Nonlinear modeling of the dynamic effects of arterial pressure and CO2 variations on cerebral blood flow in healthy humans

The effect of spontaneous beat-to-beat mean arterial blood pressure fluctuations and breath-to-breath end-tidal CO2 fluctuations on beat-to-beat cerebral blood flow velocity variations is studied using the Laguerre-Volterra network methodology for multiple-input nonlinear systems. The observations made from experimental measurements from ten healthy human subjects reveal that, whereas pressure fluctuations explain most of the high-frequency blood flow velocity variations (above 0.04 Hz), end-tidal CO2 fluctuations as well as nonlinear interactions between pressure and CO2 have a considerable effect in the lower frequencies (below 0.04 Hz). They also indicate that cerebral autoregulation is strongly nonlinear and dynamic (frequency-dependent). Nonlinearities are mainly active in the low-frequency range (below 0.04 Hz) and are more prominent in the dynamics of the end-tidal CO2-blood flow velocity relationship. Significant nonstationarities are also revealed by the obtained models, with greater variability evident for the effects of CO2 on blood flow velocity dynamics.     

Nonlinear Modeling of the Dynamic Effects of Infused Insulin on Glucose: Comparison of Compartmental With Volterra Models

This paper presents the results of a computational study that compares simulated compartmental (differential equation) and Volterra models of the dynamic effects of insulin on blood glucose concentration in humans. In the first approach, we employ the widely accepted ldquominimal modelrdquo and an augmented form of it, which incorporates the effect of insulin secretion by the pancreas, in order to represent the actual closed-loop operating conditions of the system, and in the second modeling approach, we employ the general class of Volterra-type models that are estimated from input-output data. We demonstrate both the equivalence between the two approaches analytically and the feasibility of obtaining accurate Volterra models from insulin-glucose data generated from the compartmental models. The results corroborate the proposition that it may be preferable to obtain data-driven (i.e., inductive) models in a more general and realistic operating context, without resorting to the restrictive prior assumptions and simplifications regarding model structure and/or experimental protocols (e.g., glucose tolerance tests) that are necessary for the compartmental models proposed previously. These prior assumptions may lead to results that are improperly constrained or biased by preconceived (and possibly erroneous) notions-a risk that is avoided when we let the data guide the inductive selection of the appropriate model within the general class of Volterra-type models, as our simulation results suggest.     

Analysis of focusing of pulsed baseband signals inside a layeredtissue medium

The derivation and application of a method designed to investigate the focusing properties of pulsed baseband signals of short pulsewidth (~1 ns) in biological tissue media are reported. To this end, sources fed from TEM waveguides, concentrically placed at the periphery of a three-layer cylindrical lossy model, are assumed. A Fourier-series-based methodology, appropriate for a useful class of pulse train incident signals, is presented and utilized to study the dynamics of pulse propagation inside the tissue medium. The propagation of each spectral component of the incident field within the tissue medium is analyzed by applying an integral-equation technique and a Fourier-series representation is used in order to obtain the time dependence of the electromagnetic fields produced at any point within tissue due to the pulsed excitation of the array elements. Numerical results are computed and presented at several points in a three-layer geometry, 20 cm in diameter, irradiated by an eight-element waveguide array. Focusing at a specific point of interest within tissue is achieved by properly adjusting the time delay of the signals injected to the individual applicators of the array     

Comparative estimation of periodontal conditions by means of different index systems

The aim of the present study was to compare epidemiological data of periodontal disease obtained from a sample of adults by means of different, commonly employed, partial and full-mouth index systems, in order to explore the amount of discrepancy attributed to the methodology per se. 169 dentate subjects, aged 25-64 years, were subjected to a clinical examination, including circumferential probing assessments of pocket depth (PPD) and attachment level (PAL) at all teeth present. The individual mean % of tooth sites with PPD of > or = 6 mm and the % of subjects exhibiting at least one such deep pocket were calculated based on (i) full-mouth data, (ii) data derived from the buccal and mesial surfaces from 1 randomly selected upper and 1 lower quadrant, (iii) probing assessments at the 6 "Ramfjord teeth", (iv) the full-mouth community periodontal index for treatment needs (CPITN), and (v) the partial CPITN based on 10 index teeth. The PAL data were analyzed by means of 3 versions of the extent and severity index, 1 generated by full-mouth assessments and 2 by partial assessments based on 28 and 10 tooth sites, respectively. In the entire sample, the individual mean % of sites with PPD of > or = 6 mm generated by the different systems ranged between 5.0 and 4.2 sites/subject. By full-mouth CPITN scorings, an average of 1.0 score-4 sextants/subject was recorded, while the partial CPITN generated a corresponding value of 0.8 score-4 sextants/subject.(ABSTRACT TRUNCATED AT 250 WORDS)     

