Experimental optimization of the optical and electrical properties of a half-wavelength-thick organic hetero-structure in a Micro-cavity.

In the context of progress towards the organic laser diode, we experimentally investigate the optical and electrical optimization of an OLED in a vertical λ/2 microcavity. The microcavity consists of a quarter-wavelength TiO2/SiO2 multilayer mirror, a half-wavelength-thick OLED and a semitransparent aluminum cathode. The Alq3/DCM2 guest-host system is used as the emitting layer. This study focuses on the design and the fabrication of a half-wavelength thick organic hetero-structure exhibiting a high current density despite both the thickness increase and the cathode thickness reduction. The emission wavelength, the line-width narrowing and the current-density are studied as a function of two key parameters: the hetero-structure optical thickness and the aluminum cathode thickness. The experimental results show that a 125 nm thick cavity OLED ended by a 20 nm thick aluminum cathode exhibits a resonance at 606 nm with a full width at half maximum of 11 nm, and with current-densities exceeding 0.5 A/cm². We show that even without a top high-quality-mirror the incomplete microcavity λ/2 OLED hetero-structure exhibits a clear modification of the spontaneous emission at normal incidence.

Social-ecological network analysis for sustainability sciences: a systematic review and innovative research agenda for the future.

Social-ecological network (SEN) concepts and tools are increasingly used in human-environment and sustainability sciences. We take stock of this budding research area to further show the strength of SEN analysis for complex human-environment settings, identify future synergies between SEN and wider human-environment research, and provide guidance about when to use different kinds of SEN approaches and models. We characterize SEN research along a spectrum specifying the degree of explicit network representation of system components and dynamics. We then systematically review one end of this spectrum, what we term "fully articulated SEN" studies, which specifically model unique social and ecological units and relationships. Results show more focus on methodological advancement and applied ends. While there has been some development and testing of theories, this remains an area for future work and would help develop SENs as a unique field of research, not just a method. Authors have studied diverse systems, while mainly focused on the problem of social-ecological fit alongside a scattering of other topics. There is strong potential, however, to engage other issues central to human-environment studies. Analyzing the simultaneous effects of multiple social, environmental, and coupled processes, change over time, and linking network structures to outcomes are also areas for future advancement. This review provides a comprehensive assessment of (fully articulated) SEN research, a necessary step that can help scholars develop comparable cases and fill research gaps.

Improving network approaches to the study of complex social-ecological interdependencies.

Achieving effective, sustainable environmental governance requires a better understanding of the causes and consequences of the complex patterns of interdependencies connecting people and ecosystems within and across scales. Network approaches for conceptualizing and analyzing these interdependencies offer one promising solution. Here, we present two advances we argue are needed to further this area of research: (i) a typology of causal assumptions explicating the causal aims of any given network-centric study of social-ecological interdependencies; (ii) unifying research design considerations that facilitate conceptualizing exactly what is interdependent, through what types of relationships, and in relation to what kinds of environmental problems. The latter builds on the appreciation that many environmental problems draw from a set of core challenges that re-occur across contexts. We demonstrate how these advances combine into a comparative heuristic that facilitates leveraging case-specific findings of social-ecological interdependencies to generalizable, yet context-sensitive, theories based on explicit assumptions of causal relationships.

Feedback phase sensitivity of a semiconductor laser subject to filtered optical feedback: experiment and theory.

We investigate experimentally and theoretically the dynamics of a semiconductor laser subject to filtered optical feedback. Depending on the feedback strength we find dynamical regimes with different dependence on the feedback phase. In particular, the influence of the feedback phase on cw emission and on frequency oscillations is characterized experimentally. We also measure the dependence of the filter mirror distance on the frequency oscillations. In general, good agreement between experiment and theory is found.

Frequency versus relaxation oscillations in a semiconductor laser with coherent filtered optical feedback.

We investigate the dynamics of a semiconductor laser subject to coherent delayed filtered optical feedback. A systematic bifurcation analysis reveals that this system supports two fundamentally different types of oscillations, namely relaxation oscillations and external roundtrip oscillations. Both occur stably in large domains under variation of the feedback conditions, where the feedback phase is identified as a key quantity for controlling this dynamical complexity. We identify two separate parameter regions of stable roundtrip oscillations, which occur throughout in the form of pure frequency oscillations.

Long-term results of mitral-aortic valve operations.

