[PHYSIO]-LC13-Vascular Distensibility and Functions of the Arterial and Venous Systems.pdf

NOTE: If 1 mm Hg causes a vessel that originally contained 10 millimeters of blood to increase its volume by 1 millil...

NOTE: If 1 mm Hg causes a vessel that originally contained 10 millimeters of blood to increase its volume by 1 milliliter, the OUTLINE distensibility would be 0.1 per mm Hg, or 10 percent per mm Hg ○ So, 1 mm Hg is the increase in pressure, 10 mL would be I. VASCULAR DISTENSIBILITY the original volume, and the increase in volume is 1 mL II. UNITS OF VASCULAR DISTENSIBILITY (substitute to the formula in Figure 1) → the answer is 0.1 III. VASCULAR COMPLIANCE OR VASCULAR CAPACITANCE per mmHg or 10% per mm Hg IV. VOLUME-PRESSURE CURVES OF THE ARTERIAL AND VENOUS CIRCULATIONS VEINS ARE MORE DISTENSIBLE THAN THE ARTERIES V. DELAYED COMPLIANCE (STRESS-RELAXATION) OF VESSELS VI. ARTERIAL PRESSURE PULSATIONS Arteries have strong muscle walls but have a lesser distensibility than VII. ABNORMAL PRESSURE PULSE CONTROLS the venous system. VIII. TRANSMISSION OF PRESSURE PULSES TO THE PERIPHERAL Veins are more distensible than the arteries because the special ARTERIES characteristics of the veins are responsible for the storage of large amounts of fluid Veins are capable of holding large volumes of blood therefore they are called your reservoir. I. VASCULAR DISTENSIBILITY Veins = 8x more distensible than the arteries ○ given increase in pressure causes about 8x as much increase in blood in a vein as in an artery of comparable What is Vascular Distensibility? All vessels in our body possess the size characteristics of vascular distensibility, because this is an important In the pulmonary circulation, similarly, pulmonary veins are more characteristic for them to accommodate large volumes of blood that distensible than pulmonary arteries but at a lower pressure. It’s only is passing through them. When the heart pumps, the first one to 6x higher because the cross sectional area of the vessels are not that accommodate is the proximal aorta. It will be in a pulsatile manner, big. depending on how strong the heart is pumping blood out from the Pulmonary arteries are about 1/6 (more distensible) of those in the ventricles. systemic arterial system. Since the heart is having rhythmical impulses, the blood that passes ○ PA distensibilities are about 6 times greater than through the vessels will be in rhythmical or pulsatile manner unless distensibility of systemic arteries they are already in the periphery where almost no rhythmical impulses will be appreciated. Present in all vascular vessel III. VASCULAR COMPLIANCE OR VASCULAR CAPACITANCE They have valuable characteristic of the vascular system which allows vessels to accommodate the pulsatile output of the heart and to average out pressure pulsations Defined as the total quantity of blood that can be stored in a given Vascular distensibility provides smooth, continuous flow of blood portion of the circulation for each mm Hg pressure rise through the very small blood vessels of the tissues Vascular distensibility will provide smooth continuous flow of blood from the aorta to the small vessels, it means that even a slight decrease in blood pressure will cause additional storage of blood in the vessels. Figure 2. Formula for vascular compliance. Venous System ○ The most distensible by far of all the vessels For compliance to occur, there might be an increase in volume, but is ○ The most distensible of all vascular segment is the venous inversely related to the pressure segment If there is an increase in volume, that vessel should be compliant ○ Slight increases in venous pressure cause the veins to enough to accommodate the large amount of blood. If there are store 0.5 to 1.0 liters of extra blood → veins provide a inadequacies, what can occur? 9 reservoir for storing huge quantities of extra blood which For example when there is too much blood coming from the left can be used when blood is needed somewhere else in the atrium and aorta due to aortic regurgitation, the left ventricle may circulation not be able to hold that increased amount of fluid wherein it will backflow to the pulmonary circulation and will result in congestion. II. UNITS OF VASCULAR DISTENSIBILITY Compliance and distensibility are quite different ○ A highly distensible vessel that has a small volume may have far less compliance than much less Expressed as the fractional increase in volume for each millimeter of distensible vessel that has a large volume because mercury rise in pressure compliance is equal to distensibility times volume Compliance of a systemic vein is 24 times than corresponding artery ○ About 8 times as distensible and has a volume about 3 time as great (8x3=24) ○ Vascular compliance is composed of volume and pressure. ○ If side by side comparison of a common femoral vein and Figure 1. Formula of vascular distensibility. common femoral artery, the venous system of a common femoral vein is more compliant compared to common Vascular distensibility is directly proportional to the increase in femoral artery. volume, but inversely related to the increase in pressure. ○ We have learned in the previous lecture that the venous segment has the highest volume in the systemic Page 1 of 12 [PHYSIOLOGY] 1.13 Vascular Distensibility and Functions of Arterial and Venous Systems - Dr. L. Viado circulation, as compared to the arterial partner system has the highest amount of fluid as compared to the arterial corresponding arterial system. system, the pressure there remains lower than the arterial system. A ○ It is the reason why it can accommodate large amounts change of several hundred mL in this volume can change the venous because the venous system is called as one of the pressure only 3 to 5 mm Hg. For it to reach a pressure of 0, several reservoirs in the systemic circulation. 