||Alternan responses in heart can cause conduction blocks and lead to fatal conditions such as ventricular fibrillation (VF). It would be important to know how to suppress the alternan response in hearts. In this thesis, we report a nonlinear control method to suppress the alternan responses in isolated heart experiments. In this method, the pacing period T0 is replaced by two periods; namely T1 = T0+ΔT/2 and T2 = T0-ΔT/2 where ΔT =T1-T2 is a small perturbation of the original period T0. Measured pressures of the isolated heart from the previous beat (Pn-1) and the current beat (Pn) are used to determine whether T1 or T2 should be used. In our control scheme, T1 is used when Pn > Pn-1 ; otherwise T2 is used. This method is different from the traditional proportional gain method. Results from experiments show that this T1T2 method can successfully suppress alternan response from isolated hearts.|
Another experiment in this thesis is to understand the variability of the interbeat interval which is controlled by SA node in an isolated whole heart. Primary cardiac co-cultures are also used to model the SA node in the heart. To understand the mechanism of the heart rate variability, we add a drug to suppress the contraction of the isolated whole heart, and also control the temperature of the cardiac cultures to see the effects of mechanical and temperature. The result shows that when we reduce the contraction of the isolated whole heart, the heart rate increases and the heart rate variability decreases. However, the decrement of heart rate variability is larger than the temperature effect on the isolated whole heart. For the experiment of temperature effect in cell cultures, the heart rate increases and the heart rate variability decreases when we increase the temperature.
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