AI-Guided Predictions of Blood Pressure Dysregulation Using Perfusion Index as a Novel Biomarker in Persons With Spinal Cord Injury

Introduction/Background: Persons with spinal cord injury (SCI) may experience impaired control of several autonomic functions, including blood pressure (BP) fluctuations and impaired body temperature regulation in response to exercise, cold exposure, or a full bladder. Hypertension (high BP) is commonly episodic (comes and goes) and without clinical symptoms (the person is unaware). Mechanisms for impaired BP regulation after SCI are not completely understood and contribute to the limited availability of reliable wearable devices for continuous BP monitoring in the community.

Purpose of the Study: By doing this research study, the investigators hope to learn how perfusion index (PI) and the other measured vital signs, respond to moving from the warm to cool room. The investigators will use sophisticated analysis of the data collected, which will include artificial intelligence, to determine how perfusion index can predict changes in systolic blood pressure (SBP).

The investigators have shown that PI can predict SBP (the greater of the 2 BP values, e.g., 120/80 mmHg) with high accuracy in animal studies of monkeys with SCI. Perfusion index can continuously measure (non-stop measuring) the blood flow in the skin using a pulse-oximeter (pulse oxygen meter) and other sensors on your skin. This new tool can help us to better understand why blood pressure is so unstable (goes quickly up and down) after SCI. The findings may also provide necessary information for developing new non-invasive and wearable devices to monitor blood pressure in the community, thereby allowing persons with SCI early detection, safety, and treatment of clinically silent high blood pressure episodes (episodes that you're not aware of).

Study Procedures: When the participant arrives, the investigators will take the their temperature with an ear thermometer to make sure they don't have a fever. If the participant is having a urinary tract infection (UTI), please call before traveling to the Center. Once at the Center, the investigators will use about 30 minutes in a mildly warm room (75-80 deg F) to tape temperature sensors to the participant's forehead (to measure their body temperature). The investigators will put oxygen meters on the participant's ear, finger and toe to measure perfusion index (PI: a ratio or percentage of blood flowing in your arteries compared to blood not flowing very much in your veins and tissues). The investigators will place a device on another finger that measures beat-to-beat BP device (your BP of every heartbeat).

Once the instrument setup is complete, the participant will remain seated in the wheelchair (or the investigators will provide them with one if they are an AB control) and will take the above measures for 10 minutes. Then, the investigators will move the participant into a cool room (64 deg F) for 90 minutes and continue the same measurements.

Impact: Our studies may provide the scientific community with a novel biomarker and tool to better understand mechanisms for unstable blood pressure control after SCI. The findings may also provide the scientific rationale for development of next-generation non-invasive and accurate and reliable wearable devices to monitor SBP in the community, thereby allowing persons with SCI early detection, safety, and treatment of clinically silent hypertensive episodes (autonomic dysreflexia: AD).

Study Aim: To determine the feasibility of PI as a novel non-invasive biomarker to predict SBP in persons with SCI during a cool temperature challenge.

Inclusion criteria

• The participant had a spinal cord injury (SCI: C4-T12) for more than one year and the SCI was graded as ASIA Impairment Scale (AIS) A or B (unable to voluntarily move your legs)
• The participant can also be a gender and age-matched (±5 years) able-bodied (AB) control subject (similar gender and age to a subject with SCI).
• Subjects with SCI and AB controls must be between 18 and 75 years of age.
• If the participant are going to do the study, they must avoid caffeine and alcohol, maintain normal salt and water intake, and avoid strenuous exercise for 24 hours prior to the study visit.

Exclusion criteria

• The participant has cardiovascular, kidney, or untreated thyroid disease
• The participant has had a traumatic brain injury (TBI)
• The participant has diabetes mellitus
• The participant has an acute illness or infection
• The participant is dehydrated
• The participant smokes
• The participant is pregnant
• The participant has broken, inflamed, or otherwise fragile skin
• The participant's Body Mass Index (BMI) is more than 30 kg/m2