1000 mL of volume is needed to be removed from the venous system. Random question: ○ because the venous system is able to accommodate or This is important because as we will discuss about the pressure that is react appropriately to the presence of a small amount of present from the aorta to the arterioles, fluid that is removed or infused into the venous system. Example: Blood transfusion In which segment has the highest pressure? Is it in your aorta, arterioles ○ As much as ½ liter of blood can be transfused into a or capillaries? The aorta has increased pressure. healthy person in only a few minutes without greatly How about compared to your capillaries, which one is more compliant? affecting the function of the circulation. Capillaries ○ If you transfuse 300 ml of blood it will not cause increase in pressure because the vein a large reservoir,It will accommodate the large amount of blood and maintain a normal pressure IV. VOLUME-PRESSURE CURVES OF THE ARTERIAL AND VENOUS ○ CIRCULATIONS EFFECT OF SYMPATHETIC STIMULATION OR SYMPATHETIC INHIBITION ON THE Volume-pressure curve: convenient method to use for expressing VOLUME-PRESSURE RELATIONS OF THE ARTERIAL AND VENOUS SYSTEMS the relationship of pressure to volume or in a vessel or in any portion of the circulation As shown in Figure 3, the vascular sympathetic nerves can be excited or inhibited, and their effects show differences in the volume-pressure curve Sympathetic stimulation ○ Increase vascular muscle tone For every increase in volume, there will be an increase in pressure If there is an increase in muscle tone it constricts. In the arterial system, if there is an increase in volume, pressure will also be increasing. The same goes to the venous system. So for every volume that is infused to that segment, there will be sympathetic stimulation, thereby creating an increase in pressure also in that area. Figure 3. Volume-pressure curve of the systemic arterial and venous systems, If you add a volume of 200 ml in that area the showing the effects of the inhibition or stimulation of the sympathetic nerves to pressure will increase abruptly. the circulatory system. ○ Increases the pressure at each volume of the arteries or veins The pressure volume curves are directly activated or regulated by the ○ IMPORTANCE IN ARTERIES sympathetic and parasympathetic flow. valuable means for diminishing the dimensions Sympathetic activity will constrict the peripheral vessels as opposed of one segment of the circulation → to your coronary arteries, they will dilate. transferring blood to other segments This is the volume-pressure curve. The dark red line is the Blood loss: through sympathetic sympathetic activity, to the left is the activation, to the right is the stimulation, the arterioles will try to inhibition. Same goes for the vein. constrict, and blood will be When an arterial system of an adult Is about 700 ml, what happens transferred to other segments to the pressure if the volume decreases to 400 ml? It will decrease which are in the aorta, thereby to almost zero. increasing the pressure. Whereas the vein normally has 2,500 to 3,500ml of volume. It takes Example: a patient is suffering from several hundreds of volume loss To decrease the pressure by 2-3 anaphylactic shock. So what will happen to the mmHg. arterial walls? The arterial walls will try to dilate. So at that point, there is an apparent ARTERIAL SYSTEM blood loss, although there's still the same Small amount of blood loss in this segment will abruptly cause volume of blood that is present in that arterial physiologic change. tree. So with the sympathetic stimulation, the When the arterial system of an average adult person (with the large arterioles try to contract, and then it will arteries, small arteries, and arterioles included) is filled with about transfer that volume of blood to the aorta, so 700 mL of blood, the mean arterial pressure is 100 mm Hg. However, that it will cause an increased pressure there. when it is filled with only 400 mL of blood, the pressure will abruptly increase volume = increased pressure. fall to zero. If there is sympathetic activity what happens, the vessels constrict. Which is a way of VENOUS SYSTEM preparing blood for the different systems of Small amount of blood loss in this segment will NOT cause the body. SIGNIFICANT physiologic change. In the whole systemic venous system, the volume normally ranges from 2000 to 3500 mL. So, take note, that even though the venous Page 2 of 12 [PHYSIOLOGY] 1.13 Vascular Distensibility and Functions of Arterial and Venous Systems - Dr. L. Viado ○ IMPORTANCE IN VENOUS SEGMENTS So, in a given segment with a pressure of 5 mm Hg, when there is a Stab wound with severe hemorrhage → massive transfusion or fast infusion of your IV fluids, that segment reduces the vessel sizes enough to maintain will have an additional volume. Therefore, when there is an adequate circulation when there is 25% blood increasing volume initially, there will be an increase in pressure to loss about 12 mm Hg from the pressure of 5 mm Hg. In a severe hemorrhage, volume loss is there In order to not have a high pressure for a long period of time, our and the pressure in the periphery would be vessels will try to relax so that the pressure that is initially increased, decreased. will try to decline in order to preserve the normal milieu of the body. In order to sustain an adequate measurement Example: In severe hemorrhage, of blood pressure, the venous segment, the ○ the blood pressure initially is 110/80, and then there's a venules, will try to reduce in size and To blood loss, the BP will become 50 palpatory preserve the volume of blood. ○ 50 palpatory is not adequate to have a proper circulation However, as you have learned in your in our body so there is poor perfusion or transport of physiology, there is a critical point in a venous nutrients and oxygenation. segment that if the volume of blood or blood ○ Our body initially will respond. The blood vessels will try loss is 25%, reaching its critical point, the to contract and try to increase the pressure. If there is venous segment can no longer hold a normal contraction of a vessel allegedly, there is a smaller pressure. So it will tend to collapse and cause diameter causing increase in pressure in a given same circulatory shock. volume of blood. Venous segment collapses and can no longer ○ So at that point, it will try to increase the blood pressure accommodate the hemorrhage or the blood to reach a certain level of blood pressure which is enough loss. to have a proper circulation for transport of oxygen, If there is sympathetic activity, when you hormones and other substances. increase the volume in the venous system, It ○ But, again, if blood loss reach to its critical point, then the increases the pressure but only in small there will be vascular collapse amounts. What we will have is the delayed compliance DELAYED COMPLIANCE (STRESS-RELAXATION OF VESSELS) or stress relaxation of the vessels. It means Increase intravascular volume: blood transfusion that if a vessel is exposed to a large amount of ○ causes immediate elastic distention of the vein blood, It will increase pressure immediately. If ○ but smooth muscle fibers of the vein begin to “creep” to there is increased Volume, the pressure is longer lengths/segment increased. That is the first few hours of blood ○ Tension decrease: although there is an increase in infusion. Over time there will be delayed volume, the BP will be decreased because the smooth stretching of your smooth muscle, and it will muscle will try to lengthen its segment = accommodating cause the pressure to go down because that large amount of volume vessel will try to dilate. ○ RESULT: maintain a lower pressure over time V. DELAYED COMPLIANCE (STRESS-RELAXATION) OF VESSELS It means that a vessel exposed to increased volume at first exhibits a large increase in pressure Figure 5. Effect of blood infusion to blood vessels: increase in volume and However over a period of time, there will be progressive delayed pressure (right) and the compensation (lengthening) of smooth muscles to stretching of smooth muscle in the vessel wall which allows the accommodate the increase in volume: increase in volume, decrease in pressure pressure to return toward normal over a period of minutes to hours. (left). ○ Decreases the pressure of that segment over time. ○ So after 20 to 30 minutes of blood transfusion, the Decrease intravascular volume: hemorrhage pressure will decline. ○ causes contraction of the vein to try increasing the Delayed compliance is a valuable mechanism by which the circulation pressure can accommodate extra blood when necessary ○ RESULT: maintain a high pressure over time that is possible Figure 6. Effect of blood loss to blood vessels: decrease in volume and pressure (left) and effect of venous contraction: decrease in volume and increase in pressure (right). Figure 4. Effect of intravascular pressure of injecting a volume of blood into a VI. ARTERIAL PRESSURE PULSATIONS venous segment and later removing the excess blood, showing the delayed compliance principle. The aorta receives the pulsatile blood flow coming from the LV. These Figure 4 tells us how our vessels will react when there is rapid are the pulsations every heartbeat. infusion of blood or when there is a rapid blood loss. With each beat of the heart a new surge of blood fills the arteries If vascular distensibility is ABSENT: Page 3 of 12 [PHYSIOLOGY] 1.13 Vascular Distensibility and Functions of Arterial and Venous Systems - Dr. L. Viado ○ All of this new blood would have to flow through the increased pressure in the aortic segment: peripheral blood vessels almost instantaneously when the heart contracts, the aorta will ○ blood flow will only occur during systole (the only time receive a high pressure creating a pressure of there would be blood flow is if if the heart contracts) 120 ○ no flow would occur during diastole (relaxed/no as the diastole will occur, the pressure in the