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The simple Goldman-Hodgkin-Katz model for resting-state membrane potentials has been generalized to provide a new nonlinear theoretical model for action potentials in perfused axons. Our minimalistic model appeals naturally to physically based electrodiffusion principles to describe electric-current densities inside sodium and potassium-ion channels whereas the 1952 Hodgkin-Huxley model describes such current densities in an ad hoc way. Although the two models share similar schemes for the kinetics of ion-channel gating, our relaxation times for channel gating are simpler, being independent of membrane potential. Like the theoretical model of Hodgkin and Huxley, based primarily on experimental data at [Formula: see text], our dynamical system behaves as a 4-dimensional resonator exhibiting subthreshold oscillations. Although our present analysis refers to experiments at [Formula: see text], re-parameterizations of this model should permit consideration of action potentials at alternative temperatures. The predicted speed of propagating action potentials in giant axons of squid at [Formula: see text] is in excellent agreement with the Hodgkin-Huxley experimental value at [Formula: see text]. In cases where our model predictions differ from those of the Hodgkin-Huxley model, new experiments will be required to determine which model is more accurate., (© 2021. European Biophysical Societies' Association.)

Introduction: This study compared outcomes between patients injured at a motorbike track, which requires riders to follow safety equipment guidelines, and those involved in recreational riding where safety equipment usage is voluntary., Methods: A retrospective review was conducted of all patients presenting with motorbike-related injuries at an American College of Surgeons verified level-I trauma center between January 1, 2009 and December 31, 2013. Data collected included demographics, injury details, safety equipment use, hospitalization details, and discharge disposition. Comparisons were made regarding protective equipment usage., Results: Among the 115 patients admitted, more than half (54.8%, n = 63) were injured on a motorbike track, and 45.2% (n = 52) were injured in a recreational setting. The majority of patients were male (93.9%), Caucasian (97.4%), and between the ages of 18 to 54 (64.4%). Helmet usage was higher among track riders (95.2%, n = 60) than recreational riders (46.2%, n = 24, p < 0.0001). Comparisons of injury severity and outcomes between those who wore protective equipment and those who did not were not significant., Conclusion: Even though track riders wore protective equipment more than recreational riders, there was no difference between the groups regarding injury severity or hospital outcomes. These results suggested that motocross riders should not rely on protective equipment as the only measure of injury prevention.

Background: Children with confirmed brain injury usually undergo follow-up computed tomography (CT) scan of the head within 24 hours of admission. To date, no evidence exists to validate the diagnostic or therapeutic value of these repeat CTs. The purpose of this study was to (1) evaluate progression of traumatic brain injuries, (2) determine if routine repeat imaging changes management, and (3) compare the efficacy of recognizing worsening hemorrhage with serial neurological examination versus repeat imaging., Methods: A 5-year retrospective review was conducted of all patients aged under 18 years with blunt traumatic head injury (n = 95). Data included demographics, type and size of intracranial hemorrhage, exam findings, diagnostic and management changes, and hospital outcomes., Results: Most patients (68.4%) had at least one repeat CT; of these, 67.7% (n = 44) showed no change or reduced hemorrhage. In only one patient did a repeat CT scan result in a surgical procedure; however, that CT scan was prompted by a change in neurological status. Among patients with more than two repeat head CTs, 42.9% led to a change in management, most frequently an additional CT scan. Presence of neurological symptoms was associated with having repeat CT scans (p = 0.025). Changes in Glasgow Coma Scale score were associated with increased hemorrhage (p = 0.012) but not repeat scans (p = 0.496). In the majority of cases, increased hemorrhage only resulted in an additional head CT and prolonged intensive care unit stay. Excluding patients who arrived with brain death, there was no difference in mortality between patients with and without repeat imaging., Conclusion: Findings from this study support a selective approach for repeating head CTs with emphasis on changes in neurological symptoms and Glasgow Coma Scale score. Prospective studies on timing and indications for repeat CT scans are needed to support development of clinical guidelines., Level of Evidence: Therapeutic study, level III.

