RESUMO
While droughts predominantly induce immediate reductions in plant carbon uptake, they can also exert long-lasting effects on carbon fluxes through associated changes in leaf area, soil carbon, etc. Among other mechanisms, shifts in carbon allocation due to water stress can contribute to the legacy effects of drought on carbon fluxes. However, the magnitude and impact of these allocation shifts on carbon fluxes and pools remain poorly understood. Using data from a wet tropical flux tower site in French Guiana, we demonstrate that drought-induced carbon allocation shifts can be reliably inferred by assimilating Net Biosphere Exchange (NBE) and other observations within the CARbon DAta MOdel fraMework. This model-data fusion system allows inference of optimized carbon and water cycle parameters and states from multiple observational data streams. We then examined how these inferred shifts affected the duration and magnitude of drought's impact on NBE during and after the extreme event. Compared to a static allocation scheme analogous to those typically implemented in land surface models, dynamic allocation reduced average carbon uptake during drought recovery by a factor of 2.8. Additionally, the dynamic model extended the average recovery time by 5 months. The inferred allocation shifts influenced the post-drought period by altering foliage and fine root pools, which in turn modulated gross primary productivity and heterotrophic respiration for up to a decade. These changes can create a bust-boom cycle where carbon uptake is enhanced some years after a drought, compared to what would have occurred under drought-free conditions. Overall, allocation shifts accounted for 65% [45%-75%] of drought legacy effects in modeled NBE. In summary, drought-induced carbon allocation shifts can play a substantial role in the enduring influence of drought on cumulative land-atmosphere CO2 exchanges and should be accounted for in ecosystem models.
Assuntos
Ciclo do Carbono , Secas , Clima Tropical , Guiana Francesa , Florestas , Carbono/metabolismo , Modelos TeóricosRESUMO
AIM: The Internet is an extremely powerful tool for the transmission of data and knowledge, and the question is whether this technology can be used effectively in continuing medical education. We present our experience with worldwide, web-based virtual symposia for practicing physicians. METHODS: The International Society for Holter and Noninvasive Electrocardiography (ISHNE) decided four years ago to conduct a series of cardiology-related educational activities for physicians utilizing a web-based approach. Six educational events under the format of virtual symposia were held on the Internet during the years 2002 to 2006. These Internet events included symposia on Brugada syndrome (2002), the long QT syndrome (2004), arrhythmogenic right ventricular dysplasia (2005), atrial fibrillation (2005), heart failure (2006), and sudden cardiac death (2006). RESULTS: During the past four years, there has been a dramatic and progressive increase in the number of physician registrants, the number of countries represented, and the number of lectures downloaded with each subsequent virtual symposium. For example, during the month of October 2006, the Internet-based sudden cardiac death symposium involved 14,087 physician registrants from 120 countries with 64,939 lectures downloaded. The top lecture was downloaded 11,251 times, and over 200 e-mail questions and replies were exchanged. The average time per visit to the web site was 12.5 minutes. CONCLUSION: The progressively increasing numbers of physician registrants from around the world who participated in these web-based, virtual symposia suggest that this approach is answering an unmet professional educational need. This Internet approach adds an important, new, low-cost dimension to continuing medical education.