contraction) aorta will be decreased Arterial Compliance ○ Femoral artery: pressure is decreasing / the pulsation is ○ Normally reduces the pressure pulsations to almost no not normal anymore as the blood will be forwarded here pulsations by the time the blood reaches the capillaries. ○ Radial artery: decrease also in the pulsation ○ Tissue blood flow is mainly continuous with very little ○ Arterioles and capillaries: almost no pulsation is present pulsation because of more compliant segments ○ Q: If the blood flow reaches the capillaries, will the have lesser pressure in these segments for a compliance of the capillaries increase or decrease? blood flow to occur A: increase (pulsation coming from the beating heart → ○ To accommodate the large amount of blood coming from aorta (highest compliance) → blood to the periphery → the aorta in each pulsation/contraction/cardiac cycle, capillary = ↑ compliance) these segments should decrease the pressure and ○ Q: if there is increased pressure, will there be increased become more compliant compliance? A: decrease (higher pressure of blood from aorta → PRESSURE PULSATION capillaries = ↓ compliance) Systolic pressure (SBP): highest pressure that the aorta can reach ○ as pressure is decreasing in the arterial system, for our Diastolic pressure (DBP): lowest pressure blood to flow from ↑ to ↓ pressure (pressure difference in Pulse pressure (PP): the difference between SBP and DBP vessels) : ○ PP = SBP - DBP same amount of blood that can be transferred Example: in a normal individual, the blood pressure is 120/80 during one cardiac cycle/heart beat and same ○ PP = 120 - 80 = 40 volume in each segment of the circulation to maintain that volume, the compliance of 2 Major Factors that Affect Pulse Pressure the blood vessels should be increased in the 1. The stroke volume output of the heart periphery compared to those with higher Stroke volume (SV) = end diastolic volume (EDV) - end pressure (aortic segment) systolic volume (ESV) Stroke volume is the amount of blood ejected from the ventricle with each cardiac cycle. It can be readily calculated by subtracting the end-systolic volume from the end-diastolic volume. EDV - amount of blood in LV (coming from LA) during diastole ESV - amount of blood in LV after ejection ○ amount of blood retained after contraction 2. The compliance (total distensibility) of the arterial tree 3. 3rd less important factor: character of ejection from the heart during systole Question: if the ejection fraction is decreased, what will be the pulse pressure? (ejection fraction (EF) = ([EDV - ESV]/EDV)*100%) Answer: the lesser the ejection fraction, the lower the pulse pressure Pulse pressure DIRECTLY RELATED to stroke volume ○ If one has a good stroke volume, then his pulse pressure is also good ○ The higher the stroke volume, the higher the pressure, the better, but of course only up to a certain limit INVERSELY RELATED to arterial compliance ○ If an arterial wall is more compliant, there is lesser pulse Figure 7. Changes in the contour of pulse pressure as the pulse wave travels pressure towards the smaller vessels. ATRIAL PRESSURE PULSATIONS Compared to the arterioles, the aorta has the highest compliance In general, greater stroke volume output (e.g. aortic regurgitation) → By the time the blood reaches the periphery, the waveform greater the amount of blood that must be accommodated in the disappears arterial tree with each heartbeat → greater the pressure rises during In Figure 7, when the heart pumps during systole, the ventricular systole and falls during diastole → greater pulse pressure pressure increases and overcomes the aortic valves for it to open. Conversely, the lesser the compliance of the arterial system, the When blood is ejected, the LV pressure decreases to a lower level greater the increase in pressure for a given stroke volume of blood than the aortic pressure, hence the aortic valves will try to close pumped into the arteries During diastole when the aortic valves are closed, there is a slight Pulse pressure is determined approximately by the ratio of stroke pulsation – there will be going back of blood to the aorta, like it will volume output to compliance of the arterial tree bounce back to the aorta. Some will be reflected back as the incisura Any condition that influence either of these two factors also Normally, the pressure is higher, but as we go to the capillaries and influences the pulse pressure: the arterioles, hindi na ganoon ka-ganda yung pulsation ○ proximal aorta 𝑃𝑢𝑙𝑠𝑒 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 = 𝑠𝑡𝑟𝑜𝑘𝑒 𝑣𝑜𝑙𝑢𝑚𝑒 / 𝑎𝑟𝑡𝑒𝑟𝑖𝑎𝑙 𝑐𝑜𝑚𝑝𝑙𝑖𝑎𝑛𝑐𝑒 Page 4 of 12 [PHYSIOLOGY] 1.13 Vascular Distensibility and Functions of Arterial and Venous Systems - Dr. L. Viado There will be NO incisura since the aortic valves are not closed or have abnormal closure VII. ABNORMAL PRESSURE PULSE CONTROLS For example, in a normal heart, LA has a volume of 100 mL. During ventricular filling, this 100 mL will go to the LV. When the heart pumps the blood, 90 mL will be ejected, and 10 mL will remain in the LV (because not all of the blood goes out). Then, this patient had a rheumatic heart failure and affected his aortic valve, causing aortic regurgitation. Hence, during the cardiac cycle of the patient, (remember that normally the LV will