Continuous monitoring of vascular age by pulse wave velocity using wearable ECG and PPG sensors

Lead Research Organisation: University of Surrey
Department Name: Clinical Experimental Medicine

Abstract

BACKGROUND
While healthy ageing is one of the most important challenges of our time, it is difficult to monitor ageing during normal life. Longterm vascular ageing is the results of many injurious events that occur during everyday life and currently go undetected. The ability to continuously measure ageing with low cost devices would open opportunities to test interventions that aim to slow ageing in a large number of individual people.

Progressive stiffening of the blood vessels is one of the most important features of human ageing. Importantly, arterial stiffness can be measured non-invasively as pulse wave velocity (PWV) and is viewed as the most important biomarker of vascular age, but it currently requires costly and bulky equipment and trained researchers to measure. However, personal devices like fitness bracelets and smart watches are now able to measure a variety of biological information including blood flow and electrical activity of the heart. This information could be used to calculate PWV with each heartbeat in real time and provide immediate information on the biological age of the blood vessels. More importantly, this approach would allow the identification of factors that accelerate and slow ageing in an individual person and monitor the success of 'anti-ageing' therapies in an individual person. So far, no technology is available that fulfils this task.

OBJECTIVES OF PROPOSED RESEARCH
In the current project, we wish to develop low-cost methods to allow monitoring of individual 'vascular age' at scale during real life using wearables or design a prototype device with available components. In this first phase of the project, we will set up a developmental tool kit to integrate data from ECG (electrocardiogram, electrical activity of the heart) and PPG (photoplethysmography, blood flow in the skin) sensors, calculate PWV, and create useful visualization of integrated data. We will then test the accuracy, validity, and performance of PWV measurements in people at different age and with vascular disease under different conditions and compare the results with gold standard methods (tonometry) to measure PWV. Furthermore, we will design a prototype device build from low-cost standard sensor components (by Surrey Sensors Ltd.) and evaluate if existing low-cost devices can be used for continuous monitoring of PWV over time to help us decide on the focus of the next steps.

FUTURE DIRECTION
Reaching these objectives will form the basis of moving forward with a second application next year. In this second step, we will build a small number of prototype devices to and/or develop a software solution for using sensor data from existing fitness devices for continuous PWV measurements. We will then test the utility and applicability of continuous PWV in real life in people of different ages to establish normal values. Furthermore, we hope to validate the measurements by comparing results with invasively measured PWV during routine catheter procedures in the hospital. In a third step, we plan to perform a proof-of-concept study to demonstrate the abilities of continuous PWV measurements to detect acute responses of arterial stiffness to life-style interventions such as healthy diet and chronic changes in arterial stiffening over time (vascular ageing trajectory). In a future stage, we hope to be able to test the continuous PWV measurements in larger groups of people, potentially in collaboration with industry, NHS, and using sensor data from devices that people already own. Large data sets can then be analysed together with other individual health related data by machine learning to identify ageing patterns and effect of healthcare interventions on trajectories of vascular ageing.

Publications

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Description The project is not completed due to COVID related delays in performance of clinical studies and limited availability of electronic components.

In the current project, we aimed to develop low-cost technology either using existing devices or build prototype device with available components to allow monitoring of individual "vascular age" at scale. The underlying principle is that with increasing age the blood vessel get stiffer and that the stiffness of arteries can be estimated by measuring the speed at which the pulse wave travel through the body. In principle the speed to the pulse wave can be determined by measuring the distance between the heart and an artery on the body and divide this be the time between a heartbeat and the pulse at some part of the body. The components to measure this are available in most modern smart watches, namely an electrocardiogram (ECG) and light sensor called photoplethysmography sensor (PPG, green light). The following has already been achieved:

1. We have developed mathematical models to automatically calculate the pulse wave velocity from continuous signals recorded with commercial PPG and ECG sensors place at different parts of the body including the arm or the leg.

2. We have finished a clinical study that demonstrates that the pulse wave velocity we measure increases with age in healthy people and is significantly increased in people with diabetes, that are known to suffer from accelerated vascular ageing. In addition, our data show that the pulse wave velocity measurements we get are similar to much more expensive commercial devices. Furthermore, our data show that we can detect improvements in the pulse wave velocity after study participants have consumed a food supplement (cocoa polyphenols) that is known to improve vascular function. These data clearly provide the proof of concept that the technology is capable to detect clinically relevant information with good precision and reproducibility. We are currently finalising the analyses and preparation of publication.

