PubMed Health⌕ Search

Biomedical subjects

A Juillard

Publications and source records attributed to A Juillard.

At least 19 recordsLinked to original sources
PubMed2000

Dynamical properties near the metal-insulator transition: evidence for electron-assisted variable range hopping

We report independent measurements (between 20 and 200 mK) of the electronic specific heat C(e), the electron-phonon coupling G(e-ph), and the electron-phonon relaxation time tau(e-ph) (from 10(-2) to 10(-5) s) for NbxSi1-x Anderson insulator thin films. We show that the usual equation tau(e-ph) = C(e)/G(e-ph) holds only if the resistance is solely related to the electron temperature. We conclude that at sufficiently low temperatures variable range hopping transport is assisted by electron-electron interactions alone and is independent of the phonon distribution.

Journal Article↗
PubMed1984

[Significance of repetitive ventricular extrasystoles in the acute phase of myocardial infarction].

Ventricular extrasystoles were analysed by a computerised monitor in 144 patients during the first three days of myocardial infarction. The patients had been hospitalised within 6 hours (77% of cases) and within 12 hours (92% of cases) of onset of symptoms. The patients were divided into 4 groups: Group A (46 cases) without repetitive ventricular extrasystoles; Group B (37 cases) with repetitive ventricular extrasystoles but without frequent isolated extrasystoles; Group C (25 patients) with repetitive ventricular extrasystoles and frequent isolated extrasystoles but without polymorphism or R on T phenomenon; and Group D (36 patients) with repetitive extrasystoles, frequent isolated polymorphic extrasystoles and/or R on T phenomenon. The size of infarction, as judged by peak CPK values, was smaller in Group A than in the other groups but was not significantly different in Groups B, C and D. The incidence of cardiac failure was comparable in Groups A and B and in Groups C and D, and was higher in the latter two groups than in A and B. The cardiothoracic ratio on admission was increased more often in Group D than in the other groups. Therefore, repetitive ventricular extrasystoles are the result of large infarcts. Their association with frequent isolated ventricular extrasystoles is a sign of insufficiency of the remaining myocardium. Patients with pre-existing poor myocardial function develop polymorphism and R on T phenomenon, signs which are associated with a particularly poor prognosis (hospital mortality: 42%). On the other hand, patients in Group B appeared to have satisfactory myocardial function despite the size of their infarcts, and the mortality, nil in this group, was less than in patients without arrhythmias.

Adult↗
PubMed1984

[Coexistence of left branch block and ectopic rhythm simulating alternating block].

During the acute phase of diaphragmatic myocardial infarction with septal extension, the ECG of a patient with a chronic left bundle branch block changed in a period of seconds from complete left bundle branch block to incomplete right bundle branch block then to narrow QRS complexes followed by incomplete and then complete left bundle branch block: the same QRS changes then occurred in reverse order; the atrial rhythm was absolutely stable during the recording. These appearances are explained by fusion of sinus and of an ectopic rhythm arising distal to the zone of block, the rate of which (sometimes faster and sometimes slower than the sinus rhythm) could have been influenced by an electrotonic effect after retrograde activation of the right bundle and concealed conduction in the left bundle. Appearances of bundle branch block may be recorded when the ventricle is partially activated from the point of breakthrough of the blocked branch.

Aged↗
PubMed1984

[Myocardial infarction in the young subject: a medium-term clinical and coronary angiographic study in 40 patients under 36 years of age. Comparison with coronary angiographic data of myocardial infarction in patients after 50 years of age].