OBJECTIVE: We analyzed the long-term morbidity and mortality of our experience with combined mitral-aortic surgery, as well as their determinants. METHODS: Among 2109 consecutive patients undergoing valve operations, 200 had mitral-aortic valve procedures with at least implantation of a mechanical prosthesis: 163 of 200 (81.5%) patients had double valve replacement and 37 of 200 (18.5%) had mitral valve repair and aortic valve replacement. All mechanical valves were bileaflet prostheses. Preoperatively, 171 of 200 (85.5%) patients were in New York Heart Association class III-IV. Event-free survivals were determined by means of the Kaplan-Meier method and determinants of survivals with the Cox proportional hazards model (p < 0.05) entering 39 preoperative and perioperative factors. Follow-up was complete for 96% of the patients (192/200). RESULTS: Overall survivals at 5, 10, and 15 years were 88.5% +/- 0.55%, 73.5% +/- 4%, and 53.3% +/- 8.9%, and rates of freedom from valve-related mortality were 92.9% +/- 1.5%, 85.8% +/- 3.5%, and 85.8% +/- 3.5%. The rates of freedom from permanent valve-related impairment were 91.5% +/- 1.7%, 85.4% +/- 3.5%, and 79.3% +/- 6.7%, and those from all valve-related mortality and morbidity were 74.1% +/- 2.3%, 53.8% +/- 5%, and 49% +/- 5.6%. At last follow-up, 90% (139/154) of the survivors were in New York Heart Association class I-II. Left ventricular ejection fraction less than 50%, age older than 70 years, and preoperative ventricular arrhythmias were independent risk factors for valve-related late deaths. Diabetes, ejection fraction less than 50%, and coronary artery disease were independent determinants of all valve-related events. CONCLUSIONS: Functional results of survivors of combined mitral-aortic surgery are excellent. However long-term valve-related morbidity and mortality are substantial. In the patient population studied, the predictors are determined by patient-related factors, mainly myocardial factors, but not by valve-related factors.

Semicontinuous suture technique for all prosthetic valve insertions: the "hoist" technique.

The semicontinuous suture technique as an alternative method in valve replacement is described. This specific technique is applicable for both adults and children requiring valvular prosthetic operations. This method combines advantages of the continuous and interrupted suture techniques.

Drawback of aortoplasty for aneurysm of the ascending aorta associated with aortic valve disease.

BACKGROUND: Aortoplasty has been advocated for moderate dilatation of the ascending aorta associated with aortic valve disease. We report our results with this conservative approach. METHODS: Seventeen consecutive patients with unsupported aortoplasty were reviewed. Twelve patients had aortic valve regurgitation and 5 had stenosis. The aortic wall was analyzed histologically in 14 patients. Follow-up was complete, with a mean time of 6 years (range, 2.3 to 10.5 years). RESULTS: Two patients among the 15 hospital survivors died during follow-up of causes unrelated to aortic pathology. Survival at 7 years was 86.7% (+/- 8.8%). Recurring aortic aneurysms developed in 4 patients after a mean time of 63 months, with an event-free survival at 7 years of 41% (+/- 21%). All of these 4 patients had aortic valve regurgitation and cystic medial necrosis. CONCLUSIONS: The recurrence rate of aneurysms after unsupported aortoplasty and aortic valve replacement is high in patients with aortic regurgitation. This strongly suggests that in these patients, the aortic dilatation is related to an underlying wall deficiency, associated with the aortic valve pathology, rather than to the hemodynamic stress imposed by the aortic valve disease.

Use of a left heart assist device after intracardiac surgery: technique and clinical experience.

A left heart assist device (LHAD) has been employed in 14 patients. All had advanced heart disease and were in low cardiac output after repair, such that they could not be separated from cardiopulmonary bypass despite prolonged support and adjuvant therapy, including drugs, pacing, and use of intraaortic balloon counterpulsation whenever possible. Apart from special cannulas, the equipment necessary for the LHAD is widely available. An asset of the system (left atrial-ascending aorta bypass of the left ventricle) is that it may be terminated without reentering the thorax to remove the cannulas. This is accomplished with precisely fitting obturators that obliterate the cannula lumens and allow the tubes to be permanently implanted. This concept is believed important since critically ill patients requiring support are precisely those in whom added risk would be imposed by a second operation. Of the 14 patients who have had intraoperative and postoperative support (up to 6.8 days), 9 were weaned from the device and 6 were dismissed from the hospital. Four patients remain alive and are improved, the longest at 22 months since operation. The favorable performance of the LHAD suggests that it may prove useful either when intraaortic balloon counterpulsation cannot be successfully deployed or when it has failed to achieve hemodynamic stability.

