Study of the Effect of Reflections on High-Power, 110 GHz Pulsed Gyrotron Operation.

The effect of reflection is studied experimentally and theoretically on a high-power 110 GHz gyrotron operating in the TE22,6 mode in 3 µs pulses at 96 kV, 40 A. The experimental setup allows variation of the reflected power from 0 to 33 % over a range of gyrotron operating conditions. The phase of the reflection is varied by translating the reflector along the axis. Operating at a higher efficiency point, at 4:40 T with 940 kW of output power, reflected power exceeding 11% causes a switch from operation in the TE22,6 to simultaneous operation in the TE22,6 and TE21,6 modes with a large decrease of the total gyrotron output power. This switching effect is in good agreement with simulations using the MAGY code. Operating at a more stable point, 4:44 T with 580 kW of output power, when the reflection is increased, the output power remains in the TE22,6 mode but it decreases monotonically with increasing reflection, dropping to 200 kW at 33% reflection. Furthermore, at a reflection above 22%, a power modulation at 25 to 30 MHz is observed, independent of the phase of the reflected wave. Such a modulated signal may be useful in spectroscopic and other applications.

Correction to: Study of the Effect of Reflections on High-Power, 110-GHz Pulsed Gyrotron Operation.

[This corrects the article PMC8291730.].

Nanosecond pulses in a THz gyrotron oscillator operating in a mode-locked self-consistent Q-switch regime.

An experimental study of a nanosecond pulsed regime in a THz gyrotron oscillator operating in a self-consistent Q-switch regime has been carried out. The gyrotron is operated in the TE(7,2) transverse mode radiating at a frequency of 260.5 GHz. The 5 W nanosecond pulses are obtained in a self-consistent Q-switch regime in which the cavity diffraction quality factor dynamically varies by nearly 2 orders of magnitude on a subnanosecond time scale via the nonlinear interaction of different mode-locked frequency-equidistant sidebands. The experimental results are in good agreement with numerical simulations performed with the TWANG code based on a slow time scale formulation of the self-consistent time-dependent nonlinear wave particle interaction equations.

Postoperative and long-term prognosis of myotomy-myomectomy for obstructive hypertrophic cardiomyopathy: influence of associated mitral valve replacement.

Several surgical techniques have been proposed for obstructive hypertrophic cardiomyopathy (OHCM): myotomy, mitral valve replacement (MVR), or myotomy-myomectomy (MM). We reviewed our series of 47 patients who had undergone surgery in order to determine their prognosis and to know whether MVR+MM was better than MM only. Left intraventricular gradient decreased from 86 +/- 34 mmHg to 15 +/- 20 mmHg (P < 0.0001). Postoperatively, three patients died from low cardiac output (6.4%); five died later. Annual mortality (including postoperative deaths) was 3.0%. Follow-up was 5.7 +/- 0.7 years. Survival was 87 +/- 11% at 12 years. After operation, 91% had NYHA class I or II dyspnoea (before surgery this had been 28%); chest pain was CCS class I in 88% (vs 47%); 12% had had syncope since operation (vs 53%). The gradient decrease was larger in the MM+MVR group (P < 0.05). Survival and functional improvement were similar in the two groups. Mitral regurgitation decreased from 2.7 to 0 in the MM+MVR group (P < 0.0001), whereas it decreased from 1.5 to 1.2 in the MM group (ns). MM appears to be the procedure of choice. When mitral regurgitation is important or when an intrinsic disease of the mitral valve exists, the addition of MVR should be considered.

[Which anti-ischemic treatment can be prescribed during and after the acute phase of myocardial infarction?]. / Quel traitement anti-ischémique prescrire à la phase aiguë de l'infarctus du myocarde et après?

After myocardial infarction, calcium channel blockers are the most prescribed anti-ischemic drugs followed by nitrate derivatives and beta blockers. In order to assess whether this attitude is justified by published data on their efficacy, a meta-analysis of trials of anti-ischemic drugs in myocardial infarction was performed. The early mortality was 13.3% in the group treated by IV nitrates in the acute phase of myocardial infarction and 17.2% in control groups, reducing the risk by a quarter (95% confidence interval of the odds ratio (CI): 0.55-0.95). When all nitrate derivative trials were grouped together, the reduction in the risk of death of 21% was significant (from 15% to 11.8%) (CI: 0.59-0.94). Although oral nitrate derivatives introduced during the acute phase and continued for several weeks induced a non-significant reduction in mortality of 16%, when given intravenously, the benefits on early and longer term mortality were unquestionable. The mortality was 9.8% in the groups treated by calcium channel blockers and 9.3% in control groups (NS); the recurrent infarct rate was 4.8% and 5.4% respectively (NS). In this family of drugs, there was no product which distinguished itself from the others with regard to beneficial or adverse effects. The early mortality decreased from 9.2% to 8.2% in the groups treated by oral beta-blockade--a risk reduction of 10% (NS) and from 4.2% to 3.7% with intravenous beta-blockers--a risk reduction of 12% (p = 0.03). Late mortality decreased from 9.4% to 7.6%, a reduction of 20% (p < 0.00001) in long term trials.2+ contraindication of betablockers in patients without cardiac failure.

