Lecture 11: Blood Pressure PDF

Cardiovascular System Readings: 482-488, 492-495 Lecture 11: Blood Pressure Pressure Throughout the Systemic Circulation  Blood pressure is the key driving force of the delivery system for transporting blood o Ventricular contraction is the force that creates blood flow through the cardiovascular s...

Cardiovascular System Readings: 482-488, 492-495 Lecture 11: Blood Pressure Pressure Throughout the Systemic Circulation  Blood pressure is the key driving force of the delivery system for transporting blood o Ventricular contraction is the force that creates blood flow through the cardiovascular system  All of the auto regulation and feedback regulation is centered around measuring BP and responding to elevations and decreases in BP  Blood pressure is highest in the arteries and decrease continuously as it flows through the circulatory system (lowest in the veins) o Highest pressure occurs in the aorta and results from pressure created by the left ventricle  Changes in pressure creates flow to push the cardiac output through the system  When you measure arterial blood pressure (in a person) you are measuring the blood in the arteries o Artery chamber is driving the delivery of the blood Measuring Arterial Blood Pressure  Five “Korotkoff" sounds o The snapping sound first heard at the systolic pressure. Clear tapping, repetitive sounds for at least two consecutive beats is considered the systolic pressure o Murmurs heard or most of the area between the systolic and diastolic pressures o Loud, crisp tapping sound o Sounds at pressures ~10mmHg above the diastolic, were described as “thumping” and “muting” o Silence as the cuff pressure drops below the diastolic blood pressure. The disappearance of sound is considered diastolic blood pressure – two points below the last sounds heard  Blood pressure is taken from the brachial artery o One of the major arteries in the arterial system  Measured by listening to the sounds that are produced  Pumping air into the cuff causes constriction of the brachial artery to the point where no blood is flowing anymore o Pressure in the cuff is greater than the brachial artery o Usually above 120mmHg  Slowly deflate the cuff – listen for first Korotkoff sound o Spurts of blood that starts to appear when the cuff pressure is equal to or less than the brachial artery pressure o Create a sound when the blood starts to flow through o Systolic pressure – highest pressure in the system  Continue to listen (pressure is dropping) until the Korotkoff sounds go away – diastolic pressure o Cuff has no pressure on the brachial artery o Cuff pressure is below the diastolic pressure Pulse  Pulse ~ measure of the strength of the pressure wave of circulating blood  Pulse rate is used to measure the heart rate  Feeling the pulse is feeling the pressure wave that is exerted on the arteries as they are expanding when the heart is pumping during systole This study source was downloaded by 100000818475141 from CourseHero.com on 02-07-2024 15:05:47 GMT -06:00 https://www.coursehero.com/file/31079959/Lecture-11docx/ Cardiovascular System  Readings: 482-488, 492-495 Monitored at “pressure points” where pulse is easily palpated o Arteries are easily accessible  Radial artery (wrist)  Carotid artery (neck) Blood Pressure  “Pulse Pressure” = Systolic P – Diastolic P  The area between systolic and diastolic pressure is the pulse pressure o Difference between the two  The heart spends 2/3 of its time in diastole (resting phase) and 1/3 of its time in systole o Time averaged value of the amount of time the heart is in each phase  For a person who is 120mmHg/80mmHg: what is the pulse pressure? (systolic = 120 and diastolic=80) 1 2 1 Mean Arterial Pressure=diastolic P+ ( systolic P−diastolic P ) = diastolic+ systolic 3 3 3    o Pulse pressure = 40 mmHg o MAP = 93.333mmHg Measuring blood pressure happens in the arterial bag Only point of delivery of the CV system o Once you get to the tissues its too late to control the blood flow To ensure that the blood gets back to the heart properly you need to control the venous return What controls the pressure in the “aortic bag”?  