Background: A shortage of pediatric surgeons exists. The purpose of this study was to evaluate pediatric outcomes using pediatric surgeons vs adult trauma surgeons., Methods: A review was conducted at 2 level II pediatric trauma centers. Center I provides 24-hour in-house trauma surgeons for resuscitations, with patient hand-off to a pediatric surgery service. Center II provides 24-hour in-house senior surgical resident coverage with an on-call trauma surgeon. Data on demographics, resource utilization, and outcomes were collected., Results: Center I patients were more severely injured (injury severity score = 8.3 vs 6.2; Glasgow coma scale score = 13.7 vs 14.3). Center I patients were more often admitted to the intensive care unit (52.2% vs 33.5%) and more often mechanically ventilated (12.9% vs 7.7%), with longer hospital length of stay (2.8 vs 2.3 days). However, mortality was not different between Center I and II (3.1% vs 2.4%). By logistic regression analyses, the only variables predictive of mortality were injury severity score and Glasgow coma scale score., Conclusion: As it appears that trauma surgeons' outcomes compare favorably with those of pediatric surgeons, utilizing adult trauma surgeons may help alleviate shortages in pediatric surgeon coverage., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Background: When retained hemothorax occurs, video-assisted thoracoscopy or thoracotomy is performed, but recently, tissue plasminogen activator (tPA) has been used. This study evaluated intrapleural tPA use for retained traumatic hemothoraces., Methods: A retrospective review was conducted of trauma patients treated with intrapleural tPA for retained hemothorax. Data included demographics, past medical and surgical histories, injury details, treatment details, and outcomes., Results: Seven patients (median age = 47 years, male = 6, blunt trauma = 6) met study criteria. All patients received a chest tube. Six patients later received computed tomography-guided drains for tPA infusion. Number of tPA treatments per patient varied from 1 to 5. Median total tPA dosage was 24 mg. Median time from injury to chest tube placement was 11 days and from chest tube placement to first tPA treatment was 4 days. No patients required a video-assisted thoracoscopy; however, 1 patient required thoracotomy. There were no deaths or bleeding complications attributed to intrapleural tPA., Conclusion: Although future studies are needed to identify optimum treatment guidelines, intrapleural tPA appears to be a safe and efficacious treatment option., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Whenever a spatially inhomogeneous electrolyte, composed of ions with different mobilities, is allowed to diffuse, charge separation and an electric potential difference is created. Such potential differences across very thin membranes (e.g. biomembranes) are often interpreted using the steady state Goldman equation, which is usually derived by assuming a spatially constant electric field. Through the fundamental Poisson equation of electrostatics, this implies the absence of free charge density that must provide the source of any such field. A similarly paradoxical situation is encountered for thick membranes (e.g. in ion-selective electrodes) for which the diffusion potential is normally interpreted using the Henderson equation. Standard derivations of the Henderson equation appeal to local electroneutrality, which is also incompatible with sources of electric fields, as these require separated charges. We analyse self-consistent solutions of the Nernst-Planck-Poisson equations for a 1 : 1-univalent electrolyte to show that the Goldman and Henderson steady-state membrane potentials are artefacts of extraneous charges created in the reservoirs of electrolyte solution on either side of the membrane, due to the unphysical nature of the usual (Dirichlet) boundary conditions assumed to apply at the membrane-electrolyte interfaces. We also show, with the aid of numerical simulations, that a transient electric potential difference develops in any confined, but initially non-uniform, electrolyte solution. This potential difference ultimately decays to zero in the real steady state of the electrolyte, which corresponds to thermodynamic equilibrium. We explain the surprising fact that such transient potential differences are well described by the Henderson equation by using a computer algebra system to extend previous steady-state singular perturbation theories to the time-dependent case. Our work therefore accounts for the success of the Henderson equation in analysing experimental liquid-junction potentials.

We derive a Fourier expansion for estimating laminar hydrodynamic spreading when two immiscible liquids flow steadily, side by side, at low Reynolds number, in a horizontal microchannel of rectangular cross-section. When the aspect ratio of the height of the channel to its width is small this expansion can be truncated after a couple of terms and solved to yield the steady-state position of the boundary in terms of the constant volumetric flow rates, the aspect ratio and the viscosities of the two liquids. Our formula shows that we can control the location of the liquid boundary at the outlet of the microchannel by adjusting the relative volumetric flow rates of the two inlet streams. If the microchannel is oriented vertically and the volumetric flow rates are very low, the position of the boundary is also influenced by gravitational forces that depend on the relative densities of the two liquids. We have tested solutions to our analytical expansions by running computational fluid dynamics simulations and have found excellent agreement. When the aspect ratio is 0.01 the leading term in the Fourier expansion for the spreading has an accuracy of about 1%. This accuracy deteriorates to about 12% when the aspect ratio is 0.1. An understanding of these spreading mechanisms is fundamental to the design of T-sensors and related microfluidic devices.

