Active Voice: Exercise and Inflammation in Patients with Abdominal Aortic Aneurysm
By Christopher D. Askew, Ph.D.
Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily represent positions or policies of ACSM.
Christopher D. Askew, Ph.D., is an exercise physiologist and senior researcher within the School of Health and Sport Sciences at the University of the Sunshine Coast, Australia. His research focuses on understanding the causes of exercise intolerance and the benefits of exercise therapy in patients with cardiovascular conditions. He is a past director and president of Exercise and Sport Science Australia (ESSA), and he currently serves on the Exercise Is Medicine Australia Advisory Council.
This commentary presents the author’s views on the topic of his research article, which he and his colleagues authored. Their paper appeared in the April 2018 issue of Medicine & Science in Sports & Exercise® (MSSE).
Abdominal aortic aneurysm (AAA) is an inflammatory condition characterized by weakening of the vessel wall and dilation of the abdominal aorta – to a point that it exceeds the normal diameter by 50 percent. Up to 8 percent of men and 2 percent of women over age 65 may have an AAA; however, these patients are usually asymptomatic. There is often a progressive increase in the size and diameter of an aneurysm. Patients with a small AAA (less than 50-55 millimeters in diameter) are regularly monitored using ultrasound imaging. Patients with a large AAA (greater than 55 millimeters in diameter) will be considered for surgical or endovascular repair of the aneurysm. If the aneurysm is not detected or is left untreated, the progressive growth of the aneurysm increases the risk of rupture or dissection, which is often fatal.
Historically, patients with a diagnosed AAA were advised not to exert themselves and to avoid exercise. This was due to the fear that excessive elevations in heart rate and blood pressure may exacerbate the risk of aneurysm rupture. It is now recognized that appropriately monitored exercise is safe and should be encouraged in patients with small AAA. Exercise training leads to improvements in cardiorespiratory fitness for patients with small AAA, and this contributes to a reduction in cardiovascular risk, as well as better post-operative outcomes in patients who undergo aneurysm repair. Despite this, we don’t yet understand how exercise influences the progression of an aneurysm and the factors that contribute to AAA growth.
Our study, as reported in the April 2018 issue of MSSE, aimed to determine whether the inflammatory response to a bout of exercise is altered in patients with small AAA, and whether the response is altered by the intensity of exercise. This is important to understand as the development and growth of an aneurysm is an inflammatory process, where the release of inflammatory cytokines triggers the activity of enzymes (e.g., MMP-9: matrix metalloproteinaise-9) that directly contribute to degradation of the vessel wall and weakening of the aorta. Our study included patients with small AAA and healthy control subjects who performed three tests: 1) a short bout of continuous moderate-intensity cycling; 2) a work-matched bout of higher-intensity interval cycling; and 3) a control period of seated rest. We collected blood samples and measured a range of circulating inflammatory biomarkers before, during and after each condition.
In response to moderate-continuous exercise, there was no difference in the biomarkers between AAA patients and healthy control subjects; this indicates that the inflammatory response is not exacerbated and confirms the safety of this type of exercise in patients with AAA. After a period of recovery (90 minutes) following the higher-intensity interval exercise, there was a reduction in the inflammatory cytokine tumor necrosis factor alpha (TNF-a) in the AAA patients and a reduction in MMP-9. These responses suggest that this form of interval exercise may have a favorable effect on the biomarkers linked to inflammation and AAA progression.
An interesting observation among the AAA patients was that, despite the large relative difference in workload between the conditions (Continuous: 47 Watts, Interval: 82 Watts), the heart rate (71-75 percent of maximum) and RPE (3/10) responses to the two tests were quite low and very similar. This indicates that the inflammatory responses to this form of interval exercise can be achieved without excessive rises in cardiovascular strain or effort.
This study provides support for further research to determine the efficacy of interval exercise training for patients with small AAA, and I would encourage exercise practitioners to adhere to current cardiovascular disease guidelines when managing patients with an AAA.