pump out 90 mL of blood and 10 mL remains in the LV) 80 mL of the 90 mL will go back to the LV, and in the next cycle another 100 mL from the LA will go down to the LV during diastole, so the total volume in the LV will now become 190 mL. If the LV is functioning well, 180 mL will be pumped out and 10 mL will remain. Then another next cardiac cycle begins, 100 mL from LA goes to the LV, hence there will be 110 mL volume in the LV, but since the patient has malfunctioning aortic valves, 170 mL of the blood will flow back Figure 8. Different aortic pressure pulse contours in normal, arteriosclerosis, to the LV, so the total volume of the LV becomes 280 mL. aortic stenosis, patent ductus arteriosus, and aortic regurgitation. This goes on and on, so the stroke volume will be increased every time the heart pumps out blood. Aortic stenosis What if 90 mL flowed back to the LV? The LV will now have 200 mL Valves don’t open widely (again, 100 mL from LA + the remaining 10 mL). This 200 mL is the ○ Blood flow to the heart will have a decrease of blood flow pressure of the aorta and hence the blood pressure of the patient. towards the Aorta Another example: The blood pressure of the patient is 190 mm Hg Dampen systolic pressure – there is no sharp peak in the systolic (systole). 180 mL of this blood goes back to the LV during diastole, phase the pressure in the aorta will be 10 mm Hg now. Hence, the pulse In severe conditions, there will be hypotension pressure will be 180. Be careful in giving diuretics, most of the time since there is a ○ In a normal blood pressure of 120/80, the pulse pressure decrease of forward flow in the aorta is 40. With the blood pressure of 190/10, the pulse Patent Ductus Arteriosus pressure becomes 180. Some of the blood from the aorta goes to the pulmonary circulation, This means that in a patient with aortic regurgitation that is severe, and more blood will be going to the left atrium his blood pressure will be high because the stroke volume is too high, Abrupt decline in DBP but when you see the diastolic pressure, it’s too low because almost Example: if the right ventricle ejected 100ml blood to go to the all blood will go back to the LV, hence there will be no pressure in the atrium and additional 50 ml comes from the aorta (through the aorta pulmonary trunk and pulmonary veins) = 150 ml goes to the atrium Clinically, you will see a patient with a blood pressure of 190/0. The instead of the normal 100ml diagnosis will then be aortic regurgitation since it has high stroke More volume goes to the atrium → more volume goes to the LV→ volume but a very low diastolic pressure to as low as 0, and the more volume to be ejected (stroke volume is increased) pulse pressure is large. During diastole, there will be flow of blood going to the pulmonary circulation. The volume of blood that is supposedly 50 ml that is left during diastole will go to the pulmonary trunk, so: lesser volume in the aorta during diastole = lesser pressure (similar with aortic regurgitation) – but not low enough to reach 0 mm Hg Similarity with aortic regurgitation: blood will flow back to the heart and during diastole, both will have dropped DBP Difference with aortic regurgitation: the presence of incisura because in patent ductus arteriosus, the aortic valves are functional (able to open and close) Figure 10. Malfunctioning aortic valve in aortic regurgitation. Non-compliant arteries (Atherosclerosis/Arteriosclerosis) Arteries have become hardened. Rise in pressure for a given stroke volume of blood pumped into the arteries. Pulse pressure rises to twice normal. Figure 9. Inside the heart with Patent Ductus Arteriosus. NORMAL (120-80 = 40mmHg) OLDER ADULTS (160-80 = 80mmHg) Aortic regurgitation ○ Stiff aorta The valves are not closed during diastole ○ Since the arteries of the elderly people are not compliant Blood will flow back to the LV anymore due to the calcification (no dilation), hence there would be an abrupt increase of volume in that area, the Page 5 of 12 [PHYSIOLOGY] 1.13 Vascular Distensibility and Functions of Arterial and Venous Systems - Dr. L. Viado pressure will also abruptly increase because the ventricle compliant, there will be dampening of the pressure waves. will pump against a very high pressure ○ Diastolic pressure still remains almost normal DAMPING ○ Pulse pressure is higher than a normal individual but not Progressive diminution of the pulsations in the periphery. The aorta higher than those who have aortic regurgitation will receive pressure from the LV and normal pulsation will be present in the aortic level. Only when the aortic pulsations are extremely large or the arterioles VIII. TRANSMISSION OF PRESSURE PULSES TO THE PERIPHERAL ARTERIES are greatly dilated can pulsations be observed in the capillaries CAUSES 1. Resistance to blood movement in the vessels Small amount of blood must flow forward at the pulse wave front to distend the next segment of the vessel. Greater the resistance, the more difficult it is for this to occur. The greater the resistance, the greater the damping. 