Pulmonary emphysema and periodontal disease are each characterized by the uncontrolled proteolysis of connective tissue proteins by proteinases derived from human neutrophils. Although these diseases would not appear to be related in terms of the initial insult to individual tissues, the ultimate result in each disease is the accumulation and degranulation of neutrophils at inflammatory sites, apparently as a result of frustrated phagocytosis and specific activation of these phagocytic cells. This result is easily recognized in the case of emphysema, where there is clear evidence that the primary cause of the disease is the accumulation of foreign materials in the lung (e.g., smoke condensate), followed by the recruitment of neutrophils to the organ and the release of oxidative and hydrolytic enzymes. In periodontitis, however, the problem begins with the accumulation of plaque at the base of the teeth, followed by the growth of opportunistic anaerobic bacteria below the gum line. These parasitic microbes, which are resistant to killing by both monocytes and granulocytes, secrete proteinases that can activate the kallikrein-kinin pathway, degrade clotting factors, and release the potent neutrophil chemotactic factor, C5a, from complement. It is under such conditions that neutrophils are recruited to infected sites within the periodontium. After the neutrophil-recruitment stage, the two diseases become similar in that degranulation of neutrophils occurs during attempted phagocytosis of either cigarette smoke components (emphysema) or bacteria (periodontitis), followed by inactivation of tissue proteinase inhibitors and degradation of connective tissue proteins, the ultimate result being the destruction of the alveolus or gingiva, respectively.

Plan 9 is a distributed system built at the Computing Sciences Research Center of AT&T Bell Laboratories over the last few years. Its goal is to provide a production-quality system for software development and general computation using heterogeneous hardware and minimal software. A Plan 9 system comprises CPU and file servers in a central location connected together by fast networks. Slower networks fan out to workstation-class machines that serve as user terminals. Plan 9 argues that given a few carefully implemented abstractions it is possible to produce a small operating system that provides support for the largest systems on a variety of architectures and networks. The foundations of the system are built on two ideas: a per-process name space and a simple message-oriented file system protocol.

Plan 9 is a distributed system built at the Computing Sciences Research Center of AT&T Bell Laboratories over the last few years. Its goal is to provide a productionquality system for software development and general computation using heterogeneous hardware and minimal software. A Plan 9 system comprises CPU and file servers in a central location connected together by fast networks. Slower networks fan out to workstation-class machines that serve as user terminals. Plan 9 argues that given a few carefully implemented abstractions it is possible to produce a small operating system that provides support for the largest systems on a variety of architectures and networks. The foundations of the system are built on two ideas: a per-process name space and a simple message-oriented file system protocol.The operating system for the CPU servers and termivals is structured as a traditional kernel: a single compiled image containing code for resource management, process control, user processes, virtual memory, and I/O. Because the file server is a separate machine, the file system is not compiled in, although the management of the name space, a per-process attribute, is. The entire kernel for the multiprocessor SGI Power

No abstract

HOCINI, M., ET AL.: Multiple Sources Initiating Atrial Fibrillation from a Single Pulmonary Vein Identi fied by a Circumferential Catheter. The pulmonary veins are the predominant source of ectopic activity initiating AF. The reproducibility of intrapulmonary vein activation during ectopic activity and/or initia tion of multiple AF episodes was examined. Eighty-nine pulmonary veins (PVs) among 29 patients un dergoing radiofrequency ablation of AF were studied with a 15-to 20-mm diameter, circumferential PV catheter equipped with ten electrodes and a deflectable shaft. Local electrograms were recorded simulta neously during sinus rhythm, ectopic activity, or AF onset, spontaneously or induced via the catheter left in a stable position. Fifty-four arrhythmogenic veins were identified, 39 showing isolated ectopy, and 8 displayed repetitive ectopy (in salvos). The earliest site of activation and the sequence ofintra-PV activa tion during isolated ectopy was identical to that observed during consecutive ectopic complexes in 77% and variable in 23% during isolated ectopy. The earliest activity was sometimes limited to a single bipole. During repetitive ectopy and AF initiation, multiple sources and/or variable activation patterns were noted in 53% of instances, indicating the presence of multiple arrhythmogenic foci within the same PV. Simultaneous electrogram recordings with a circumferential PV catheter identified the presence of multipie arrhythmogenic foci within a single PV. (PACE 2000; 23:[Pt. II] -.1828-1831) atrial fibrillation, pulmonary vein, ablationAddress for reprints: Mélèze Hocini, M.D., Hôpital Cardi ologique du Haut-