| 10:40-11:20 am |
Robert Gilmour
Cornell University
Control of local electrical dynamics in the heart
Heart rhythm disorders such as ventricular fibrillation are the leading cause of death in the US and other developed countries. The underlying mechanisms for such arrhythmias have not been adequately defined. One putative mechanis involves the alternation of the duration of consecutive cardiac action potentials, a phenomenon
known as electrical alternans. Spatially discordant alternans may create sufficient heterogeneity of electrical properties to initiate
one or more spiral waves of electrical excitation, thereby disrupting
normal cardiac rhythm. Given this scenario, suppression of alternans
is expected to be antiarrhythmic. To determine the extent to which
alternans control can be achieved in cardiac tissue using properly
timed premature stimuli, we paced isolated canine Purkinje fibers from
one end using a feedback control method. Spatially uniform control of
alternans was possible when alternans amplitude was small. However,
control became attenuated spatially as alternans amplitude increased. The amplitude variation along the cable was well described by a theoretically expected standing wave profile that corresponds to the first quantized mode of the one-dimensional Helmholtz equation. These results confirm the wavelike nature of alternans and may have important implications for their control using electrical stimuli.
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| 11:20-11:40 am |
Anton Burykin
Washington University in St. Louis School of Medicine
Email: burykin@wudosis.wustl.edu
authors: Anton Burykin, Timothy G. Buchman, Washington University in St. Louis, School of Medicine, Department of Surgery
Cardio-Respiratory Dynamics in Critical Care: Synchronization and
Variability
We studied changes in (1) cardio-respiratory interactions and (2)
dynamics of cardiovascular system during transitions from mechanical to spontaneous ventilation in critically ill patients. The study population
consists of patients admitted to a surgical intensive care unit following
surgery, trauma or complications. This observational study exploits a
standard clinical practice - the spontaneous breathing trial (SBT). The SBT consists of a period of mechanical ventilation, followed by a period of spontaneous breathing, followed by resumption of mechanical ventilation. We collected continuous respiratory, cardiac (ECG), and perfusion (blood pressure and pulse oximetry) traces of mechanically ventilated patients before, during and after SBT. The data were analyzed by means of spectral analysis, phase dynamics (instantaneous phase and frequency synchronization), and information-theoretic measures (approximate and sample entropies). Mechanical ventilation appears to affect not only the lungs but also the cardiac and vascular systems. Spontaneous cardiovascular rhythms are entrained by the mechanical ventilator and are drawn into synchrony. Sudden interruption of mechanical ventilation causes gross desynchronization, which is restored by reinstitution of mechanical ventilation. The data suggest that (1) therapies intended to support one organ system may propagate unanticipated effects to other organ systems and (2) sustained therapies may adversely affect recovery of normal organ system interactions.
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