Viscoelastic characterization of the primate finger pad in vivo by microstep indentation and three-dimensional finite element models for tactile sensation studies.

When we touch an object, surface loads imposed on the skin are transmitted to thousands of specialized nerve endings (mechanoreceptors) embedded within the skin. These mechanoreceptors transduce the mechanical signals imposed on them into a neural code of the incident stimuli, enabling us to feel the object. To understand the mechanisms of tactile sensation, it is critical to understand the relationship between the applied surface loads, mechanical state at the mechanoreceptor locations, and transduced neural codes. In this paper, we characterize the bulk viscoelastic properties of the primate finger pad and show its relationship to the dynamic firing rate of SA-1 mechanoreceptors. Two three-dimensional (3D) finite element viscoelastic models, a homogeneous and a multilayer model, of the primate fingertip are developed and calibrated with data from a series of force responses to micro-indentation experiments on primate finger pads. We test these models for validation by simulating indentation with a line load and comparing surface deflection with data in the literature (Srinivasan, 1989, "Surface Deflection of Primate Fingertip Under Line Load," J. Biomech., 22(4), pp. 343-349). We show that a multilayer model with an elastic epidermis and viscoelastic core predicts both the spatial and temporal biomechanical response of the primate finger pad. Finally, to show the utility of the model, ramp and hold indentation with a flat plate is simulated. The multilayer model predicts the strain energy density at a mechanoreceptor location would decay at the same rate as the average dynamic firing rate of SA-1 mechanoreceptors in response to flat plate indentation (previously observed by Srinivasan and LaMotte, 1991 "Encoding of Shape in the Responses of Cutaneous Mechanoreceptors," Information Processing in the Somatosensory System (Wenner-Gren International Symposium Series), O. Franzen and J. Westman, eds., Macmillan Press, London, UK), suggesting that the rate of adaptation of SA-1 mechanoreceptors is governed by the viscoelastic nature of its surrounding tissue.

Procalcitonin (PCT) Level in the Emergency Department Identifies a High-Risk Cohort for All Patients Treated for Possible Sepsis.

WHAT IS ALREADY KNOWN?: The benefits of measuring PCT in the Emergency Department (ED) are not yet fully characterised.PCT is widely used in the intensive care setting to guide antimicrobial prescribing. WHAT THIS ADDS?: Measurement of PCT as a routine in the emergency department for all patients treated for possible sepsis identifies a high-risk cohort. KEY IMPROVEMENT IN PATIENT CARE: A PCT measurement of >0.2ug/L in the Emergency Department identifies a patient at increased risk of deterioration and of in-hospital death. BACKGROUND: Early recognition and management of sepsis in the Emergency Department (ED) is a clinical challenge. Our aim was to determine if measuring the biomarker PCT in patients with suspected sepsis enables the identification of patients at increased risk of deterioration or in-hospital death in the ED setting of a district general hospital in the United Kingdom. METHODS: A prospective observational study was conducted on all patients aged 18 and over presenting to ED fulfilling NICE criteria for moderate to high risk of sepsis admitted to hospital. Patients had a PCT test alongside the sepsis six protocol. PCT was measured using Brahms's chemiluminescent micro particle assay (CMIA) for the quantitative determination of PCT in human serum and plasma on the Abbott Alinity I analytical platform. The cost per test was approximately 13 GBP.The analysis was performed on patients having a PCT in ED over a 7-month period, with in-depth scrutiny of an appropriate subgroup. A high level quality improvement (QI) approach was used in the study. RESULTS: A total of 1242 patients were included in the study. Mean/median age was 67.9/72, (range 18-102). 88.7% of deaths occurred in patients over 65 years of age. 42.4% (n=532) had a PCT level in ED of >0.2 ug/L. This identified a high risk group with a 2.4 fold increase in mortality rate (7.7%:18.2% p value <0.001). The median length of stay (LOS) was 5 (IQR 9) and 8 days (IQR 11) in patients with a first PCT of ≤0.2 ug/L versus >0.2 ug/L respectively. CONCLUSION: An immediate PCT on patients presenting to ED with signs of sepsis in a non-specialised acute trust identifies those patients at an increased risk of deterioration and in hospital death.