PubMed Health⌕ Search

Biomedical subjects

Y E Langlois

Publications and source records attributed to Y E Langlois.

At least 19 recordsLinked to original sources
PubMed1994

Limitations of ultrasonic duplex scanning for diagnosing lower limb arterial stenoses in the presence of adjacent segment disease.

PURPOSE: The purpose of this study was to provide a quantitative evaluation of the effect of adjacent segment lesions on disease classification in lower limb arteries by ultrasonic duplex scanning. METHODS: Lower limb arterial duplex scanning from the distal aorta to the popliteal artery was performed in 55 patients. Arterial lesions evaluated by visual interpretation of Doppler spectra were compared blindly with those measured by angiography. RESULTS: To recognize severe stenoses (50% to 100% diameter reduction) in any arterial segment, duplex scanning had sensitivity and specificity rates of 74% and 96%, respectively. However, sensitivity and specificity rates increased to 80% and 98%, respectively, when there was no 50% to 100% diameter-reducing lesion in adjacent segments, whereas they decreased to 66% and 94%, respectively, when there was at least one 50% to 100% diameter-reducing lesion in adjacent segments. Moreover, among the 48 duplex misclassifications underestimating or overestimating the degree of arterial stenoses, 30 (62.5%) involved a segment with at least one 50% to 100% lesion in adjacent segments. The segments mostly affected by proximal and distal arterial lesions were the popliteal arteries and the common and deep femoral arteries, where it was found that 86% (24/28) of the misclassifications involved the presence of either proximal or distal severe stenoses. CONCLUSION: The results demonstrated that the presence of multiple stenoses was an important limitation of duplex scanning for the detection and quantification of lower limb arterial disease.

Aorta, Abdominal↗
PubMed1993

Cardiac Doppler blood-flow signal analysis. Part 1. Evaluation of the normality and stationarity of the temporal signal.

The normality (Gaussian property) and stationarity of the cardiac Doppler blood-flow signal were evaluated on short-time segments distributed over the cardiac cycle. The basic approaches used to perform statistical tests on the nonstationary and quasiperiodic cardiac Doppler signal are presented. The results obtained from the data of ten patients having a normal aortic valve and ten patients having a stenotic valve indicate that a complex Gaussian random process is an acceptable approximation for the clinical cardiac Doppler signal. For segments of 10 ms or less, 82 per cent of them were accepted to be stationary with a significance level of 0.05, whereas for durations greater than 40 ms, the percentage of stationary segments was less than 75 per cent. It was concluded that the 10 ms window generally used in practice is a good choice for Doppler spectrogram estimation, but a shorter time interval would be preferable.

Aortic Valve↗
PubMed1993

Cardiac Doppler blood-flow signal analysis. Part 2. Time/frequency representation based on autoregressive modelling.

Doppler spectrograms obtained by using autoregressive (AR) modelling based on the Yule-Walker equations were investigated. A complex AR model using the in-phase and the quadrature components of the Doppler signal was used to provide blood-flow directions. The effect of model orders on the spectrogram estimation was studied using cardiac Doppler blood flow signals taken from 20 patients. The 'final prediction error' (FPE) and the 'Akaike's information criterion' (AIC) provided almost identical results in model-order selection. An index, the spectral envelope area (SEA), was used to evaluate the effect of window duration and sampling frequency on AR Doppler spectrogram estimation. The statistical analysis revealed that the SEA obtained from AR modelling was not sensitive to window duration and sampling frequency. This result verified the consistency of the AR Doppler spectrogram. The white-noise characteristics of the AR modelling error signal indicated that the Doppler blood-flow signal can be adequately modelled as a complex AR process. With appropriate model orders, AR modelling provided better Doppler spectrogram estimates than the periodogram.

Aortic Valve↗
PubMed1992

Effect of ensemble averaging on amplitude and feature variabilities of Doppler spectrograms recorded in the lower limb arteries.

