A Study on the Physiological Characteristics of Spatial Peripheral Blood Flow Velocity Based on Photoplethysmography and Its Potential Application as a Peripheral Biosignal = 광용적맥파 기반 공간말초혈류속도의 생리학적 특성 및 말초생체신호로서의 활용 가능성 연구

다국어 초록 (Multilingual Abstract)

The purpose of this dissertation is to introduce and validate novel hemodynamic indices—spatial pulse wave velocity (SPWV) and spatial peripheral blood flow velocity (SPBFV)—measured through the integration of magnetoplethysmography (MPG) and photoplethysmography (PPG). These indices expand upon the established parameters of pulse wave velocity (PWV) and peripheral blood flow velocity (PBFV), providing extended insight into vascular elasticity, peripheral resistance, and microcirculatory blood flow within the human body.

In the first part of the study, SPWV was measured by attaching an MPG sensor to the radial artery near the wrist and a PPG sensor to the finger, while SPBFV was measured by attaching PPG sensors to the wrist and fingertip, respectively. SPWV was defined as the distance between the radial artery and fingertip divided by the time difference between the peak values of MPG and PPG signals, yielding values in the range of 1.2–1.9 m/s. SPBFV was defined similarly, using dual PPG sensors, producing values in the range of 19–25 cm/s. The results indicated that these parameters are sensitive to vascular conditions such as arterial stiffness, vascular compliance, and peripheral resistance.

In the second part of the study, SPBFV was examined in children and adolescents aged 9–14 years to investigate age-related vascular changes. The pilot study involved six participants with normal body mass index (BMI), and repeated measurements were conducted in a controlled laboratory environment. The results demonstrated a linear decrease in heart rate from 109 to 69 beats per minute with increasing age, paralleled by a linear decline in SPBFV from 24 to 23.1 cm/s. An inverse relationship between systolic blood pressure and SPBFV was also observed. These findings suggest that SPBFV reflects developmental changes in vascular structure, including the expansion of capillary surface area in peripheral tissues during adolescence, and may serve as an early indicator for diagnosing pediatric vascular and circulatory disorders.

In the third part, a wrist-wearable SPBFV monitoring device was designed and implemented to enable continuous, noninvasive vascular health assessment in daily life. The device incorporated an ESP32-C3 microcontroller, dual DFRobot PPG sensors, and wireless communication via the MQTT (Message Queue Telemetry Transport) protocol. The system allowed real-time signal acquisition, peak detection through adaptive thresholding and moving average filtering, and visualization using a node-red dashboard with data storage in a MySQL (My Structured Query Language) database. Clinical evaluation was conducted on three non-risk participants: a - xviii - 49-year-old male, a 26-year-old male, and a 26-year-old female. Results showed that the 49-year-old subject exhibited a lower median SPBFV (25.91 cm/s) compared with younger participants (28.92 cm/s for the female and 31.50 cm/s for the male), reflecting age-related vascular stiffening and decreased hemodynamic regulation.

Taken together, the findings from these three studies demonstrate that SPWV and SPBFV are valuable additions to conventional hemodynamic parameters. These indices are noninvasive, simple to measure, and capable of providing continuous physiological information. Moreover, the development of a wearable monitoring device suggests strong potential for clinical translation, remote healthcare applications, and integration into AI-driven digital healthcare platforms. Therefore, SPWV and SPBFV may serve as critical biomarkers for early diagnosis, prevention, and long-term management of cardiovascular and cerebrovascular diseases.

Keywords: Spatial pulse wave velocity (SPWV), Spatial peripheral blood flow velocity (SPBFV), Magnetoplethysmography (MPG), Photoplethysmography (PPG), Noninvasive hemodynamic indices, Wearable devices, Digital healthcare

목차 (Table of Contents)

• List of Figures ­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­ ------------------------------------------------------------------------ⅴ
• List of Tables ­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­------------------------------------------------------------------------- xiii
• Abbreviations ­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­ ------------------------------------------------------------------------xiv
• Abstract ­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­ ------------------------------------------------------------------------------xvi
• Chapter Ⅰ. Introduction ­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­ --------------------------------------------------------------- 1
• 1-1. Background and necessity of the study ­­­­­­­­­­­­­­ ------------------------------------------ 1
• 1-2. History and development of PPG and MPG ­­­­­­­­­­­­­­-------------------------------------- 11
• 1-3. Distinction from previous studies and originality ­­­­­­­­­­­­­­-------------------------------- 15
• 1-4. Research objectives and methodology ­­­­­­­­­­­­­­ ----------------------------------------- 20
• Chapter Ⅱ. Theoretical background ­­­­­­­­­­­­­­­­­­­­­­­­­­ ------------------------------------------------- 23
• 2-1. Principles and applications of PPG ­­­­­­­­­­­­­­ ---------------------------------------------- 23
• 2-2. Principles and applications of MPG ­­­­­­­­­­­­­­ ---------------------------------------------28
• 2-3. Concept of SPBFV and SPWV ­­­­­­­­­­­­­­ -------------------------------------------------- 35
• 2-4. Importance of noninvasive biosignal measurement ----------------------------­­­­­­­­­­­­­­ 38
• 2-5. Development and necessity of personalized preventive medicine ­­­­­­­­­­­­­­-------------- 41
• Chapter Ⅲ. Characteristics of SPWV and SPBFV using MPG and PPG --------------- 44
• 3-1. Structure and prototype of the clip-type pulsimeter composed of a
• permanent magnet and a hall sensor ------------------------------------------------ 44
• 3-2. Operating and measurement principles of MPG using a clip-type pulse wave
• measurement device equipped with a permanent magnet and a hall sensor -----­­­­--- 49
• 3-3. Comparison of the properties of SPWV and SPBFV measured by MPG and PPG ­­­­­­­­­­­­- 55
• 3-4. Summary -------------------------------------------------------------------------67
• Chapter Ⅳ.
• A study on the characteristics of SPBFV in children and adolescents using PPG ----­­­­­­­­­ 69
• 4-1. Arterial distribution network and prediction of vascular blood flow using PPG ---­­­­­­­­­­­­ 69
• 4-2. Analysis of pilot clinical study results on SPBFV in children and adolescents ----­­­­­­­­­ 76
• 4-3. Summary ­-------------------------------------------------------------------------84
• Chapter Ⅴ.
• Development and characterization of a wrist-worn device for measuring
• SPBFV using PPG ­---------------­---------------­---------------­----------------------- ­­­­­­­­­­ 86
• 5-1. Wearable SPBFV measurement device using two PPG sensors ------------------­­­­­­­­ 86
• 5-2. Analysis and comparison of measurement data --------------------------------- 93
• 5-3. Summary ------------------------------------------------------------------------ 105
• Chapter Ⅵ.
• Overall summary and general conclusion ------------------------------------------- ­­­­­­­­­­­­­­­ 108
• 6-1. Characteristics of SPWV and SPBFV using MPG and PPG ----------------------- 108
• 6-2. A study on the characteristics of SPBFV in children and adolescents
• using PPG ---------------------------------------------------------------------- 110
• 6-3. Development and characterization of a wrist-worn device for measuring
• SPBFV using PPG --------------------------------------------------------------- 111
• 6-4. Significance of SPWV ---------------------------------------------------------- 113
• 6-5. Significance of SPBFV ---------------------------------------------------------- 117
• 6-6. General conclusion ------------------------------------------------------------ 121
• References ­------------------------------------------------------------------------- 123
• Korean Abstract ------------------------------------------------------------------- 129
• Appendix --------------------------------------------------------------------------- 132
• List of Publications ----------------------------------------------------------------- 161