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Arterial stiffness after SCI and interventions

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By:

Ishan Dixit

This is a summary of a literature review done by Amanda H. X. Lee, Aaron A. Philips, and Andrei V. Krassioukov. This literature review paper combines the findings of many individual studies about accelerated cardiovascular disease progression after spinal cord injury (SCI). The review also explores research that has been done by others on possible therapeutic interventions for improving arterial stiffness.

To read the original article, please click here.


What is “central arterial stiffness,” and why is it important?

Arterial stiffness is the consequence of many modifiable and non-modifiable factors that include age, gender, physical activity levels, family history, diet, body composition, and blood pressure level. An increase in arterial stiffness is directly correlated with cardiovascular (CV) disease and the hardening and loss of elasticity of the arteries in the heart and brain. It is best measured by Aortic pulse wave velocity (aPWV). An individual with an aPWV measurement of greater than 10 meters/second is considered to be at risk for CV disease.

Due to it’s degenerative nature, central arterial stiffness can act as a symptom and a cause for many CV diseases. In detail, during heart contraction blood has to be pumped out into the body at a rhythmic timing so that it returns from the peripheries by the time the heart is ready for filling up again. As the blood travels, it counters resistance, especially in a stiffened arterial system, in which the blood doesn’t arrive with the necessary timing as the heart is ready for filling. Due to the irregular volumes filling up the ventricles (sometimes too much, other times too little), the workload on the left ventricle—the chamber of the heart that pumps blood around the body—increases, which is an independent risk factor for arteries in the brain and death of heart tissue due to decreased blood supply (myocardial infarction).

How does SCI contribute to arterial stiffness?

It’s been demonstrated that aPWV is elevated by 2-3 meters/second after spinal cord injury (SCI). Substantial evidence is available, showing the acceleration of CV disease due to SCI. For example, there is a 40-year acceleration of age-related CV decline in terms of the effects of arteriosclerosis when aPWV is measured and taken into account.

Other implications and contributing factors of arterial stiffness after SCI:

Fluctuations in blood pressure
Due to elevated blood pressure, periodic episodes of hypertension can result from autonomic dysreflexia. Rapid, unregulated increases in blood pressure can be characterized as life-threatening for those with high level SCI (above T6).

Impairment of the nervous system
SCI can lead to permanent disruption of a structure called the sympathetic nerve chain, which runs down along your spine inside your chest. This structure, when activated, is important for increasing blood pressure and heart rate. Disruption to the sympathetic nerve chain, caused by the injury itself or surgeries after SCI, can consequently lead to remodelling of the blood vessels coming out of the heart and increased arterial stiffness. A secondary consequence of the loss of input from this nerve chain is low blood pressure.

Deconditioning
After SCI, not only the skeletal muscles used for limb movement are affected, but also the smooth muscles lining the arteries experience rapid deconditioning and stiffness. Some studies have shown that physical activity is inversely correlated to central arterial stiffness. The correlation of injury levels to high level (cervical) or low level (thoracic) is also an important issue, because individuals with higher lesion levels experience more severe CV abnormalities, such as sudden bouts of hypertension.

Interventions for improving arterial stiffness

Small bouts (~42 mins/day) of aerobic exercise over a 13- to 14-week period can result in an improvement and potential prevention of a number of CV risk factors. These improvements can vary depending on the intensity of exercise employed and the severity of arterial stiffness of the individual. However, data does suggest that SCI athletes are prone to less arterial stiffness than than the able-bodied (AB) population or SCI non-athletes. Some research does contradict the effectiveness of only upper body exercise due to the lack of other muscle groups being activated. This suggests that a more integrated knowledge and research is required to assess the role of specific lower or upper body exercise in relieving arterial stiffness.

Dietary interventions show a reduction in arterial stiffness. These include the incorporation of omega-3 polyunsaturated fats (especially EPA and DHA), plant-derived isoflavones found in legumes and beans, and fermented milk products. Long-term caffeine avoidance is advised because of the immediate effects of caffeine constricting the arteries. Even though sodium increases blood pressure, decreasing its consumption is not viable. This is due to the very important role sodium plays in maintaining a healthy blood volume in the body. Additionally, a low-cholesterol and low-saturated-fat diet for 8 weeks yielded a decreased aPWV. PUFA (polyunsaturated fatty acids) dietary supplements show the greatest promise because of their abilities to improve arterial stiffness without causing hypotension after SCI.

Several pharmacological drugs have been tested to reduce arterial stiffness. Antihypertensive drugs have shown the most promise by far to reduce vascular stiffness in the non-SCI population. These drugs reduce effectiveness of the systemic mechanisms that increase blood pressure and volume. However, since these pharmaceuticals have only been tested on AB populations, their effectiveness of SCI patients is still in consideration particularly to target aortic stiffness.

Conclusions

The risk of CV decline is higher in the SCI population due to changes in physical activity patterns, restricted motor function and damage to the vascular system. Although there is some evidence that exercise contributes to a decrease in arterial stiffness, the most promising of the aforementioned interventions is the increase of dietary PUFA. The increase of PUFA is highly recommended due to the low cost, consistent positive outcomes, fewer side effects than other methods, and the smaller likelihood of worsening the blood pressure difficulties this population already faces.