I am not a doctor or physician, but would like to share my views on your question if it can give you clue, but should not be treated as an alternative to any medical opinion and this question should be discussed with your physician or your doctor.
Basically aneurysm is permanent localized abnormal dilation of the blood vessel or heart that is caused by congenital or acquired causes. And abdominal aortic aneurysm is an enlarged area in the lower part of the major vessel that supplies blood to the body (aorta). The aorta runs from your heart through the center of your chest and abdomen.
Harvard Medical School has very clearly explained, on its website, the mechanism of tear and wear of the aorta during the lifetime as follows. Like all arteries, the aorta's wall has three layers: a thin inner layer lined with endothelial cells, a middle layer composed of smooth muscle cells and elastic tissue, and an outer layer of supporting tissues. But the middle layer of the aorta distinguishes it from other arteries; it is composed of layer upon layer of elastic tissue, which makes it very thick and strong. It needs that strength to absorb the tremendous force of blood being propelled directly from the heart. And after absorbing the force when the heart pumps blood, the aorta gives some of it back: as the heart relaxes to refill with blood between beats, the elastic fibers in the aorta recoil, pushing the blood along its route to the rest of the body.
The aorta expands with each heartbeat and narrows down again between beats. It's a demanding routine, and over the years it can take quite a toll. In many older people, the elastic tissue in the aorta stiffens, making the artery less flexible; the process contributes to systolic hypertension and all its complications. And over time, the aorta itself can widen and weaken, developing into an aneurysm.
The following risk factors can be held responsible for the aneurysms.
Non-modifiable risk factors: These factors are irreversible and cannot be changed. The more of these risk factors you have, the greater your chance of developing aneurysms. They are (i) Family history/Genetics and (ii) Most aneurysms tend to develop after the age of 40
Modifiable risk factors: These factors can be modified, treated or controlled through medications or lifestyle changes.
- High blood pressure
- High cholesterol
- Smoking
- Obesity or having a body mass index “BMI” of 30 or greater
- Other conditions that contribute to development of aneurysms
- Trauma from injury
- Atherosclerosis
So, in short, aneurysms have a variety of causes including high blood pressure and atherosclerosis, trauma, heredity, and abnormal blood flow at the junction where arteries come together. However, the most common cause of aortic aneurysms is "hardening of the arteries" called arteriosclerosis. Healthy dietary changes, stopping smoking, and exercise can be powerful weapons against high blood pressure and high cholesterol, two major contributors to atherosclerosis.
So, keeping in view the above gist about the aneurysm, it does not seem any correlation between doing uddiyana bandha and/or nauli for prolonged periods of time and occurrence of abdominal aortic aneurysm. Your question indicates that you are under the impression that while doing these yogic exercises can cause the abdominal wall to press the aorta and cause rupture. In this regard, I may inform you that aneurysms occur because of a weakened wall in an artery, aorta, the main artery that carries blood from your heart to the rest of your body. An aneurysm can grow as blood pressure increases. If it grows too large, it can become more likely to burst or split open, which can be life threatening. Burst aneurysms have been linked to exercises like push-ups and weight lifting, which produce spikes in blood pressure as the breath is held and the abdominal muscles are contracted.
As regards the yogic exercises, the book “Anatomy of Hatha Yoga” states there are no contraindications for ashwini mudra and mula bandha, but agni sara, uddiyana bandha and their derivatives (nauli, etc.) are powerful exercises whose indiscriminate use is not recommended. If you have high blood pressure, even the mildest of abdominopelvic exercises should be approached gingerly. Even if you are on medication that successfully lowers your blood pressure, all intense abdominopelvic exercises should be avoided. Holding your breath at the glottis after inhalation is always contraindicated. Holding your breath after exhalation, as in uddiyana bandha, is less dangerous but also inadvisable because we would expect it to quickly increase venous return, that is the flow of blood back to heart.
So, you need to take care of the exercises that should not cause high blood pressure. As earlier stated, high blood pressure can cause more trouble to already weak and dialated aneurysm in aorta. You should be more careful if AAA is symptomatic in your case. The size of your AAA is of less risk as can be seen from reference material linked below.
So, while you perform any exercise, you should be well aware of avoiding intensive exercises as well as focus on healthy diet to prevent further complications of AAA. Eating a healthy diet containing plenty of fruits, whole grains, and vegetables may help prevent an aneurysm from forming.
I have used the following references and the book “Anatomy of Hatha Yoga” to reply to your question. You may also use the following references to get a clear picture of AAA.
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