Biomedical subjects

D Morlet

Publications and source records attributed to D Morlet.

15 recordsLinked to original sources

PubMed1999

Mismatch negativity and late auditory evoked potentials in comatose patients.

OBJECTIVES: The purpose of this study was to assess the patterns of mismatch negativity (MMN) and N100 component in comatose patients and to evaluate their prognostic value vis-à-vis return of consciousness. METHODS: MMN and auditory (early, middle-latency and late) evoked potentials were recorded in 52 normals and in 128 comatose patients (comas due to neurosurgical and neurological problems). At the time of recording, all patients scored lower than 8 on the Glasgow scale. RESULTS: Visually detected N100 and MMN were confirmed by cross-correlation of sub-averages. The MMN was present in 33/128 patients and the N100 component in 84/128. The amplitudes of MMN and N100 waves detected in comatose patients were statistically different from those of normal subjects. By 3 months after the onset of coma, 95 patients had returned to consciousness, most of them with moderate to severe disability. A ratio of 30/33 patients with MMN and 70/84 with N100 had regained consciousness. The presence of a MMN together with a N100 component was more specific (90.9%) than the presence of a N100 component irrespective of MMN (57.6%) in terms of predicting return to consciousness, but its sensitivity was lower (respectively 31.6% for MMN and 73.7% for N100). The mean period that elapsed between the recording of evoked potentials and a return to consciousness was 6.3+/-4 days. MLAEPs were also highly specific, but BAEPs were not. CONCLUSION: MMN and auditory evoked potentials provide a reliable assessment of the functional status of comatose patients. When present, MMN and the N100 differ from those found in normal subjects in terms of latencies and amplitudes. As a predictor of return of consciousness MMN had high specificity and low sensitivity, whereas the N100 had high sensitivity and low specificity. This study demonstrates that the recording of MMN and the auditory N100 can be a very useful aid in the assessment of coma and in predicting whether or not a patient will regain consciousness.

Adolescent↗

PubMed1997

Dynamics of MLAEP changes in midazolam-induced sedation.

This study aimed at assessing the effects of midazolam (MDZ) sedation on auditory brainstem (BAEP) and middle latency (MLAEP) evoked potentials in intensive care conditions. Ten ventilated comatose patients were receiving an intravenous MDZ bolus dose (0.2 mg/kg) followed by a 2 h continuous infusion (0.1 mg/kg/h). MLAEPs and BAEPs elicited by clicks (90 dB HL + masking) were simultaneously and continuously monitored during the first 6 h and for 30 min the next morning. We found no effect of MDZ sedation on BAEPs. Only MLAEP components were modified. However, none of the patients presented any total abolition of the MLAEPs. Bolus injection led to very early alteration of cortical responses, beginning after 5 min and lasting almost 1 h (maximum Pa latency increase, 3.1 ms; maximum Pa-Nb amplitude decrease, 46%). During continuous infusion, MLAEPs remained slightly, although significantly, altered (Pa latency, +1.3 ms; Pa-Nb amplitude, 27%). The Nb wave seemed to be modified earlier and to return to normality later than the Pa wave. These findings incite a careful interpretation of MLAEP tracings acquired during the first hour following MDZ bolus injection. If possible, MDZ should be administered as continuous infusion for reliable interpretation of evoked potential changes in intensive care unit, or during surgery.

Adult↗

PubMed1997

Effects of altitude hypoxia on middle latency auditory evoked potentials in humans.

BACKGROUND: This paper presents an investigation of auditory evoked responses in humans subjected to high altitude hypoxic conditions. METHODS: Middle latency (MLAEPs) as well as short latency (BAEPs) evoked potentials were recorded in 10 healthy subjects, first at sea level (N), then 24 h (H1) and 72 h (H3) after their arrival at an altitude of 4350 m. At the same time, arterial blood parameters (PaO2, PaCO2 and pH) were measured and the clinical status of the subjects was assessed. RESULTS: In altitude conditions, the amplitude of BAEP peak V decreased (-17%). The MLAEP waves showed variations in the shape of their latest waveforms. Their amplitudes, however, were not affected. The Pa-Nb interpeak latency significantly decreased (-2.2 ms) between N and H1, and remained stable during the stay at high altitude. CONCLUSION: A correlation was found between the relative decrease of PaCO2 and the shortening of Nb wave latency, suggesting that the variations in MLAEPs could be preferentially related to the ventilatory response of the subjects in hypoxic conditions. However, no correlation was found between the clinical status of the subjects (Acute Mountain Sickness score) and the parameters of the waves.

