A two-compartment kinetic model: Rigorous and approximate solutions

We have found an approximate solution of a two-compartment kinetic model. The model considered allows exchange of tracer between the two compartments, and loss of this tracer from one compartment. This solution was used to calculate the turnover rates of the two compartments from the retention of the tracer in the model. Hence, by measuring in a whole body counter the retention of an isotope tracer in such a system, it is possible to calculate the turnover rates of the two compartments of the system. Using an English Electric KDF 9 computer to solve 64 stated models, we have been able to define the range of kinetic constants over which the use of the mathematical approximation is justifiable.

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Zusammenfassung Wir fanden eine Näherungsgleichung für ein kinetisches 2-Kompartment-Verteilungsmodell. Das Modell erlaubt den Austausch von Tracersubstanzen zwischen zwei Räumen und die Angabe des Tracers aus einem Raum. Die Gleichung wurde verwendent, um die Umsatzrate in den zwei Räumen nach der Retention des Tracers im Modell zu berechnen. Durch Messung der Retention eines Isotops in einem derartigen System mit dem Ganzkörperzähler ist es dann möglich, die Umsatzraten in beiden Verteilungsräumen zu berechnen. Ein English Electric KDF 9 Computer, der 64-stufige Vorlagen löst, ermöglicht es, den Bereich der kinetischen Komponenten zu definieren, über welchen die Verwendung der mathematischen Nährung gerechtfertigt ist.

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Résumé Nous avons trouvé une solution approximative d'un modèle cinétique à 2 compartiments. Le modèle considéré perment l'échange du traceur entre 2 compartiments et la perte de ce traceur à partir d'un seul compartiment. Cette solution est utilisée pour calculer les taux de renouvellement des 2 compartiments à partir de la rétention du traceur dans ce modèle. Ainsi, en mesurant la rétention de l'isotope traceur dans un tel système à l'aide d'un comptage «in toto» il est possible de calculer les taux de renouvellement des 2 compartiments du système.En utilisant un calculateur électronique KDF 9 pour résoudre 64 modèles établis, nous avons été capables de préciser les limites des constantes cinétiques dans lesquelles l'utilisation de l'approximation máthématique est justifiée.

     

Brain activation associated with visual motion studied by functional magnetic resonance imaging in humans

Localized brain activation in response to moving visual stimuli was studied by functional magnetic resonance imaging (fMRI). Stimuli were 100 small white dots randomly arranged on a visual display. During the Motion condition, the dots moved along random, noncoherent linear trajectories at different velocities. During the Blink condition, the dots remained stationary but blinked on and off every 500 ms. The Motion and Blink conditions continuously alternated with 10 cycles per run and 6–8 runs per experiment. In half of the runs, the starting stimulus condition was Motion, while in the remaining runs it was Blink. A series of 128 gradient echo echoplanar images were acquired from 5–7 slices during each run using a 1.5 T GE Signa with an Advanced NMR echoplanar subsystem. The time series for each voxel were analyzed in the frequency domain. Voxels which demonstrated a significant spectral peak at the alternation frequency and whose phase changed in response to stimulus order were considered activated. These activated voxels were displayed upon high resolution anatomical images to determine the sites of activation and were also transformed into the coordinates of Talairach and Tournoux ([1988] Co-planar Stereotaxic Atlas of the Human Brain, New York: Thieme) for comparison to prior neuroimaging studies. Seven of ten subjects showed clusters of activation bilaterally at the junction of the temporal and occipital lobes (area 37) in response to moving stimuli. Most activated voxels were located within or adjacent to a region designated the parietal-temporal-occipital fossa, or PTOF. Five subjects also showed activation to moving stimuli in midline occipital cortex. The activated voxels in midline cortex had a significantly shorter phase delay in their MR signal change relative to voxels in PTOF. © 1995 Wiley-Liss, Inc. 1

1 This article is a US Government work and, as such, is in the public domain in the United States of America

     

Correlation of quantitative measures with the modified Ashworth scale in the assessment of plantar flexor spasticity in patients with traumatic brain injury

This study of plantar flexor spasticity describes relationships among a traditional qualitative spasticity scale, three potential quantitative spasticity measures and a measure of voluntary ankle muscle function. Thirty-four volunteer adult patients with traumatic brain injuries participated. There were 28 males and 6 females; the mean age was 30.3 years. A battery of five randomly sequenced tests was performed for each subject on one ankle. Tests were: modified Ashworth scale (MAS) scoring; H-reflex testing with and without Achilles tendon vibration; H-reflex testing with and without dorsiflexor contraction; reflex threshold angle and timed toe tapping (TTT). Twenty-six subjects returned to have the second ankle tested, resulting in 60 ankles for the analyses. Spearman's coefficients for correlation of quantitative spasticity measures with MAS scores ranged from 0.39 to 0.49 with associated probabilities 0.002. Pearson coefficients for correlation of quantitative spasticity measures with TTT scores were lower but also significant (P 0.07). Multiple correlation for the set of quantitative measures yieldedR = 0.614 (P < 0.001) with MAS scores andR = 0.365 (P = 0.045) with TTT scores. These findings reveal statistically significant relationships of low to moderate strength among potential quantitative spasticity measures, a traditional qualitative spasticity scale and a simple measure of voluntary ankle muscle function. Understanding these relationships is an essential part of the ongoing search for quantitative spasticity measures.The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense.     