[Coronary accelerated arteriosclerosis and vasospasm in the transplanted heart]. / Athérosclérose accélérée et spasme coronaire sur coeur transplanté.

Accelerated atherosclerosis of cardiac grafts is one of the factors limiting long-term survival after cardiac transplantation. The authors report the case of a patient who had a cardiac arrest associated with severe atherosclerosis 18 months after transplantation. The severity of the coronary lesions was underestimated by coronary angiography. An ergometrine test induced coronary spasm, a phenomenon which has only rarely been observed in transplanted hearts. The patient died one month later despite calcium inhibitor therapy. Autopsy revealed very severe triple vessel disease. This case illustrates the possible rapid evolution of coronary artery disease in cardiac transplant recipients, the difficulty in evaluating the severity of the lesions by coronary angiography and the additional possibility of observing coronary spasm in these cases.

Influence of associated valvular lesions on long-term prognosis of mitral stenosis. A 20-year follow-up of 202 patients.

Other valvular lesions associated with pure MS were studied in 202 consecutive patients whose mean age was 43.4 +/- 12.7 years; 76.7% were females. MS was isolated in 63.4%, associated with aortic regurgitation (AR) in 27.7%, aortic stenosis in 1.0%, tricuspid stenosis (+aortic valve lesion) in 1.0%. In isolated MS, 42.4% were NYHA class III or IV, compared with 49.0% in MS + aortic valve lesion. One hundred and sixty-nine (85.4%) patients were operated on; 23.1% had mitral valve replacement, 76.9% had closed (31.4%) or open (45.6%) mitral commissurotomy; 7.1% had associated aortic valve replacement. There were perioperative complications in 20.4%, and the perioperative death rate was 4.1%. Two patients were reoperated in the postoperative course, and 28 patients after this period. The follow-up was 13.3 +/- 4.5 years. The survival rate was 77.7 +/- 4.6% (SE) for isolated MS, and 71.1 +/- 6.3% for MS associated with an aortic valve lesion (NS). The prognosis of MS is very good: the survival rate at 20 years follow-up is 75%. The association of aortic stenosis or tricuspid stenosis does not appear to alter this survival, but numbers are small. Important aortic regurgitation is a significant predictor of higher mortality in patients with MS.

Effect of intravenous L-alanine administration on plasma glucose, insulin and glucagon, blood pyruvate, lactate and beta-hydroxybutyrate concentrations in newborn infants. Study in term and preterm newborn infants.

Ten term and eleven preterm newborn infants with appropriate weights for their gestational age were infused for one minute with L-alanine (150 mg/kg) at the age of 29 to 76 hours (mean 48 hours) and circulating levels of glucose, lactate, pyruvate, D-betahydroxybutyrate (D-BOHB), insulin and glucagon were monitored. Plasma glucose concentrations increased from 2.7 +/- 0.16 (mean +/- S.E.M.) to 3.7 +/- 0.2 mmol/l after 50 min (p less than 0.01) in term infants. In preterm infants, after an initial decrease of the glucose level from 3.1 +/- 0.16 to 2.6 +/- 0.16 mmol/l (p less than 0.05), it returned to the baseline level at 50 min: 3.0 +/- 0.2 mmol/l. The blood concentration of D-BOHB decreased in term infants from 192 +/- 37 to 112 + 6 micrometer/l (p less than 0.01) after 40 min. In preterms, its decrease was not significant (p greater than 0.05). Plasma glucagon level rose from 53 +/- 5 to 70 +/- 8 pmol/l after ten minutes (p less than 0.01) in terms infants and from 61 +/- 6 to 75 +/- 9 after 20 min (p less than 0.01) in preterm infants. There were no significant changes in plasma insulin concentrations in either group. Forty minutes after L-alanine infusion, I/G ratios were lower in preterm infants (1.26 +/- 0.14) than in term infants (1.71 +/- 0.25) (p less than 0.01). There was no relationship between the glycemic responses to L-alanine and the basal levels of D-BOHB. The data suggest that the glycemic effect of L-alanine infusion and circulating glucagon depends upon a specific stage in maturation. The antiketogenic effect of L-alanine infusion is observed in term infants as in adults.