In the previous blog post we discussed briefly about the role of the Autonomic system, how it gets disrupted in SCI & about Autonomic Dysreflexia & Bradycardia. No we will look into other entities caused by dysautonomia in SCI…

Orthostatic Hypotension

What is this entity? This is defined as a reduction in blood pressure when body position changes from supine to upright. The symptoms associated with OH include lightheadedness, dizziness,pallor, and syncope.

Pathophysiology... Immediately after SCI, there is a complete loss of sympathetic tone, resulting in neurogenic shock with hypotension, bradycardia, and hypothermia. The hypotension occurs as a result of systemic loss of vascular resistance, accumulation of blood within the venous system, reduced venous return to the heart, and decreased cardiac output. Over the course of time, the sympathetic reflex activity returns, with normalization of blood pressure. However, supraspinal control continues to be absent in those individuals with high-level and neurologically complete SCI, and they continue to be prone to orthostatic hypotension (OH). One study has suggested that chronic hypotension in persons with SCI can result in cognitive deficits.

How to manage it?   Management of OH includes the application of elastic stockings and abdominal binders, adequate hydration, gradually progressive daily head-up tilts, and sometimes the administration of salt tablets, midodrine, or fludrocortisone. Some research has shown positive results with L-threo-3,4-dihydroxyphenylserine (droxidopa) for treating OH without causing hypertension1.

Thermal Regulation

Pathophysiology… Body temperature is controlled physiologically primarily by the hypothalamus and secondarily by personal behavior to increase or decrease heat loss. With an increase in core temperature, sympathetic inhibition occurs with vasodilation and sweating. A decrease in core temperature causes a sympathetic stimulus, with vasoconstriction and shivering. With high-level and neurologically complete SCI, the afferent and efferent pathways are interrupted. As a result, vasomotor control and the ability to shiver and sweat are lost.

Who is at risk? Thermal regulation is impaired in persons with SCI, especially in those with complete lesions, because of loss of supraspinal control. Injuries above the eighth thoracic vertebra are often associated with fluctuating temperature, hypothermia and hyperthermia2.

Patterns seen.. There are several patterns of temperature dysregulation seen in these patients. They include:

1. High or low temperature secondary to environmental exposure

2. Fever without infectious source (more common in the first weeks to months after injury)

3. Exercise-induced hyperthermia

Management… It is vital to exclude medical causes (such as infection or thromboembolic disease) for high or low temperature. People with SCI are at particular risk of infections of the chest, renal tract or skin. People can manage temperature dysregulation by controlling the temperature of their environment, dressing in appropriate clothing and regulating exertion with exercise3. It’s also noteworthy that chronic tetraplegics also frequently have subnormal body temperatures (<97.70F) in a normal ambient environment4.

In these two blog posts we delved into the manifestations of autonomic dysfunction in spinal cord injury. An in depth knowledge of these is essential to pick them up & manage them optimally. Thank you for reading these posts…

References

1.      Braddom’s Physical Medicine and Rehabilitation, 6th Edition, David C.Xifu MD

2.      https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4303786/

3.     https://www.health.qld.gov.au/__data/assets/pdf_file/0019/672130/gp-temp-regulation.pdf

4.     DeLisa’s Physical Medicine & Rehabilitation Principles and Practice, 5th Edition