Clearance of Extracellular K+ during Muscle Contraction—Roles of Membrane Transport and Diffusion

Excitation of muscle often leads to a net loss of cellular K+ and a rise in extracellular K+ ([ K+ ]o), which in turn inhibits excitability and contractility. It is important, therefore, to determine how this K+ is cleared by diffusion into the surroundings or by reaccumulation into the muscle cells. The inhibitory effects of the rise in [K+ ]o may be assessed from the time course of changes in tetanic force in isolated muscles where diffusional clearance of K+ is eliminated by removing the incubation medium and allowing the muscles to contract in air. Measurements of tetanic force, endurance, and force recovery showed that in rat soleus and extensor digitorum longus (EDL) muscles there was no significant difference between the performance of muscles contracting in buffer or in air for up to 8 min. Ouabain-induced inhibition of K+ clearance via the Na+,K+ pumps markedly reduced contractile endurance and force recovery in air. Incubation in buffer containing 10 mM K+ clearly inhibited force development and endurance, and these effects were considerably reduced by stimulating Na+,K+ pumps with the β2-agonist salbutamol. Following 30–60 s of continuous stimulation at 60 Hz, the amount of K+ released into the extracellular space was assessed from washout experiments. The release of intracellular K+ per pulse was fourfold larger in EDL than in soleus, and in the two muscles, the average [K+ ]o reached 52.4 and 26.0 mM, respectively, appreciably higher than previously detected. In conclusion, prevention of diffusion of K+ from the extracellular space of isolated working muscles causes only modest interference with contractile performance. The Na+,K+ pumps play a major role in the clearance of K+ and the maintenance of force. This new information is important for the evaluation of K+-induced inhibition in muscles, where diffusional clearance of K+ is reduced by tension development sufficient to suppress circulation

Glucose-Insulin Dynamical Model for Type 2 Diabetic Patients

In this paper, a literature review is made for the current models of glucose-insulin dynamics of type 2 diabetes patients. Afterwards, a model is proposed by combining and modifying some of the available models in literature to take into account the effect of multiple glucose meals, multiple metformin doses, insulin injections, physical exercise, and stress on the glucose-insulin dynamics of T2D patients. The model is proposed as a candidate to be validated with real patients data in the future

Risk scoring systems for adults admitted to the emergency department: a systematic review

<p>Abstract</p> <p>Background</p> <p>Patients referred to a medical admission unit (MAU) represent a broad spectrum of disease severity. In the interest of allocating resources to those who might potentially benefit most from clinical interventions, several scoring systems have been proposed as a triaging tool.</p> <p>Even though most scoring systems are not meant to be used on an individual level, they can support the more inexperienced doctors and nurses in assessing the risk of deterioration of their patients.</p> <p>We therefore performed a systematic review on the level of evidence of literature on scoring systems developed or validated in the MAU. We hypothesized that existing scoring systems would have a low level of evidence and only few systems would have been externally validated.</p> <p>Methods</p> <p>We conducted a systematic search using Medline, EMBASE and the Cochrane Library, according to the PRISMA guidelines, on scoring systems developed to assess medical patients at admission.</p> <p>The primary endpoints were in-hospital mortality or transfer to the intensive care unit. Studies derived for only a single or few diagnoses were excluded.</p> <p>The ability to identify patients at risk (discriminatory power) and agreement between observed and predicted outcome (calibration) along with the method of derivation and validation (application on a new cohort) were extracted.</p> <p>Results</p> <p>We identified 1,655 articles. Thirty were selected for further review and 10 were included in this review.</p> <p>Eight systems used vital signs as variables and two relied mostly on blood tests.</p> <p>Nine systems were derived using regression analysis and eight included patients admitted to a MAU. Six systems used in-hospital mortality as their primary endpoint.</p> <p>Discriminatory power was specified for eight of the scoring systems and was acceptable or better in five of these. The calibration was only specified for four scoring systems. In none of the studies impact analysis or inter-observer reliability were analyzed.</p> <p>None of the systems reached the highest level of evidence.</p> <p>Conclusions</p> <p>None of the 10 scoring systems presented in this article are perfect and all have their weaknesses. More research is needed before the use of scoring systems can be fully implemented to the risk assessment of acutely admitted medical patients.</p

Accurate switching intensities and length scales in quasi-phase-matched materials

We consider unseeded Type I second-harmonic generation in quasi-phase-matched (QPM) quadratic nonlinear materials and derive an accurate analytical expression for the evolution of the average intensity. The intensity-dependent nonlinear phase mismatch due to the QPM induced cubic nonlinearity is found. The equivalent formula for the intensity for maximum conversion, the crossing of which changes the nonlinear phase-shift of the fundamental over a period abruptly by $\pi$, corrects earlier estimates by more than a factor of 5. We find the crystal lengths necessary to obtain an optimal flat phase versus intensity response on either side of this separatrix intensity.Comment: 3 pages with 3 figure