IMPEDANCE TECHNIQUES - NONINVASIVE PRIZEWINNERS

Impedance techniques are noninvasive and simple methods for the quanti fication of fluid volumes in the body. Tissue impedance, determined at multiple frequencies, offers the possibility of detecting total body water and extracellular and intracellular fluid volume. The major clin ical applications are assessment of dry weight and the study of fluid shifts within the body, e.g., during hemodialysis, and in the thorax ( pulmonary edema). Impedance cardiography monitors the heart-synchronou s impedance changes in the thorax. It is an accurate method to calcula te stroke volume, left ventricular ejection fraction, and systolic tim e intervals. Both methods have been validated extensively and deserve more appreciation for noninvasive monitoring in medicine.