Bioimpedance measurement with respect to pulsatile pulmonary blood flow.

We used four-electrode electrical impedance plethysmography (IPG) to estimate regional pulmonary perfusion at three lung volumes, RV, FRC, and TLC. To define the region, the upright lung was divided into four equal sampling areas dorsally along the paravertebral space. The Kubicek formula was used to calculate pulmonary perfusion. Regional base resistance (Ro) decreased from the top to about 3/4 down the lung and then leveled off. The regional perfusion (Qz) showed an increase from the apex to about 3/4 down the lung and thereafter decreased toward the base, except at TLC. The regional distribution of the electrical derivative of resistance (dR/dt) resembled that of Qz because there was no statistically significant difference in ventricular ejection time or heart rate among studies. The value of the arithmetic sum of regional Ro was significantly larger than that of Ro for the total sampling field while the reverse was true for Qz. These discrepancies can be explained on the basis of the lead field theory applied to IPG. The regional perfusion gradient determined by IPG represents the pulsatile perfusion gradient in vivo because the outputs from the impedance analyzer are intimately linked to the pulse-synchronous pulsatile nature of pulmonary blood flow. Safe, simple, and noninvasive IPG can be used to study regional pulmonary perfusion in clinical situations, high altitude, or unusual environments.