Relationships Among Band Tension, Sensor Pressure, Patient Comfort, and Puslatile Signal Quality for Wrist Worn Health Monitoring Devices

This paper presents the design and testing of a wrist worn health sensing band used to gather relationship data among band tension, sensor pressure, patient comfort, and measured pulsatile signal quality. It uses micromachined carbon-infiltrated carbon nanotube electrodes to detect a patient’s pulse using a bioimpedance approach. The micromachined electrodes experience no corrosion, and they are both strongly conductive and hypoallergenic. A simple mathematical model was developed to show the relationship between pressure on the wrist and tension in the wristband. The wristband was tested by being worn by 10 different research subjects over 15 tests. During each test, the tension in the band was varied, and the tension, pressure, and bioimpedance signal were measured and recorded. The test subject also reported a comfort and pain level score for each level of band tension. The results show that the model correctly predicts that tension varies linearly with pressure, and that the pressure vs. tension slope increases with increasing wrist width. There also exists a linear relationship between tension and patient pain/comfort, but pressure does not show an effect on the patient discomfort or pain experienced. Signal quality when measured in the range of 0–4 N of tension and 0–20 kPa of sensor pressure does not have a direct correlation to either tension or pressure.