TNO Finger Pressure Reference Guide - Integral Process

TNO Finger Pressure Reference Guide 18This is usually observed immediately after starting a new measurement and whenthe smooth muscle tone is not stable. If these so-called multi-step Physiocals arefrequently observed during a measurement accuracy of the finger blood pressuremay be reduced.2.9 Example of a Physiocal with variable pressure levelsIf during a finger blood pressure measurement the device is unable to recognizebeats in either the finger blood pressure or the plethysmogram the Physiocalalgorithm uses variable pressure levels instead of constant pressure levels during aPhysiocal. In this situation it is assumed that there is no intra-arterial pressurechange during a heart beat, as is the case during certain phases of open heartsurgery. However, it is also possible that this special Physiocal is performed after aperiod of movement artifacts during which the software was unable to recognizeheart beats. During a special Physiocal an inverted pressure waveform issuperimposed on the constant levels. The resulting plethysmogram is used as if theintra-arterial pressure was varying and not the cuff pressure.200Finger blood pressure (mmHg)1501005000 5 10Time (s)Figure 2.9 Special Physiocal with variable pressure levels2.10 Pressure staircase at the start of a measurementDuring the start-up phase of a finger blood pressure measurement, the cuff pressureis increased stepwise while analyzing the plethysmogram. Based on the amplitudeand shape of the plethysmogram the stepwise increase in pressure is stopped as