1,721,226 research outputs found
Electrolyte and pH dependence of heart rate during hemodialysis: A computer model analysis
No full textThe influence of hemodialysis-induced modifications in extracellular fluid characteristics on heart rate was investigated by using a detailed computer model of sinus-node electrical activity. Changes similar to those occurring in the course of hemodialysis in extracellular concentrations of sodium (from 138 to 140 mM), potassium (from 6 to 3.3 mM), and calcium (from 1.2 to 1.5 mM) ions as well as in pH (from 7.31 to 7.4) and intracellular volume were simulated. The model predicted that such changes may largely influence the rhythm of the sinoatrial node pacemaker, causing the heart rate to range from 69 to 86 bpm. Heart rate increases after removing potassium (up to 7 bpm) and also after calcium perfusion (up to 11 bpm) whereas restoring pH slows heart beat (up to 6 bpm). Extracellular sodium has no significant influence, but the heart rate strictly depends on intracellular sodium concentration (5 bpm/mM). A complex dependence of heart rate on electrolytes and pH was also recognized. Providing extracellular potassium concentration is maintained above 5 mM, heart rate exhibits low sensitivity to changes in calcium and potassium. When potassium concentration is reduced below 4.5 mM, heart rate sensitivity to calcium and potassium increases significantly to 10 and 30 bpm/mM, respectively. A sustained increase in heart rate always corresponds to an increase in intracellular sodium concentration
Effects of early environment on field CA2 pyramidal neurons in the guinea-pig
No full textPrevious work showed that isolation rearing produces remarkable changes in the dendritic pattern and soma of the principal neurons in the dentate gyrus and hippocampal fields CA3 and CA1 of the guinea-pig. The aim of the present study was to obtain information about the effects of early postnatal isolation on neuron morphology in field CA2, the "resistant sector" of the hippocampal formation. Male and female guinea-pigs were assigned at 6-7 days of age to either a control (social) or an isolated environment where they remained for 80-90 days. The apical and basal dendritic trees and the soma of CA2 pyramidal neurons were analyzed and quantified in Golgi-stained brains. The results showed that in both males and females early isolation caused no effects on the length and dendritic branching density of the apical tree of field CA2 pyramidal neurons. In males but not in females isolation caused a spine density reduction in the inner apical tree. Isolation notably influenced the morphology of the basal tree, but in males only. Isolated males exhibited a significant reduction in the length of the basal tree and number of dendritic branches accompanied by a reduction in spine density. The comparison of animals reared in the same environment showed that in the control environment males had more apical and basal dendritic branches and a larger neuron soma than females. In the isolated environment the sex differences in the apical tree disappeared and those in the basal tree changed direction.The results demonstrate structural changes in field CA2 pyramidal neurons following neonatal isolation, with a specific reactivity to environment of the basal tree of males. The dendritic atrophy in field CA2 of isolated males is in line with previous evidence that males react to isolation mainly with dendritic atrophy, though field CA2 neurons appear to be less damaged than those of the other hippocampal fields. This is in line with the resistance of this field to neurodegeneration. The absence of structural changes in field CA2 of isolated females confirms, once again, that males are more liable to be endangered by early isolation than female
Effects of early environment on pyramidal neuron morphology in field CA1 of the guinea-pig
No full textWe previously demonstrated that early isolation has profound effects on the morphology of the dentate granule cells and field CA3 pyramidal neurons. Aim of the present study was to analyze the effects of early environment on the morphology of field CA1 pyramidal neurons, the third element of the hippocampal trisynaptic circuit. The dendritic trees and the soma of field CA1 pyramidal neurons were quantified in Golgi-stained brains of guinea-pigs of both sexes raised in either a social or an isolated environment. Based on the different pattern of the apical dendritic tree two major classes of CA1 pyramidal neurons were recognized (monotufted neurons and bitufted neurons). In males isolation induced in both neuron types a decrease in the number of low order apical branches but in the apical tree of the monotufted neurons isolation induced an increase in the number of intermediate order branches and dendritic length. In isolated females the apical tree of the monotufted neurons showed a very scarce atrophy. In contrast, the apical tree of the bitufted neurons from isolated females showed a decrease in the number of low and intermediate order branches and dendritic length. In isolated males the basal tree of the bitufted neurons had a large