Clinical evaluation of the effect of tetracycline root preparation on guided tissue regeneration in the treatment of Class II furcation defects

Changes in tension were monitored isometrically on helical strips from both femoral and saphenous human veins obtained during autopsy and during surgical removal of varicose veins respectively. Both venous tissues contracted in response to 5-hydroxytryptamine (5-HT), 5-carboxamidotryptamine (5-CT) and 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT). While 5-HT was about 2 times more potent in saphenous (pD2 = 7.35) than in femoral veins (pD2 = 7.04), 5-CT stimulated the saphenous vein (pD2 = 7.62) at about 20 times lower concentrations than were required for stimulation of the femoral vein (pD2 = 6.27). 8-OH-DPAT induced venoconstriction only when used at very high concentrations and pD2 values could not be determined. These data suggested different subtypes and/or distribution of 5-HT receptors in both venous preparations. Further evidence for this was obtained by the observation that spiperone (a 5-HT receptor blocker with high affinity for 5-HT2 and 5-HT1A sites) produced a parallel shift to the right of the 5-HT curve in femoral veins but elicited a biphasic displacement of the 5-HT curve in saphenous veins. In the femoral vein, spiperone showed a pA2 value of 9.20 +/- 0.08, statistically not different from that calculated for the spiperone sensitive 5-HT effect in saphenous vein (pA2 = 9.14 +/- 0.08). The results suggest that regional variations in the distribution of 5-HT receptor subtypes do exist, human femoral veins possessing mainly 5-HT2 receptors whereas in human saphenous veins both 5-HT1-like and 5-HT2 receptors are present.     

Autonomic neural control of cerebral hemodynamics

Despite the rich innervation of the cerebral vasculature by both sympathetic and parasympathetic nerves [1], the role of autonomic control in cerebral circulation and, particularly, cerebral hemodynamics is not entirely clear [2]. Previous animal studies have reported inconsistent results regarding the effects of electrical stimulation or denervation on cerebral blood flow (CBF), cerebral pressureflow relationship, and cerebral vessel response to metabolic stimuli [3]--[5]. Moreover, with the advance of transcranial Doppler ultrasound (TCD), which yields accuratemeasurements of CBF velocity (CBFV) with high time resolution [6], it has been found that in humans CBFV in the middle cerebral artery decreased substantially during lower body negative pressure (LBNP) and head-up tilt in the absence of systemic hypotension, which suggests the presence of cerebral vasoconstriction associated with augmented sympathetic nerve activity during orthostatic stress [7]. These observations were based on assessing static measures of cerebral circulation, i.e., mean values of artevial blood pressure (ABP) and CBF with a low time resolution.     

Removal of heavy metals from wastewater using CFB-coal fly ash zeolitic materials

Polish bituminous (PB) and South African (SA) coal fly ash (FA) samples, derived from pilot-scale circulated fluidized bed (CFB) combustion facilities, were utilized as raw materials for the synthesis of zeolitic products. The two FAs underwent a hydrothermal activation with 1 M NaOH solution. Two different FA/NaOH solution/ratios (50, 100 g/L) were applied for each sample and several zeolitic materials were formed. The experimental products were characterized by means of X-ray diffraction (XRD) and energy dispersive X-ray coupled–scanning electron microscope (EDX/SEM), while X-ray fluorescence (XRF) was applied for the determination of their chemical composition. The zeolitic products were also evaluated in terms of their cation exchange capacity (CEC), specific surface area (SSA), specific gravity (SG), particle size distribution (PSD), pH and the range of their micro- and macroporosity. Afterwards the hybrid materials were tested for their ability of adsorbing Cr, Pb, Ni, Cu, Cd and Zn from contaminated liquids. Main parameters for the precipitation of the heavy metals, as it was concluded from the experimental results, are the mineralogical composition of the initial fly ashes, as well as the type and the amount of the produced zeolite and specifically the mechanism by which the metals ions are hold on the substrate.