Harold M. Hastings

Learn More
It has become widely accepted that the most dangerous cardiac arrhythmias are due to reentrant waves, i.e., electrical wave(s) that re-circulate repeatedly throughout the tissue at a higher frequency than the waves produced by the heart’s natural pacemaker (sinoatrial node). However, the complicated structure of cardiac tissue, as well as the complex ionic(More)
INTRODUCTION Discordant alternans has the potential to produce larger alternans of the ECG T wave than concordant alternans, but its mechanism is unknown. METHODS AND RESULTS We demonstrate by one- and two-dimensional simulation of action potential propagation models that discordant alternans can form spontaneously in spatially homogeneous tissue through(More)
Mathematical models of cardiac cells have become important tools for investigating the electrophysiological properties and behavior of the heart. As the number of published models increases, it becomes more difficult to choose a model appropriate for the conditions to be studied, especially when multiple models describing the species and region of the heart(More)
BACKGROUND Interleukin 1beta (IL-1beta) is a multifunctional cytokine that up-regulates the inflammatory response. It is not known whether IL-1beta plays a major role in human malignancy. To determine whether IL-1beta might be involved in breast carcinoma progression, the authors measured the IL-1beta content in tissue extracts from >200 invasive breast(More)
The size of realistic cardiac tissue models has been limited by their high computational demands. In particular, the Luo-Rudy phase II membrane model, used to simulate a thin sheet of ventricular tissue with arrays of coupled ventricular myocytes, is usually limited to 100 x 100 arrays. We introduce a new numerical method based on domain decomposition and a(More)
STUDY OBJECTIVE Asthma morbidity is greater in younger patients. The reasons are not fully understood, although identifying demographic patterns of seasonality may help determine causes and potential prevention. The objective of this study is to determine the relationship between age and seasonal asthma periodicity in patients presenting to the emergency(More)
We consider competition in patch-dynamical and more general diffusion-extinction models. These models identify three time scales in ecology. We begin with a reformulation of Levin's 1978 basic model, using a geometric description of diffusion. As in Levin's model, diffusion drives short-term dynamics, and longer-term dynamics depends upon a(More)
We describe a useful setting for interactive, real-time study of mathematical models of cardiac electrical activity, using implicit and explicit integration schemes implemented in JAVA. These programs are intended as a teaching aid for the study and understanding of general excitable media. Particularly for cardiac cell models and the ionic currents(More)
Electrogram recordings of ventricular fibrillation appear complex and possibly chaotic. However, sequences of beat-to-beat intervals obtained from these recordings are generally short, making it difficult to explicitly demonstrate nonlinear dynamics. Motivated by the work of Sugihara on atmospheric dynamics and the Durbin-Watson test for nonlinearity, we(More)
Ventricular fibrillation (VF) remains a major cause of death in the industrialized world. Alternans (a period-doubling bifurcation of cardiac electrical activity) have recently been causally linked to the progression from ventricular tachycardia (VT) to VF, a more spatiotemporally disorganized electrical activity. In this paper, we show how alternans and(More)