A series of 40 myocardial infarctions, occurring in patients under 36 years of age was studied retrospectively (Group I: mean age 31.3 years). The medium term results of coronary angiography in this group were compared with those of 60 myocardial infarctions after 50 years of age (Group II: mean age 56.6 years). Group I had a clear male predominance (92.5%), a high incidence of smoking (69%), hypercholesterolaemia (69%); myocardial infarction was the first manifestation of their disease in 54% and it was often extensive (42%). A comparative angiographic study between the two groups showed: 1) Less widespread lesions in Group I, as assessed by the number of main arteries stenosed (p less than 0.001), the coronary index (p less than 0.01) and the mean coronary score using Friesinger's method (p less than 0.01). 2) A higher incidence of subnormal coronary angiogrammes in Group I (absence of 50% stenosis) (15%) and of single vessel disease (40%): compared with Group II in which multivessel disease was observed in 86.5% of cases. 3) Collateral circulation was less common in Group I (p less than 0.01). On the other hand, a comparative study of regional and global left ventricular function showed no difference between the two groups. Two subgroups were distinguished in Group I: in one subgroup, multiple lesions similar to those found in Group II, suggestive of premature coronary atherosclerosis (52.5%); the other group (47.5%) presented unilocular lesions i.e. focal mono-arterial lesions compatible with other causes of infarction (thrombosis and/or spasm). These patients were younger (p less than 0.05) and had significantly fewer cardiovascular risk factors (p less than 0.01). Despite the fact that the coronary lesions were limited, the myocardial damage was comparable with the other groups as the collateral circulation was much less developed (p less than 0.02). These appearances were only observed in 3.5% of patients in Group II. The study of the angiographic outcomes of these two types of lesions should show a difference and could contribute to the understanding of their mechanisms.

Adult↗
PubMed1984

[Sustained ventricular tachycardia 7 years after complete correction of tetralogy of Fallot].

The authors report a case of sustained ventricular tachycardia which occurred seven years after complete surgical correction of Fallot's tetralogy in a 13 year old girl. This arrhythmia was well tolerated haemodynamically, showed right-sided delay and was associated with mitral valve prolapse. After reviewing the literature, several physiopathological mechanisms are discussed: --the role of residual intraventricular conduction defects in sustaining the tachycardia; --the role of the ventriculotomy scar or of other associated lesions (mitral valve prolapse in this case) in the genesis of ventricular extrasystoles; --the postoperative haemodynamic status in the tolerance of the arrhythmias. This is a rare complication with an incidence of less than 2% of survivors followed-up over long periods. There is a risk of sudden death in 38% of these patients with ventricular arrhythmias which justifies Holter monitoring and ECG stress testing for their detection.

Adolescent↗
PubMed1984

[Time of occurrence of primary ventricular tachycardia in the acute phase of myocardial infarction].

The hour of day of primary ventricular tachycardia (VT) in the acute phase of myocardial infarction was studied in 63 consecutive patients without cardiac failure or antiarrhythmic therapy, admitted to hospital less than 6 hours after the onset of chest pain. There were 19 women and 44 men, with an average age of 63 years. The site of infarction was anterior in 23 cases, posterior in 34 cases and circumferential in 6 cases. The cardiac rhythm was analysed from the 6th hour following the onset of chest pain for 4 days, using a HP 98220 A computerised analyser CPK levels were measured daily. Ventricular tachycardia occurred in 73% of cases with no significant difference between daytime (18 patients) and night time (28 patients). The patients developing VT did not differ from the remainder with respect to age, sex, or site of ECG changes, but peak CPK levels were significantly higher than in patients without VT. The risk of VT decreased slowly as the interval from the onset of chest pain increased and fell practically to zero after the 40th hour. Diurnal and nocturnal VT were independent of age, sex or site of infarct. However, nocturnal VT correlated independently of the time of onset of chest pain to high values of CPK. There was no difference with respect to age, sex, location of infarct or incidence of ventricular tachycardia between infarcts with pain starting during the day, and infarcts with pain starting at night. However, when the pain started during the day, the peak CPK was significantly higher and there were significantly more attacks of nocturnal ventricular tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1983

Sinus node electrogram recording in 59 patients. Comparison with simultaneous estimation of sinoatrial conduction using premature atrial stimulation.

