A non-homogeneous Markov chain model for follow-up studies with application to epilepsy.
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Adolescent↗
Biomedical subjects
D Commenges
Publications and source records attributed to D Commenges.
A statistical method for the estimation of neuronal response latency and its functional interpretation.
The functional role of many central nervous structures has been inferred from the temporal relationship of a neuronal response with the different sensory and motor events in an experimental design such as when an animal performs a trained movement in response to a conditioned stimulus. However, this kind of data analysis leads to problems in estimating the occurrence and latency of any neuronal response. We examine these problems and propose a novel technique of data analysis to estimate the point of change in a sequence of neuronal discharge. Furthermore, data can be tested to see whether the neuronal response is related to the conditioned stimulus or the motor act. The method can also be used in the simple situation of determining the latency of a neuronal response after a stimulus.
Animals↗
Long-term prognosis in two forms of childhood epilepsy: typical absence seizures and epilepsy with rolandic (centrotemporal) EEG foci.
Findings in children seen between 1955 and 1965 during the year of onset of typical absence seizures (90 patients) or rolandic epilepsy (79 patients) were analyzed by actuarial methods. One hundred and eighteen patients were followed for more than 15 years. Rolandic epilepsy is a true benign epilepsy ending with puberty. Although school and family problems are common during the acute stage of the disease, the social adaptability of such patients is excellent. We considered only typical absences occurring as a first epileptic sign in normal children. Myoclonic or atonic absences have a poor prognosis. Many patients with simple and automatic absences experience remission 15 years after withdrawal of medication. The overall cessation rate in those experiencing absences was only 57.5%, however, and 36% of patients developed tonic-clonic seizures. Social adaptability was often inadequate. Simple and automatic absences (constituting a homogeneous group) are not truly a benign form of epilepsy, even though prognosis for those afflicted is better than that for those with other forms of primary generalized epilepsy.
Adolescent↗
Deconvolution analysis of radionuclide angiocardiography curves: problems arising from fragmented bolus injections.
Deconvolution analysis of radionuclide angiocardiography time-activity curves (TAC) in the cases of fragmented bolus injections was studied by using a new deconvolution technique based on the maximum a posteriori estimator. This method was first tested by simulation studies which showed its capability for accurate handling of deconvolution both for single and double peak input functions. These simulations have proved this technique to have advantages over a Fourier transform division method used with a low-pass filter. In patient studies, deconvolution of pulmonary TAC by superior vena caval TAC produced poor results in double peak (fragmented) bolus injections, compared with single peak bolus injections (SPBI). This discrepancy seems to be due to the fact that the postulates of linearity and invariance, on which deconvolution analysis is based, do not hold for the 'cardiopulmonary system' which extends from the superior vena cava to the lung. The differences between the model and the real system appear unimportant for SPBI. However, differences become apparent for fragmented bolus injections. Deconvolution analysis should be avoided with this type of input function in this cardiopulmonary system.
Aged↗
A deconvolution program for processing radiotracer dilution curves.
We present a computer program for deconvolution of noisy signals. The unknown signal is modelled as a stochastic process and the solution is given by the 'maximum a posteriori estimator'. This is computed by two algorithms: the first uses and the Kalman filter; the second the conjugate gradient technique which permits introduction of a positivity constraint. The program has proved to give accurate results in stimulation studies. It has been applied to the deconvolution analysis of radionuclide angiocardiography time-activity curves. This improves the reliability of the results in left-to-right cardiac shunt quantitation.
Angiocardiography↗
[Influence of histological type on the kinetics of tumor growth and cellular proliferation in autochtonous tumors of mice].
The influence of the tumoral histological characters upon growth kinetics and cellular proliferation parameters was studied for autochtonous chemo-induced tumors in mice. In our experimental conditions, the initial minimum volume from which epithelial tumors on one hand and connective tumors on the other hand are observed and then follow a Gompertzian law, was defined. The change of the histological characters of malignancy was observed during the tumoral growth. Intermitotic delays, durations of the cell cycle phases, growth fraction and degree of cell loss were calculated for epithelial and connective tumors.
Animals↗
The analysis of neuronal discharge sequences: change-point estimation and comparison of variances.
A key problem in neurophysiology is to determine whether, after presentation of a stimulus, there has been a modification in the discharge of a recorded neuron and if so, an attempt is made to estimate the latency of the response. The estimation problem can be considered as that of the estimation of a change-point in a sequence of random variables. The gamma distribution is adequate to model the distribution of intervals between action potentials for different types of neurons. Simulations show that the maximum likelihood estimator based on this model is efficient and robust. An additional problem, in the case of experiments in which a movement follows the stimulus, is to determine whether a response is related to the stimulus or to the movement. A test based on the comparison of marginal scales of a bivariate distribution is proposed. The whole procedure has been tested in simulation and with real examples.
Action Potentials↗
[Application of a Markov model to the follow-up of hyperthyroid patients treated with radioactive iodine].
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Follow-Up Studies↗
[CD8 hyperlymphocytosis in HIV infection. 63 cases. GECSA (Groupe d'Epidémiologie Clinique du SIDA en Aquitaine)].
A group of 63 patients infected by HIV and presenting with CD8 hyperlymphocytosis (CD8+) has been studied. CD8 hyperlymphocytosis was defined by the presence, during at least three months, of at least 1,500 CD8 circulating lymphocytes. The CD8+ patients (n = 63) were identified and followed within the cohort (1,444 patients) of the "Groupe d'Epidémiologie Clinique du SIDA en Aquitaine " (GECSA). CD8+ patients were compared with a control group of 126 HIV infected patients without CD8 hyperlymphocytosis recruited within the GECSA cohort and followed in the same manner during two years. The occurrence of opportunistic infections was less frequent in CD8+ patients. The proportion of patients with a CD4 lymphocyte count below 200/mm3 was lower in the CD8+ group than in the CD8- group at inclusion and at the last check-up (P less than 0.01). A tendency for longer survival and delayed onset of AIDS was noted in CD8+ patients. Such a difference in prognosis might be due to a peculiar cytotoxic response against HIV among CD8+ patients. Further follow-up of a larger group of patients is needed to confirm this hypothesis.
Acquired Immunodeficiency Syndrome↗
[Human activities, hydro-agricultural management and urinary schistosomiasis. Methodological approach and results (a preliminary study in Upper-Volta)].
In the schistosomiasis endemic sub-sahelian region, a study of the prevalence of the disease was carried out on three different areas: the highest was around a small river, the lowest in the hydro-agricultural management region, mean prevalence was noted around a natural lake. Human activities have been classified with regards to the areas of transmission. Activity is closely linked to prevalence. For the populations, symptoms of urinary schistosomiasis (Rudzenga) constitute a real disease, traditional healers are the masters of earth (Tengsoba), water has hardly any importance in transmission.
Adolescent↗