2. Compliance of the vessels Greater the quantity of blood required at the pulse wave front to cause an increase in pressure. The greater the compliance, the greater the damping, the greater the amount of blood needed at the pulse wave front to cause an increase in pressure NOTE: DEGREE OF DAMPING = RESISTANCE X COMPLIANCE Degree of Damping is directly proportional to the resistance and compliance of the blood vessels. Figure 11. Progressive stages in the transmission of the pressure pulse along the ↑ resistance, ↑ degree of damping and ↑ compliance, ↑ degree of aorta. damping. When the heart ejects blood into the aorta during systole IX. CLINICAL METHOD FOR MEASURING SYSTOLIC AND DIASTOLIC Proximal portion of the aorta becomes initially distended PRESSURE ○ The proximal portion of aorta is the one that receives the ejected blood first, hence increasing the pressure ○ This pressure increase will open up another segment of Initially, we do the palpatory method: we want to know the highest the aorta so that the blood will pass through blood pressure that can be noted during palpation. ○ This will repeat to open up another segment in the aorta until it goes to the periphery → pulsatile Palpatory Method The inertia of the blood prevents sudden blood movement all the First, we palpate the radial artery, then inflate the cuff taking note of way to the periphery the systolic pressure. Feel the pulses as you inflate the cuff until the Korotkoff sound, or Rising pressure in the proximal aorta (during contraction) the pulsation is absent. When you do not feel the arterial pulse Rapidly overcomes this inertia. anymore, that is the highest pressure that you should remember ○ This pressure increase will open up another segment of first. Deflate the valve about 2-3 mmHg per second until you feel the the aorta so that the blood will pass through radial pulse again. The measurement of the first pulse coinciding the The wave front of distention spreads farther and farther along the pressure in the BP apparatus is palpatory systolic blood pressure. aorta → this phenomenon is called transmission of the pressure The highest pressure that can be recorded once the pulse is felt + pulse in the arteries 20mmHg from the time you do the auscultatory method PRESSURE PULSES ARE DAMPED IN THE SMALLER ARTERIES, ARTERIOLES, AND Auscultatory Method CAPILLARIES Stethoscope is placed over the antecubital (brachial) artery and a blood pressure cuff is inflated around the upper arm. When the cuff pressure is great enough to close the artery during part of the arterial pressure cycle If you have a palpatory systolic BP of 120, inflate the cuff 20 mmHg higher than 120 mmHg. After reaching 140 mmHg, you now start to deflate If you only do the auscultatory method, you will miss the highest pressure that can be recorded. KOROTKOFF SOUNDS - appreciated Named after Nikolai Korotkoff, a Russian physician who described them in 1905 A sound is then heard with each pulsation. Sound produced during the deflation of the cuff. Caused by blood jetting through the partly occluded vessel and by the vibrations of the vessel wall. Jet causes turbulence in the vessel beyond the cuff and sets up the vibrations heard through the stethoscope. NO Korotkoff sounds are heard in the lower artery Figure 12. Changes in the pulse pressure contour as the pulse wave travels ○ The pressure in the cuff is first elevated well above toward the smaller vessels. Since the arterioles and arteries are more arterial systolic pressure Page 6 of 12 [PHYSIOLOGY] 1.13 Vascular Distensibility and Functions of Arterial and Venous Systems - Dr. L. Viado ○ As long as the cuff pressure is higher than the systolic NORMAL ARTERIAL PRESSURE AS MEASURED BY THE AUSCULTATORY METHOD pressure, the brachial artery remains collapsed so no Effects of aging on the blood pressure control mechanisms result in blood jets into the lower artery during any part of the progressive increase in pressure with age. pressure cycle ○ Slight extra increase in systolic pressure usually occurs beyond the age of 60 years old. Always know the proper technique of blood pressure measurement: ○ Due to decreased distensibility, or “hardening” of the First, put the arm in the heart level with adequate support (to avoid arteries tensing of muscle - increases blood pressure) ○ Result of atherosclerosis Arm placed above the heart: subjected to gravitational pull = Kidneys are primarily responsible for this long-term regulation of pressure of blood going towards the heart is decreased arterial pressure by stimulating the RAA System. Arm placed below the heart: pressure of blood going towards the Because of the hardened arteries, there will be an increase in heart is increased due to gravitational pull pressure. From a normal teenager, the systolic blood pressure is usually 100 and it will go up to a certain point as the patient grows BLOOD PRESSURE older. The diastolic doesn’t increase that much, usually from 50 to 60 As soon as the pressure in the cuff falls below systolic pressure (point to 80. As the patient grows older, there is widening in the pulse B, Figure 13), blood begins to flow through the artery beneath the pressure. cuff during the peak of systolic pressure. One begins to hear tapping sounds from the antecubital artery in synchrony with the heartbeat. As soon as these sounds begin to be heard, the pressure level indicated by the manometer connected to the cuff is about equal to the systolic pressure. When the pressure in cuff is lowered even further, the