Magnetically induced electric fields and currents in the circulatory system.

Blood flow in an applied magnetic field gives rise to induced voltages in the aorta and other major arteries of the central circulatory system that can be observed as superimposed electrical signals in the electrocardiogram (ECG). The largest magnetically induced voltage occurs during pulsatile blood flow into the aorta, and results in an increased signal at the location of the T-wave in the ECG. Studies involving the measurement of blood pressure, blood flow rate, heart sounds, and cardiac valve displacements have been conducted with monkeys and dogs exposed to static fields up to 1.5 tesla (T) under conditions producing maximum induced voltages in the aorta. Results of these studies gave no indication of alterations in cardiac functions or hemodynamic parameters. Cardiac activity monitored by ECG biotelemetry during continuous exposure of rats to a 1.5-T field for 10 days gave no evidence for any significant changes relative to the 10 days prior to and following exposure. Theoretical modeling of magnetic field interactions with blood flow has included a complete solution of the equation describing the flow of an electrically conductive fluid in the presence of a magnetic field (the Navier-Stokes equation) using the finite element technique. Magnetically induced voltages and current densities as a function of the applied magnetic field strength have been calculated for the aorta and surrounding tissues structures, including the sinoatrial node. Induced current densities in the region of the sinoatrial node are predicted to be >100 mA/m2 at field levels >5 T in an adult human under conditions of maximum electrodynamic coupling with aortic blood flow. Magnetohydrodynamic interactions are predicted to reduce the volume flow rate of blood in the human aorta by a maximum of 1.3%, 4.9%, and 10.4% at field levels of 5, 10, and 15 T, respectively.