Etiologic diagnosis of pericardial disease: the value of routine tests during surgical procedures.

BACKGROUND: The cause of pericardial disease often is unclear. Pericardial surgery provides a unique opportunity to obtain tissue and fluid samples for diagnostic tests. We report our experience with these tests and assess their value in etiologic determination. STUDY DESIGN: The medical records of 92 who underwent 95 operations for pericardial disease were reviewed. The procedures included 75 biopsies and drainages and 20 pericardiectomies. We analyzed the diagnostic yields of routine histology of the removed pericardial specimens, together with culture, cytology, and biochemistry examinations of the fluid drained. RESULTS: A specific etiologic diagnosis was obtained in 20 patients (22 percent): 12 neoplasias, 5 infections (1 bacterial, 4 tuberculoses), 2 chylopericardia, and 1 amyloidosis. Diagnosis was made histologically in 10 (10.5 percent) of 95 examinations, cytologically in 12 (16 percent) of 73 examinations, by culture in 5 (7 percent) of 73 examinations, and by biochemistry in 2 (3 percent) of 73 examinations. Pericardial disease was the first manifestation of an underlying extrapericardial disorder in 11 patients (12 percent), and 8 of these patients had neoplasias and 3 had tuberculoses. Twenty-seven patients (29 percent) had underlying neoplastic disease, and in 15 patients, neither cytology nor histology revealed neoplastic involvement of the pericardium. In 2 of the 15 patients, who died shortly after the operation, pericardial invasion was demonstrated at postmortem examination. CONCLUSIONS: One fifth of the patients had a specific etiologic diagnosis with important implications for prognosis and management, supporting the routine use of diagnostic tests in all pericardial surgical procedures. Negative cytology and histology results do not rule out pericardial invasion in patients with neoplastic disease.

Perioperative morbidity and mortality in combined aortic and mitral valve surgery.

BACKGROUND AND AIMS OF THE STUDY: Despite many significant improvements in cardiac surgical technique, the operative risk for combined aortic and mitral valve surgery remains between 5% and 12%. Identification of high-risk patients will allow surgeons to develop strategies to improve these results. METHODS: The 30-day postoperative mortality and complication rates were analyzed in a group of 206 patients operated on over a 16-year period with cold crystalloid cardioplegia. Thirty-three possible risk factors for death and low output syndrome (LOS) were entered into univariate and multivariate logistic regression analysis. RESULTS: There were 10 perioperative deaths (4.9%). Major complications occurred in 38 patients (18.4%), 19 with LOS. On univariate analysis, right atrial pressure (RAP) > or = 8 mmHg (p = 0.001), aortic stenosis (p = 0.009) and systolic pulmonary artery pressure > or = 60 mmHg (p = 0.095) were found to be risk factors for death, as were RAP > or = 8 mmHg (p = 0.001), previous heart surgery (p = 0.007), serum creatinine > or = 120 mumol/l (p = 0.03), tricuspid valve disease (p = 0.038) and aortic stenosis (p = 0.09) for LOS. On multivariate analysis, RAP > or = 8 mmHg (p < 0.001) and aortic stenosis (p = 0.002) were identified as independent risk factors for death, as were RAP > or = 8 mmHg (p = 0.001) and previous heart surgery (p = 0.008) for LOS. CONCLUSIONS: Mitro-aortic valve surgery involves complex procedures with substantial mortality and morbidity. The risk factors point toward the importance of operating before the stage of advanced heart failure and toward the key role of better myocardial protection techniques in these compromised hearts with limited reserves.

Surgery in native valve endocarditis: indications, results and risk factors.

Seventy-nine patients (mean age 49 years) underwent valve replacement or repair for active (58.2%) or healed (41.8%) native valve endocarditis between 1976 and 1992. The most common indication for surgery was congestive heart failure (73.4%), followed by multiple systemic emboli (21.5%). Emergency operation was necessary in 27.8% of the cases. Operative mortality was 3.8% (3 patients) and late mortality 15.1% (12 patients). Streptococci were the most common infecting agents (41.8%), followed by Staphylococcus aureus (11.4%). No organisms were isolated in 27 cases (34.2%). Follow-up spanned 379.8 patient-years with a maximum of 15.8 years. Fifteen late valve-related events (periprosthetic leak, recurrent endocarditis, thrombo-embolic events and hemolysis) and 20 other late complications (anticoagulant-related hemorrhage, arrhythmias or congestive heart failure) occurred in 22 patients. The linearized rate for all late complications is 5.8% per patient-year. The influence of eight preoperative variables on overall mortality and late valve-related complications was assessed: age, valve(s) affected, active or healed infection, bacteriology, annular abscess, emergency or elective surgery, preoperative renal function and NYHA class. Only Staphylococcus aureus (P = 0.0012) was a significant predictor of late valve-related complications. Furthermore, no difference in survival or in valve-related complications was found between the active and healed infections.

