Impedance cardiography. Current status and clinical applications.

Impedance cardiography is a highly reproducible, rapid and safe method for the evaluation of cardiac performance in the clinical setting. Measurements of stroke volume (SV), end diastolic volume (EDV), and end systolic volume (ESV) with calculation of cardiac output (CO) were obtained in normal, healthy people (group 1, n = 21) and in patients with congestive heart failure (group 2, n = 18). Individuals were placed on a tilt table and cardiac profiles (measurements of CO, SV, EDV, and ESV) were performed at 45 degrees head up, 15 degrees head up, and supine. Group 1 responded by increasing CI from 2.9 +/- 0.81 L/min/M2 at 45 degrees to 3.3 +/- 1.0 L/min/M2 at 15 degrees to 3.7 +/- 1.0 L/min/M2 supine. There was no corresponding rise seen in group 2, with CIs of 2.1 +/- 0.83 L/min/M2, 2.0 +/- 0.78 L/min/M2 and 2.0 +/- 0.76 L/min/M2 at each position, respectively. In addition, while the EDV increased at each position in group 1 (45 degrees: 71 +/- 21 cc/M2, 15 degrees: 88 +/- 26 cc/M2, Supine: 102 +/- 29 cc/M2), no such increase was evident in group 2 (45 degrees: 57 +/- 29 cc/M2, 15 degrees: 52 +/- 20 cc/M2, Supine: 60 +/- 24 cc/M2). The inability of group 2 patients to elevate CI and the absence of any discernible change in EDV suggests an insufficiency of cardiac reserve with noncompliant ventricles. This information is currently being used to assess operative risk and to study effects of treatment modalities.