Distributed gain in plasmonic reflectors and its use for terahertz generation.

Semiconductor plasmons have potential for terahertz generation. Because practical device formats may be quasi-optical, we studied theoretically distributed plasmonic reflectors that comprise multiple interfaces between cascaded two-dimensional electron channels. Employing a mode-matching technique, we show that transmission through and reflection from a single interface depend on the magnitude and direction of a dc current flowing in the channels. As a result, plasmons can be amplified at an interface, and the cumulative effect of multiple interfaces increases the total gain, leading to plasmonic reflection coefficients exceeding unity. Reversing the current direction in a distributed reflector, however, has the opposite effect of plasmonic deamplification. Consequently, we propose structurally asymmetric resonators comprising two different distributed reflectors and predict that they are capable of terahertz oscillations at low threshold currents.

2D metamaterials with hexagonal structure: spatial resonances and near field imaging.

The current and field distribution in a 2D metamaterial consisting of resonant elements in a hexagonal arrangement are found assuming magnetic interaction between the elements. The dispersion equation of magnetoinductive (MI) waves is derived with the aid of the direct and reciprocal lattice familiar from solid state theory. A continuous model for the current variation in the elements is introduced leading to the familiar wave equation in the form of a second order differential equation. The current distributions are shown to exhibit a series of spatial resonances for rectangular, circular and hexagonal boundaries. The axial and radial components of the resulting magnetic field are compared with previously obtained experimental results on a Swiss Roll metamaterial with hexagonal boundaries. Experimental and theoretical results are also compared for the near field image of an object in the shape of the letter M followed by a more general discussion of imaging. It is concluded that a theoretical formulation based on the propagation of MI waves can correctly describe the experimental results.

Use of low-dose ketamine and/or midazolam for pediatric cardiac catheterization.

Ketamine and midazolam are commonly used in children undergoing cardiac catheterization. However, there is controversy regarding the safety of administering these agents in the absence of an anesthesiologist. We retrospectively reviewed pediatric cardiac catheterization procedures at our institution between 1996 and 1997. A total of 154 patients (0.3-192 months) underwent a total of 205 procedures. They received ketamine (n = 79, 1.05 +/- 0.88 mg/kg/hr), midazolam (n = 35, 0.14 +/- 0.09 mg/kg/hr), or both (n = 91; ketamine, 1.13 +/- 0.84 mg/kg/hr; midazolam, 1.57 +/- 1.03 mg/kg//hr). In 18.5% of patients there were complex cardiac lesions. Mean procedure time was 79 +/- 36.2 minutes. Pre- and postprocedure systolic and diastolic mean blood procedure 72 +/- 14 and 68 +/- 12 mmHg, respectively. Pre- and postprocedure O2 saturation was 93.19 +/- 8.72 and 93.63 +/- 8.3, respectively. One patient required intubation, and 15% required oxygen therapy. The mortality rate was zero. The anesthesiologist's assistance was requested by the cardiologist in 21 procedures (group A) and not requested in 184 procedures (group B). The two groups were not different in relation to the drug used (p = 0.283) or the complexity of the cardiac lesions (p = 0.051). However, there was significant difference between the two regarding the need for supporting drugs (3/21 vs 3/184, p = 0.02) or oxygen treatment (7/21 vs 26/184, p = 0.014). No patients in group B required intubation, whereas 14% and 1.6% required oxygen therapy and supporting drugs, respectively. We conclude that low-dose ketamine and midazolam can be administered safely to most pediatric patients by the cardiologist, who can safely predict the need for an anesthesiologist.

Bubble contrast echocardiography in detecting pulmonary arteriovenous malformations after modified Fontan operations.

The development of pulmonary arteriovenous malformations is a well-known complication after Fontan operations, and may result in significant morbidity due to increasing arterial desaturation. We compared the use of bubble contrast echocardiography and pulmonary angiography in detecting such malformations. We also examined which anatomical and haemodynamic variables were associated with their development. Our study includes 20 patients who had undergone modified Fontan procedures, 10 with atriopulmonary and 10 with total cavopulmonary connections, in Gothenburg between 1980 and 1991. All patients underwent cardiac catheterisation and pulmonary angiography. Bubble contrast echocardiography was performed at the same time, with injection of agitated polygelin colloid solution (Haemaccel, Hoechst) into the right and left pulmonary arteries, respectively. Transoesophageal echocardiography was used to detect the appearance of bubble contrast in the pulmonary venous atrium. The aim was also to evaluate the role of hepatic venous blood. Of the 20 patients, 9 (45%) had a positive contrast echocardiography study, compared with only 2 (10%) detected by pulmonary angiography. Patients with positive contrast echocardiography had a significantly lower arterial oxygen saturation than those with negative studies, both at rest (88% vs 95%, p < 0.01) and during exercise testing (78% vs 89%, p = 0.01). Bubble contrast echocardiography is much more sensitive in detecting pulmonary arteriovenous malformations than pulmonary angiography. By injecting echo contrast into the right and left pulmonary arteries, the method can be made highly selective. Pulmonary arteriovenous malformations develop much more frequently in patients with the Fontan circulation than previously reported.