Systematic surgical closure of patent foramen ovale in selected patients with cerebrovascular events due to paradoxical embolism. Early results of a preliminary study.

OBJECTIVE: To define therapeutic strategy for management of patients with ischemic stroke due to a high probability of paradoxical embolism through a Patent Foramen Ovale (PFO). METHODS: Since 1988 all consecutive patients with cerebrovascular events and PFO from the Stroke Registry of our population-based primary-care center are prospectively studied and followed. Since 1992, among 118 patients with cryptogenic embolic brain infarct or transient ischemic attack (TIA) and PFO, 32 consecutive patients younger than 60 years who presented at least two of the following criteria were admitted for surgery: history of Valsalva strain before stroke (11); multiple clinical events (13); multiple infarcts on brain Magnetic Resonance Imaging (MRI) (15); atrial septal aneurysm (ASA) (16); large right-to-left shunt (> 50 microbubbles) (12). RESULTS: Operative time 135' +/- 33'. CPB time 34' +/- 14'. Aortic crossclamping time 16' +/- 6'. Post-operative bleeding 485 +/- 170 ml. No homologous blood transfusion required. No neurological, cardiac or renal complications. All patients were followed-up corresponding to a cumulative time of 601 patient-months. This revealed no recurrent vascular events nor silent new brain lesions on brain MRI. Systematic simultaneous contrast Trans Esophageal Echocardiography (TEE)-Trans Cranial Doppler showed a small residual interatrial shunt in two patients. CONCLUSION: Surgical closure of a patent foramen ovale can be accomplished with very low morbidity and reduce efficiently the risk of stroke recurrence. It seems to be the option of choice in selected patients with a higher (> 1.5%/year) risk of stroke recurrence.

Acute ascending aortic dissection complicating open heart surgery: cerebral perfusion defines the outcome.

OBJECTIVE: This retrospective study was designed to assess the risks of acute ascending aorta dissection (AAD) as a rare but potentially fatal complication of open heart surgery. METHOD: Among 8624 cardiac surgical procedures under cardiopulmonary bypass (CPB) and cardioplegic myocardial protection from 1978 to 1997, 10 patients (0.12%) presented with a secondary or so called 'iatrogenic' AAD. There were seven men and three women, mean age 64 +/- 9 years, ranging from 47 to 79. The original procedures involved five coronary artery bypass grafts (CABG), one repeat CABG, one aortic valve replacement (AVR), one AVR and CABG, one mitral valvuloplasty (MVP) and CABG and one ascending aorta replacement. We retrospectively analyzed their hospital records. RESULTS: Group I consisted of seven patients with AAD intraoperatively and group II consisted of three patients who developed acute AAD 8-32 days after cardiac surgery. In group I, treatment consisted of the original procedure, plus grafting of the ascending aorta in six patients and closed plication and aortic wrapping in one. In group II, two patients received a dacron graft and one patient developed lethal tamponnade due to aortic rupture before surgery. Postoperatively, six patients responded well and three died (33%), two patients from group I on the 2nd postoperative day with severe post-anoxic encephalopathy, and one from group II with severe peroperative cardiogenic shock. CONCLUSION: Preventing AAD with the appropriate means remains standard practice in cardiac surgery. If AAD occurs, it requires prompt diagnosis and interposition graft to allow a better prognosis. Intraoperative AAD happens at the beginning of CPB jeopardizing perfusion of the supra-aortic arteries.

Tricuspid valve involvement in combined mitral and aortic valve surgery.

