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Lisa Liu
This is a summary of a research study done by Dr. Christopher West and his colleagues at ICORD. Dr. West’s research interests are focussed on understanding cardiovascular adaptations after spinal cord injury, and the benefits of exercise to these processes.
Original Article: West, C. R., Popok, D., Crawford, M.A., and Krassioukov, A. V. (2015), Characterizing the Temporal Development of Cardiovascular Dysfunction in Response to Spinal Cord Injury. Journal of Neurotrauma. doi:10.1089/neu.2014.3722.
Purpose of the Study
Spinal cord injury (SCI) often disrupts the regulation of the cardiovascular system. However, very little is known about these disruptions in the period from the onset of SCI to the chronic stages.
A major consequence of SCI is the development of autonomic dysreflexia (AD). AD is a life-threatening, sporadic condition seen in people with SCI at or above the T6 vertebrae (just below the shoulder blade). AD is associated with extremely high blood pressure, which, left untreated, can lead to many cardiovascular problems.
In this study, the main focus was to track the development of AD and observe any changes to the cardiovascular system by looking at blood pressure (BP), core body temperature, and heart rate (HR) post-SCI during the acute phase (first week after SCI), sub-acute phase (second week after SCI), and chronic phase (third week and onward) in the hopes of gaining a better idea of the timeline of events that occur in the cardiovascular system post-SCI.
How was it done?
BP, core body temperature, and HR of six rats with complete SCI between the T2-T3 vertebrae were monitored 24 hours a day for the 3 days pre-SCI and every other day after SCI for 28 days. By using a combination of the aforementioned 24/7 monitored data in a newly-developed AD detection algorithm, researchers were also able to identify BP levels and HR that resembled hypertension seen during AD, and used those levels to indicate one episode of a naturally occurring AD event in the early weeks of SCI.
What did they find?
Blood Pressure: On day 2 post-SCI, BP was found to be lower than pre-SCI levels. By the 4th and 6th day, BP recovered to pre-SCI levels. However, from day 8 onward, BP levels remained consistently lower than pre-SCI levels.
What does this mean? The constant hypotension during the chronic phase of SCI is thought to be due to the inability of the nerves to regulate arterial BP. Compared to previous studies on rats with a lower (T5) incomplete injury where BP completely recovers, this finding confirms that complete SCI results in much more disastrous consequences for the cardiovascular system.
Core Body Temperature: Similar to blood pressure, it was observed that in the first four days, body temperature fell greatly below pre-SCI levels but after that day, body temperature returned to pre-SCI levels and remained so for the rest of the study.
What does this mean? The dip in body temperature is due to a loss of control over the nerve’s ability to expand and contract the blood vessels in the body according to the environment. Permanently expanded blood vessels lose heat more quickly. Therefore the rats experienced lower core body temperatures. Since BP and body temperature both returned to normal levels by day 4, it suggests that at the end of the acute phase, some of the neurogenic shock had diminished, and control over blood vessels returned.
AD events: During the acute phase, there was an average of around 10 AD events per day. During the sub-acute phase, the numbers decreased to fewer than 5 a day. At the onset of the chronic phase, the daily occurrences of AD spiked up to 39. By the end of the study, the AD events increased in number, duration, and in severity.
What does this mean? The discovery of the number of AD events occurring by day 28 is very important due to the dangerous symptoms of the condition. While AD results in severe high blood pressure, the body during the chronic phase is normally in a state of very low blood pressure. This results in extreme swings of blood pressure whenever an AD event occurs. The lethal combination of such polar blood pressures could lead to major damage to the heart and blood vessels.
Future considerations
This study is the first to follow various aspects of the cardiovascular system, like body temperature regulation, as well as the frequency of AD events after SCI, all at the same time. With still many questions to be answered, and the discovery of the high number of AD events occurring by day 28, the progression of cardiovascular impairments due to SCI is still far from being completely understood. However this study is an important step towards clinical and preventative treatment following SCI, particularly for those with cardiovascular problems. With the knowledge gained from this experiment, new strategies can be developed to minimize post-SCI symptoms for a healthier and more stable life.
