Device Development for Physiological Monitoring

Medical professionals often use a set of metrics that describe a patient’s physiological state in order to detect or monitor medical problems. For example, a person’s “vital signs” consist of their body temperature, pulse, respiratory rate, and blood pressure. Body temperature can vary depending on gender, recent activity, food and fluid consumption, and even time of day, while severe deviations from normal temperature are generally indicators of disease or injury. Similarly, hypertension (high blood pressure) directly increases the risk of heart attack and stroke (1). Molecular-level metrics, such as blood glucose levels and electrolyte levels, are also key indicators of health (2,3,4). Current methods to measure such metrics often rely on bulky equipment or invasive techniques (2,3). A key goal in device development for physiological monitoring is to create a multi-functional, flexible, and compact device that can analyze data in real-time. 

Pioneering research by Gao et al. focused on wearable sensor technology, a field that is “essential to the realization of personalized medicine through continuously monitoring an individual’s state of health” (2). In particular, wearable devices can be continuously worn against the skin without interrupting or limiting the user’s function (2,3). Previous work led to commercially available sensors for physical activity and vital signs — the Fitbit is a popular wrist-worn device that measures heart rate and movement — but Gao et al. further explored molecular-level metrics through chemical analysis of sweat (2). Human sweat is rich in physiological information and can enable non-invasive monitoring (2,3). Sweat analysis is commonly applied to disease diagnosis, drug detection, and athlete performance optimization, though not typically in real-time. Excess ion loss in sweat can result in imbalance and dehydration, while sweat glucose is metabolically related to blood glucose (2). 

Researchers developed a sweat-based, non-invasive, multiplexed, and fully integrated device that can be worn on the forehead, wrist, or arms. This device measures glucose, lactate, sodium, and potassium in sweat, as well as skin temperature. Two key areas of progress were 1) its mechanical flexibility and endurance and 2) the combination of skin-conforming plastic-based sensors with silicon integrated-circuit components (2). 

Further advances were made by Sempionatto et al., who recently published their results in Nature Biomedical Engineering (3). As the body’s physiological responses to stimuli includes both metabolic and physical changes, the ideal physiological monitoring device would be able to monitor both types of metrics, such as blood pressure and metabolites. Parallel sensing is expected to have clinical value — for example, septic shock commonly involves a sudden drop in blood pressure alongside a rapid increase in blood lactate levels. Researchers developed a “non-invasive skin-worn device for the simultaneous monitoring of blood pressure and heart rate via ultrasonic transducers and of multiple biomarkers via electrochemical sensors” and demonstrated that it captured the effects of food intake, exercise, alcohol consumption, and more complex scenarios involving multiple stimuli (3). 

Recent advances in device development for physiological monitoring have helped pave the way toward accurate, convenient, and continuous data collection for clinical monitoring and research (2,3). The urgent need for remote monitoring has been particularly highlighted during the COVID-19 pandemic (3). These devices will enrich our understanding of the body’s response to daily activities and may help predict abnormal physiological changes, while addressing the common issue of compliance. Future research can focus on incorporating artificial intelligence for signal processing and additional sensors in order to increase the power of wearable sensor technology. 

References 

1. Johns Hopkins Medicine. Vital Signs (Body Temperature, Pulse Rate, Respiration Rate, Blood Pressure). Conditions and Diseases, Health, Johns Hopkins Medicine. (n.d.) https://www.hopkinsmedicine.org/health/conditions-and-diseases/vital-signs-body-temperature-pulse-rate-respiration-rate-blood-pressure  

2. Gao W, Emaminejad S, Nyein HYY, Challa S, Chen K, Peck A, Fahad HM, Ota H, Shiraki H, Kiriya D, Lien D-H, Brooks GA, David RW, & Javey A. Fully integrated wearable sensor arrays for multiplexed in situ perspiration analysis. Nature Letters, 2016, 529:509-514. doi: 10.1038/nature16521 

3. Sempionatto JR, Lin M, Yin L, De la paz E, Pei K, Sonsa-ard T, Silva ANDL, Khorshed AA, Zhang F, Tostado N, Xu S, & Wang J. An epidermal patch for the simultaneous monitoring of haemodynamic and metabolic biomarkers. Nature Biomedical Engineering, 2021. doi: 10.1038/s41551-021-00685-1 

4. University of Rochester Medical Center. Basic Metabolic Panel (Blood). Health Encyclopedia, University of Rochester Medical Center. (n.d.) https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=basic_metabolic_panel_blood