Empirically classifying network mechanisms.

Network data are often explained by assuming a generating mechanism and estimating related parameters. Without a way to test the relevance of assumed mechanisms, conclusions from such models may be misleading. Here we introduce a simple empirical approach to mechanistically classify arbitrary network data as originating from any of a set of candidate mechanisms or none of them.

Can Community Structure Causally Determine Dynamics of Constituent Species? A Test Using a Host-Parasite Community.

Structures of communities have been widely studied with the assumption that they not only are a useful bookkeeping tool but also can causally influence dynamics of the populations from which they emerge. However, convincing tests of this assumption have remained elusive because generally the only way to alter a community property is by manipulating its constituent populations, thereby preventing independent measurements of effects on those populations. There is a growing body of evidence that methods like convergent cross-mapping (CCM) can be used to make inferences about causal interactions using state space reconstructions of coupled time series, a method that relies on only observational data.

Modulated parasystole originating in the sinoatrial node.

A computer model of "modulated sinus parasystole" was devised in which two sinus pacemakers interacted electrotonically, entraining each other's periodicity according to their beat-to-beat phasic relationships. Depending on the preestablished rules, the model gave rise to various rhythm patterns that were similar to those recorded in patients with sinoatrial arrhythmias. The validity of the model in predicting clinically observed rhythm disturbances was tested in a case of sinoatrial extrasystolic activity.

Successful treatment of drug-resistant atrial tachycardia and intractable congestive heart failure with permanent coupled atrial pacing.

Temporary coupled atrial stimulation slowed the ventricular rate by nearly 50% in an adolescent patient with intractable congestive heart failure and focal repetitive atrial tachycardia that was resistant to drug treatment. Because of the success with the temporary pacemaker, a specially designed permanent pacemaker was implanted to provide coupled atrial stimulation. The necessary electrophysiologic conditions for ventricular slowing by coupled atrial pacing are: (1) an atrial effective refractory period shorter than that of the atrioventricular junction, and (2) depolarization of the ectopic atrial pacemaker by the responses to coupled atrial stimulation.