BACKGROUND: Combined mitral and aortic valve disease requiring surgery may involve the tricuspid valve as well. Our treatment policy is conservative especially for tricuspid regurgitation which is operated on when severe only. METHODS: A retrospective study was performed at a tertiary and secondary referral center for cardiovascular disease. Over a 15-year period, 65 consecutive patients underwent aortic and mitral surgery with concomitant tricuspid regurgitation and/or stenosis. Fifty-five/65 (85%) patients were in NYHA class III-IV. Fifty-eight/65 (89%) patients had tricuspid regurgitation secondary to right chamber dilatation and 7/65 (11%) had tricuspid stenosis and/or regurgitation because of previous endocarditis. Twenty-two/65 (34%) tricuspid valves were operated on: 18/22 (82%) de Vega annuloplasty, 2/22 (9%) commissurotomies and 2/22 (9%) prosthetic valves. Mortality and complications were recorded during a mean follow-up of 5.3 yrs (range, 6 months-15.3 yrs). Event-free survivals were determined using the Kaplan-Meier method. RESULTS: Hospital mortality was 6.2% (4/65) and the complication rate was 18.5% (12/65). The freedom from late valve related mortality and morbidity at 5, 10 and 15 years was 86+/-5.5%, 81.9+/-6.8%, and 81.9+/-6.8% respectively. One valve related complication was due to the tricuspid valve. At last follow-up, 87% (47/54) of the survivors were in NYHA class I-II. CONCLUSIONS: With a conservative policy of tricuspid valve intervention, functional results of this patient population are good and long-term valve related morbidity and mortality are mainly related to the mitral and aortic valve procedures.

Temporary mechanical support of left ventricular failure following open heart surgery.

Patients coming to open heart surgery with advanced cardiac dysfunction may require mechanical cardiac support to avoid life-threatening low cardiac output in the postoperative period. 15 patients who could not be withdrawn from cardiopulmonary bypass because of low cardiac output were supported with a left heart bypass system (left atrium to ascending aorta). Ten were ultimately separated from the device, 6 were dismissed from the hospital and 4 remain well (the longest 2.6 years postoperative). A major asset of the device is that thoracic reentry is not required when support is discontinued.

Surgical treatment of tachyarrhythmias.

Tachyarrhythmia surgery should be divided into two separate groups: supraventricular and ventricular. Supraventricular tachyarrhythmias (SVT): The first surgical cure of the Wolff-Parkinson-White syndrome (WPW) in 1968 led to a better understanding of the pathophysiology and anatomy of this syndrome. WPW should now be classified by its anatomical location as defined by the preoperative and intraoperative mapping. At present, there are two surgical approaches for WPW, endocardial or epicardial. Improvement of the surgical results has broadened the indications for surgery of WPW, making it the most commonly performed operation for SVT. Surgical treatment is briefly discussed for AV nodal reentrant tachycardia, ectopic (focal) atrial tachycardia, atrial flutter, and atrial fibrillation. Ventricular tachyarrhythmias (VT): Different types of direct operations have been applied to the treatment of VT in ischemic heart disease. Because of the fairly high mortality and recurrence rate of these major operations in patients with poor ventricular function, there is now a marked increase in the use of implantable cardioverter-defibrillators as an indirect surgical approach.

Direct repair of right atrial rupture after blunt chest trauma without cardiopulmonary bypass.

Tamponade from free wall rupture of the cardiac chambers following blunt thoracic trauma is relatively frequent. Diagnosis requires a high index of suspicion and is rapidly confirmed by echocardiography. Emergent surgery is always mandatory despite apparent stable vital signs. We report a successful repair of a lacerated right atrium without cardiopulmonary bypass (CPB), saved in extremis after undue in-hospital delay.

Hyperkalemia. A prognostic factor during acute severe hypothermia.

When hypothermic patients appear to be dead, the decision to resuscitate may be difficult due to lack of reliable criteria of death. To discover useful prognostic indicators, we reviewed the hospital charts of nine hypothermic victims of snow avalanches (group A: median value of rectal temperature, 29.6 degrees C; range, less than 12 degrees C to 34 degrees C) and of 15 patients with hypothermia following acute drug intoxication and/or cold exposure (group B: 28.8 degrees C; range, 25.5 degrees C to 32 degrees C. In group A, plasma potassium level on admission was extremely high (14.5 mmol/L; range, 6.8 to 24.5 mmol/L) compared with that obtained in group B (3.5 mmol/L; range, 2.7 to 5.3 mmol/L). All patients in group A were in cardiorespiratory arrest. None could be successfully resuscitated despite effective rewarming by cardiopulmonary bypass or peritoneal lavage. In contrast, all of the patients in group B recovered from hypothermia, including two in cardiorespiratory arrest. Thus, extreme hyperkalemia during acute hypothermia appears to be a reliable marker of death. It might be used to select those patients in whom heroic resuscitation efforts can be useful.