Comparison of volume changes in the forearm assessed by impedance and water-displacement plethysmography

The ability of impedance plethysmography to measure changes in volume of the forearm in normal subjects is assessed by comparison with water-displacement plethysmography. The forearms were subjected to venous occlusion and simultaneous assessment of absolute volume changes of the same section of arm were made using the two techniques. The linear correlation between the two measurements had a coefficient of 0·93 but the impedance values were lower than those from water displacement by a factor of 0·41. These results are discussed by comparison with those from similar measurements described in the literature.