Adaptation, Physiological↗

PubMed1995

Wavelet analysis of high-resolution ECGs in post-infarction patients: role of the basic wavelet and of the analyzed lead.

Wavelet analysis provides a fruitful alternative to standard techniques for the detection of fractionated potentials in signal averaged high-resolution (SA-HR) ECGs. In this study, an attempt is made to optimize the discrimination of post infarction patients prone to ventricular tachycardia (VT), using wavelet analysis. Optimization is based on the choice of the ECG leads or lead combinations to be analyzed, and on the analyzing wavelet to be computed. A set of 40 post-infarction patients (20 patients with VT and 20 patients without any arrhythmia) is analyzed. Individual leads and lead combinations of the SA-HR ECGs are processed using a multiparametric algorithm, based on coherent detection of aligned local maxima of the wavelet transform. Seven basic wavelets are tested: the Morlet's wavelet, and the six first derivatives of a Gaussian function. The first derivative of a Gaussian function provides poor results, and is discarded. All other wavelets prove to perform equivalent classification. A vector magnitude computed from the wavelet transforms of the three SA-HR ECGs achieves better results than individual leads. An optimized risk stratification algorithm leads to 90% sensitivity and 100% specificity in the 40 patients learning set.

Adult↗

PubMed1995

[Value of coronary angiography in the diagnosis of coronary artery disease of the transplanted heart. Coronary angiography and arteriosclerosis of the graft].

The diagnostic value of coronary angiography, a widespread method of detection of transplant coronary artery disease, was studied in 17 cardiac transplant patients with reference to histological examination. In the 6 coronary segments studied, the only significant but weak correlation that was found was for the distal left anterior descending artery: the correlations were not statistically significant in the other 5 segments. Coronary angiography underestimated lesions and false negative results were frequently reported (66 and 27% respectively). The limitations of coronary angiography may be explained by the technical artefacts related to both methods of evaluation and the anatomically diffuse and distal nature of transplant coronary artery atherosclerosis. A more reliable diagnostic method would seem to be required in view of the clinical importance of this pathology.

Coronary Angiography↗

PubMed1993

Wavelet analysis of high-resolution signal-averaged ECGs in postinfarction patients.

The authors present an original method for the discrimination of patients prone to ventricular tachycardia. The wavelet transform, which is a new time-scale technique suitable for transient signal detection, was applied to bipolar unfiltered X, Y, Z signal-averaged electrocardiograms in 20 postinfarction patients with sustained ventricular tachycardia, in 20 myocardial infarction patients without ventricular tachycardia, and in 10 healthy subjects. An improved automated algorithm for the detection and localization of sharp variations of the signal, based on coherent detection of the local maxima of the wavelet transform, was developed. A risk stratification method, based on the detection of at least one singularity at or after a point defined with reference to the QRS onset, was assessed. The optimum cutoff point, found 98 ms after the onset of QRS, provides a specificity of 90% and a sensitivity of 85%. The authors conclude that wavelet analysis makes it possible, in this group of patients, to discriminate those with ventricular tachycardia. It yields better results than those obtained from the conventional time-domain approach.

Algorithms↗

PubMed1993

A new method to assess the difficulty of a medical diagnosis: application to electrocardiographic interpretation.

A new method to assess the relative difficulty of a medical diagnosis and the efficacy of a diagnostic procedure is described. The cases within a population are classified by N independent interpreters, i.e., medical experts or computer programs. The percentages of correctly diagnosed cases by N (unanimity), N-1, N-2, ..., zero interpreters, respectively, are calculated. These N + 1 percentages are presented in a histogram. A cumulative plot is derived from the "unanimity" value. The ratio "unanimity value"/"zero value" is proposed as an index of diagnostic performance. An application to the CSE database is presented which is composed of 1,220 electrocardiographic tracings interpreted by 13 cardiologists and 15 computer programs. The cumulative plots, the performance index and Log (index) values, established for eight different diagnostic statements, clearly show the relative degree of diagnostic difficulty for each of them and the particular efficacy of each approach, i.e., electrocardiography versus vectorcardiography, and computerized versus human interpretation.

