Error magnitude of measurement sensors in air segment plethysmography

Besides examining the properties of the material involved, this investigation assesses the so-called static and dynamic measurement errors of sensors used for air segment plethysmography. The static error which has been found with the new BN sensors amounts to 8% (old models: 31%-44%). The folding of the interior membrane of the sensor resting upon the skin, which increases proportionately to the stiffness of the material, is discussed as a source of error. If a lockable steel wrapping is employed as an exterior cover for the sensors, the static measurement error decreases by 30%-50%. These results suggest a recommendation to use a metal wrapping for the sensors as described above even with routine air segment plethysmographic examinations, and additionally to correct by mathematical means the static measurement error (which has to be determined for each sensor individually). The measurement error of the sensors of the new BN series amounts to less than 5% for a frequency of not more than 0.5 Hz; this means that blood flow values amounting to more than 50 ml/(min X 100 ml) are indicated correctly with respect to the actual frequency. If the usual linen covering is used instead of the steel cover, the linearity of the frequency is only valid up to 0.1 Hz--the corresponding blood flow value being 15 ml/(min X 100 ml).