Lay Summary by Tiffany Fong
Edited by Rona Herzog
This is a summary of a research article conducted by several ICORD researchers, including Dr. Christopher West, Aaron Phillips, Jordan Squair, Alexandra Williams, Matthias Walter, Dr. Tania Lam, and Dr. Andrei Krassioukov. Click here to access the original article.
The cardiovascular (CV) system is responsible for delivering blood throughout the body. Effective delivery is based on the volume and rate of blood pumped from the heart as well as pressure maintained throughout the CV system.
The autonomic nervous system (ANS) is responsible for the involuntary and regulatory control of bodily functions and regulates delivery of oxygenated blood by controlling both rate of contraction (i.e., heart rate) and strength of contraction (i.e., volume pumped).
The ANS is additionally responsible for maintaining effective blood pressure (BP). One of the most common daily activities – transitioning from sitting to standing, or simply standing for prolonged periods – is indirectly influenced by the ANS as well as the receptors in the blood vessel musculature to ensure blood vessels constrict correctly to maintain a constant BP. Without this function, BP could drop, resulting in reduced oxygen delivery to the brain leading to light-headedness, dizziness, or even blackouts.
For individuals with SCI, the ANS regulation of HR and BP is disrupted. During exercise, for example, HR does not increase sufficiently to pump enough oxygenated blood to meet the oxygen demands of working muscles. Similarly, the ANS has difficulty maintaining the correct BP when during exercise. These conditions contribute to the well-documented lower CV fitness levels in individuals with SCI, which can have highly debilitating consequences on quality of life and increase cardiovascular disease burden.
Purpose of study:
This study set out to determine the effects of epidural stimulation on the CV system of an individual with a C5 complete SCI.
What is epidural stimulation?
As the spinal cord runs through vertebrae, a space is created between the cord and the vertebrae, called the epidural space. Epidural stimulation includes an electrode array implanted in this epidural space, which is then connected to a pulse generator surgically implanted into the body. Signals can be sent through the electrode and controlled externally by a remote. The electrode serves as a way to provide input to the spinal cord below the level of the injury that would usually be provided by the brain.
This study was conducted with one subject. The individual had previously been fitted with an electrode inserted into his spine at the T11-L1 levels (lower middle back). He completed various cardiovascular assessments with electrode stimulations alternately turned on and off, with CV metrics recorded for each condition.
After observing CV function with electrode stimulation on versus off, it appeared that electrical stimulation improved CV function as measured by improved BP, cardiac function and brain blood flow.
One of the major findings was that BP increased in a controlled fashion and did not uncontrollably continue increasing. Uncontrolled, continuous increase of BP following stimulation can occur for those with SCI since ANS regulation is lost and cannot provide negative feedback when pressure increases too much, a condition known as autonomic dysreflexia. Thus, it appears epidural stimulation restores the regulatory function for BP.
Another important finding was the integrated improvements for CV function as indicated by the variety of measured responses (BP, heart function and brain blood flow), which reinforces the interconnected control the ANS neurons in the spinal cord have over the body’s blood vessels, heart, and brain.
How are these findings significant to the SCI community?
While this study consisted of only one participant, the findings were significant, and as noted in the study, this research was likely the first of its kind to demonstrate such widespread improvements across the entire cardiovascular system. This is a promising study that has potential for epidural neuroprosthetics to be used to help individuals with SCI improve CV fitness and function, and provide an alternative to pharmacological aids.