Biomedical Imaging and Instrumentation (Lecture) PDF

ECE 21132 (IC-ELE3-BII): Biomedical Imaging and Instrumentation (Lecture) MODULE 2: Biomedical Transducers and Sensors Lecture 4: Blood Pressure Measurement...

ECE 21132 (IC-ELE3-BII): Biomedical Imaging and Instrumentation (Lecture) MODULE 2: Biomedical Transducers and Sensors Lecture 4: Blood Pressure Measurement Lecture 5: Blood Flow Measurement Dr. Seigfred V. Prado, SMIEEE Electronics Engineering Department 1 Electronics Engineering Department 2 High blood pressure?! Electronics Engineering Department 3 Electronics Engineering Department 4 Blood Pressure ▪ Blood pressure is the force exerted by circulating blood against the walls of blood vessels, primarily arteries. ▪ It is a critical vital sign used to assess cardiovascular health. Electronics Engineering Department 6 Components of Blood Pressure ▪ Systolic Blood Pressure (SBP) ▪ The peak pressure in the arteries during ventricular contraction (systole). ▪ Diastolic Blood Pressure (DBP) ▪ The lowest pressure in the arteries during ventricular relaxation (diastole). ▪ Normal Blood Pressure ▪ Normal adult BP is generally around 120/80 mmHg. Electronics Engineering Department 7 Components of Blood Pressure ▪ Mean Arterial Pressure (MAP) ▪ The average pressure in the arteries during a single cardiac cycle, calculated as: 1 𝑀𝐴𝑃 = 𝐷𝐵𝑃 + (𝑆𝐵𝑃 − 𝐷𝐵𝑃) 3 ▪ Pulse Pressure (PP) ▪ The difference between the systolic and diastolic blood pressure. It represents the force that the heart generates each time it contracts. 𝑃𝑃 = 𝑆𝐵𝑃 − 𝐷𝐵𝑃 Electronics Engineering Department 8  Source: https://www.texasheart.org/ Electronics Engineering Department 9  HIGH BLOOD PRESSURE (HYPERTENSION) Electronics Engineering Department 10 Electronics Engineering Department 11 Electronics Engineering Department 12 Physiology of Blood Pressure ▪ Factors Affecting Blood Pressure ▪ Cardiac Output (CO) ▪ The amount of blood the heart pumps per minute. It is measured as the product of the stroke volume (SV) and heart rate (HR). 𝐶𝑂 = 𝑆𝑉 × 𝐻𝑅 ▪ Total Peripheral Resistance (TPR) ▪ The resistance offered by the arteries to the blood flow. 𝐵𝑃 = 𝐶𝑂 × 𝑇𝑃𝑅 ▪ Blood Volume (BV) ▪ The total volume of blood in circulation. ▪ Elasticity of Arterial Walls ▪ Affects how much the arteries can stretch and recoil. Electronics Engineering Department 13 Techniques for Measuring Blood Pressure ▪ Invasive (Direct) Blood Pressure Measurement ▪ Performed using intra-arterial catheters inserted directly into an artery ▪ Provides continuous, real-time measurements and is used in critical care settings ▪ Example: Arterial Line (catheter connected to a pressure transducer) Electronics Engineering Department 14 Techniques for Measuring Blood Pressure ▪ Invasive (Direct) Blood Pressure Measurement Electronics Engineering Department 15 Techniques for Measuring Blood Pressure ▪ Non-Invasive (Indirect) Blood Pressure Measurement ▪ Most common method for routine clinical and home blood pressure monitoring 1. Auscultatory Method (Manual) ▪ The traditional method using a sphygmomanometer (cuff and mercury or aneroid gauge) and stethoscope. Electronics Engineering Department 16 Techniques for Measuring Blood Pressure ▪ Non-Invasive (Indirect) Blood Pressure Measurement Mercurial Sphygmomanometer Aneroid Sphygmomanometer Electronics Engineering Department 17 Techniques for Measuring Blood Pressure ▪ Non-Invasive (Indirect) Blood Pressure Measurement 2. Oscillometric Method (Automatic) ▪ Commonly used in automated digital BP monitors ▪ Working Principle: Measures oscillations in the arterial wall as the cuff is deflated, which are used to determine SBP and DBP. Electronics Engineering Department 18 Techniques for Measuring Blood Pressure Electronics Engineering Department 19 Techniques for Measuring Blood Pressure Electronics Engineering Department 20  Chandrasekhar, Anand, et al. "Formulas to explain popular oscillometric blood pressure estimation algorithms." Frontiers in physiology 10 (2019): 1415. Electronics Engineering Department 21 Techniques for Measuring Blood Pressure ▪ Non-Invasive (Indirect) Blood Pressure Measurement 2. Oscillometric Method (Automatic) ▪ Calibration of a Pressure Sensor in an Oscillometric BP Monitor ▪ Actual Reading = Expected Output Voltage + Offset Voltage ▪ Expected Output Voltage = Sensitivity × Pressure Electronics Engineering Department 22 Techniques for Measuring Blood Pressure ▪ Non-Invasive (Indirect) Blood