3. We have commissioned a market research study to help inform the next steps of product development by looking at existing devices on the market. Two main customer segments were investigated: (1) Clinical devices for healthcare professionals and (2) Consumer devices. Preliminary findings indicate that: (1) Existing clinical devices measuring arterial stiffness use various methodologies with different degrees of clinical validation. These are currently used as research tools and have not yet entered routine clinical practice (2) A range of wearable devices with PPG sensors exist on the market to measure a range of physiological parameters other than arterial stiffness. Extremely few consumer devices offer the measurement of arterial stiffness. These devices have either been launched very recently or are still in development and there is a lack of peer-reviewed clinical validation of the arterial parameters measured. To the best of our knowledge, no existing device records PPG and ECG at the same time for the purpose of measuring arterial stiffness. Therefore, we have started building our own prototype.

4. We are in the process of building a minimal viable prototype from low cost components that can record ECG and PPG at the same time. In parallel we have developed a custom software that can calculate pulse wave velocity continuously from this sensors attached to the body using the mathematical models described under (1.). We expect the first prototype device to be ready within the next month. With this prototype we aim at getting more preliminary data also in the healthcare sector to support justification for further development.
Exploitation Route We are developing fundamental principles of pulse wave velocity detection with wearable devices and picture of the market with potential users and health applications. Together with our proof of concept data, we are confident that we can find partners and funders to help us develop this further.
Sectors Agriculture, Food and Drink,Digital/Communication/Information Technologies (including Software),Electronics,Healthcare,Leisure Activities, including Sports, Recreation and Tourism,Pharmaceuticals and Medical Biotechnology

 
Title Proof of concept study to test if pulse wave velocity measurements with photoplethysmography with or without electrocardiogram correlate with age and detect a now response 
Description The goal of the ESRC Healthy Ageing Catalyst award was to evaluate ways of developing a vascular age monitor. The studies performed so far serve the purpose to provide proof of concept that our basic set-up/methodology is capable of detecting age dependent changes of the vasculature and detect the effects of known interventions. In the first study, we tested if pulse wave velocity can be measured with photoplethysmography sensors with or without electrocardiogram data and if this correlates with age. In this proof of concept study, we tested the approach together with other modalities and devices that can measure pulse wave velocity. In a second study, we have tested if the set-up can detect a decrease in pulse wave velocity induced by a dietary intervention with cocoa flavanols. Based on the analysis of the data we will decide how to further develop the approach. 
Type Diagnostic Tool - Non-Imaging
Current Stage Of Development Initial development
Year Development Stage Completed 2021
Development Status Under active development/distribution
Clinical Trial? Yes
Impact Currently there is no notable impact. 
 
Description Presentation to SPAR (Symmetric projection attractor reconstruction) group on first results of PPG sensors to measure vascular age 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Professional Practitioners
Results and Impact I presented the preliminary results to member of an informal research group that is interested in signal processing. About 20 people attended (students, physicians and researchers). We discussed how their major topic (Symmetric projection attractor reconstruction) could be useful to analyse the data.
Year(s) Of Engagement Activity 2021
 
Description Talk about vascular ageing to member of the public in the SHARP: Surrey Healthy Ageing Research Partnership 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact I gave a presentation entitle 'Interventions to slow cardiovascular ageing' to a group of interest people of the general public in the context of the SHARP: Surrey Healthy Ageing Research Partnership. After the presentation there was a long discussion about ageing etc.
Year(s) Of Engagement Activity 2021
URL https://www.surrey.ac.uk/events/20211209-sharp-surrey-healthy-ageing-research-partnership-healthy-ag...
 
Description Talk at Sechenov University, Moscow (Development of sensors for personalised vascular medicine: vascular function, stiffness and peripheral artery disease) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact To facilitate collaborations with researchers in Moscow I gave a presentation entitled 'Development of sensors for personalised vascular medicine: vascular function, stiffness and peripheral artery disease' at the Vth Sechenov International Biomedical Summit 2021 (SIBS-2021). Organized and hosted by the Sechenov University, the hybrid event took place November 9-10, 2021. I presented preliminary results of the work performed as part of the ESRC grant. More than 100 participants (scientists and students) were online. Great discussion about limitations and potential collaborations.
Year(s) Of Engagement Activity 2021
URL https://sechenov-sibs.confreg.org/programma/