Korotkoff sounds change in quality, having less of the tapping quality and more of a rhythmical and harsher quality Finally, when the pressure in the cuff falls near diastolic pressure, the sounds suddenly change into a muffled sound (point C, Figure 13) One notes the manometer pressure when the Korotkoff sounds change to the muffled quality, and this pressure is about equal to the diastolic pressure, but it slightly overestimates the diastolic pressure determined by direct intra-arterial catheter As the pressure in the cuff falls a few mm Hg further, the artery does Figure 14. Changes in systolic, diastolic, and mean arterial pressures with age. not close anymore during diastole, and this means that the basic The shaded areas show the approximate normal ranges. factor causing the sounds (the jetting of blood through a squeezed artery) is already absent MEAN ARTERIAL PRESSURE Hence, the sounds completely disappear Average of the arterial pressures measured millisecond by Pressure at which the Korotkoff sounds completely disappear should millisecond over a period of time. be used as the diastolic pressure. Cardiac cycle has longer diastolic phase ≠ average of SBP and DBP - AR and AVF Remains nearer to diastolic pressure than to systolic pressure during When you elevate your arm during BP monitoring, there is an the greater part of the cardiac cycle increase in gravitational effect. Forward flow of the blood is from the Mean arterial pressure is near the diastolic pressure because the arms to the heart. Pressure should decrease quickly if the arm is diastolic pressure is longer. elevated. The blood flow from the subclavian vein to the right atrium ○ Except in tachycardia (It is an increase in heart rate. The will be faster due to gravity. Whereas if the arms are lower, you will mean arterial pressure will increase. The diastolic phase have to push upward the column of blood going to the heart level. will be shortened. The left ventricular filling will be That is the reason why when we elevate the patient's hand above the decreased. The coronary artery blood flow will also be heart level, the blood pressure is slightly decreased. Increase blood decreased.) pressure if the arm is lower than the heart level. MAP is therefore determined about 60% by the diastolic pressure and 40% by the systolic pressure MAP = [2(DBP) + SBP]/3 MAP is very important in neurology, in patients who have had strokes. Ischemic stroke will have a different MAP than hemorrhagic stroke, which will have a very low MAP (100-110). Ischemic stroke will need a higher pressure so that blood flow can occur to the different parts of the Circle of Willis, so ideal MAP is between 120-130. That's why there is permissive hypertension in patients with ischemic stroke, we do not give hypertensive drugs. X. VEINS AND THEIR FUNCTIONS Provide passageways for flow of blood to the heart Figure 13. The auscultatory method for measuring the systolic and diastolic Capable of constricting and enlarging depending on the body's needs arterial pressure. ○ If there is a massive hemorrhage, there will be contraction of the vessels. And if there is a massive transmission, the The auscultatory method is not entirely accurate, but it gives values veins will enlarge to accommodate the large amount of within 10% of those determined by direct catheter measurement fluid. from inside the arteries ○ Storing either small or large quantities of blood and making this blood available when it is required Page 7 of 12 [PHYSIOLOGY] 1.13 Vascular Distensibility and Functions of Arterial and Venous Systems - Dr. L. Viado Venous pump ○ This happens when the heart pumps with exceptional ○ peripheral veins can also propel blood forward vigor or when blood flow into the heart from the ○ help to regulate cardiac output peripheral vessels is greatly depressed, just like what happens after severe hemorrhage VENOUS PRESSURE – RIGHT ATRIAL PRESSURE (CENTRAL VENOUS PRESSURE) VENOUS RESISTANCE AND PERIPHERAL VENOUS PRESSURE Venous Resistance CENTRAL VENOUS PRESSURE = RAP or RIGHT ATRIAL PRESSURE Large veins have so little resistance to blood flow when they are Blood from all the systemic veins flows into the right atrium of the distended heart ○ 0 mm Hg – no importance Regulated by the following: 1. Ability of the heart to pump blood out of the right atrium and LOW RESISTANCE AREA ventricle into the lungs Large veins that enter the thorax are compressed by the surrounding 2. Tendency for blood flow from peripheral veins into the right atrium. tissues. Arms veins are compressed by their sharp angulations over the 1st At the insertion of the superior and inferior vena cava in the right rib. They have low resistance. atrium, the pressure there is zero. However in the right atrium, due Neck veins pressure often leads veins to collapse due to a very low to atrial contraction, there is a little pressure created but low enough atmospheric pressure. Usually zero pressure. as compared to the left atrial cavity. Abdomen veins are often compressed by different organs and by the Indirect way to measure Right Atrial Pressure is the use of jugular intra-abdominal pressure. Very low pressure 5-6mmHg. venous pressure. Measure the distance from the Sternal Angle of NOTE: Louis to the highest column of blood in the jugular vein in