Diagnosis↗

PubMed1990

Methodology of ECG interpretation in the Lyon program.

To provide an in-depth interpretation of the spatial QRS-T contour, we established a set of vectorcardiographic parameters computed octant by octant. For each statement the criteria constitute a model which is closely related to pathophysiological patterns. The diagnostic strategy is of the heuristic type. For each diagnosis a table lists several criteria providing both specific and differential diagnostic information. Inter-table competition is handled by specific logic. The program classifies diagnoses according to the number of non-satisfied criteria. Three versions are available including 124, 51 and 7 diagnoses, respectively. The first, intended for interpretation of complex situations, has given satisfactory results in such situations. Rhythm analysis is performed from 8-second recordings. All functions--acquisition, quality control, choice of a dominant complex, wave recognition, parameter extraction, interpretation, editing, storage--are integrated into a mobile cart. A complementary program performs serial analysis of successive tracings. It highlights with great precision morphological changes in the spatial loops and interval variations.

Diagnosis, Computer-Assisted↗

PubMed1990

Value of scatter-graphs for the assessment of ECG computer measurement results.

A new method is presented, different from usual methods, for the discussion of the results of computer ECG measurement programs, based on a new graphical evaluation method. The proposed "scatter-graphs" both highlight the main program results and facilitate the comparison between various wave-recognition algorithms. They allow the distinction between the reliability of an algorithm, which is its capacity to provide a maximum of measurements with a minimum amount of errors, and its precision, i.e., the standard deviation of the differences between its point estimates and the reference. The method proves to be a powerful tool for the discussion of individual, as well as the median program results in CSE Measurement Study. It allows to highlight limitations induced in performance assessment by the variability of the reference itself, and to state that the median program is at least as close to the "Gold Standard" as the median of the referees.

Algorithms↗

PubMed1990

[Early vectorcardiographic diagnosis of rejection in long-term follow-up of heart transplantation].

A series of 194 transplant subjects was followed-up by over 2,600 vectorcardiograms. Several cases of rejection were chosen among the most patent and best documented cases (eight cases of acute rejection and seven cases of chronic rejection) and 15 control cases where all tests, including the vectorcardiogram, had always remained negative. Two criteria of rejection were used, i.e. the amplitude of the left maximum QRS vector less than 1.10 mV and relative right spatial area greater than 35 per cent. By accumulating all traces for each patient, recorded during and outside the rejection phase, it was found that the mean of the individual means was 0.96 mV for the left amplitude in cases of rejection versus 1.74 mV in the control group, and 44 versus 22 per cent for the right area. The first trace which, on the curves showing the progress of each patient, was likely to signal acute or chronic rejection always had a left amplitude less than 1 mV (mean 0.89 mV) and a right area greater than 33 per cent (mean 45%). The first suspicious trace always preceded the detection of signs by echography or biopsy (except in one case where it occurred at the same time). The interval varied from 16 to 112 days in five cases of rejection assessed as acute, and from 63 to 600 days in seven cases of chronic rejection. There was no echographic control in two other cases, but death occurred 45 and 63 days after the first vectorcardiographic signs. The vectorcardiogram improves after recovery from acute rejection.(ABSTRACT TRUNCATED AT 250 WORDS)

Follow-Up Studies↗

PubMed1989

Planarity of the spatial QRS loop. Comparative analysis in normals, infarcts, ventricular hypertrophies, and intraventricular conduction defects.

