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My research interest is to understand the control mechanisms involved in beat-to-beat regulation of heart rate, and to estimate them noninvasively. My motivation for this work is to develop a tool which will enhance our understanding of the cardiovascular system and engender methods for earlier diagnosis and better treatment of disease.
I have already done preliminary modeling and estimation work using an "integrate and fire" model of the sinoatrial (SA) node. This model includes some aspects of SA node physiology that have not typically been included in previous studies: physiological noise and refractory period. By using this model to construct a likelihood function, I was able to solve the inverse problem of estimating instantaneous heart rate (a more physically meaningful signal than the currently used tachogram or average heart rate) from a sequence of observed heartbeats. This work lays the foundation for estimating how heart rate is controlled by the autonomic nervous system in a continuous-time manner.
To this end, I will add more physiological constraints to my existing model. This will be done by developing a cellular-level model of the SA node cell and the effect of neurotransmitter release from the two branches of the autonomic nervous system. This complex mathematical model will then be used to generate physiologic constraints and cost functions that will consequently be used to advance the estimation algorithm mentioned above. Once complete, this model and estimation method would be an invaluable tool for solving the inverse problem of estimating the hidden parameters (ANS tone) from the easily observable heart rate signal.
The result of this work would give us a window through which we can unintrusively peer into the world of cardiovascular regulation, understand cardiovascular disease mechanisms, discover new molecular drug targets, and create better diagnostics.
Scepanovic, D., Cohen, R.J., "Method for measuring physiological stress" PCT patent application Serial number PCT/US07/81081, filed October 11, 2007.
Scepanovic, D., Cohen, R.J., "Method for measuring physiological stress" Provisional patent application US Serial number 60/851241, filed October 12, 2006.
Scepanovic, D., Xiao, X., Lee, K., Cohen, R.J., "Time Domain Methods for Estimating Autonomic Indices from Single-Lead ECG" BMES 2006, Cardiovascular Engineering
Scepanovic, D., "Synthesis and Implications of Auditory Filter Shape Normalized Stimuli for Studying Speech Encoding," Masters Thesis in Biomedical Engineering. 2005, The Johns Hopkins University: Baltimore. p. 251.
Scepanovic, D., Kirshtein, J., Jain, A.K., Taylor, R.H.,"Fast Algorithm for Probabilistic Bone Edge Detection (FAPBED)," Proc. of SPIE Vol. 5747 (SPIE, Bellingham, WA, 2005).
Heinz, M.G., Scepanovic, D., Issa, J., Sachs, M.B., and Young, E.D. (2004). "Normal and impaired level encoding: Effects of noise-induced hearing loss on auditory-nerve responses," In D. Pressnitzer, A. de Cheveigne, S. McAdams, L. Collet (Eds.) Auditory Signal Processing: Physiology, Psychoacoustics, and Models. New York: Springer-Verlag.
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