Cuffless, Non-Invasive Blood Pressure Monitoring

Somnotouch-NIBP (Somnomedics GmbH, Randersacker, Germany) is a cuffless, non-invasive system which estimates BP based on the PTT technique (TestBP). Allowing for continuous beat-to-beat BP monitoring. Finger photoplethysmography, three ECG leads and a watch-like-device with integrated actigraph are the hardware of the device. Transit time of a pulse wave from the corresponding ECG R-wave to the finger photoplethysmography signal is measured^{6 (link)}. Systolic and diastolic BP levels are calculated using non-linear modelling incorporating changes of the PTT and its relation to BP. The measurements are derived after an initial single-cuff based calibration measurement on the contralateral upper arm^{8 (link)}. Increasing pulse wave propagation results in shorter PTT and is associated with higher BP values. Logically, decreasing pulse wave propagation and longer PTT is linked to lower BP values. Arterial wall stiffness and tension influence pulse wave propagation and PTT, both of which effect BP^{9 (link),10 (link)}. In this study the reference device (RefBP) was the cuff-based Spacelabs 90217A (Spacelabs Healthcare Inc., USA) 24 h BP monitor^{11 (link)}. In July 2018, Somnomedics completed an update of the software. This update of the Domino light software version 1.4 led to the current version 1.5 (02/07/2018).