Bioelectric impedance as an index of thoracic fluid.

Background: Thoracic electrical impedance (TEI) has been suggested as a means to monitor thoracic fluid changes. It was hypothesized that TEI would correlate significantly with an intrathoracic blood volume (pulmonary capillary blood volume) during postural shifts.

Methods: TEI was compared with pulmonary capillary blood volume (Vc) in six men and six women during postural stress. The diffusion capacity for carbon monoxide (DLCO) was used to determine Vc. Subjects were supine for 15 min and then stood quietly for 5 min. Measurements were made at the end of each period. Heart rate (HR), stroke volume (SV), and BP were determined for each posture.

Results: Women had higher TEI values at rest, confirming previous data. Cardiopulmonary variables change similarly for each gender on standing. TEI correlated significantly with Vc (p<0.01), and Vc was significantly correlated with SV (p<0.01). Total lung capacity and residual volumes were unchanged with posture.

Conclusion: It is concluded that TEI can serve as a useful clinical and research monitor of thoracic fluid volume changes, even small volume changes, and correlates with a measured thoracic fluid compartment.