Transcutaneous-PO2 monitoring for detection of exercise-induced right-to-left shunts in children with congenital heart defects: a case report.

UNLABELLED: A 2-y-old boy with scimitar syndrome underwent surgery involving the redirection of partial anomalous pulmonary venous return to the left atrium. Heart catheterization after the operation did not reveal any significant intra-cardiac shunts. An exercise test performed at the age of 10 y revealed a reduction in working capacity. At the age of 12 y, the patient became unconscious and experienced seizures during heavy physical exercise. EEG and Holter ECG examinations were normal. In a second exercise test, a fall in transcutaneous PO2 was demonstrated at the start of the test. A new heart catheterization revealed communication between the inferior vena cava and the left atrium owing to a misplaced patch. No right-to-left shunt was found at rest, probably as a result of drainage of the inferior vena cava to the superior vena cava by the azygous vein. An exercise test after re-operation revealed normal conditions. CONCLUSION: Haemodynamic studies during heart catheterization in children are usually performed at rest. This could result in exercise-induced right-to-left-shunts being overlooked. The use of PtcO2 monitoring during exercise tests is a non-invasive means of exposing these shunts.

Comparison between the safety profile and clinical results of the Cook detachable and Gianturco coils for transcatheter closure of patent ductus arteriosus in 272 patients.

OBJECTIVES: We evaluated the occlusion rate and safety of Cook detachable coils versus Gianturco coils in transcatheter closure of patent ductus arteriosus (PDA). BACKGROUND: The Cook detachable coil recently was introduced in an attempt to improve the safety of transcatheter closure of PDA. METHODS: Between January 1994 and September 1998, 272 patients underwent transcatheter PDA closure. Cook detachable coils were used in 137 patients, with a mean age of 43.9 months and weight of 13.8 kg. In 135 patients, Gianturco coils were used, with a mean age of 56.8 months and weight of 17.8 kg. The mean narrowest diameter of the PDA in the Cook detachable coil group was 2.85 mm versus 2.32 mm for the Gianturco coil group. RESULTS: The Cook detachable coil group was younger and weighed less than the Gianturco group (P < 0.05 and 0.02, respectively). Their narrowest PDA diameter was larger (P < 0.01). Embolization rate was significantly lower in the Cook coil group (9[6.5%] of 137 vs 22 (16.3%) of 135; P = < 0.013). The mean follow-up for the Cook coil group was significantly shorter (0.55 years) than for the Gianturco coil group (1.18 years; P < 0.001). On an intention-to-treat basis, complete occlusion by echocardiography was achieved in 99 (72.3%) of 137 patients in the Cook detachable coil group, which was significantly less than the Gianturco coil group (114 [84.4%] of 135; P = 0.008). CONCLUSION: Cook detachable coils for transcatheter closures of the PDA are safer than Gianturco coils. Hence, children with large ductal can be treated earlier in life. Short-term complete occlusion rate was lower in the Cook detachable coil group. This rate can be explained by a shorter follow-up time, larger ductal diameter, and the different materials used for the detachable coils.

Double-chambered right ventricle in 73 patients: spectrum of the disease and surgical results of transatrial repair.

OBJECTIVE: To review the spectrum of double-chambered right ventricle (DCRV) and the outcome of surgical repair in patients diagnosed between February 1988 and March 1999. DESIGN: The charts of patients with DCRV were studied. SETTING: Tertiary care hospital. PATIENTS AND METHODS: A total of 73 patients were identified. Sixty-nine underwent surgical repair, while four are awaiting surgery. The repair was through a transatrial approach in 61 patients, while in eight an additional ventriculotomy was performed. MAIN RESULTS: An associated ventricular septal defect (VSD) was present in 56 of 73 patients (77%). These patients were significantly younger (P<0.05) than the 17 patients without a VSD. Among patients with a VSD, the 31 requiring patch closure were significantly younger than the 25 patients having direct closure. Five older patients among those with intact septum had impaired right ventricular (RV) function as well as higher intraventricular gradients. At surgery the intraventricular obstruction was relieved by myomectomy. There was no hospital or late mortality. Following surgery, at a mean follow-up of 13.6 months, no increase in the intraventricular gradient was detected by Doppler echocardiography. CONCLUSIONS: The development of DCRV is associated with VSD in early life. The probability of the presence of a VSD decreases with age. The disease is progressive, resulting in increased intracavitary gradient within the RV and in RV impairment if it is not treated in a timely fashion. Transatrial repair is safe with excellent midterm results. In the presence of high gradients within the RV, a ventriculotomy may be necessary to obtain acceptable results.

