Modeling and Simulation of Aircell Actuator Seat Cushion With Pneumatic Line Lag and Capacitative Effects

This article presents the development of a hybrid model with pneumatic lag effects for the smart seat cushion which can be extended to any active aircell cushion. Smart seat cushion is one such rehabilitation device which reduces the risk of pressure injury formation by automatically performing repositioning exercises for wheelchair users. Operation of the smart seat cushion device can be greatly enhanced by accurate prediction of pneumatic line lag during its various modes of operation. The proposed model combines a linear model from literature to capture the effects of pneumatic line lag and a bang-bang scheduling controller to enable efficient use of pneumatic components in the smart seat cushion device. The resulting simulation is validated by conducting multiple runs of uniform inflation experiment with the device, and comparing the closed loop behavior of the model. The hybrid modeling allows accurate prediction of pneumatic line lag in the smart seat cushion during various modes of redistribution and offloading. The modeling accuracy and the prediction of switching times for discrete states can be improved by data sampled at a higher rate from the device.

A novel technique for the assessment of mechanical properties of vascular tissue

Accurate estimation of mechanical properties of the different atherosclerotic plaque constituents is important in assessing plaque rupture risk. The aim of this study was to develop an experimental set-up to assess material properties of vascular tissue, while applying physiological loading and being able to capture heterogeneity. To do so, a ring-inflation experimental set-up was developed in which a transverse slice of an artery was loaded in the radial direction, while the displacement was estimated from images recorded by a high-speed video camera. The performance of the set-up was evaluated using seven rubber samples and validated with uniaxial tensile tests. For four healthy porcine carotid arteries, material properties were estimated using ultrasound strain imaging in whole-vessel-inflation experiments and compared to the properties estimated with the ring-inflation experiment. A 1D axisymmetric finite element model was used to estimate the material parameters from the measured pressures and diameters, using a neo-Hookean and Holzapfel–Gasser–Ogden material model for the rubber and porcine samples, respectively. Reproducible results were obtained with the ring-inflation experiment for both rubber and porcine samples. Similar mean stiffness values were found in the ring-inflation and tensile tests for the rubber samples as 202 kPa and 206 kPa, respectively. Comparable results were obtained in vessel-inflation experiments using ultrasound and the proposed ring-inflation experiment. This inflation set-up is suitable for the assessment of material properties of healthy vascular tissue in vitro. It could also be used as part of a method for the assessment of heterogeneous material properties, such as in atherosclerotic plaques.

THE SIMULATION STUDY ON THE DEFORMATION OF RABBIT CORNEA AFTER REFRACTIVE SURGERY WITH DIFFERENT CUTTING THICKNESS

Based on the inflation tests data of rabbit cornea, finite element analysis has been applied to determine the material parameters, simulate corneal refractive surgery and study postoperative corneal deformations. The corneal profile and apical displacement data were recorded during the inflation experiment of five rabbit corneas. Inverse finite element method was applied to determine the material parameters from the corneal apical displacements. Based on the determined material parameters and the corneal profile information, we established five corneal geometry models that simulate refractive surgery with different cutting amounts. We analyzed displacements at corneal apex and cutting edge, corneal surface curvatures under different pressures. Both Ogden model ([Formula: see text]) and Yeoh model ([Formula: see text]) gave good fits to the experiment data. The maximum of error square sum between the calculated value and the experimental value of the displacements per point at the corneal profile was less than 0.06[Formula: see text]mm. For each model with the increase of pressure, the displacement at cutting edge was larger than that at corneal apex, both of them increased, and curvature radius of anterior and posterior corneal surface increased slowly, but the refractive power decreased slowly and tended to be a stable value. Under the same pressure, the larger the cutting amount, the larger the displacements at corneal apex and cutting edge with a cutting edge displacement of about 1.10 (less ablation model) and 1.02 (larger ablation model) times the corneal vertex displacement. Both Ogden model and Yeoh model can be used to describe corneal mechanical responses of inflation experiment. After refractive surgery, the displacement at cutting edge is larger than that at corneal apex, the curvature radius of anterior (posterior) corneal surface increases (decreases), and the refractive power decreases.

Effect of antigravity suit inflation on cardiovascular, PRA, and PVP responses in humans

Blood pressure, pulse rate (PR), serum osmolality and electrolytes, as well as plasma vasopressin (PVP) and plasma renin activity (PRA), were measured in five men and two women [mean age 38.6 +/- 3.9 (SE) yr] before, during, and after inflation of an antigravity suit that covered the legs and abdomen. After 24 h of fluid deprivation the subjects stood quietly for 3 h: the 1st h without inflation, the 2nd with inflation to 60 Torr, and the 3rd without inflation. A similar control noninflation experiment was conducted 10 mo after the inflation experiment using five of the seven subjects except that the suit was not inflated during the 3-h period. Mean arterial pressure increased by 14 +/- 4 (SE) Torr (P less than 0.05) with inflation and decreased by 15 +/- 5 Torr (P less than 0.05) after deflation. Pulse pressure (PP) increased by 7 +/- 2 Torr (P less than 0.05) with inflation and PR decreased by 11 +/- 5 beats/min (P less than 0.05); PP and PR returned to preinflation levels after deflation. Plasma volume decreased by 6.1 +/- 1.5% and 5.3 +/- 1.6% (P less than 0.05) during hours 1 and 3, respectively, and returned to base line during inflation. Inflation decreased PVP from 6.8 +/- 1.1 to 5.6 +/- 1.4 pg/ml (P less than 0.05) and abolished the significant rise in PRA during hour 1. Both PVP and PRA increased significantly after deflation: delta = 18.0 +/- 5.1 pg/ml and 4.34 +/- 1.71 ng angiotensin I X ml-1 X h-1, respectively. Serum osmolality and Na+ and K+ concentrations were unchanged during the 3 h of standing.(ABSTRACT TRUNCATED AT 250 WORDS)