decrease in the total number of branches and dendritic length. In contrast, in isolated females the basal tree of both neuron types showed an increase in the number of low order branches. In males but not in females isolation caused a reduction in the soma dimensions of both neuron types. No isolation-induced changes were observed in dendritic spine density in either the apical or basal dendrites. The results demonstrate remarkable structural changes in CA1 pyramidal neurons following early isolation and a different reactivity to environment of the two CA1 pyramidal neuron types, their apical and basal trees and the two sexes. The neuroanatomical changes caused by isolation in field CA1 and in the two other elements of the trisynaptic circuit are likely to be associated with changes in the physiology of the hippocampal formation and in cognitive processes such as learning and memory in which the hippocampal formation plays a pivotal role. © 2003 IBRO. Published by Elsevier Science Ltd. All rights reserved
Analysis of oscillatory components of short-term heart rate variability in hemodynamically stable and unstable patients during hemodialysis
No full textShort period oscillatory components embedded in heart rate variability (HRV) were studied during hemodialysis induced hypovolemia in 15 hypotension- resistant (stable) and 15 hypotension-prone (unstable) patients. Hemodialysis was undertaken so that a similar blood volume reduction was induced in all patients (p > 0.05) without causing acute hypotension events. Autoregressive HRV power spectrums were calculated using an eigenanalysis-based approach. The frequencies of the main HRV rhythmic components were estimated through the Pisarenko harmonic decomposition. Percent changes during the hemodialysis in both heart rate and arterial pressure were similar in the stable and unstable groups (p > 0.05). The HRV spectral density showed markedly different power distributions. In the stable patients, power was mainly in the low frequency band (74 ± 7 nU in the low frequency [LF] band vs. 21 ± 6 nU in the high frequency [HF] band) whereas in stable patients, it was mainly in the high frequency band (39 ± 10 nU in the LF band vs. 47 ± 7 nU in the HF band). The frequency of the main oscillation was 0.1 P 0.02 Hz in stable patients and 0.18 ± 0.04 Hz in unstable ones (p < 0.01). These HRV spectral parameters have a clear diagnostic value in discriminating between stable and unstable patients when their hemodynamic behaviors are similar
Heart rate variability spectral indices for haemodynamic classification of haemodialysis patients
No full textThe usefulness of spectral indices extracted from the heart rate variability (HRV) in discriminating between hypotension-prone and hypotension-resistant haemodialysis patients was investigated. In 30 patients, classified as hypotension resistant (stable group) or hypotension prone (unstable group), beat-to-beat heart period was measured during haemodialysis sessions terminated without collapses. HRV was analysed in the frequency domain combining classic autoregressive spectral estimation with two eigen decomposition-based techniques: the reduced rank approximation (RRA) of the autocorrelation matrix and the Pisarenko harmonic decomposition (PHD). Five spectral indices were obtained: the ratio between the powers in the LF and HF bands (LF/HF), the same ratio calculated after application of RRA (LF/HF(RRA)), the frequency of the main oscillatory component of HRV estimated through PHD with a decomposition order equal to 1 (F1) and equal to 2 (F2) and the difference between the frequencies of the two oscillatory components resolved in the latter case (F(d)). The performances of these indices in discriminating between the two groups of patients were evaluated estimating the misclassification probability (F(m)) of a Bayesian quadratic classifier. The HRV spectral pattern was markedly different: in the stable patients power was mainly in the low-frequency band, whereas in the unstable group it was mainly in the high-frequency band. The frequency of the main oscillatory component was significantly greater in the unstable group than in the stable one Spectral indices displayed good discrimination power, increasing with the length of the dialysis interval. Best performances were achieved by LF/HF(RRA) both over short dialysis periods (P(m) ≃ 12% over 20 rain intervals) and over longer periods (P(m) = 3.3% over 160 min); similar results were obtained with F(d) over short periods and LF/HF over long periods. Spectral HRV indices demonstrate, therefore, a diagnostic value in discriminating between hypotension-resistant and hypotension-prone patients
A novel pump-free ultrafiltration rate modulation system for continuous renal replacement therapy applications
