The interaction between the cardiac hemodynamics and brain activity has been extensively studied in the past. However these studies have involved not only an increase in heart rate but also an increase in blood pressure. One method to evaluate for underlying coronary artery disease is to perform stress testing. Often, myocardial stress is achieved by the patient walking on a treadmill or riding a stationary bicycle while being monitored. In patients that are unable to exercise, pharmacologic stress testing is performed, either with vasodilatory agents (e.g. adenosine) or dobutamine, which is a pro-inotropic and chronotropic drug. During dobutamine infusion, the heart rate increases, but there is a negligible increase in blood pressure. The result is that the heart rate increases as a function of the dosage. Thus by monitoring brain activity while patients are undergoing dobutamine stress testing the effect of increased blood pressure on the brain is removed. It was found in the results of one patient that there are fi ve areas of the brain which show a change in the frequency of EEG activity that is a function of dobutamine dosage. Using Fourier transforms it was established that this change occurred at a frequency around 12.5 Hz. The regions of the brain where the increased activity were a function of heart rate occurred in the CZ-PZ, C4-P4, T5-O1, T4-T6 and C3-P3 regions. In undertaking these calculations it was realized that the stress on the ventricle could be calculated. The physicians monitor ECG of the patient to evaluate the cardiac status of the patient. Since currently the attending physician does not have data on the stress being applied to the myocardium, it would be useful to have this calculated on a real time basis. The motivation for the present preliminary study is to both investigate the feasibility of producing such information for clinicians as well as to investigate the variation between different patients as the heart rate varies. It was found that generally the surface shear stress increased with heart rate around most of the left ventricle. While the time averaged shear stress may be important for diagnosis the maximum shear stress probably is the limiting factor in terminating testing.
brain, diagnostic tool, echocardiogram, electroencephalogram, frequency, heart, stress
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