Vascular Physiology Lecture 3 PDF

Vascular physiology Lecture 3 By Dr. Asem Alkhalaileh Overview: Concept 1: Arterial Pulse Concept 2: Elastic arteries Concept 3 : Delayed compliance Concept 4 : Changes in CVS caused by gravitational forces  Concept 1: Arterial Pulse  Arterial pulse As blood flows through the vessel...

Vascular physiology Lecture 3 By Dr. Asem Alkhalaileh Overview: Concept 1: Arterial Pulse Concept 2: Elastic arteries Concept 3 : Delayed compliance Concept 4 : Changes in CVS caused by gravitational forces  Concept 1: Arterial Pulse  Arterial pulse As blood flows through the vessels of the circulatory system, it moves out of the left ventricle and into the aorta where it is then pushed through the rest of the circulatory system. During systole, the left ventricle contracts, the blood ejects into the ascending aorta then the aortic wall acutely dilates and generates a pressure wave that moves along the arterial tree. The blood that is forced into the aorta during systole moves the blood in the vessels forward and sets up a pressure wave that travels along the arteries (pulse wave) The pressure wave expands the arterial walls as it travels, and the expansion is palpable as the (pulse) Arterial pulse: Features of the pulse wave or pressure wave Systolic pressure is the peak point of pulse wave or pressure wave in aorta (120mmHg) Diastolic pressure is the lowest point of pulse wave or pressure wave in aorta (80mmHg) Diastolic pressure correspond to end ventricular diastolic pressure and opening of aortic valve Note: the diastolic pressure in aorta dose Not equal to diastolic pressure in ventricle this to allow blood to flow even in the diastolic phase of aorta. Arterial pulse: Features of the pulse wave or pressure wave Anacrotic limb: represent gradual increase in aortic pressure Dicrotic limb: represent gradual decrease in aortic pressure Incisura: represent the closer of aortic valve and correspond to closer of aortic valve Dicrotic notch: present slight elevation in aortic valve after closer of aortic valve and it also helps in the perfusion of the heart through the coronary vessels as it pushes the blood through the coronaries  H1-Receptor Antagonists Rapidly absorbed following oral administration. 1 ) The ventricular pressure gradually starts increasing & will try to push the blood toward the Aorta (but it CANT as the aortic valve is closed) Widely distributed throughout the body and 2)As the valve opens (diastolic pressure) the blood will flow towards the aorta , the pressure inside the ventricles will keep increasing to push the blood first-generation agents also enter the CNS. into the Aorta 3) then the ventricles will relax again and pressure will decrease Second-generation agents are primarily 4) but now the pressure is greater in the Aorta metabolized by CYP3A4 system and are subject 5) and blood will try to go back to the ventricles(due to the difference in pressure causes blood flow) 6) blood flow is inhibited by aortic valve to tremendous drug-drug interactions. 7) the blood will collect in the valve —-dicrotic notch 8) pressure will decrease to wait for the next beat(blood flow) 80 DIASTOLIC BP 9) this is called pulse wave (changes in the atrial wall) The pulse wave will occur rapidly #pulse wave velocity Arterial pulse: Pulse wave velocity and amplitude Pulse wave velocity is the rate at which pressure waves move down the vessel. Pulse wave velocity can be measured between any two arteries Pulse wave velocity equal to the distance between the arteries (taken from the surface of the body) divide by time taken to travel between those two arteries. Velocity = distance / time Arterial pulse: Pulse wave velocity and amplitude For example: Carotid–femoral pulse-wave velocity (PWV), calculated by measuring the time taken for the Pulse wave (or pressure wave) to travel the distance between the carotid and the femoral artery, which is generally measured over the body surface. Pulse wave velocity is the reference measurement of arterial stiffness (marker of vascular damage). Higher aortic pulse wave velocity means that the vessels are less elasticity and a significant predictor of cardiovascular complications (like stroke). The pulse wave velocity increase as we get far from aorta (Pulse wave velocity is about 4m/sec