An almost perfect planarity of the spatial QRS loop is known as a characteristic of normal hearts. The Lyon VCG program routinely computes an original planarity index based on the relative magnitude of a so-called geometrical area vector (GAV%). It provides an indirect assessment of any kind of loop distortion (distorted segments lying outside the preferential plane, concavities, figures of eight, narrow configuration). Mean intraindividual variations of GAV%, studied in three different conditions, showed its relatively good stability. Eleven groups totaling 1,435 subjects were investigated. The highest GAV% values (mean, 88%) and the smallest scatter (sigma = 7) were found in normal tracings. GAV% was lower in right (mean, 82%) and left (76-82%) ventricular hypertrophies, in inferior (82%) and anterior (61%) myocardial infarctions, and in right (55%) and left (49%) bundle branch blocks. The diagnostic value of this index was tested for the normal-abnormal discrimination. Using a threshold of 80%, specificity was 89.6%, sensitivity was 78.6% for anterior myocardial infarction, right BBB was 86.6%, left BBB was 91.0% and other groups had unsatisfactory sensitivity. Poor correlations were observed with six other structural parameters, demonstrating that GAV% is relatively independent and may provide new diagnostic information.

Adolescent↗

PubMedDate not supplied

Pharmacokinetics of midazolam and its main metabolite 1-hydroxymidazolam in intensive care patients.

The pharmacokinetics of midazolam and of its main metabolite, 1-hydroxymidazolam, were investigated in intensive care patients after intravenous bolus of 0.2 mg/kg followed by a 0.1 mg/kg/h intravenous infusion of midazolam over 2 hours. A wide interpatient variability of the main pharmacokinetic parameters of midazolam was found. The mean values of elimination half life and volume of distribution, 4.5 +/- 5.4 h and 1.7 +/- 0.7 l/kg respectively, were higher than those reported in healthy subjects. Total plasma clearance was significantly increased in patients taking drugs that induce hepatic metabolism. Significant concentrations of the unconjugated form of 1-hydroxymidazolam were recovered in plasma. The volume of distribution and the elimination half life of the metabolite were higher than those of the parent drug. These results show that 1-hydroxymidazolam might contribute to the pharmacodynamic effect of midazolam and consequently must be taken into account during pharmacokinetic and pharmacodynamic studies.

Adolescent↗

PubMedDate not supplied

An improved method to evaluate the precision of computer ECG measurement programs.

We present a new graphical evaluation method aimed at displaying the main characteristics of computer ECG measurement program results. The proposed graphs provide information on the number of rejected measurements and gross program errors, and on the precision of the results, i.e. the scatter of the differences between fiducial point estimates given by the programs and the reference. 'Scatter-graphs' concerning P, QRS and T wave boundary recognition from the programs participating in the European Concerted Action on 'Common Standards for Quantitative Electrocardiography (C.S.E.)' are analysed and discussed (10 standard 12-lead ECG programs and 9 Vectorcardiographic (VCG) programs from 10 European, 5 American and 1 Japanese Centers). The method proved to be a powerful tool for a direct and global qualitative comparison of the efficiency of the algorithms elaborated by the program developers, and allowed some of the strategies adopted in these programs to be highlighted.

Algorithms↗

PubMedDate not supplied

Mismatch negativity and N100 in comatose patients.

Mismatch negativity (MMN) and N100 auditory evoked potential were recorded in 52 healthy subjects and in 128 severely comatose patients. The MMN was present in 33/128 patients and N100 in 84/128. A ratio of 30/33 patients with MMN and 70/84 with N100 regained consciousness in a mean time of 6.3 +/- 4 days after the recording session. Thus, in terms of predicting return to consciousness, the MMN was more specific (90.9%) than the N100 (57.6%), but its sensitivity was lower (31.6% for MMN and 73.7% for N100, respectively). The amplitudes of MMN and N100 in comatose patients were smaller than those of healthy subjects. It is concluded that MMN and N100 can be very useful in predicting whether or not a comatose patient will regain consciousness.

Adolescent↗

PubMedDate not supplied

Mismatch negativity and N100 monitoring: potential clinical value and methodological advances.

Continuous long-term recording of brainstem (BAEPs), middle-latency (MLAEPs) and long-latency auditory evoked potentials, including the mismatch negativity (MMN), brings additional information on the immediate functional state and the outcome of patients in coma or recovering after surgery, in relation with clinical observations and therapeutics. A recently designed monitoring system is introduced, aimed at the continuous recording of late auditory potentials (N100 and MMN) as well as BAEPs and MLAEPs. Specific methodological aspects are emphasized. Long-term monitoring data from one patient recorded in the recovery room after surgery are displayed, allowing an illustration of the techniques used and of the problems raised.

Adult↗