AJP - Regulatory, Integrative and Comparative Physiology, Vol 236, Issue 3 168-R174, Copyright © 1979 by American Physiological Society
Intrathoracic electrical impedance measurements from an esophageal probe
M. M. Mitchell and R. S. Newbower
The sensing of intrathoracic electrical impedance from an esophageal probe
may allow relatively noninvasive monitoring of cardiac and respiratory
functions of particular interest in anesthesia and intensive care. We have
obtained a partial solution of the intrathoracic current-field problem for
impedance measurements made from a four-terminal linear array of electrodes
located in the esophagus. It allows prediction that aortic root motion will
exceed aortic distension as a major determinant of the cardiac
intrathoracic esophageal impedance signal. This prediction was confirmed
for a specific carefully selected and placed electrode array in
anesthetized dogs. In general, motions of organs will be more important
than volume changes in affecting the esophageal impedance signal. Thus,
timing information (preejection period and left ventricular ejection time)
is available from electrodes on an esophageal probe, but cardiac output
information appears to be inaccessible for fundamental reasons.