Full text linkPurpose: Extracorporeal ultrafiltration is an attractive alternative to diuretics for removing excess plasma water in critically ill patients suffering from fluid overload. In continuous renal replacement therapy (CRRT), ultrafiltration occurs in isolated form (SCUF) or supplemented by replacement fluid infusion (CVVH) and the net fluid removal rate is controlled by peristaltic pumps. In this work, a pump-free solution for regulating the ultrafiltration rate in CRRT applications is presented. Methods: The system consists of a motorized clamp on the ultrafiltration line, whose intermittent opening is modulated with a closed-loop control system based on monitoring of ultrafiltrate collected and any replacement fluid infused. The system was tested on two platforms for SCUF and CVVH, with “low-flux” and “high-flux” hemofilter, with various ultrafiltration setpoints and patient net weight loss targets. Results: In all configurations the set ultrafiltration rate was achieved with a maximum error of 5% and the values recorded were kept within ± 100 ml/h with respect to the setpoint, as recommended by international standard IEC 60601-2-16. The net fluid removal trend was highly correlated with that expected (95%<99%) and the weight loss target was reached in the expected time. For low ultrafiltration rates (60-150 ml/h) the system accuracy was better with the “low-flux” hemofilter. Conclusion: The developed clamp system represents a valid alternative to state-of-the-art solutions with peristaltic pumps in terms of performance, with potential usability advantages. The compliance with safety requirements given by international standard IEC 60601-2-16 is a prerequisite for clinical use
Effects of early isolation on layer II neurons in the entorhinal cortex of the guinea pig
No full textPrevious studies showed that early environmental conditions severely affect the morphology of the granule cells in the hippocampal dentate gyrus and pyramidal neurons in fields CA3 and CA1. The aim of the present study was to determine whether early isolation affects neuron morphology in layer II of the entorhinal cortex, from which the perforant path to the dentate gyrus and CA3 takes its origin. Male and female guinea pigs were assigned at 6-7 days of age to either a control (social) or an isolated environment where they remained for 80-90 days. The brains were Golgi-Cox stained and neurons were sampled from layer II of the entorhinal cortex. Morphometric analysis was carried out on star cells, the most abundant neuron population. Isolated males had star cells with less dendritic branches, a shorter dendritic length and a smaller dendritic spine density than control males. In contrast, isolated females had more dendritic branches than control females, though this difference was of small magnitude. While isolated males had star cells with a smaller soma than control males, isolated females had a soma larger than control females. In both environments sex differences were found in the star cell morphology. In the control environment males had more dendritic branches, a greater dendritic length, a larger soma but a smaller spine density than females. In the isolated environment males had less branches, a shorter dendritic length, a smaller spine density and a smaller soma than females. The results indicate that early isolation affects the structure of the star cells in the entorhinal cortex and that males and females react to isolation in an opposite manner. A similar sexually dimorphic response to early isolation was previously observed in the dentate gyrus and fields CA3 and CA1. The presence of widespread effects of isolation in the entorhinal cortex and numerous hippocampal structures suggests that the outcome of early isolation might be a change in learning and memory functions requiring the hippocampal region. © 2003 IBRO. Published by Elsevier Science Ltd. All rights reserved
Estimation of respiratory parameters during mechanical ventilation: A simple method taking account of tubing compliance
No full textA lumped parameter non linear model of a typical ventilator-patient circuit was used to simulate flow and pressure signals in a wide variety of respiratory disorders. Patient lungs were described by the series connection of a compliance (CL = constant) and a resistance proportional to the airflow (KL, = proportionality constant). Aim of this work is to present an estimation algorithm which allows to reduce the error on the estimate of the patient respiratory parameters when using pressure and flow signals at the ventilator side instead of the patient side. The proposed algorithm is based on a simplified model of the ventilator-patient circuit, which incorporates the tubing compliance (Ctube) and neglects the pressure losses along the tubes during flow. Ctube CL and KL are recursively estimated by minimizing a weighted pressure RMSE. The patient parameter estimates, thus obtained, are compared with the "true" values and those provided by the same algorithm when Ctube. is omitted in the simplified model. Simulation results show that the respiratory circuit may significantly affect the estimate of CL and KL when using airflow and pressure at the ventilator side. The proposed estimation approach appears capable to greatly improve the estimate, in particular in the presence of an increased respiratory resistance
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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