The objective of the present study was to analyse the effect of averaging Doppler blood flow signals in lower limb arteries on amplitude and feature variabilities. Doppler signals recorded in 41 iliac and 35 superficial femoral arteries having different categories of stenosis were averaged over 1-15 cardiac cycles. Based on the relative decreasing rate of an index of variability, results indicated that amplitude variability of the spectrograms was exponentially reduced to 30, 6 and 1 per cent when averaging five, ten and 15 cardiac cycles, respectively. Nine diagnostic features were extracted from Doppler spectrograms and their variations from one cardiac cycle to the next quantified. Based on the relative decreasing rate of these variations, results indicated that feature variability was exponentially reduced to 30, 4 and 1 per cent when averaging five, ten and 15 cardiac cycles, respectively. The effect of averaging on the discriminant power of the features to separate the different categories of stenosis was also investigated by performing t-test analyses. Results showed that averaging between five and ten cardiac cycles provided the better discriminant power for most cases, whereas averaging over more than ten cardiac cycles was of little benefit. Based on the spectral analysis technique used in the present study, we conclude that averaging over ten cardiac cycles is sufficient for the analysis of Doppler spectrograms recorded in the lower limbs.

Blood Flow Velocity↗
PubMed1992

Optimal time-window duration for computing time/frequency representations of normal phonocardiograms in dogs.

The optimal duration of the time-window used to compute the time-frequency representation (spectrogram) of the phonocardiogram was studied in four dogs by using intracardiac and thoracic measurements of the PCG. The power and cross-spectrograms of the intracardiac and thoracic PCGs were computed using a fast Fourier transform algorithm and a sine-cosine window with 10 per cent decaying functions. A coherence spectrogram was also computed for each dog to study the linear relationship between the two signals and determine the optimal time-window duration. Results show that the optimal range of the time-window duration is between 16 and 32 ms. A time-window shorter than 16 ms spreads out low-frequency components into the higher frequencies and generates a spectrographic representation with poor frequency resolution (> or = 62.5 Hz). A window larger than 32 ms increases the frequency resolution but smears the spectrographic representation of the signal in the time domain and thus cannot correctly reflect the time-varying properties of the signal. In both cases, the amplitude of the coherence function computed between the left ventricular and the thoracic phonocardiograms is overestimated.

Animals↗
PubMed1991

Interaction between the aortic valve leaflets and a Millar dual-micromanometer catheter during recording of the aortic component of the second heart sound in dogs.

The influence of the closure of the aortic valve leaflets on a dual-micromanometer Millar catheter is investigated with respect to the power spectrum of the aortic component (A2) of the second heart sound in dogs. The catheter inserted through the aortic valve is used to simultaneously record A2 in the left ventricle and in the aorta and to study the transmission of A2 up to the body surface. Results indicate that the interaction of the valve leaflets with the Millar dual-micromanometer catheter during the closure and vibration of the aortic valve does not produce a clapping artefact. The main effect is a change in the natural modes of vibration (resonant frequencies) of the aortic valve resulting from a modification of the vibrating structure (combined structure composed of the catheter, the aortic valve and the surrounding blood and tissues) because of the tight mechanical coupling between the aortic valve leaflets and the catheter. In addition, this modification of the natural modes of resonance does not invalidate the estimation of the frequency response of the transfer function between the aortic root and the thoracic recording site, even if the mean gain of the transfer function is affected and the phase slightly increased with frequency. On the contrary, the interaction of the aortic valve leaflets with the catheter seems to slightly increase the spectral contribution (coherence) of the intra-aortic A2 to the thoracic A2.

Animals↗
PubMed1991

Acoustic transmission of the aortic component of the second heart sound within the ascending aorta of dogs.

