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A T Winfree

Publications and source records attributed to A T Winfree.

10 recordsLinked to original sources
PubMed1990

Vortex action potentials in normal ventricular muscle.

A remarkable feature of healthy ventricular myocardium, exposed by electrical stimulation and high-resolution mapping, is that, despite its gross nonuniformities and structural discontinuities on the submillimeter scale, it behaves electrically so much like a continuous uniformly anisotropic excitable medium. Such media are susceptible to a self-sustaining high-frequency periodic mode of activity in the form of freely movable paired vortices in two dimensions or vortex filaments in three dimensions. These can be evoked by a timely stimulus of the right size, for example, in myocardium by an electrical stimulus during the vulnerable period. Such stimuli may occur at random within complex patterns of stimulation and activation, even in healthy uniform tissue. Discontinuities and heterogeneity apparently make diseased tissue more vulnerable. Such vortices may underlie common reentrant tachycardias that degenerate into ventricular fibrillation, the commonest cause of sudden cardiac death. If the normal mechanism here reviewed also plays a role in diseased tissue, then it provides a quantitative basis for design of improved procedures for management of reentrant ventricular tachycardias that threaten to degrade to fibrillation.

Action Potentials↗
PubMed1989

Electrical instability in cardiac muscle: phase singularities and rotors.

A dynamical system is "excitable" at some stage in its behavior (e.g. at a rest state or while it is nearly at rest prior to a spontaneous event) if a small, but not too small, stimulus of the right kind elicits an immediate big reaction that eventually leads back to the original state. During this return to excitability a typical system is not excitable. An excitable system need not have an attracting rest state; a spontaneous oscillator can be excitable, too, as is common in biological and in chemical excitable kinetics. In a medium characterized by such excitable dynamics at every point, the excitation can propagate as a travelling pulse. Undamaged cardiac muscle shares with other excitable media certain features of such pulse propagation in two and three dimensions. Among the new electrophysiological phenomena thus anticipated are paired mirror-image vortices ("rotors") organized around phase singularities. These should arise in the myocardium near the intersection of a moving critical contour of phase in the normal cycle of excitation and recovery with a momentary critical contour of local stimulus strength. Such intersections, and the corresponding aftermath of paired rotors, should only occur following certain combinations of stimulus size and stimulus timing. Plotting those combinations on a "vulnerability diagram", one delineates a domain for creation of rotors (corresponding to tachycardia) surrounded on all sides by a halo of combinations at which just a few repetitive responses follow stimulation. The experiments called for to check these implications have now been carried out in the special case of electrically-induced tachycardia in healthy canine ventricle. They support the two-dimensional theory, so a new experiment is suggested to demonstrate wholly intramural three-dimensional vortex filaments.

Animals↗
PubMed1978

A single spiral artefact in arthropod cuticle.

Spirals are often seen in sections transverse to the axes of bumped structures in arthropod cuticle. (Sections through arthropod cornea or exocones yield excellent examples.) As arthropod cuticle has a helicoidal architecture (Bouligand, 1965), it might be expected that the spirals are a simple consequence of that structure. According to a symmetry argument, the spirals thus predicted must be double spirals. In contrast, the observed spirals are usually single. We propose that the single spirals result from an interaction between the microtome knife and the cuticle architecture. The direction of knife travel defines an orientation within the cuticle, subverting the symmetry arguments that require double spirals. Bouligand (1972) presented a model for the interaction of the knife with the cuticle. However, we offer arguments and observations show that Bouligand's model is incorrect. We argue from detailed observations of the single spiral that it is indeed a knifing artifact and that its explanation probably lies within a certain class of models. Two related models based on relative movements of cuticle components are examined via computer techniques.

Animals↗
PubMed1977

Phase control of neural pacemakers.

An electrical stimulus resets the phase of a spontaneously rhythmic neuron. The "new phase" versus "old phase" curve shows either of two distinct topological characters, depending on the stimulus magnitude. These features, and a phase singularity implicit in them, are common to many stable oscillations deriving from continuous feedback between two or more biophysical quantities.

Action Potentials↗
PubMed1977

Postnatal development of the cerebellar cortex in the rat. V. Spatial organization of purkinje cell perikarya.

The development of the spatial organization of Purkinje cell perikarya was examined in the rat cerebellum from birth to adulthood. Dispersion of the perikarya following birth is made possible by the rapid expansion of the cortical surface. Their subsequent regular monocellular alignment is ensured by mechanical factors, the pressure exerted from below by the expanding granular layer and the barrier formed above by the pile of parallel fibers which prevent the penetration of the bulky perikarya into the molecular layer. The perikarya remain in this position even after the slender stem dendrite pierces the molecular layer along the descending axons of basket cells. The increase in interperikaryal distance between Purkinje cells is rapid up to day 12, then declines. This is temporally associated with the growth of the basket cell plexus and glial envelope around the perikaryon. The increase in perikaryal size continues up to day 30. This may be temporally associated with the growth of the Purkinje cell dendritic arbor as reflected by the expansion of the molecular layer up to day 30. The spatial arrangement of Purkinje cells within the monocellular sheet was graphically displayed with computer aid. In the adult cerebellum a hexagonal arrangement could be recognized in a proportion of "near-neighborhoods," consisting of about six Purkinje cells and their neighbors. When the neighborhoods were extended with fixed orientation with respect to the axis of the folium, the hexagonal arrangement disappeared. When orientation was ignored, the superimposed near-neighborhoods could be rotated to produce a hexagonal pattern. In the infant cerebellum the hexagonal arrangement could not be demonstrated before the alignment of Purkinje cells in a monolayer. Thereafter there appeared to be an increase with age in the proportion of hexagonally arranged near-neighborhoods. It was concluded that in the monocellular ganglionic layer Purkinje cells are not aligned in regular rows with respect to the geometrically arranged elements of the supraganglionic layer. The formation of an imprecise hexagonal pattern, like the alignment of Purkinje cells in a monolayer, was attributed to mechanical factors.

Age Factors↗