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(Circulation. 1970;41:651.)
© 1970 American Heart Association, Inc.

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The First Derivative Thoracic Impedance Cardiogram

ZUHDI LABABIDI M.D.¹; D. A. EHMKE M.D., PH.D.¹; ROBERT E. DURNIN M.D.¹; PAUL E. LEAVERTON PH.D.¹; RONALD M. LAUER M.D.¹

¹ From the University of Iowa, Section of Pediatric Cardiology, Department of Pediatrics, and the Department of Preventive Medicine and Environmental Health, University Hospitals, Iowa City, Iowa.

When an alternating current of high frequency is applied to the thorax, the first derivative of the impedance to this current is affected by the cardiac cycle resulting in a characteristic wave form.

Phonocardiograms, electrocardiograms, and first derivative thoracic impedance cardiograms were recorded simultaneously in 91 subjects. The first derivative thoracic impedance cardiograms were found to have sharply demarcated points which occur synchronously with the first heart sound, aortic second sound, pulmonic second sound, mitral opening snap, third heart sound, and fourth heart sound. The first derivative thoracic impedance cardiogram may thus be used not only as a reference tracing to help identify heart sounds on the phonocardiogram, but also for directly timing the intervals within the cardiac cycle.

Key Words: Phonocardiogram • Temporal relationships of phonocardiogram

Submitted on June 23, 1969
Accepted on December 16, 1969

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