in the aorta, 8m/sec in large arteries, and 16m/sec in the small arteries of young adults.) this because the arteries get stiffer and increase resistance as we get far distally. The pulse wave velocity increase with advancing age and diseased arteries (atherosclerosis). Arterial pulse: Pulse wave velocity and amplitude ❑ Notes: Pulse wave velocity (passes in the wall of artery) increases as we get far from the aorta. Blood flow velocity (passes inside the lumen of the artery) decrease as we get far from the aorta. Pulse wave amplitude (i.e., the difference between systolic and diastolic pressure) will increase as: ①The artery get stiffer with increasing age, atherosclerosis, and ②Getting far from aorta. Arterial pulse: Pulse wave velocity and amplitude Arterial pulse: Pulse wave velocity and amplitude Generally, there are 2 main components of Pulse wave: A. forward moving wave The pulse wave or pressure wave is generated when the heart (ventricles) contracts during systole. This wave travels down the aorta from the heart. B. reflected wave. The pulse wave or pressure wave reflected wave gets reflected at the bifurcation or the "cross-road" of the aorta into 2 iliac vessels. Arterial pulse: Pulse wave velocity and amplitude The cause of augmentation of Pulse wave amplitude is due to Overlap of forward and backward traveling of pulse waves in the ascending aorta. Under physiologic conditions (i.e., in young individuals with elastic central arteries) the reflected pulse wave returns to the ascending aorta during diastole of the subsequent cardiac cycle. In patients with stiff central arteries (i.e., in the elderly or in patients with atherosclerosis) the higher pulse wave velocity results in premature arrival of the backward-traveling pulse wave (during systole rather diastole), leading to appearance of inflection point and augmentation of aortic systolic and pulse pressure. Thus causing: (1) augmentation of central systolic blood pressure increasing cardiac loading (2) reduction of central diastolic blood pressure decreasing coronary perfusion Arterial pulse: Pulse wave velocity and amplitude  Concept 2: Elastic arteries Elastic arteries: Pressure and flow functions The large elastic arteries include aorta and its main branches such as carotid, iliac, and axillary arteries. These vessels contain elastic tissue in their walls in abundance, which provides them two properties: ❶ Distensability (during systole) ❷ Elastic recoil (during diastole) Elastic arteries: Pressure and flow functions ❶ Distensability (during systole) The heart acts as pump and eject blood with each systole. The distensibility of the elastic arteries allows them to A. accommodate the blood pumped by the heart with only moderate increase in pressure from 80 mmHg to 120 mmHg. B. Due to distension at these vessels, a part of energy released from the heart is stored as potential energy in the wall of aorta. Elastic arteries: Pressure and flow functions ❷Elastic recoil (during diastole) During diastole, the stretched elastic wall of the aorta recoils and the potential energy stored in the wall released onto the blood. This causes the blood to flow during diastole also, in this way the pressure in the aorta does not fall below 80mmHg. This recoil effect is called (windkessel effect). ‫ ان اﻟﺪم ﯾﻤﺸﻲ ﻓﻲ اﻟﺸﺮاﯾﯿﻦ ﺣﺘﻲ ﯾﺼﻞ اﻟﻰ اﻻﻧﺳﺟﺔ ﻧﺘﯿﺠﺔ ل ﻗﻮﺗﯿﻦ اوﻻ اﺛﻨﺎء )‪ (Systole‬ﯾﻜﻮن ﺑﺴﺒﺐ ﻗﻮة دﻓﻊ‬ ‫اﻟﻘﻠﺐ ﺣﯿﺚ ﯾﺴﺒﺐ ﺟﺮﯾﺎن اﻟﺪم ﻣﻊ ﺗﻮﺳﻊ اﻟﺸﺮاﯾﯿﻦ‬ ‫ اﻣﺎ اﺛﻨﺎء ال )‪(Diastole‬ف ﯾﻜﻮن ﺳﺒﺐ دﻓﻊ اﻟدم ﻧﺎﺗﺞ ﻋﻦ رﺟﻮع اﻟﺸﺮاﯾﯿﻦ اﻟﻰ ﺣﺎﻟﺘﮭﺎ ﻗﺒﻞ اﻟﺗوﺳﻊ وﻛﺄﻧﮭﺎ‬ ‫ﺗﻌﻤﻞ ك ﺑﺪﯾﻞ ﻟﻠﻘﻠﺐ ﺧﻼل ال)‪(Diastole‬‬ ‫ و ﺑﺎﻟﺘﺎﻟﻲ ﻧﻀﻤﻦ ﺟﺮﯾﺎن اﻟﺪم اﺛﻨﺎء ال )‪ (Systole‬و ال )‪ (Diastole‬وﻟﮭﺬا اﻟﺴﺒﺐ ﻣﻦ ﻣﺼﻠﺤﺘﻨﺎ ان ﻻ ﯾﻨﺨﻔﺾ‬ ‫اﻟﻀﻐﻂ اﻟﻰ اﻟﺼﻔﺮ اﺛﻨﺎء ال )‪ (Diastole‬وأﻻ ﺗﻮﻗﻒ ﺟﺮﯾﺎن اﻟﺪم ﺧﻼل ال )‪(Diastole‬‬ Elastic arteries: Windkessel effect Windkessel when loosely translated from Germany to English means 'air chamber' but is generally taken to imply an elastic reservoir. Windkessel effect is a term used in describe the shape of the arterial blood pressure waveform walls in large elastic arteries, where the diameter is stretched during systole and recoil on the blood during diastole. This is because large elastic arteries contain a relatively large amount of elastic tissue. ❑ Clinically applied aspects Due to age-related degenerative changes and