The new approach
Every BIA device is purpose-built to perform a “body composition analysis”. Some simple Z devices are assessing 2 level limited model, splitting the whole body into fat and lean. This is a very primitive approach, comparable to anthropometry, skin fold, densitometry, and it is totally insensitive to detect nutrition or hydration hindrances.
Other devices, using phase sensitive or multiple frequency technology, have extended the body composition concept to the “three compartment model” hence separating the FFM assessment in a split between intra and extra cellular spaces (ECM/BCM).
Theoretically this method should deliver more viable clinical information, however it is always limited by the assumption of a fixed hydration rate in the lean tissues. That is FFM = TBW/0,733.
The limitation of body composition assessments, irrespective of the method applied, derives from a set of major deficiencies:
• Hydration cannot be assumed.
• Hydration is never steady state.
• Any model proposed is pseudo anatomical.
• The human body is by far too anisotropic to be modelled.
The clinical utility of BIA can be achieved solving the equation like and ECG interpretation methodology, that is using a stand-alone procedure based on patterns of direct impedance measurements, in other words likewise a thermometer there should be no need to associate a measure with weight, height, gender, age to detect abnormality.
Body soft tissues generate an impedance complex that can be directly evaluated in terms of normal ranges of the specific whole body resistivity (WBRz/Stature height) and whole body permittivity (WBXc/Stature height) and current flow distribution analysis within the intra and extra cellular conductive spaces, measured directly by our devices and supported by adequate epidemiology and consistency of the measures.
An analogy to help understanding our philosophy are the body temperature or the blood pressure assessment: to classify feverish states thermometer data do not require to be associated with height, weight or any additional co-predictor and the same applies to a sphygmomanometer. And impedance analysis, if duly normalized, can produce similar clinical useful results if the electrical measurements are aimed at what they really directly sense: quality and not quantity.
The combined use of three parameters (readily and consistently measured by our technology since >25 years) are applied to a set of nomograms constructed and validated by several thousand assessments of normal subjects. The graphical location can alert the clinician if the total body (conductive) soft tissue observed is within normal bioelectrical ranges, which are strictly related and indicative of the real hydration and nutrition state at the time of the observation and avoiding the bias of theoretical models, anthropometry and invalid or not applicable assumptions.