The spectral characteristics of the acoustic transmission of the aortic component of the second heart sound within the ascending aorta was studied using a Millar dual-micromanometer catheter. The tip micromanometer was located close to the aortic valve leaflets while the second micromanometer was located 3 cm above the aortic valve. The frequency response of the transmission properties (amplitude and phase) of the blood and the aortic wall was modelled by an equivalent acoustic transmission system. The signal recorded by the tip micromanometer located near the aortic valve was considered to be the input signal of the equivalent system and the signal recorded by the second micromanometer was used as the output signal. Results of the spectral analysis of the input and output signals show that the acoustic transmissibility of blood in the ascending aorta is high at 20 Hz (the attenuation is negligible). Between 20 and 60 Hz, the transmissibility decreases at a rate of -3 dB per octave while between 60 and 120 Hz it decreases at a rate of -14 dB per octave. Above 120 Hz the transmissibility is low and the resulting attenuation is greater than 20 dB. The phase of the transfer function is shifted by -60 degrees at 20 Hz and decreases at a mean rate of -2.0 degrees Hz-1 between 20 and 100 Hz and -0.75 degrees Hz-1 up to 400 Hz. The phase velocity of the sound transmission is relatively constant (5.5 ms-1) between 40 and 100 Hz and increases up to 9 ms-1 at 300 Hz.

Animals↗
PubMed1991

Computer analysis and pattern recognition of Doppler blood flow spectra for disease classification in the lower limb arteries.

In the present study, a computer processing method was developed to objectively classify disease in the lower limb arteries evaluated by noninvasive ultrasonic duplex scanning. This method analyzes Doppler blood flow signals, extracts diagnostic features from Doppler spectrograms and classifies the severity of the disease into three categories of diameter reduction (0-19%, 20-49% and 50-99%). The features investigated were based on frequency features obtained at peak systole, spectral broadening indices and normalized amplitudes of the power spectrogram computed in various positive and negative frequency bands. A total of 379 arterial segments studied from the aorta to the popliteal artery were classified using a pattern recognition method based on the Bayes model. Two classification schemes using a two-node decision rule were tested. Both schemes gave similar results, the first one provided an overall accuracy of 83% (Kappa = 0.42) and the second an overall accuracy of 81% (Kappa = 0.35) when compared with conventional biplane contrast arteriography. These performances, especially for the 0 to 19% lesion category, are better than the one obtained by the technologist (accuracy = 76% and Kappa = 0.33), based on visual interpretation of the Doppler spectrograms. To recognize hemodynamically significant stenoses (50-99% lesions), the pattern recognition system has a sensitivity and a specificity of 50% and 99%, respectively, using classification scheme I. With classification scheme II, the sensitivity and the specificity are 50% and 98%, respectively. Visual interpretation of the Doppler spectrograms leads to a sensitivity and a specificity of 50% and 98%, respectively. These results are the first to be obtained by a pattern recognition system in classifying lower limb arterial stenoses.

Adult↗
PubMed1991

Change in amplitude distributions of Doppler spectrograms recorded below the aortic valve in patients with a valvular aortic stenosis.

Amplitude distributions of Doppler spectrograms were characterized in a group of 22 patients having no aortic pressure gradient and another group of 26 patients having a stenotic aortic valve. Specifically, for each patient, the ratios of the mean amplitude in three normalized frequency bands (low, middle and high) to the mean amplitude of the Doppler spectrogram computed in selected portions of the systolic period were considered. Pulsed-wave Doppler spectrograms were recorded by positioning the sample volume in the left ventricular outflow tract, approximately 1 cm below the aortic valve. Statistically significant differences were found between the middle (p = 0.041) and high (p = 0.028) frequency bands of Doppler signals recorded from the two groups of patients. The differences observed are believed to be attributed to blood flow eddies generated below the stenotic aortic heart valve and to changes in blood flow orientation.

Adult↗
PubMed1990

Spectral analysis and acoustic transmission of mitral and aortic valve closure sounds in dogs. Part 3. Effects of altering heart rate and P-R interval.

A surgical protocol was designed to implant, in seven dogs, a programmable sequential atrioventricular pacemaker after destruction of the bundle of His to produce a chronic heart block. The heart rate and P-R interval were then varied independently and their influence on the spectra and acoustic transmission of the mitral M1 and aortic A2 valve closure sounds was studied. Results indicate that the major effects of varying the P-R interval are a strong change in the intensity of M1 and modifications of its acoustic transmission across the heart/thorax acoustic system. No similar influence is observed on the intensity and acoustic transmission of A2. Varying the heart rate has a small effect of the intensity of M1 but none on the intensity of A2. In addition, changes in either the P-R interval or the heart rate do not seem to modify the spectral profile of the intracardiac and thoracic M1 and A2 components.