Pressure Measurement 3. Continuous Non-Invasive Method ▪ Based on volume clamp or tonometry principles ▪ Uses a cuff around a finger to maintain a constant blood volume using photoplethysmography (PPG) signals Electronics Engineering Department 23 Sample Problem 1 ▪ A patient’s blood pressure reading is 120/80 mmHg. Calculate the Mean Arterial Pressure (MAP). ▪ Answer: ~93.33 mmHg Electronics Engineering Department 24 Sample Problem 2 ▪ A patient’s blood pressure is measured as 130/85 mmHg. The stroke volume is 70 mL, and the heart rate is 75 beats per minute. Calculate the pulse pressure and cardiac output. ▪ Answers: PP = 45 mmHg and CO = 5.25 L/min Electronics Engineering Department 25 Sample Problem 3 ▪ A capacitive pressure sensor in a BP monitor has a sensitivity of 5 mV/mmHg. During calibration, the sensor reads 600 mV when the actual pressure is 120 mmHg. Determine the offset voltage of the sensor. ▪ Answers: Expected Output Voltage = 600 mV Offset Voltage = 0 mV Electronics Engineering Department 26 Sample Problem 4 ▪ Design a low-pass filter with a cutoff frequency of 5 Hz to remove noise from an ECG signal in a BP measurement system. ▪ Answer: Use a resistor of 10 kΩ and a capacitor of 3.18 𝜇F for the RC low-pass filter. Electronics Engineering Department 27 Electronics Engineering Department 28 Blood Flow ▪ Blood flow is the movement of blood through the circulatory system, including arteries, veins, and capillaries. ▪ It is essential for transporting oxygen, nutrients, hormones, and waste products throughout the body. Electronics Engineering Department 29 Physiology of Blood Flow ▪ Mechanisms of Blood Flow ▪ Laminar Blood Flow ▪ Blood flows in parallel layers with the highest velocity at the center and the lowest near the vessel wall; typical in healthy vessels. ▪ Turbulent Blood Flow ▪ Irregular, chaotic flow that occurs when blood moves rapidly or when there are obstructions, like in stenotic arteries or at bifurcations. Electronics Engineering Department 30 Physiology of Blood Flow ▪ Factors Affecting Blood Flow ▪ Cardiac Output (CO) ▪ The total volume of blood pumped by the heart per minute. ▪ Blood Vessel Compliance ▪ The ability of blood vessels to expand and contract with changes in pressure. ▪ Higher compliance means lower resistance. ▪ Blood Viscosity ▪ The thickness of blood, primarily influenced by the concentration of red blood cells (hematocrit). ▪ Higher viscosity increases resistance and reduces flow. Electronics Engineering Department 31 Blood Flow Dynamics ▪ Poiseuille’s Law ▪ Describes the relationship between blood flow rate (Q), pressure gradient (ΔP), vessel radius (r), blood viscosity (𝜂), and vessel length (L): Units: 𝟒 P in Pascals (Pa) 𝚫𝑷 ∙ 𝝅 ∙ 𝒓 r in meters (m) 𝑸= 𝜂 in Pa∙s 𝟖∙𝜼∙𝑳 L in meters (m) Q in m3/s ▪ Implications: ▪ Blood flow is directly proportional to the fourth power of the vessel radius. ▪ A small change in radius significantly affects flow. ▪ Blood flow is inversely proportional to viscosity and vessel length. Electronics Engineering Department 32 Blood Flow Dynamics ▪ Reynold’s Number (Re) ▪ A dimensionless number used to predict flow patterns (laminar or turbulent) in blood vessels Units: 𝜌 in kg/m3 𝝆∙𝝊∙𝑫 𝜐 in m/s 𝑹𝒆 = D in meters (m) 𝜼 𝜂 in Pa∙s ▪ Where: Re is unitless ▪ 𝜌 = blood density ▪ 𝜈 = velocity ▪ 𝐷 = vessel diameter ▪ 𝜂 = viscosity ▪ Note: Re < 2000 indicates laminar flow, while Re > 2000 indicates turbulent flow Electronics Engineering Department 33 Blood Flow Measurement Techniques ▪ Invasive Techniques 1. Electromagnetic Flowmeters ▪ Based on Faraday’s law of electromagnetic induction, where blood flow generates a voltage in a magnetic field proportional to its velocity ▪ Used in intraoperative monitoring and animal studies Electronics Engineering Department 34 Blood Flow Measurement Techniques Electronics Engineering Department 35 Blood Flow Measurement Techniques ▪ Invasive Techniques 2. Thermodilution Method ▪ Involves injecting a cold saline solution into a blood vessel and measuring the temperature change downstream ▪ The rate of temperature change correlates with the flow rate. ▪ Commonly used in cardiac catheterization to measure cardiac output Electronics Engineering Department 36 Blood Flow Measurement Techniques Electronics Engineering Department 37 Blood Flow Measurement Techniques ▪ Non-Invasive Techniques 1. Doppler Ultrasound ▪ Utilizes the Doppler effect, where the frequency shift of ultrasound