Atherosclerosis changes the elasticity of large vessels is decreased and so Windkessel effect becomes diminished with age due to arteriosclerosis. Therefore, in old age systolic blood pressure increase Elastic arteries: Windkessel effect How to fire extinguishers/water hose release the substance or water rapidly? What actually happens is that air is pumped in high pressure -when the hose opens, the pressure will decrease and air will try to expand -pushing the water out Elastic arteries: Windkessel effect ❑ How could elastic artery maintain constant blood supply to tissue? Since the rate of blood entering these elastic arteries exceeds that leaving them due to the peripheral resistance there is a net storage of blood during systole which discharges during diastole. The distensibility of the large elastic arteries is therefore analogous to a capacitor ‫اﻟﻤﻜﺜﻔﺎت ھﻲ اﻻﺟﮭﺰة اﻟﺘﻲ ﻟﮭﺎ ﻗﺪرة ﻋﻠﻰ ﺧﺰن اﻟﻄﺎﻗﺔ اﻟﻜﮭﺮﺑﺎﺋﯿﺔ وھﻨﺎ اﻟﺸﺮﯾﺎن ﯾﺴﺘﻄﯿﻊ ان‬ ‫ﯾﺨﺰن اﻟﻄﺎﻗﺔ ﻓﻲ اﻟﺠﺪران‬ This mechanism helps to maintain constant blood supply to tissues during systole and diastole. Elastic arteries: Functions of elastic arteries ❶ Elastic vessels reduce velocity of blood flow to some extent during ventricular contraction (systole) due to property of distensibility. ❷ Elastic vessels cause increase in velocity of blood flow to some extent during ventricular diastole by elastic recoil. Thus, the windkessel effect reduces the energy expenditure of heart. ❸ Pumping action of the heart along with elastic recoil of aorta together constitutes a driving force tor blood to move forward (towards periphery). This force is called vis-a-tergo force (a force push from behind) and is an important determinant tor venous return. ❹ Conversion of pulsatile blood flow from heart to a steady continuous flow. The elastic vessels act together with arterioles (resistance vessels) to convert this pulsatile flow into a steady continuous flow in the tissue capillaries, which allows maximum exchange between the blood and tissue. Systole and diastole pressure will stay till Arterioles In Arterioles the pressure will become one pressure only (no systolic and diastolic) This is important as we have said they have the greatest resistance (50) they decrease pressure by increasing resistance, allowing blood flow to the capillaries with low pressure to allow exchange of substances  Concept 3: Delayed compliance  After the blood pressure has dropped from 12 to 9 -Blood pressure were further drop due to the relaxation of smooth muscles(This is called delayed compliance) - then I have removed the extra blood added, causing Delayed compliance: further decrease in blood pressure - after sometime the blood pressure will return to normal (Stress Relaxation) of Vessels five this is due to contraction of smooth muscles The term “delayed compliance” means that a vessel exposed to increased volume at first exhibits a large increase in pressure, but progressive delayed stretching of smooth muscle in the vessel wall allows the pressure to return toward normal over a period of minutes to hours. The pressure is recorded in a small segment of a vein that is occluded at both ends, an extra volume of blood is suddenly injected until the pressure rises from 5 to 12 mm Hg. Even though none of the blood is removed after it is injected, the pressure begins to decrease immediately and approaches about 9 mm Hg after several minutes. In other words, the volume of blood injected causes immediate elastic distention of the vein, but then the smooth muscle fibers of the vein begin to “creep” ‫زﺣﻒ‬ to longer lengths, and their tensions correspondingly decrease. This effect is a characteristic of all smooth muscle tissue and is called stress-relaxation  Delayed compliance: (Stress Relaxation) of Vessels Delayed compliance is a valuable mechanism by which the circulation can accommodate extra blood when necessary, such as after too large a transfusion. Delayed compliance in the reverse direction is one of the ways in which the circulation automatically adjusts itself over a period of minutes or hours to diminished blood volume after serious hemorrhage. For the bladder to accept the urine it has to increase in size - to prevent increase in pressure when this occurs -smooth muscles will start to relax to increase the size and acceptance