Effects of Bio-Impedance Sensor Placement Relative to the Arterial Sites for Capturing Hemodynamic Parameters

Accurate measurement of the heart pulse waveform based on blood volume changes inside the arteries is crucial for reliable estimation of hemodynamic parameters such as blood pressure and cardiac output. Placement of blood volume sensors such as bio-impedance sensors close to the arterial sites is essential for the accurate measurement of the pulse waveform. The effect of sensor location relative to the wrist arteries on the pulse waveform had not been studied previously on human subjects. In this paper, we explore the effect of arterial and off-arterial placement of the bio-impedance sensor on important pulse waveform features such as pulse transit time (PTT), which is the travel time of the arterial pressure pulse between two sensors, and diastolic peak error (DPE), a measure of pulse signal sharpness. Placing the current injection and voltage sensing electrodes of a bio-impedance sensor on the radial artery provide greater accuracy for such features. We find that arterial PTT has a significantly lower standard deviation compared to off-arterial PTT indicating better signal quality. Similarly, we observe that DPE is much smaller for arterial bio-impedance which confirms our expectations. Based on these features, the location of the artery can be determined using an array of sensors placed around the artery.