Blood Pressure: A Comprehensive Guide PDF

# Blood Pressure The image shows a red heart with a digital blood pressure monitor, displaying 120/80. A blue ECG line is running along the bottom. ## What is blood pressure? - Blood pressure is the force or pressure of the blood against the walls of the blood vessels. - Arterial blood pressure...

# Blood Pressure The image shows a red heart with a digital blood pressure monitor, displaying 120/80. A blue ECG line is running along the bottom. ## What is blood pressure? - Blood pressure is the force or pressure of the blood against the walls of the blood vessels. - Arterial blood pressure is a measure of the pressure exerted by the blood as it flows through the arteries. It is the result of the ejection of blood from the left ventricle into the aorta. - Blood pressure is mentioned in terms of systolic blood pressure over diastolic blood pressure. - **Systolic blood pressure** is the highest pressure attained in arteries during systole. - **Diastolic blood pressure** is the lowest arterial pressure during diastole. ## How blood pressure works during the cardiac cycle An image shows a cross section of a human heart, demonstrating blood flow during diastole and systole. - **Diastole**: the ventricles fill with blood. - **Systole**: the ventricles contract and the heart pumps blood. ## How systolic pressure works The systolic pressure is the pressure as a result of contraction of the ventricles. When the left ventricle contracts and pushes blood into the aorta, the pressure produced within the arterial system is called systolic blood pressure. In adults, it is about: $120 \ mmHg$ ## How diastolic pressure works - The diastolic pressure is the pressure when the ventricles are at rest. - When complete cardiac relaxation occurs and the heart is resting after the ejection of blood, the pressure within the arteries is called diastolic blood pressure. - In an adult, it is about $80 \ mmHg$. ## How blood pressure is measured - Arterial blood pressure is measured with a sphygmomanometer. - Blood pressure is recorded as a fraction: systolic pressure over the diastolic pressure, and expressed in millimeters of mercury ($mm \ Hg$). - A typical blood pressure for a healthy adult is $120 / 80 \ mmHg$. ## What is pulse pressure? - The difference between systolic and diastolic blood pressures is the pulse pressure. - A normal pulse pressure is about $40 \ mmHg$. ## Factors affecting blood pressure The following are factors affecting blood pressure: - **Age**: The pressure rises with age, reaching a peak at the onset of puberty, and then tends to decline - **Exercise**: Physical activity increases the cardiac output and hence the blood pressure. - **Stress**: Stimulation of the sympathetic nervous system increases cardiac output and vasoconstriction of the arterioles, thus increasing the blood pressure. - **Race**: African Americans tend to have higher blood pressures than European Americans. The exact reasons are unclear. - **Sex**: Females have lower blood pressures than males due to hormonal variations. After menopause, women have higher blood pressures. - **Medications**: Many medications, including caffeine, may increase or decrease the blood pressure. - **Obesity**: Predispose to hypertension. - **Positions**: Sitting, standing, or lying down position cause slight variation in BP. - **Diurnal variations (time of day)**: Pressure is lowest early in the morning when the metabolic rate is lowest, then rises throughout the day and peaks in the late afternoon or evening. - **Medical conditions**: Any condition affecting the cardiac output, blood volume, blood viscosity, and/or compliance of the arteries has a direct effect on the blood pressure. - **Temperature**: Because of increased metabolic rate, fever can increase blood pressure. However, external heat causes vasodilation and decreased blood pressure. Cold causes vasoconstriction and elevates blood pressure. ## Regulation of blood pressure The regulation of blood pressure is done in the following ways: 1. **Regulation by the cardiovascular center** 2. **Neural regulation** 3. **Hormonal regulation** 4. **Auto regulation** ### 1. Regulation by the cardiovascular center - The cardiovascular (CV) center in the medulla oblongata controls neural, hormonal, and local negative feedback systems that regulate blood pressure. - Groups of neurons within the CV center regulate heart rate, contractility (force of contraction) of the ventricles, and blood vessel diameter. - Some neurons stimulate the heart (cardiostimulatory center); others inhibit the heart (cardioinhibitory center). - Some neurons control blood vessel diameter by causing constriction (vasoconstrictor center) or dilation (vasodilator center), which is referred to as the vasomotor center. - All groups of neurons in the CV center communicate with one another and function together. An image shows a diagram of the brain, including the cardiovascular center, with arrows showing input from different brain regions and output to different effectors. - **Input to the cardiovascular center** (nerve impulses): - From higher brain centers: cerebral cortex, limbic system, and hypothalamus - From proprioceptors: monitor joint movements - From baroreceptors: monitor