of urine The same thing occurs in blood vessels -blood vessel smooth muscle wall will begin relaxing decreasing pressure -this period when the smooth muscle wall relaxes is called delayed compliance  Concept 4: Changes in CVS caused by gravitational forces  Gravitational forces Effects of gravity on hydrostatic pressure In any body of water that is exposed to air, the pressure at the surface of the water is equal to atmospheric pressure, but the pressure rises 1 mm Hg for each 13.6 millimeters of distance below the surface. This pressure results from the weight of the water and therefore is called gravitational pressure or hydrostatic pressure. The hydrostatic pressure is the pressure at a point that a fluid at rest exerts due to the force of gravity. The hydrostatic pressure (P) is affected by 3 factors: ✔ g: acceleration gravity ✔ h: height ✔ ρ (Rho): density If you considered the heart as the starting point— everything above the heart will decreases (as it opposes the gravity)—-and everything in the heart will increase (with gravity down) Gravitational forces Effects of gravity on hydrostatic pressure Hydrostatic pressure results from a difference in vertical height in a fluid filled system. Because of gravity, fluid has weight that generates force, which is proportional to its vertical height. In supine person, the hydrostatic pressure effect eliminated because the entire cardio-vascular system is at essentially the same horizontal level. There is one point in the circulatory system at which gravitational pressure factors caused by changes in body position of a healthy person usually do not affect the pressure measurement by more than 1 to 2 mm Hg. To measure blood pressure accurately, it is important to place the sphygmomanometer cuff at the zero reference (phlebo-static) level, which is equivalent to the level of the right atrium, which is at or near the level of the tricuspid valve, which is called the reference level for pressure measurement. But when you stand the hydrostatic pressure will increase and show Gravitational forces Effects of gravity on hydrostatic pressure The reason for lack of gravitational effects at the tricuspid valve is that the heart automatically prevents it in the following way: An increase in pressure at the tricuspid valve slightly above normal will increase the right ventricle pressure so the heart will pump blood more rapidly, so the pressure at the tricuspid valve will go back to the normal mean value. Conversely, a decrease in pressure at the tricuspid valve slightly below normal will decrease the right ventricle pressure so the heart will pump less blood, so blood dams up in the venous system, this will increase the pressure at the tricuspid valve back toward the normal mean value. Gravitational forces Effects of gravity on hydrostatic pressure In other words, the heart acts as a feedback regulator of pressure at the tricuspid valve. When a person is lying on his or her back, the tricuspid valve is located at almost exactly 60 per cent of the chest thickness in front of the back. This is the zero-pressure reference level for a person lying down. Both arteries and veins at any given horizontal level are affected by the same hydrostatic pressure of blood so that the pressure gradient between arteries and veins is not alerted. Gravitational forces Effects of gravity on Venous pressure The heart will be considered as the reference point for each arterial and venous pressure. For venous pressure will be 0 mm Hg (right atrial pressure) ❑ The effect of the gravitational on the pressure in the circulatory system will be: 0.77 mmHg will be added to pressure for each cm when the point below the heart. 