Animals↗
PubMed1990

Spectral analysis and acoustic transmission of mitral and aortic valve closure sounds in dogs. Part 4: Effect of modulating cardiac inotropy.

A surgical protocol was designed to implant in dogs a programmable atrioventricular pacemaker and to destroy the bundle of His with one to four 0.1 ml formaldehyde injections. The heart rate and P-R interval were paced at 100 beats min-1 and 75 ms, respectively. Cardiac inotropy was then varied in five animals by using injections or infusions of cardiotonic drugs (Dobutamine, Betalol and Quinidine). Their effect on the spectra and acoustic transmission of the mitral M1 and aortic A2 closure sound components produced within the left heart and transmitted up to the body surface was studied. Results indicate that changes in cardiac inotropy strongly modify the intensity of M1 and A2 but do not markedly affect their spectral distribution. They also affect the transfer function of the heart/thorax acoustic system, but this influence is small compared with that of a 12 min reference interval. In addition, it was shown that the intensity of M1 is more sensitive to the cardiotonic agents than the intensity of A2.

Animals↗
PubMed1990

Spectral analysis and acoustic transmission of mitral and aortic valve closure sounds in dogs. Part 1. Modelling the heart/thorax acoustic system.

A system model based on the simultaneous recording and analysis of the intracardiac and thoracic phonocardiograms to estimate the time-varying properties of the heart/thorax acoustic system of the dog is described. The presence of instrumental noise in the recording of intracardiac phonocardiograms is characterised, and it is demonstrated that its effect on the estimate of the transfer and coherence functions of the system can be quantified and corrected. Application of the model to study the spectral characteristics and the acoustic transmission properties of the mitral component M1 of the first heart sound and of the aortic component A2 of the second heart sound in the dog shows that the heart/thorax acoustic system acts like a bandpass filter having a higher attenuation for A2 than for M1. Between 20 and 100 Hz, the mean attenuation of M1 is 30 dB while that of A2 is 46 dB. Above 100 Hz, the attenuation slope is -12 dB per octave for M1 and -6 dB per octave for A2.

Animals↗
PubMed1990

Spectral analysis and acoustic transmission of mitral and aortic valve closure sounds in dogs. Part 2. Effects of neuromuscular blockade, sternotomy and pacemaker control, and a two-week recovery period.

The paper describes the effects of neuromuscular blockade, sternotomy and atrio-ventricular pacing, and a two-week recovery period on the spectra and acoustic transmission of mitral M1 and aortic A2 sound components in dogs. Results indicate that neuromuscular blockade does not affect the attenuation properties of the heart/thorax acoustic system even if it modifies the intensity of M1 and the phase of the transfer function. The immediate effect of sternotomy and cardiac pacing is an important increase in the attenuation of the heart/thorax acoustic system. This increased attenuation is different for both sounds (20 dB for M1 and 11 dB for A2) and disappears after a two-week recovery period. However, the resulting controlled dog model shows slightly different acoustic characteristics than those of the normal animal model.

Animals↗
PubMed1990

Computer evaluation of Doppler spectral envelope area in patients having a valvular aortic stenosis.

The reliability of three algorithms to estimate the maximal and minimal frequency contours of Doppler spectrograms was evaluated in a group of 48 patients. Two algorithms had previously been used in the literature. These are the Modified Threshold Crossing Method and the Hybrid method. The third algorithm is new and is the Maximal Background Noise Threshold Crossing Method. A new approach was also proposed in the present study to estimate the background noise level of Doppler spectrograms. This level was used as a threshold in the computation of the spectral envelopes. Two diagnostic spectral parameters (the spectral envelope area and the systolic velocity integral) extracted from Doppler spectrograms recorded in the left ventricular outflow tract were also evaluated and tested to discriminate between 23 patients having no aortic pressure gradient and 25 patients with a stenotic aortic valve. Results describe the influence of the threshold level used in the Modified Threshold Crossing Method and the Hybrid method on the variability of the spectral contours. It is clearly demonstrated that the variability of minimal frequency contours is higher than that of maximal frequency contours. All three algorithms provided similar diagnostic performances with the spectral envelope area (71% to 73% of correct classifications) while the Maximal Background Noise Threshold Crossing Method and the Hybrid method provided the best results for the systolic velocity integral (69% of correct classifications). Because the systolic velocity integral combined with the continuity equation is used in the literature to evaluate noninvasively the aortic valve area, these results suggest the use of the spectral envelope area instead of the systolic velocity integral.