blood pressure - From chemoreceptors: monitor blood acidity (H), CO2, and O2. - **Output to effectors** (increased frequency of nerve impulses): - **Heart**: - **Vagus nerves (parasympathetic)**: decreased rate - **Cardiac accelerator nerves (sympathetic)**: increased rate and contractility - **Blood vessels (sympathetic)**: vasoconstriction - **Sympathetic stimulation** via cardiac accelerator nerves increases heart and contractility, which leads to increased blood pressure. - **Parasympathetic stimulation** via vagus nerve leads to inhibitory action, which decreases heart rate and blood pressure. - The cardiovascular center also sends impulses to smooth muscle in blood vessel walls via vasomotor nerves. This produces sympathetic stimulation and results in vasoconstriction, thus increasing blood pressure. ### 2. Neural regulation - The nervous system regulation of blood pressure is a negative feedback mechanism via baroreceptor reflexes and chemoreceptor reflexes. #### 2.i. Baroreceptor reflexes - Baroreceptors are pressure-sensitive sensory receptors located in the aorta, internal carotid arteries, and other large arteries in the neck and chest. - They send impulses to the cardiovascular center to help regulate blood pressure. - The two most important baroreceptor reflexes are the carotid sinus reflex and the aortic reflex. - **Carotid sinus reflex**: Baroreceptors in the wall of the carotid sinuses initiate this reflex, which helps to regulate blood pressure in the brain. Nerve impulses from the carotid sinus reach the cardiovascular center via glossopharyngeal nerves - **Aortic reflex**: Baroreceptors in the wall of the aorta initiate this reflex, which regulates systemic blood pressure. Nerve impulses from aortic baroreceptors reach the cardiovascular center via vagus (X) nerves. An image shows a diagram of the baroreceptor reflex affecting blood pressure. - **Decreased blood pressure**: - Decreased impulses from baroreceptors to the CV center - Decreased parasympathetic stimulation - Increased sympathetic stimulation - Increased secretion of epinephrine and norepinephrine by the adrenal medulla - Increased heart rate - Vasoconstriction - Increased systemic vascular resistance - **Increased blood pressure** #### 2.ii. Chemoreceptor Reflexes - Chemoreceptors are sensory receptors that monitor the chemical composition of blood located close to the baroreceptors of the carotid sinus and arch of the aorta. - Chemoreceptors detect changes in blood level of O2, CO2, and H+. - Hypoxia (lowered O2 availability), acidosis (an increase in H+ concentration), or hypercapnia (excess CO2) stimulates the chemoreceptors to send impulses to the cardiovascular center. - In response, the CV center increases sympathetic stimulation to arterioles and veins, producing vasoconstriction and increases blood pressure. ### 3. Hormonal Regulation - Hormonal regulation of blood pressure is done by the following systems: 1. Renin-angiotensin-aldosterone system 2. Epinephrine and norepinephrine 3. Antidiuretic hormone (ADH) 4. Atrial natriuretic peptide #### 3.i. Renin-angiotensin-aldosterone system An image shows a diagram showing the mechanisms of the Renin-angiotensin-aldosterone system. - **When renal blood flow is reduced, blood volume decreases, or blood pressure drops**, the enzyme renin is secreted by kidney cells. - Renin converts the plasma protein angiotensinogen, produced by the liver, to angiotensin 1. - Angiotensin converting enzyme (ACE) converts angiotensin 1 to angiotensin 2. - Angiotensin 2 causes vasoconstriction and increases blood pressure. - Angiotensin 2 also stimulates secretion of aldosterone, which causes vasoconstriction and increases blood pressure. #### 3.ii. Epinephrine and norepinephrine An image shows a diagram of the release and effects of epinephrine and norepinephrine. - In response to sympathetic stimulation, the adrenal medulla releases epinephrine and norepinephrine. - These hormones increase cardiac output by increasing the rate and force of heart contractions, thus increasing blood pressure. #### 3.iii. Antidiuretic hormone (ADH) An image shows a diagram of the release and effects of ADH. - **Decreased blood volume** leads to the release of ADH from the posterior pituitary. - ADH promotes the movement of water from kidney tubules into the bloodstream, increasing blood volume and urine output. - ADH also causes vasoconstriction, ultimately increasing blood pressure. #### 3.iv. Atrial natriuretic peptide (ANP) - Atrial natriuretic peptide (ANP) is released by cells in the atria of the heart. - ANP lowers blood pressure by causing vasodilation and by promoting the loss of salt and water in the urine, which reduces blood volume. ### 4. Auto regulation - The ability of a tissue to automatically adjust its blood flow to match its metabolic demands is called autoregulation. - In heart autoregulation, it is an important contributor to increased blood flow through the tissue. - **Stimuli that cause autoregulatory changes in blood flow are:** - **Physical changes**: warming promotes vasodilation, and cooling causes vasoconstriction - **Vasodilating and vasoconstricting chemicals** The last image shows a heart, a blood pressure monitor, a stethoscope, and a bulb. It displays "THANK YOU."