Increase in size of the pulmonary autograft after the Ross operation in children: growth or dilation?

OBJECTIVE: We sought to assess growth properties of the pulmonary autograft after the Ross operation in children. METHODS: Eight infants with critical aortic stenosis who underwent the Ross operation early in life (median age, 6.4 months) were followed up regarding the possible growth of the autograft. The pulmonary autograft was measured repeatedly by echocardiography during the follow-up, ranging from 6 months to 7 years (median, 5.2 years). Twelve normal children who served as control subjects were similarly followed from 3.9 to 5.8 years (median, 4.9 years). RESULTS: Somatic growth during the follow-up period was significant and was reflected in a doubling of the body surface area, which increased from 0.33 +/- 0.14 m(2) to 0.74 +/- 0.21 m(2). The proximal part of the autograft increased from 13.6 +/- 3.6 mm to 23.3 +/- 3.7 mm (mean +/- SD) and the distal part from 10.5 +/- 2.5 mm to 15.9 +/- 2.8 mm. Growth pattern of the autograft was analyzed by relating measured diameters to predicted normal diameters (ie, Z values). During the first year after the operation, the mean Z value of the proximal autograft increased from 0.2 to 2.2, indicating a more rapid increase than the predicted increase and was also significantly higher than that of the control group (P =.01). After the first year, Z-value changes in patients and control subjects were very similar. CONCLUSIONS: We thus conclude that the pulmonary autograft in the aortic position after the Ross operation does increase in size and that the pattern of this increase is suggestive of passive dilation in the early postoperative period, followed by normal active growth.

Radiographic characteristics of Cook detachable and Gianturco coils as well as clinical results of transcatheter closure of the patent ductus arteriosus.

PURPOSE: To describe the radiographic appearance of the Gianturco and the Cook detachable coils and present the clinical results in patients who underwent transcatheter closure of patent ductus arteriosus. MATERIALS AND METHODS: Between January 1994 and June 1997, eighty-two patients underwent closure of patent ductus arteriosus (PDA) using either Gianturco or Cook detachable coils. The chest x-ray and echocardiography of all patients were reviewed and the following parameters were evaluated: 1) the size of the heart (cardiothoracic ratio), 2) the position and the type of the coils in the postero-anterior and the lateral projection, 3) the number of coils used, 4) the existence of residual ductal flow, 5) Doppler velocity in the left pulmonary artery. RESULTS: Complete occlusion was achieved in 94%, and cardio-thoracic ratio regressed from 0.57 to 0.53 (p < 0.01), after a mean follow-up of 1.2 years. The identification of the different coils on the chest radiograph was successful in only 47% of cases, difficulties arising especially, when multiple coils were used. In 55 patients (67%) the coil position was judged to be optimal, in 27 patients (33%) suboptimal. The latter correlates with the presence of residual shunt. Multiple coils correlated more with a left pulmonary artery flow velocity exceeding 1.5 m/s. CONCLUSION: Coil-occlusion of patent ductus arteriosus is effective and leads to reduced cardio-thoracic ratio. Radiographic coil identification is possible but may be difficult if multiple coils are deployed. Suboptimal coil position led more often to residual PDA shunt. Multiple coils are more commonly associated with increased LPA velocities, but hemodynamic significant obstruction to flow is rare.

Endomyocardial biopsy in heart-transplanted children: comparison of sheaths to guide biopsy forceps.

The risk of perforation during 65 endomyocardial biopsies (380 specimens) was investigated using two different sheaths to guide the biopsy forceps in five heart-transplanted children aged 1.6-12.9 years. One of the sheaths guided the biopsy forceps simply into the right ventricle (prefabricated 110 degrees curved tip); the other (specially curved sheath) had two curves, the distal one of which guided the forceps posteriorly toward the interventricular septum. The position of the sheath was evaluated by biplane fluoroscopy and, in children

Resonant two-wave mixing in photorefractive materials with the aid of dc and ac fields.

A recently predicted resonant effect for the enhancement of two-wave mixing in photorefractive materials is investigated. The resonance occurs when the frequency of the applied ac field agrees with the eigenfrequency of the excited space-charge wave. Experimentally a clear resonance is found, as predicted by the theory, for high dc electric fields, but the resonance is smeared out for lower fields. A modified theory, taking into account the second temporal harmonic of the space-charge wave, shows good agreement with the experimental results.