Assuntos
Cardiologia/educação , Educação Médica Continuada/métodos , Eletrocardiografia , Internet , Interface Usuário-Computador , Humanos , Sociedades MédicasRESUMO
BACKGROUND: AutoCapture (AC) is a programmable feature that enables the pacemaker to both track the capture threshold and automatically adjust the output on a beat-by-beat basis. Although AC safely and significantly reduces the current drainage, some authors have argued that the longevity benefit of such a system is overstated. This study aims to estimate the longevity extension that can be obtained, in the clinical routine, by turning the AC on in comparison to pacemakers programmed to operate at the shipped and manually optimized output. METHODS: We selected 83 consecutive patients who received implanted St Jude's Affinity pacemakers >6 months earlier. Eight patients died or were lost to follow-up and in 9 subjects the AC could not be turned on. In the remaining 66 patients, current drain and estimated longevity were compared in 3 situations: (1) AC on; (2) AC off, optimized programming (100%-150% voltage threshold); (3) AC off, shipped output (3.5 V). RESULTS: Five patients had large variations (>1 V) of the AC threshold. Current drainage was 8.0 +/- 0.9 mA in the AC group, 8.7 +/- 1.8 mA with AC off and optimized programming, and 11.3 +/- 2.3 mA at shipped output (P <.01). Estimated longevity was significantly extended (P <.01) by AC (12.1 +/- 1.0 years) when compared to shipped (8.9 +/- 1.7 years) and optimized programming (11.3 +/- 1.4 years). CONCLUSION: Reprogramming the pacemaker output significantly enhanced its estimated longevity; AC added a moderate but significant extension over manual reprogramming and was associated with increased safety in patients with large ventricular threshold variations.
Assuntos
Fontes de Energia Elétrica , Bloqueio Cardíaco/terapia , Marca-Passo Artificial , Síndrome do Nó Sinusal/terapia , Algoritmos , Calibragem , Estimulação Cardíaca Artificial , Falha de Equipamento , Feminino , Bloqueio Cardíaco/fisiopatologia , Humanos , Masculino , Pessoa de Meia-Idade , Fatores de TempoRESUMO
La AutoCaptura facilita el diagnóstico de la inestabilidad del cabo-electrodo, así como los defectos mecánicos que se producen en los cabos-electrodos, basado en la documentación exacta de los cambios del umbral que facilitaban la capacidad del médico de manejar una estimulación cardíaca artificial segura y apropiada para el paciente. Los autores hacen una retrospectiva sobre el tema de ajuste automático del umbbral de comando, la AutoCaptura, presentando sus ventajas terapéuticas y diagnósticas. Analizan de tal manera la influencia que la AutoCaptura tiene en la longevidad (vida útil) del generador de pulso como la evolución de los umbrales de comando, tanto como los umbrales crónicos cuando se utilizan los actuales cabos-electrodos datados de esteroides. Además, discuten sobre las posibles causas del aumento del umbral de comando después de haber ocurrido la maduración del cabo-electrodo y la nueva perspectiva que se abre para la obtención del diagnóstico más preciso con la utilización del registro del umbral de largo plazo. Los autores concluyen, que con las actuales aprobaciones de la eficacia y los beneficios de la AutoCaptura, este es una característica esencial que debe ser incorporado a todos los marcapasos
Assuntos
Marca-Passo ArtificialRESUMO
Os ressincronizadores biventriculares podem apresentar sinais e/ou sintomas indicativos de mau funcionamento. Além dos maus funcionamentos próprios da estimulação uni ou bicameral, o sistema tricameral pode, também, apresentar comportamentos exclusivos deste modo de estimulação. A dificuldade diagnóstica é derivada do fato de ser relativamente recente a possibilidade rotineira da estimulação tricameral, além de, por vezes, o mau funcionamento passar despercebido pela ausência de sintomatologia exuberante. Esta dificuldade é minimizada com o conhecimento das ocorrências e o perfeito entendimento das possibilidades de mau funcionamento de um sistema tricameral.
Assuntos
Humanos , Estimulação Cardíaca Artificial/métodos , Marca-Passo ArtificialRESUMO
Os autores fazem uma retrospectiva sobre o tema do ajuste automático de limiar de comando ou autocaptura, apresentando suas características terapêuticas e diagnósticas. Analisam sua influência na longevidade do gerador de pulso e na evolução dos limiares de comando, agudos ou crônicos, quando se utilizam os atuais cabos-eletrodos dotados de esteróides. Discorrem sobre as possíveis causas de aumento do limiar de comando após a maturação do cabo-elétrodo e a nova perspectiva que se abre para a obtenção de disgnósticos mais apurados com a utilizaão do Registro de Limiar de Longo Prazo. Concluem que, dada a atual comprovação da eficácia e dos benefícios da autocaptura, esta característica é essencial e deve ser incorporada a todos os marcapassos