Mean arterial pressure is a function of cardiac output and resistance in the arterioles o Both regulate aortic blood volume at entry and exit  Arterial bag has an input and an output  MAP – volume that fills the bag and the time averaged pressure in the bag  Cardiac output becomes a primary contributor o The amount of flow coming in is a contributor to how much volume is in the bag o Just as important as the amount of flow that is leaving the bag – resistance arterials  Mean average pressure is just a function of the flow in and the flow out o Function of cardiac output and the total resistance on the arterial vasculature (arteries and the capillary beds)  MAP is influenced by cardiac output and the total resistance of the system  Arteriolar resistance is influenced by both local and systemic mechanisms: o Local control of arteriolar resistance o Sympathetic reflexes o Hormones Blood Pressure is needed to drive flow into tissues  When you have constriction the blood will be redistributed o This is how blood flows to from the arterial bag to all of the tissues  Physiological conditions when one tissue has dilated artery and another has a constricted artery  After eating a meal o Dilate the gut arteries so blood can gather nutrients and take them to the rest of the body o Reduce blood flow to tissues that may not be part of the nutrient uptake  At a steady state: Average delivery of the total cardiac output to the different tissues in the body  Based on constriction and resistance of the tissues o 5L/min gets divided up between all of the tissues of the body This study source was downloaded by 100000818475141 from CourseHero.com on 02-07-2024 15:05:47 GMT -06:00 https://www.coursehero.com/file/31079959/Lecture-11docx/ Cardiovascular System Readings: 482-488, 492-495 Total Resistance Influences Mean Arterial Pressure  Primary determinant of a blood vessels’ diameter  Control point for resistance is the arteriole o Main site of variable resistance in the systemic circulation  Resistance opposes flow  Flow of blood in the systemic circuit is o Directly proportional to the pressure gradient o Inversely proportional to the resistance to flow  Once you start to branch off the main arteriole bag, gives you multiple control points for flow out of the bag  All the control points can be opened or closed o All squeezed – high total peripheral resistance  High resistance in all of those arteries that are squeezed shut o All open – low total peripheral resistance  Low resistance to the blood flow out of the arterial bag  Sum total of the total resistance of the arteries and capillary beds for the vasculature system  Can used Ohm’s Law to determine flow and pressure gradients in the system  Total flow is the cardiac output  Pressure gradient is the pressure in the arteries minus the pressure in the veins o Pressure gradient is the driving force for blood flow  When the resistance arterials are squeezing the peripheral resistance is increasing Cardiac Output Influences Mean Arterial Pressure  Effectiveness of the heart as a pump is determined by heart rate and stroke volume  Cardiac output is the total flow in the system  Increase of flow (CO) into the arteries causes an increase of blood and an increase in MAP o Could be elevating CO but could be opening up new pathways for blood flow and reducing the resistance to blood flow on the other end  Blood flow out of the arteries is influenced by peripheral resistance; resistance to flow offered by the arterioles This study source was downloaded by 100000818475141 from CourseHero.com on 02-07-2024 15:05:47 GMT -06:00 https://www.coursehero.com/file/31079959/Lecture-11docx/ Cardiovascular System Readings: 482-488, 492-495 Blood Distribution Influences Mean Arterial pressure  Relative distribution of blood between arterial and venous blood vessels is determined by: o Diameter of the veins o Stiffness of the vein  Innervated with the sympathetic nervous system  Help squeeze the blood back to the heart  Increase diastolic volume  Increase the Frank-Starling effect by creating lengthening of the sarcomeres giving stronger forces of contraction  The CO is determined by how blood is shifted from the venous side to the arterial side o The total blood flow through all of the arterioles of the body always equals the cardiac output  If there is squeezing on the venous bag you get more blood back to the heart  Blood is pumped to the arteriole side – blood pressure will increase  Stronger driving pressure for blood delivery to all of the tissues Blood Volume Influences Mean Arterial Pressure  Blood volume: o Controlled by the kidney’s (excretion of excess volume) o Doesn’t control the distribution between the arteries and the veins o Defines what the maximum pressure can be o If the total amount of blood is high both bags (arterial bag and venous bag) will be more full  BP will be higher o When blood