A physical model, which regards a colloidal dispersion as a single fluid continuum, is used to investigate cellular convection accompanying gravitational sedimentation in a hemispherical bowl with a thin cylindrical shaft along its vertical axis of symmetry. We have adapted the stream-function-vorticity form of the Navier-Stokes equations to describe momentum conservation in axially symmetric containers. These hydrodynamic equations have been coupled to the mass balance equation for binary hydrodynamic diffusion in the presence of a vertical gravitational field. Using finite-element software we have solved the equations governing coupled diffusive and hydrodynamic flow. A rapidly intensifying horizontal toroidal vortex develops around the axis of the bowl. This vortex is characterized by downward barycentric flow along the curved surface of the bowl and upward flow in the vicinity of its axis. We find that after a short period of time this large-scale cellular convection associated with the curved boundary of the bowl greatly enhances the rate of sedimentation. Copyright 1999 Academic Press.

We present theoretical evidence for transient roll-cell convection induced in the vicinity of freshly prepared electrolyte/water interfaces. The mechanism relies on a hitherto unrecognized type of double-diffusive convection. Electrolyte diffusion down the strong concentration gradient at the interface produces local heating just below the interface as the electrolyte becomes more dilute. If the concentration gradient at the interface is sufficiently large, temperature gradients on the order of one Kelvin per centimeter can be induced by this mechanism. We assume the horizontal electrolyte/water interface is contained in a long prism with a square vertical cross section and that the electrolyte solution is denser than the supernatant water layer. Provided that the sidewalls of the prism are thermally conducting, convection commences at the junction of the interface (at half the height of the square section) and these walls. In each vertical semi-cross-section, two roll cells evolve at the interface and the lower cell rapidly gains intensity at the expense of the counter-rotating upper cell. After a short period of time the lower cell migrates diagonally downward to lie just beneath the interface and the associated region of local heating. Although the fluid velocities associated with this roll cell initially increase with time, they do not appear to be sufficiently strong to distort the vertical stratification of the electrolyte's concentration profile. In a cylindrical annulus standing on its circular base the dominant roll cell takes the form of a toroidal vortex resembling a Taylor vortex. Copyright 1999 Academic Press.

Physical rehabilitation after lower limb traumatic amputation due to acts of war has not yet been investigated. It has been shown that patients suffering non-war injuries rehabilitate well. This study shows that despite the difficult circumstances and limited resources available in an area of conflict, good rehabilitation of war victims is possible. However, economic rehabilitation is worse than that seen in non-war populations. Given that this type of injury is very common in war zones worldwide, this failure of economic rehabilitation may represent a major healthcare issue.

Shot blasted titanium alloy femoral components with a coarse finish were withdrawn from use in 1987 following reports of early component failure. We reviewed all coarse titanium femoral stems used in primary total hip arthroplasty in our institution between 1985 and 1987 and compared them to a similar stem made of vitallium which was also used over the same period. We found that, at an average of 5.2 years following implantation, over two-thirds of titanium components were associated with endosteal lysis. In many of the cases the early lytic changes were asymptomatic with significant bone loss occurring prior to presentation. We discuss our findings in relation to revision surgery. We advocate that all those with coarse stem titanium components should be positively reviewed to detect early lytic change before extensive bone destruction occurs.

A new unconstrained elbow replacement is described and the results of 44 primary and 5 revision operations assessed. A high incidence of pain relief (82%) and functional improvement (73%) was achieved. However 23% of primary replacements later underwent loosening as assessed radiologically and 12% have undergone revision for pain. Minor complications not affecting the final result occurred in 28%. The causes and significance of the complications are analysed.

The Guildford Elbow Joint prosthesis uses a non-rigid hinge articulation combined with intra-medullary stems to replace the humero-ulnar joint. The metal-on-plastic articulating surfaces are designed to allow some subluxation and accessory movements while remaining self-centering and stable under load. The intra-medullary stems are shaped to provide a good fit in the curves shafts of the ulna and humerus and should provide good fixation without the removal of large amounts of bone. The prosthesis is fixed with acrylic cement. The design follows, where possible, the normal anatomy and function of the elbow. A correct operative technique is important, but the procedure shows no particular difficulties.