High speed and wearable speckle contrast optical spectroscopy for cuffless blood pressure measurements

Project Summary: Hypertension is the leading cause of cardiovascular disease (CVD) and affects nearly half of adults in the US. Periodic cuff-based blood pressure (BP) measurements with a sphygmomanometer are the predominant method of monitoring BP, but have been shown to be a poor reflection of a person’s usual BP. Conversely, ambulatory blood pressure monitoring (ABPM), in which patients wear a BP cuff on their arm for 24 hours while measurements are recorded every 30-60 minutes, more accurately predicts future CVD. Unfortunately, ABPM is cumbersome and uncomfortable for patients, preventing its widespread adoption. In addition, ABPM devices often disrupt sleep, thereby affecting nocturnal BP, leading to potentially biased estimates of CVD risk. A cuffless and non-invasive ABPM would facilitate greater patient access and more frequent BP measurements, potentially transforming the management of hypertensive patients. We have recently demonstrated that high-speed (390 Hz) speckle contrast optical spectroscopy (SCOS) can provide accurate cuff-less BP measurements in healthy subjects during exercise. SCOS utilizes speckle-based measurements to measure blood flow in tissue. Our preliminary results have shown that the addition of blood flow index (BFi) information improves BP estimation significantly, reducing errors within the Association for the Advancement of Medical Instrumentation (AAMI) standards. While promising, the technology must be converted from its current benchtop state to a wearable device capable of multi-hour ambulatory monitoring. Additionally, the technique needs to be tested in a wider range of subjects, including those with hypertension. To tackle these challenges, our team will develop the first high speed wearable SCOS system with FPGA-based real-time processing to achieve extraction of BFi and photoplethysmography (PPG) cardiac signals on the wrist and finger (Aim 1). We will embed two small (3.7 X 3 mm) 180 Hz CMOS detectors with high pixel density (640 X 480), and the unit will be battery operated and designed for long-term (8 hour) real-world measurements. Simultaneously, we will validate SCOS for cuffless blood pressure monitoring in patients with hypertension (Aim 2). We will measure N = 50 patients with elevated BP using our benchtop SCOS system during an isometric hand grip exercise and develop subject-specific machine learning models to predict BP. Finally, we will validate wearable SCOS for cuffless ABPM (Aim 3). First, N=20 healthy volunteers will be measured during various motions to establish artifact removal algorithms. Then, hypertensive subjects (N=50) will be measured during a continuous 2 hr measurement that includes a positional test and a handgrip exercise test. Then, to more rigorously test the wearable SCOS device in the real-world, an additional cohort of N = 35 healthy volunteers will be assessed for 8 hr during their normal daily activities. Finally, N=10 subjects will be measured during vigorous exercise. If successful, this project will provide a new highly accurate and continuous ABPM methodology that is far less disruptive to patients, thus improving access to ABPM for hypertension management.