volume increases, blood pressure increases o When blood volume decreases, blood pressure decrease  Effective way of treating hypertension patients is by giving them diuretics o Diuretics make patients pee more often This study source was downloaded by 100000818475141 from CourseHero.com on 02-07-2024 15:05:47 GMT -06:00 https://www.coursehero.com/file/31079959/Lecture-11docx/ Cardiovascular System   Readings: 482-488, 492-495 o Gets rid of excess water in the body and reduces the blood volume Cardiovascular compensation for a decreased blood volume includes: o Vasoconstriction (holding the blood in the vessels) o Increased sympathetic stimulation of the heart to increase cardiac output (pump more blood into the vessels to increase the BP) Events that might cause significant changes in blood volume include: o Dehydration o Hemorrhage o Ingestion of a large quantity of fluid RAAS (renin-angiotensin-aldosterone system) Controls Blood Volume  Kidney’s help control the blood volume  Stimulus – lower blood pressure, results in lower blood flow to kidney’s o The kidney’s have the ability to sense blood pressure o Pressure receptors in the juxtaglomerular apparatus  If the receptors sense low pressure they produce the hormone renin  Renin is secreted from the kidney’s and is a circulating enzyme in the blood  Another circulating enzyme is called Angiotensinogen that gets converted by renin to Angiotensin 1  Angiotensin 1 moves through the circulation and encounters another enzyme called ACE (present in high concentrations in the lungs)  Angiotensin 1 is converted to Angiotensin 2  Angiotensin 2 is a very potent molecule that goes to the adrenal cortex and regulates the production of aldosterone  Aldosterone has effects on the kidneys to retain salt and water o Also increases salt and water uptake  NET EFFECT: Is an increase in the blood volume o Also an increase in the pressure  Angiotensin has the same physiological effect on blood vessels as norepinephrine o Does not use the ß-AR receptor but the angiotensin receptors o Releases calcium into the smooth muscle cells and causes vasoconstriction of the arteries o Secondary to the effects on the kidney you get the effects of squeezing on the arterioles at the end of the arterial bag  Also helps to lift the blood pressure Slow Response: Aldosterone  Aldosterone signaling is a fairly slow response o Adrenal cortex o Reabsorption of salt (Na) and water by kidney o Renin-angiotensin-aldosterone system o Feedback loop – salt intake vs renin secretion  The kidney also has rapid responses o If the BP is high the body will get rid of more water (urine) Blood Pressure (Fast vs. Slow Control Mechanisms) This study source was downloaded by 100000818475141 from CourseHero.com on 02-07-2024 15:05:47 GMT -06:00 https://www.coursehero.com/file/31079959/Lecture-11docx/ Cardiovascular System   Readings: 482-488, 492-495 Slow Response o Increase in blood volume causes an increase in blood pressure o Excretion of fluids and decrease in the blood volume Fast Response o Compensation of the cardiovascular system o Cardiovascular system will respond very quickly in both directions  Extrinsic fast response to a change in the BP o Within a few heart beats at most can get back to cardiac homeostasis  Can be from both an increase or decrease of BP o Increase in blood pressure means the system wants to vasodilate the blood vessels and decrease the cardiac output  Open the arterials and release more blood into the venous side  Withdrawal of the sympathetic signals and increase the parasympathetic signals o Stretch and baroreceptors spread out the arterial bag at key points to constantly monitor the pressure Baroreceptor Reflex – Fast Response (within a few heartbeats)  Stretch-sensitive mechanoreceptors known as baroreceptors are located in the walls of the carotid arteries and aorta – they monitor the pressure of blood o Blood flowing to the brain is monitored by carotid baroreceptors o Blood flowing to the body is monitored by aortic baroreceptors  The baroreceptors are continuously firing action potentials are normal blood pressure o When the BP increases the firing rate of the receptors also increases o When the BP decreases the firing rate of the receptors also decreases 1. Change in the blood pressure a. Can be increase or decrease b. Baroreceptors are on key points of the vasculature, have a resting level that allows them to sense higher stretches or lower stretches in pressure 2. Immediately after the baroreceptors sense a change they