Directly measured sinoatrial conduction time was compared with sinoatrial conduction time assessed simultaneously by the single premature atrial stimulus technique in 59 patients: 20 with normal sinus function, 35 with sinus dysfunction, and four with sinus bradycardia but negative indirect methods. In patients with normal sinus function direct sinoatrial conduction time was 102.5 +/- 34 ms (mean +/- 2 SD) and was identical to indirect sinoatrial conduction time. Neither direct sinoatrial conduction time in the basal and return cycle, nor post-return and basal cycle lengths were different. Sinoatrial and atriosinus conduction durations were similar. In sinus dysfunction direct sinoatrial conduction time (average 160 +/- 47 ms) was longer than in normal sinus function. Prolonged direct sinoatrial conduction time may therefore be considered as a criterion of sinus dysfunction. In sinus dysfunction no significant correlation was observed between direct and indirect sinoatrial conduction times. Direct sinoatrial conduction time was equal to (17 patients), longer than (12 patients), or shorter than (six patients) indirect sinoatrial conduction time. These differences can be explained by delayed or incomplete premature depolarisation penetration into the sinus node rather than by the classical pacemaker shift.

Adolescent↗
PubMed1983

[Comparison of various indirect methods for evaluation of sinus function].

Sinus node function was evaluated by Mandel, Strauss and Narula's methods in 60 consecutive patients: 20 females, 40 males; average age 59 +/- 17 years. Three had second degree sinoatrial block, 2 had bradycardia-tachycardia syndromes and 10 had sinus bradycardia. The corrected sinus node recovery time was 414 +/- 417 ms. It exceeded 520 ms in 8 cases, 5 where the two other methods confirmed sinus node dysfunction, 1 where the two other methods showed no abnormality. In the last two patients pathological results with Narula's method coincided with normal values with Strauss' method but the basal sinus cycle and the post return cycle differed from one method to the other. The atriosinoatrial conduction time estimated by Narula's method was 274 +/- 117 ms. In the thirteen cases where it exceeded 300 ms abnormal results were also recorded with Strauss' (11 cases) and/or Mandel's method (7 cases). The atriosinoatrial conduction time assessed by Strauss' method was 239 +/- 106 ms. It exceeded 300 ms in 18 patients. In these patients the results of Narula and Mandel's methods were normal in 7 cases. This discordance cannot be explained either by variations in the catheter position, or by the duration of the basal sinus or the post return cycles. This raises the question of penetration of the sinus node by the last stimulus when Narula's technique is used. A significant linear correlation was observed between the atriosinoatrial conduction time assessed by Narula's method and the atriosinoatrial time assessed by Strauss' method (N = 60; r = 0,59) and with the corrected sinus node recovery time (N = 60; r = 0,43) and a double linear correlation was found with these two parameters (N = 60; r = 0,62). There was no significant linear correlation between the atriosinoatrial conduction time assessed by Strauss' method and the corrected sinus node recovery time (N = 60; r = 0,27). The atriosinoatrial conduction time evaluated by Narula's method seems to be intermediary between the two other parameters which seem to be independent of each other.

Adolescent↗
PubMed1983

[Effects of diltiazem on cardiac and coronary circulation, at rest and during rapid auricular electric stimulation].

