Numerical simulation of a flow measurement microsensor in a real human aorta model

Master's thesis in the field of mechanical engineering - energy conversion trend

Abstract

Numerical simulation of a flow measurement microsensor in a real human aorta model

Arterial diseases, especially arteriosclerosis and vasodilation, are among the most important causes of sudden death in the world. There are different methods for diagnosing these diseases, and in this research, the design and analysis of a microsensor, which works based on new ideas to detect dilatation or occlusion of blood vessels, has been discussed. Due to the change in the cross section of the artery in both mentioned diseases, the speed of blood flow will also change. Therefore, a thermal flow rate measuring microsensor installed on a catheter has been used to measure the blood flow rate and thus diagnose these diseases. At first, the design of the microsensor structure and its geometric optimization were discussed, then the numerical analysis of the effects caused by the entry of this microsensor into the human aorta was performed, and the real geometry of the aorta was extracted from CT angiography photographs. By placing this microsensor in different areas of the aorta, we investigated the distribution of pressure, velocity and temperature in the aorta. The results showed little changes in pressure and temperature distribution. Also, the average flow speed at one point increased slightly with the presence of the microsensor. As a result, the presence of the microsensor will slightly reduce the measurement accuracy. Also, the results showed that the power consumption of the microsensor designed in this research is in the range of low power consumption.

Key words: arteriosclerosis, vasodilation, microsensor, aorta, CT angiography.

1-1-Introduction

Today, the mortality rate due to non-communicable diseases Cardiovascular diseases are on the rise in the countries of the world, especially developing countries. The most important vascular diseases are arteriosclerosis [1] and arteriosclerosis [2].

Vascular dilation or aneurysm is the enlargement or protrusion of the vessel wall that occurs due to the weakness of the wall and usually in the aorta or arteries that supply the brain, legs, or They nourish the wall of the heart, it is created. Aneurysm in the aorta[3] causes pressure on the adjacent organs and depending on the location of the aneurysm, causes symptoms of pressure and shortness of breath. Aneurysm in an artery in the leg causes insufficient blood to reach different parts of the leg, which causes weakness and paleness in the leg. The presence of an aneurysm in the heart causes an irregular heartbeat. The presence of an aneurysm in a cerebral artery will have complications such as weakness, paralysis and vision changes.

Atherosclerosis occurs when fat deposits and other substances accumulate in the arteries of the body and cause them to clog, which slows down or even stops blood flow in the body. Now, in order for the blood flow to follow its normal course with a constant pressure, the heart has to pass the blood through these arteries with a higher pressure, which results in the enlargement of the heart and its damage. Also, if the heart does not have enough blood to work, it will have chest pain or a heart attack. Chest pain is a pressing pain or feeling of pressure in the chest. It is also possible that a piece of deposits is separated from the artery wall and moves along with the blood flow and blocks a small artery in a distant place.

Due to the risks mentioned for vascular diseases, early diagnosis of these diseases is especially important. Considering that in both mentioned types of vascular diseases, the cross-sectional area and as a result the speed of blood flow in the artery changes, therefore, using a high-precision flow measurement microsensor [4] that causes the least changes in the body's circulatory system, would be a good idea to detect blockages or dilatation in the veins. The use of equipment made in micro dimensions for medical applications is expanding due to low energy loss, high accuracy, high sensitivity and small size, as well as being more effective and less expensive in health care measures. 

1-2- Objective

Our goal in this study is to simulate a type of flow measurement microsensor of hot film type in the real human aorta model, which reveals the expansion or occlusion of the vessels based on new ideas.Hot film sensors have many advantages such as small size, high accuracy, short time response, easy manufacturing and cheap price in mass production [1]. One of the advantages of this type of microsensor in the diagnosis and treatment of vascular diseases, compared to angiography, is the absence of the use of contrast material, which has many side effects. But the treatment method is the same as angiography. For example, ballooning and stenting [5] can be used in the area where vascular occlusion is detected by a microsensor. Injection of any type of contrast agent may cause side effects such as the risk of allergic reaction, kidney failure, heart rhythm disorder, and convulsions.

Arteries [6] (arteries) which themselves are divided into two groups of arteries and small arteries [7] (arterioles).

Arteries [8] (veins) which are themselves divided into two groups of veins and small veins [9] (venules). venules are located.

Large veins are high-pressure blood vessels that carry blood away from the heart to small arteries. Then the blood enters the capillaries and the exchange of oxygen, carbon dioxide and nutrients and metabolic wastes takes place and enters the small veins. From there, low-pressure blood enters the large veins and returns to the heart.

All arteries take blood away from the heart and all veins bring blood closer to the heart. As a result, all arteries contain purified blood, except for the pulmonary artery, which carries unpurified blood from the right ventricle to the lungs to be purified. All veins contain unfiltered blood, except for the four pulmonary veins that return filtered blood from the lungs to the left atrium[2]. At the beginning of the exit of the aorta from the left ventricle, the aortic valve is located. The function of the aortic valve is to close when the left ventricle expands and prevent blood from returning from the aorta to the heart. After leaving the left ventricle, the aorta is divided into three parts: ascending aorta[11], aortic arch[12], and descending aorta[13]. Coronary arteries originate from the beginning of the aorta and therefore are the first arteries that receive blood containing a lot of oxygen and deliver it to the heart muscles. The two coronary arteries (left and right) are relatively small and each is only 3 or 4 mm in diameter. After the ascending aorta, we reach the aortic arch. The brachiocephalic artery[14] separates from the aortic arch, and this artery itself is divided into two branches, the right subclavian artery[15] and the right carotid artery[16]. The second main artery that separates from the aorta is the left carotid artery[17] and the third artery is the left subclavian artery[18].

Arterial disease, particularly atherosclerosis and aneurysm are considered as two important causes of sudden deaths in the world. There are different methods to diagnose these diseases. In this study, design and analysis of a microsensor, based on a new idea for detecting atherosclerosis and aneurysm, has been investigated. According to the change in arterial cross sectional area of ????both diseases are listed, blood velocity also changes. So, a thermal microflow sensor which is installed on a catheter, is used to measure the velocity of blood flow and consequently diagnose these diseases. Initially, designation of microsensor structure and optimization of its geometry and then numerical study on effects of entering the microsensor into the human aorta were performed. The real geometry of the aorta is extracted from CT angiography images. By placing the microsensor in different areas, the aortic pressure, velocity and temperature distribution were studied. Results indicate small changes in pressure and temperature distribution. Furthermore, the mean flow velocity in a cross sectional area had a slight increase with the presence of catheter. As a result, the presence of the catheter will slightly deteriorate the measurement accuracy.