send signals to the medullary cardiovascular control center a. Key place in the brain that controls sympathetic and parasympathetic signaling (autonomic balance) for the CV system b. Integrating center that receives all of the signals c. The center controls parasympathetic output and sympathetic output 3. Parasympathetic neurons (Vagus) innervate the SA node and the AV node a. Heart rate control 4. Sympathetic neurons innervate the SA node as well as the ventricles a. Can affect contractility (Inotropy) b. Also have effect on the blood vessels i. Alpha-adrenergic receptors and the ability of norepinephrine to cause vessels to constrict and in the absence of norepinephrine to dilate c. Can also have effect on the veins i. Determine whether the venous return increases or decreases back to the heart ii. Sympathetic signals cause the venous bag to squeeze and send blood back to the heart This study source was downloaded by 100000818475141 from CourseHero.com on 02-07-2024 15:05:47 GMT -06:00 https://www.coursehero.com/file/31079959/Lecture-11docx/ Cardiovascular System Readings: 482-488, 492-495 iii. Lack of sympathetic signals allows the veins to stay big and compliant (keeping the blood in the low pressure zone) 5. Together the parasympathetic and sympathetic neurons control the cardiac output a. Cardiac output is a key determinant of mean arterial pressure  All of the pathways work together through the integrating center to determine blood pressure control  Blood Pressure stimulus – DOWN o Integrating signals would want the BP to go back up o Increase the sympathetic signals  Higher heart rate  Higher Inotropy  Increased cardiac output  Squeeze blood to the heart from the veins  Stop the blood from exiting the arterial bag o Increase the mean arterial pressure  Blood Pressure stimulus – UP o Activate parasympathetic signals o Slow heart rate to reduce cardiac output o Withdraw sympathetic output from all other areas that are controlling MAP o BP would decrease Baroreceptor Reflex – Response to increased BP  Pathway that drives response to increased or decreased blood pressure  Increase in BP o Firing of receptors o Signal travel back to the control center o Control center activated the sympathetic and parasympathetic nerves o Alpha-AR effects on the arterioles o ß-AR on myocardium or the SA node o Changes in forces, contraction, and heart rate effect the cardiac output o Changes in vasoconstriction effect the peripheral resistance o Everything is driving to reduce blood pressure  Reduces BP is sensed by the baroreceptors and they stop sending signals to the integrating center Baroreceptor Reflex – Response to decreased BP  Response to orthostatic hypotension  Number of reasons for low BP o Physiologic mechanism: if you stand up too quickly, gravity causes blood to pool in the lower extremities o When you stand up gravity tends to draw the blood to the bottom of the venous bag  Short term decrease in the venous return that limits the Frank-Starling stretch in the heart, limiting the force of contraction (less blood in the ventricles during the next contraction)  Brain does not get any oxygen for 2-3 heartbeats and individual can faint  As soon as the pressure drops the system notices the decreased pressures and the baroreceptors stop sending ‘ok’ signals to the medulla  When the brain doesn’t get the signals it activates the sympathetic nervous system and shuts down the parasympathetic system o Shut down all the effects that slow down the heart rate and activated the signals to increase the heart rate This study source was downloaded by 100000818475141 from CourseHero.com on 02-07-2024 15:05:47 GMT -06:00 https://www.coursehero.com/file/31079959/Lecture-11docx/ Cardiovascular System    Readings: 482-488, 492-495 Arteries and veins are the primary vessels that squeeze the blood back to the heart o Arterioles were constricting and preventing blood from leaving the arterial bag (increased resistance) o Pressure in the arterial bag also increases o Arterial bag feeds the brain o Arteries squeeze to keep the blood in the distribution vesicle As peripheral resistance increases and cardiac output increased the blood pressure returns to normal When blood pressure returns to normal the baroreceptors send ‘normal’ signals to the medulla o Comes back to normal within ¾ heart beats This study source was downloaded by 100000818475141 from CourseHero.com on 02-07-2024 15:05:47 GMT -06:00 https://www.coursehero.com/file/31079959/Lecture-11docx/ Powered by TCPDF (www.tcpdf.org)