To determine whether leg position or distance between the inner electrodes affect the magnitude of impedance change during deep inspiration, 30 adult patients (60 limbs) were studied with the Minnesota Impedance Cardiograph. Phlebography was performed in 19 limbs and correlated with the impedance findings.
There was no difference in the results of impedance testing between the straight- and bent-knee positions, nor was there a difference for the two electrode positions.
The phlebographic correlation indicated that none of the techniques was accurate enough to warrant use of the impedance method as the sole diagnostic maneuver in deep phlebothrombosis.
Deuvaert FE, Dmochowski JR, Couch NP. Positional Factors in Venous Impedance Plethysmography. Arch Surg. 1973;106(1):53-55. doi:10.1001/archsurg.1973.01350130055012