A Novel Minimally Occlusive Cuff Method Utilizing Ultrasound Vascular Imaging for Stress-Free Blood Pressure Measurement: A-Proof-of-Concept Study

Kouzani A, Mosadegh B, Gharaie S. Blood Pressure Sensors: Materials, Fabrication Methods, Performance Evaluations and Future Perspectives

Advancements in materials science and fabrication techniques have contributed to the significant growing attention to a wide variety of sensors for digital healthcare. While the progress in this area is tremendously impressive, few wearable sensors with the capability of real-time blood pressure monitoring are approved for clinical use. One of the key obstacles in the further development of wearable sensors for medical applications is the lack of comprehensive technical evaluation of sensor materials against the expected clinical performance. Here, we present an extensive review and critical analysis of various materials applied in the design and fabrication of wearable sensors. In our unique transdisciplinary approach, we studied the fundamentals of blood pressure and examined its measuring modalities while focusing on their clinical use and sensing principles to identify material functionalities. Then, we carefully reviewed various categories of functional materials utilized in sensor building blocks allowing for comparative analysis of the performance of a wide range of materials throughout the sensor operational-life cycle. Not only this provides essential data to enhance the materials' properties and optimize their performance, but also, it highlights new perspectives and provides suggestions to develop the next generation pressure sensors for clinical use.

Comprehensive analysis of effective reflection distance and its association with wave reflection strength under diverse hemodynamic conditions in anesthetized dogs

Pressure wave reflection is associated with cardiovascular risk. The conceptual distance to a theoretical major reflection site, termed effective reflection distance (ERD), has been associated with aging and augmentation index (AIx) clinically. However, it remains unclear whether and how ERD varies and associates with AIx when the hemodynamic condition is acutely perturbed in a patient. The objective of this study was to address this issue in rigorously controlled animal experiments. In 13 anesthetized dogs, we measured arterial pressure, aortic flow and femoral arterial flow, while altering the hemodynamic condition over wide ranges by administering zatebradine (bradycardic agent), nitroprusside (vasodilator), noradrenaline (vasoconstrictor), dobutamine (inotrope), and dextran (volume-expander). Using the measured data, we determined ERD based on an arterial model comprising a tube with a complex frequency-dependent load (ERD_TL), which has been considered a physiologically valid model. We also determined ERD based on wave separation (ERD_WSA) and pressure-based analyses (ERD_AW). ERD_TL was shortened significantly in response to nitroprusside or dobutamine infusion, and was significantly and negatively associated with AIx in multiple regression analysis using pooled data. ERD_WSA or ERD_AW did not necessarily correlate with ERD_TL in terms of responses to drug administration or association with AIx. In conclusion, under diverse hemodynamic conditions, ERD_TL changes sensitively and shows physiologically reasonable association with AIx. This result substantiates the importance of paying close attention to medications during clinical analysis of wave reflection. Caution is required when using ERD_WSA or ERD_AW as an alternative to ERD_TL.

Human Vital Signs Detection Methods and Potential Using Radars: A Review

Continuous monitoring of vital signs, such as respiration and heartbeat, plays a crucial role in early detection and even prediction of conditions that may affect the wellbeing of the patient. Sensing vital signs can be categorized into: contact-based techniques and contactless based techniques. Conventional clinical methods of detecting these vital signs require the use of contact sensors, which may not be practical for long duration monitoring and less convenient for repeatable measurements. On the other hand, wireless vital signs detection using radars has the distinct advantage of not requiring the attachment of electrodes to the subject's body and hence not constraining the movement of the person and eliminating the possibility of skin irritation. In addition, it removes the need for wires and limitation of access to patients, especially for children and the elderly. This paper presents a thorough review on the traditional methods of monitoring cardio-pulmonary rates as well as the potential of replacing these systems with radar-based techniques. The paper also highlights the challenges that radar-based vital signs monitoring methods need to overcome to gain acceptance in the healthcare field. A proof-of-concept of a radar-based vital sign detection system is presented together with promising measurement results.