare its results with the usual method of fitting such models using potassium A-current data from a pyloric dilator cell of the lobster Panulirus interruptus and sodium current data from an electrocyte cell of the electric fish Sternopygus macrurus. The set of parameter values for the model determined by this software yield current traces that are substantially closer to the observed data than those determined from the usual fitting method. This improvement is due to the fact that the software fits all of the parameters simultaneously utilizing all of the data rather than fitting steady-state and time constant parameters disjointly using peak currents and portions of the rising and falling phases. I analyze the convergence properties of the software's fitting algorithm using simulated data showing that accurate parameter values are obtained for most of the parameters using any reasonable initial values. The software also incorporates a linear pre-estimation procedure to help in determining reasonable initial values for the full non-linear algorithm. I illustrate and discuss some of the inadequacies of voltage-clamp data.