Low-power detection of sternocleidomastoid muscle contraction for asthma assessment and control

Sternocleidomastoid (SCM) is a paired muscle that stretches along both sides of the neck area. It acts as an accessory muscle of inhalation. Abnormal SCM contraction during asthma is usually a sign of further respiratory impairment. Thus, monitoring SCM muscles has great significance in asthma assessment and control. In this work, we develop a wearable monitoring system based on an optical sensor that consists of an LED and a photo detector (PD). A voltage comparator enables the microcontroller unit (MCU) to remain in sleep mode until waken upon detecting contraction. Experimental results show that our optical sensor consumes much lower power than surface electromyography (sEMG), the most commonly used technique while offering more comfort and compactness. It is also robust to motion artifact and DC baseline wandering. These properties simplify the hardware design, while the use of the comparator further reduces the system power consumption to >450 μW on average, making it the best option for low power monitoring.