The effects on cardiac performance and systemic and coronary blood flow of rapid atrial pacing alone and associated with an intravenous infusion of a slow calcium channel inhibitor, diltiazem, at a dose of 20 mg/kg were studied in 20 patients with chronic coronary artery disease. Atrial pacing increased coronary flow and myocardial oxygen consumption: it decreased coronary arterial resistance and the coronary arteriovenous difference in lactates. Left ventricular end diastolic pressure rose significantly compared to the basal state in the period following pacing. The administration of diltiazem was associated with a significant fall of femoral arterial pressure, of coronary arteriovenous difference and myocardial consumption of oxygen, and an increase in the coronary arteriovenous difference in lactate. Left ventricular end diastolic pressure did not differ significantly from the basal values recorded after terminating atrial pacing. Left ventricular end diastolic volume decreased. Diltiazem opposed or cancelled the undesirable effects of rapid atrial pacing with respect to coronary arteriovenous difference in lactate content. The beneficial action of diltiazem does not seem to be closely related to its hemodynamic effects. It could be related to a reduction in myocardial oxygen demands due to a decrease in systolic ventricular strain and the specific metabolic effects of the drug, and also to an increase in myocardial oxygen supply due to the reduction in left ventricular end diastolic stress and the coronary vasodilation caused by the drug.

Adult↗
PubMed1983

[Lengthening of the direct sinoatrial conduction time: a criterion of sinus node dysfunction].

In order to determine the significance of prolongation of the direct sinoatrial conduction time (DSACT), an attempt was made to record the sinus node potential in 110 patients which was successful in 84 cases. The DSACT was normal in 45 cases (Group A) and prolonged (over 130 ms) in 39 cases (Group B). The symptomatology, standard ECG and the results of investigation of sinus node function by atrial stimulation of the two groups were compared. The DSACT was prolonged in all 13 patients with paroxysmal sinoatrial block or the sick sinus syndrome, in 71% of 15 patients with permanent sinus bradycardia, in 88% of 22 patients with a corrected sinus node recovery time of over 525 ms, in 82% of 38 patients with a sinoatrial conduction time estimated by the extrastimulus method of over 130 ms or an abnormal zone II, in 80% of 39 patients with sinoatrial conduction times estimated by Narula's method of over 130 ms; therefore, 87% of the 35 patients with probable sinus node dysfunction had long DSACT. On the other hand only 2 out of 35 patients (6%) with apparently normal sinus node function had prolonged DSACT. These results indicate that prolongation of the DSACT is a sensitive and specific criterion of sinus node dysfunction. In cases of sinus node dysfunction dizziness and/or syncope without any known cause were common complaints in patients in Group B but absent in patients in Group A. A prolonged DSACT could be of prognostic significance in sinus node dysfunction.

Aged↗
PubMed1982

[Rate-pressure product and myocardial oxygen requirements].

The relationship between the rate-pressure product, myocardial oxygen consumption and the production or uptake of lactate by the myocardium was studied in 45 patients under basal conditions and rapid atrial pacing (except in 3 cases with atrial fibrillation). The underlying pathology was ischemic heart disease in 25 cases, non obstructive cardiomyopathy in 9 cases, and obstructive cardiomyopathy in 11 cases. Contrary to what has been reported in normal subjects, a significant linear relationship between the rate-pressure product or indexed rate-pressure (multiplied by body surface area) and myocardial oxygen uptake. The divergence of these results may be due to the method of measuring coronary sinus blood flow, these authors having used the N 20 whereas in this study the flow was measured by thermodilution. In particular, it is possible that this divergence results from abnormalities of ventricular volume, compliance and contractility in the patients under study: these abnormalities may disturb the relationship between the rate-pressure product and myocardial oxygen consumption in normal subjects. A double linear relationship, different in each of these groups, was observed at rest between the indexed rate-pressure product and oxygen uptake, and the uptake or production of lactate: in myocardial ischemia without ischemia at rest, in non obstructive cardiomyopathy in sinus rhythm. The significance of these relations differed in each of these groups. Under atrial pacing, the increase in indexed rate-pressure product compared to basal conditions was proportional to the presence of absence of ischemia. Variations of the indexed rate-pressure product seem to be related to myocardial oxygen consumption and not to myocardial oxygen requirements. The variations of the rate-pressure product, during the administration of drugs, for example, do not reflect myocardial oxygen needs. During exercise ECG, the maximal increase in the indexed rate-pressure product reflect the functional reserve of the myocardium.

Blood Pressure↗