A new stroke volume equation for thoracic electrical bioimpedance: theory and rationale.

A new stroke volume equation for thoracic electrical bioimpedance is proposed. This empirically derived formula differs from previous equations in that: the thoracic volume conductor is modeled geometrically as a frustum (truncated cone), rather than a cylinder; the specific resistivity of blood, rho, is appropriately eliminated as an independent variable; the equation employs a percentage of overall body height in lieu of a measured thoracic length; and a new term, delta, is introduced to scale the parent equation for deviation from ideal body weight.