^{James Watrous
Ph.D., Georgetown University}

Research interests: non-linear characteristics of physiological time series, with special emphasis on cardiovascular dynamics.

^{My research focus is the analysis of the time series generated by the electrical activity of the heart and the use of this information to characterize the dynamical state of the cardiovascular system.  The analysis begins with the collection of electrocardiogram data (ECG).  A typical record is shown in Fig. 1.  For many years it was believed there was a regularity in the ECG which characterized the healthy, or normal state.  The diseased or unhealthy condition was always associated with some sort of irregularity, regardless of type.  Today, however, our view of what constitutes a normal sinus rhythm has changed considerably.  Using the techniques of nonlinear analysis and applying concepts of chaos theory, there is a new way of looking at heart function.  Fig. 2 shows what a typical ECG looks like under the new paradigm.  Instead of plotting the data as a function of time, the figure shows the ECG data plotted in phase space.  This technique enables us to examine the variability within the ECG. That variability can also be seen by looking at the time between each R wave; the tallest peak in Fig. 1, and the largest loop in Fig. 2.   A typical record showing R-R interval variability is seen in Fig. 3.  In the diseased state, there are very distinct changes in the R-R intervals, usually resulting in a more cyclic pattern.  There are two questions my laboratory is currently studying: 1) How do the dynamical properties of the cardiovascular system change with age? 2) What role does the autonomic nervous system play in regulating the dynamical properties of the heart?}

 Fig. 1: Typical ECG

 Fig. 2: ECG phase portrait

 Fig. 3:  R-R time intervals