0.77 mmHg will be subtracted from pressure for each cm when the point above the heart. -When standing the veins in the neck don’t show (zero hydrostatic pressure, atmospheric pressure) ; but the veins in the hands show as they have high pressure (are far from the heart) Gravitational forces Effects of gravity on Venous pressure ❑ In the upright position: ❶ the venous pressure above the heart is decreased by the force of gravity. ❷ the venous pressure below the heart is increased by the force of gravity. The neck veins collapse above the point where the venous pressure is closed to zero, and the pressure all along the collapsed segment is close to zero rather than sub-atmospheric. The dural sinuses have rigid walls and cannot collapse. The pressure in them is therefore always sub-atmospheric. The magnitude of the negative pressure is proportionate to the ventricular distance above the top of the collapsed neck vein, and in the superior sagittal sinus may be as much as (-10 mmHg due to 13cm distance) because of the hydrostatic “suction” between the top of the skull and the base of the skull. Therefore, if the sagittal sinus is opened during surgery, air can be sucked immediately into the venous system; the air may even pass downward to cause air embolism in the heart, and death can ensue. Gravitational forces Effects of gravity on Venous pressure When gravitational force acts on the lower parts of body especially in the erect posture The gravitational force tries to pull down blood from the dependent parts of the body ► decrease the venous return from the lower limbs ►this keeps on increasing the pressure in veins in the dependent parts of body. The highest point is found in the ankle (+90mmHg) People who have been standing almost stationary for prolonged time, have tendency to fall unconscious is because of decreased venous return. Indeed, 10 to 20 per cent of the blood volume can be lost from the circulatory system within the 15 to 30 minutes of standing absolutely still, as often occurs when a soldier is made to stand at rigid attention. This because decreases the cardiac output and hence reduces blood flow to brain Gravitational forces Effects of gravity on Venous pressure The effects of gravity on venous return seem paradoxical because when a person stands up ①The hydrostatic forces cause the right atrial pressure to decrease and ②The venous pressure in the dependent limbs to increase. This increases the pressure gradient for venous return from the dependent limbs to the right atrium; however, venous return paradoxically decreases. The reason for this is when a person initially stands and before the baroreceptor reflex is activated, cardiac output and arterial pressure decrease because ↓venous return + ventricular preload falls+↓right atrial pressure →↓stroke volume ( Frank-Starling mechanism) →↓cardiac output →↓ arterial pressure→↓flow through the entire systemic circulation falls including venous pressure →↓ pressure gradient driving flow throughout the entire venous system falls more than right atrial pressure. Gravitational forces Effects of gravity on Venous pressure The falling down of such people in fact is a natural defense mechanism to facilitate venous return and restoration of blood flow to brain. When a person is in recumbent posture, the gravitational force acts equally on all the parts of body. This is going to facilitate venous return Gravitational forces Effects of gravity on Arterial pressure The heart will be considered as the reference point for each arterial and venous pressure, for arterial pressure will be 100mmHg (mean aortic pressure) The effect of the gravitational on the pressure in the circulatory system will be: 0.77 mmHg will be added to pressure for each cm when the point below the heart. 0.77 mmHg will be subtracted from pressure for each cm when the point above the heart. In adult human in upright position, when the mean arterial pressure at heart level is 100mmHg, The mean pressure in large artery in the head (30 cm above the heart) is 77 mmHg = [100 – (0.77 X 30)]. The pressure in large artery in the foot (105 cm below the heart) is 180 mmHg = [100 + (0.77 X 105)]. Gravitational forces Effects of gravity on Arterial pressure The gravitational factor also affects pressures in the peripheral arteries and capillaries. In addition to this, pulling down of blood in the arterial compartment due to gravitational force, increases the hydrostatic pressure in the capillaries. The overall effect will be more fluid transudation from the intra-vascular compartment to interstitial spaces ►This will give rise to edema. This may be one of the reasons for swelling of legs in long-distance flights; wherein prolonged erect posture in the absence of muscular contractions will lead to swelling of legs. The stasis of blood in the venous compartment, at times may lead to intravascular clotting and this is known as deep vein thrombosis.