Post-stroke depression: Relationships with morphological damage and cognition over time

The aim of the present study was to investigate the relationships between poststroke depression (PSD), lesion location and cognitive deficits after stroke. We studied 20 patients within the first month after clinical onset (T1), and one year later (T2). PSD was observed in 55% of patients at T1 and 35% of patients at T2. At T1, depression was reliably correlated with dorsal lesions in the right-hemisphere and anterior lesions in the left hemisphere. Lesion location was no longer a significant factor determining PSD at T2. Changes in PSD, from T1 to T2, were inversely correlated with the performances in cognitive tests exploring the domains of attention, visuospatial learning, executive/motor functions, and with the global composite cognitive score. Our data suggest that: 1) in the mix of influences that may produce PSD, lesion location is the main factor determining mood changes after stroke in the first month; 2) PSD produces deficits in attention, learning, and executive/motor functions, without affecting language and other cognitive domains.

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Sommario Scopo di questo studio sono i rapporti tra la depressione post-stroke (PSD), la localizzazione della lesione cerebrovascolare e i disturbi cognitivi conseguenti alla lesione. Abbiamo studiato 20 pazienti entro il primo mese dall'episodio ictale (T1) ed un anno dopo (T2). La PSD era osservabile nel 55% dei pazienti a T1 e nel 35% dei pazienti a T2. A T1, la PSD era significativamente correlata con lesioni dorsali nell'emisfero di destra e con lesioni anteriori nell'emisfero di sinistra. Queste correlazioni non erano più significative a T2. Le variazioni della PSD da T1 a T2 erano inversamente correlate con le prestazioni dei pazienti a compiti cognitivi di attenzione, apprendimento visuospaziale, funzioni esecutivo/motorie, e con un punteggio cognitivo composito.Questi dati suggeriscono che: 1) tra le numerose cause che possono produrre la PSD, la localizzazione della lesione sembra essere il fattore principale nel primo mese dopo l'episodio cerebrovascolare; 2) la PSD produce disturbi attentivi, di apprendimento visuospaziale ed esecutivi/motori senza determinare disturbi nella sfera del linguaggio e di altre funzioni cognitive.

     

Long-term outcome and cost-effectiveness of parenteral nutrition for acute gastrointestinal failure

Although there are several published audits of long-term home parenteral nutrition for chronic gastrointestinal failure, there is little data concerning the long-term outcome following prolonged in-patient parenteral nutrition for an episode of acute gastrointestinal failure. Between 1983 and 1 July 1993, 162 patients received total parenteral nutrition (TPN) in our unit for acute gastrointestinal failure for a total of 4997 patient days and using 192 central venous catheters. Over the 10 years there were 11 mechanical complications resulting in one death. Although the overall catheter infection rate was 5.7%, in the last 4 years it was 0%, associated with a reduction in the frequency of site dressing and change of giving set from three times to once weekly. All patients had lost more than 10% of their body weight before TPN. In the non-malignant group, fed for more than 21 days (mean 50 days), the 10-year survival was 74% at a cost of 4723 pounds sterling per year of life saved. In the malignant group, the 5-year survival was 27% at a cost of 8351 pounds sterling per year of life saved. These costs compare favourably with other technologies, such as dialysis for acute renal failure. Better patient selection, fewer complications and lower costs are obtained when this treatment is carried out by an expert team.     

Nuclear magnetic resonance and its biological problems

Among the main reasons for the interest aroused by the production of images by nuclear magnetic resonance, the successes obtained by TC and the possibility of avoiding the use of ionizing radiations in the new procedure are well worth mentioning. This possibility had induced operators to consider the possible effects of an examination with nuclear magnetic resonance "a priori" unimportant or only noticeable as regards a subjective symptomatology of scarce importance and, at most they advise a few general precautionary measures in the selection of patients. The separate study of the effects of individual forms of energy which act in nuclear magnetic resonance has, however, shown the utility of extending research of tests in wider physiopathological fields and deepening studies of molecular biology, even though results to date appear reassuring.     

Dispositional optimism predicts survival status 1 year after diagnosis in head and neck cancer patients.

PURPOSE: The aim of this study was to investigate the hypothesis that, independent of other known prognostic factors, pessimistic head and neck (H&N) cancer patients have a greater risk of being dead 1 year after diagnosis than do optimistic patients. PATIENTS AND METHODS: A prospective observational study design was used with a cohort of H&N cancer patients diagnosed during the period from March 1, 1997, to August 31, 1998, at the Centre Hospitalier Universitaire, Clermont-Ferrand, France. Dispositional optimism (DO) was evaluated at baseline using a French version of the Life Orientation Test translated and validated for this study. One-year survival status was collected on all subjects. The analysis of the hypothesized association between DO and 1-year survival was performed using multiple logistic regression analysis, controlling for other sociodemographic and clinical variables. RESULTS: The sample size was 101 patients, representing all but one of those patients fitting the inclusion criteria who were diagnosed during the recruitment period. Of these, 51 were alive at 1 year after diagnosis, 45 were dead, and five were lost to follow-up. The multivariate analysis was performed on the data from the 96 subjects in whom 1-year survival status was known. Controlling for known predictors of H&N cancer survival, pessimistic subjects (odds ratio [OR], 1.12; 95% confidence interval [CI], 1.01 to 1.24) and those living alone (OR, 4.14; 95% CI, 1.21 to 14.17) were more likely than optimistic subjects and those living with others to be dead at 1 year. CONCLUSION: The results of this study of a cohort of French H&N cancer patients indicate that dispositional optimism predicts 1-year survival independent of other sociodemographic and clinical variables.