Aortic valve replacement with a pulmonary autograft in infants with critical aortic stenosis.

Seven patients with critical aortic stenosis underwent aortic valve replacement with a pulmonary autograft (the Ross operation) between the ages of 5 weeks and 9 months. The operation was considered mandatory for survival because of continued severe heart failure or valve avulsion. Six of the patients had undergone unsuccessful previous palliations, such as commissurotomy, balloon dilation, and transventricular valvotomy, performed singly (n = 1) or in combination (n = 5). The other patient with a severely hypoplastic aortic valve ring underwent the Ross procedure as a primary operation. Two operative deaths occurred. In both cases severe endocardial fibroelastosis was detected at autopsy. One late death 1 year after the operation resulted from progressive hypertrophic cardiomyopathy and pulmonary hypertension. The rest of the patients are doing well, without medications. Apart from trivial regurgitation in two patients, the pulmonary autograft is performing well.

Status of survivors after atrial redirection for transposition of the great arteries: a complete long-term follow-up.

All 32 survivors with transposition of the great arteries, born in 1964-83 and operated on at our institution using atrial redirection, were evaluated by cardiac catheterization, echocardiography and Holter monitoring. There were 17 Mustard patients, age 17.1 years (+/-3.5, 12.0-22.0) and 15 Senning patients, age 9.4 years (+/-1.6, 7.2-12.1). All but one had simple transposition. Six had caval obstruction, one had pulmonary venous obstruction, three had large atrial shunts, four had considerable pulmonary hypertension, seven had mild ventricular outflow tract obstruction, four had significant tricuspid regurgitation, 11 had systemic ventricle dysfunction (one severe), 14 had sinus node dysfunction (three symptomatic) and two had atrioventricular block (one with pacemaker). Eight Mustard patients (47%) and one Senning patient (7%) had symptomatic cardiac sequelae, and only one patient (Senning) was free from sequelae, illustrating that these patient groups will need continuing medical attention.

High-frequency resonances in photorefractive crystals.

Two-wave mixing in photorefractive materials is investigated for the case of applied dc electric fields and large detuning frequencies and for high-frequency alternating electric fields. The appearance of high-frequency resonances is demonstrated.

Spatial frequency filtering in holographic image reconstruction.

We show that reconstructing a hologram by its object beam leads to spatial filtering, namely, to the suppression of spatial frequency components that are perpendicular to the plane of the recording beams. We conduct experiments by rotating the transparencies of Ronchi gratings and crossed gratings and measuring the corresponding diffraction efficiencies. Good agreement is found with a theory based on image reconstruction with a beam that does not quite satisfy the Bragg condition.

Effect of subharmonics on two-wave gain in Bi(12)SiO(20) under alternating electric fields.

It is demonstrated that the emergence of subharmonics during two-wave mixing in a Bi(12)SiO(20) photorefractive crystal under applied alternating electric fields will markedly reduce two-wave gain. The repetition frequency at which the observed drop in two-wave gain appears is correlated with threshold conditions for the subharmonic instability for a wide range of experimental parameters.

Scatter rings in bismuth silicate illuminated by a single beam.

We have observed cones of diffracted light by illuminating a crystal of bismuth silicate with a single beam of light while applying an electric field across the crystal. The scatter rings are a result of the preferential amplification of noise, which we explain here using the Ewald sphere construction.

Balloon dilation of stenotic aortic valve in children. An intraoperative study.

Ten children in the age range of 3 to 17 years with moderate to severe aortic valve stenosis (gradients of 55 to 109 mm Hg) underwent cardiac operations. At the time of the operation, during bypass, balloon dilation of the stenotic valve was performed and the results were visually assessed by the surgeon. Of the 10 consecutive cases, only three showed dilation results that were comparable to what seems optimal from a surgical point of view. The adverse effects in the remaining seven patients and the corrective measures taken were as follows: (1) too extensive a rupture requiring stabilizing sutures in one patient; (2) too short a rupture, requiring additional commissurotomy in three patients; (3) rupture into the valve leaflet, requiring valve suture and corrective comissurotomy in another three patients. This last, rather serious complication occurred in patients having functionally bicuspid valves with slightly thickened free valve edges, whereas valves with severely thickened edges ruptured in the commissure line but often to an insufficient degree. Because of the high incidence of suboptimal separation of the stenotic aortic valves with balloon dilation, we recommend that further evaluation of long-term results and identification of unsuitable cases should precede widespread use of the technique.