The Finapres NOVA uses the Volume-Clamp method to calculate a reconstructed brachial artery pressure (reBAP) signal from the pressure and photoelectric plethysmography sensors inside the unit's finger cuffs. However, a brachial calibration (BraCal) using an arm blood pressure cuff is required to compare the calculated value with one measured invasively and to comply with AAMI/ANSI/ISO 81060-2:2013.
The Systolic pressure of the reBAP signal (averaged over 10 beats prior to the BraCal) is subtracted from the Systolic measured value calculated by the arm cuff (averaged over 2 measurements). When the subtraction is done, the Delta (∆) value shows the difference between the actual measured value and the reBAP value calculated from the finger cuff. After the BraCal is complete, a marker is added to the channel, showing the average arm measurement (Systolic and Diastolic pressures) and the Delta (∆) value. In the picture below, the delta value is zero.
The Delta (∆) value is a key indicator of how well the finger cuff was initially fitted to the subject. The allowable range of the Delta (∆) value is between -15 and +15 mmHg. The closer the delta is to 0 mmHg, the better. If the value is outside of the allowed range, negative or positive, you will need to adjust the finger cuff as noted below:
- "+" Delta (∆) value = the cuff is too loose, and you will need to tighten it
- "-" Delta (∆) value = the cuff is too tight, and you will need to loosen it
For further technical assistance with this or any other issue, please contact ADInstruments Technical Support by clicking HERE.