waves reflected by moving red blood cells is proportional to their velocity Electronics Engineering Department 38 Blood Flow Measurement Techniques ▪ Non-Invasive Techniques 2. Laser Doppler Flowmetry ▪ Uses low-power laser light to detect frequency shifts caused by moving red blood cells, providing information about microcirculation Skin surface Electronics Engineering Department 39 Blood Flow Measurement Techniques ▪ Non-Invasive Techniques 3. Magnetic Resonance Imaging (MRI) – Phase Contrast Technique ▪ Encodes velocity information of moving blood into phase shifts, allowing quantitative assessment of flow ▪ Provides comprehensive 3D flow maps and volumetric flow rate measurements Electronics Engineering Department 40 Sample Problem 1 ▪ A blood vessel has a radius of 0.2 cm, a length of 10 cm, and the blood has a viscosity of 0.04 Poise. The pressure difference across the vessel is 20 mmHg. Calculate the blood flow rate using Poiseuille’s Law. ▪ (Note: 1 Poise is 0.1 Pa∙s; 1 mmHg = 133.322 Pa; 1 m3 = 1000 L) ▪ Answer: Q = 2.09 x 10-7 m3/s = 12.54 mL/min Electronics Engineering Department 41 Sample Problem 2 ▪ Blood flows through an artery with a diameter of 1 cm at a velocity of 50 cm/s. The density of blood is 1.06 g/cm3 and the viscosity is 0.04 Poise. Determine if the flow is laminar or turbulent. (Note: 1 Poise is 0.1 Pa∙s) ▪ Answer: Re = 13,250 (Since Re > 2000, the flow is turbulent.) Electronics Engineering Department 42 Advances in Biomedical Engineering Related to Blood Pressure and Blood Flow ▪ Stents ▪ A stent is a small, expandable tube used to keep blood vessels, ducts, or other passageways in the body open. ▪ Stents are most commonly used in arteries, such as coronary arteries, that have been narrowed or blocked due to plaque buildup (a condition known as atherosclerosis). ▪ The primary goal of a stent is to restore and maintain adequate blood flow to the heart or other organs. Electronics Engineering Department 43 Electronics Engineering Department 44 Advances in Biomedical Engineering Related to Blood Pressure and Blood Flow ▪ Angioplasty and Stenting ▪ The most common procedure for placing a stent is percutaneous coronary intervention (PCI), also known as angioplasty. ▪ A catheter with a deflated balloon at its tip is inserted through a small incision, usually in the groin or wrist, and guided to the narrowed area of the artery. ▪ The balloon is inflated to compress the plaque against the artery wall and expand the stent, which is positioned over the balloon. ▪ Once the stent is in place, the balloon is deflated and removed, leaving the stent to keep the artery open. Electronics Engineering Department 45 Advances in Biomedical Engineering Related to Blood Pressure and Blood Flow ▪ Smart Stents with Biosensors ▪ Smart stents are enhanced versions of conventional stents used to keep arteries open. ▪ They are embedded with sensors that can monitor parameters such as blood flow, pressure, and even detect restenosis (re-narrowing of the artery). ▪ They can wirelessly transmit data to external devices, allowing for early detection of complications like blockages or thrombosis. ▪ Biodegradable Stents: Made from materials like magnesium alloys, these stents dissolve naturally over time, reducing the risk of long-term complications associated with permanent stents, such as late stent thrombosis. Electronics Engineering Department 47 Electronics Engineering Department 48 Advances in Biomedical Engineering Related to Blood Pressure and Blood Flow ▪ 3D-Printed Vascular Grafts ▪ A vascular graft (also called vascular bypass) is a surgical procedure that redirects blood flow from one area of the body to another by reconnecting the blood vessels. ▪ 3D printing technology is being used to create custom vascular grafts that are patient-specific and designed to mimic the natural properties of blood vessels. ▪ Materials like collagen, elastin, and synthetic polymers are used for better integration with the body’s tissues. Electronics Engineering Department 49 Electronics Engineering Department 50 Advances in Biomedical Engineering Related to Blood Pressure and Blood Flow ▪ Microbots for Drug Delivery ▪ Microscopic robots that can travel through the bloodstream to deliver drugs directly to targeted areas, such as atherosclerotic plaques or thrombus sites. ▪ These microbots can potentially offer more precise and localized treatments. Electronics Engineering Department 51