Aged↗
PubMed1984

Natural history of carotid artery disease on the side contralateral to endarterectomy.

The natural history of the nonoperated carotid artery opposite an endarterectomy was examined in 134 patients by means of ultrasonic duplex scanning over a period extending to 48 months. None of the nine deaths that occurred during follow-up was stroke related. A total of 22 arteries showed progression of disease over this period. By life-table analysis the mean annual rate of progression for all categories of disease was 12.6% and 7.4% for progression to a diameter reduction greater than 50%. Disease progression was more rapid in patients under 65 years of age. Symptoms occurred in 13 patients for an overall incidence of 10% and a mean annual rate estimated at 5%. All symptoms indicated transient ischemic attacks; there were no strokes. There was a strong relationship between the development of symptoms and stenoses greater than 80% either at the initial examination or secondary to progression. No correlation was found between the presence of bruits or their change over time and the progression or appearance of symptoms. Conservative management of nonoperated vessels opposite an endarterectomy appears appropriate until symptoms develop or a lesion greater than 80% is detected.

Adult↗
PubMed1983

Is siphon disease important in predicting outcome of carotid endarterectomy?

The prevalence of atherosclerosis at the carotid bifurcation and in the siphon was reviewed in 141 patients who underwent 149 endarterectomies. The relationship between the presence and severity of siphon lesions and focal neurologic symptoms, both before and after operation, was also examined. Siphon disease was found in 84% of the 282 sides. Most lesions (42%) were in the 20% to 49% diameter-reduction category. Only 9% were stenoses greater than 50%, and 10% were occlusions. The majority (65%) were smooth. No relationship was found between the severity of disease at the carotid bifurcation and in the siphon. No pattern of siphon disease could be related to the occurrence of symptoms. Furthermore, no relation was found between the severity of siphon disease and recurrent symptoms after endarterectomy.

Carotid Arteries↗
PubMedDate not supplied

Computer based pattern recognition of carotid artery Doppler signals for disease classification: prospective validation.

A computer based pattern recognition method has been developed to classify the percent diameter reduction in nonoccluded internal carotid arteries. Using a combined B-mode/pulsed Doppler unit, the system utilizes spectral waveforms obtained from the low common and proximal internal carotid artery locations. The ECG-R wave is used as a time reference to synchronize the averaging of Doppler spectra from 20 heart cycles. An averaged waveform is generated and represents the spectral data from which features are extracted for analysis. A stepwise selection algorithm identifies a feature subset for partitioning the entire range of disease into two states, less than and greater than a decision point. Three such partitions are made, leading to the following categories: Normal, 1-20, 21-50 and 51-99% dia. reduction. A classifier was trained, tested prospectively against unknown data and the results compared to angiography. Of the 170 vessels tested, 141 (82%) were classified in the same category by angiography and the computer system. Agreement for each category was 93% (27/29) for the normals, 81.5% (44/54) for the 1-20% lesions, 78% (29/37) for the 21-50% lesions and 82% (41/50) for the 51-99% lesions. The computer method and angiography differed by more than one category in only one of the 170 tests. The level of agreement corrected for chance (Kappa +/- SE(K] was 0.769 +/- 0.039. Future efforts will be directed toward dividing classification of disease further (especially in the 51-99% category), developing a dedicated microprocessor for on-line analysis of the signals and using the system for prospective epidemiological studies of various populations.

Adult↗