the neck. Large veins have some resistance to blood flow. The average That distance plus 5, which is the distance from the sternal angle of functional pressure in most vessels will be 17mmHg. Even if there is louis to the right atrium, will give us the Right Atrial Pressure, which low resistance in the venous segments, there is still pressure. is around 8 cm H2O. Anything higher than that would tell us that the Supine position: Peripheral Venous Pressure (PVP) in small veins is +4 RAP will be increased. to +6 mm Hg > RAP. Another way to measure Right Atrial Pressure is through invasive procedures like inserting a catheter into central venous lines. Either inserted into: ○ Radial Veins ○ Femoral Vein ○ Jugular Vein Deep Vein Thrombosis (DVT) - increased in right atrial pressure because the clot will be dislodged from the lower extremities to the lungs creating an impediment slope If there is increase in blood flow from the venous segment to the heart, it will cause an increase in right atrial pressure Factors Increasing Venous Return: Increased blood volume Increased vessel tone → resultant increased peripheral venous pressures Dilation of the arterioles → decreases the peripheral resistance → allows rapid flow of blood from the arteries into the veins. Figure 15. Compression points that tend to collapse the veins entering the RIGHT ATRIAL PRESSURE thorax. Regulations of Cardiac Output are the same as CVP; when the ejection fraction is good the cardiac fraction is also good. Low cardiac Effect of High Atrial Pressure on Peripheral Venous Pressure output, low stroke volume = more blood in the left side of the heart. Blood begins to back up in the large veins. Therefore, it will increase the pressure in the left side of the heart ○ From the right atrium, it will go to the inferior vena cava. that will result in the back leak of the blood volume from the LV and Then it goes to the liver and it will cause suspension and it will go back to the left atrium. If the blood volume is still high, it stretching of the Glisson’s Capsule, which will cause right will go back to the pulmonary circulation causing dyspnea. Then, it abdominal quadrant pain, abdominal bloatedness, and will be going back to the right ventricle and to the right atrium sometimes cause edema in the lower extremities. causing high right atrial pressure Collapse points in the veins open up when the RAP rises above +4 to Cardiac Output = Stroke Volume x Heart Rate +6 mm Hg Amount of blood pumped by the heart depends: ○ In the jugular veins, the neck veins are always collapsing ○ Ability of the heart to pump depending if the right atrial pressure will be increased. ○ Tendency for blood to flow into the heart from the Rise in peripheral venous pressure in the limbs peripheral vessels. ○ If there is a right atrial pressure, it will be reflected in the Normal right atrial pressure is about 0 mm Hg, which is equal to the intra abdominal cavity, which will also increase in the atmospheric pressure around the body pressure. thereby the pressure in the intra abdominal Increase to 20-30 mm Hg under very abnormal conditions. cavity will be reflected in the lower extremities. ○ Serious heart failure and after massive blood transfusion Because the heart must be weakened significantly to cause RAP > +4 – greatly increases the total blood volume and causes to +6 mm Hg excessive quantities of blood to attempt to flow into the ○ Peripheral venous pressure is not noticeably elevated heart from the peripheral vessels even in the early stages of heart failure as long as the Lower limit to the RAP is -3 to -5 mm Hg below atmospheric pressure person is at rest – similar pressure in the chest cavity that surrounds the heart. Page 8 of 12 [PHYSIOLOGY] 1.13 Vascular Distensibility and Functions of Arterial and Venous Systems - Dr. L. Viado Effect of Intra-abdominal Pressure (IAP) on Venous Pressure of Leg Pressure in the veins of the feet is about +90 mmHg Pressure in the abdominal cavity of a recumbent person normally ○ Meaning, in some occupations wherein the person is averages about +6 mmHg standing for several hours, examples are security guard, Factors will increase IAP (> +15 to +30 mmHg) military and prolonged sitting halos same ang mechanism ○ Pregnancy ng standing absolutely still. Although, lesser ang pressure ○ Large tumor naman dun sa lower extremity. However, matagal padin ○ Abdominal obesity nakababa yung lower extremity mo. So more because of ○ Ascites (excessive fluid in the abdominal cavity) the gravitational pressure, there will be higher pressure of IAP causes increased venous pressure in the leg. the feet area as compared to those who are lying down. ○ Abdominal veins will open and allow the blood to flow Because of the gravitational weight of the blood in the veins between from the legs to the heart the heart and the feet ○ If the intra-abdominal pressure is +20 mmHg the lowest The venous pressures at other levels of the body are proportionately possible pressure in the femoral veins is also about +20 between 0 and 90mmHg. mm Hg ○ As you have mentioned, there are occupations that will increase the pressure of the lower extremity because of the gravitational pressure. So between the heart which is EFFECT OF GRAVITATIONAL PRESSURE ON VENOUS PRESSURE 0 mmHg to the legs which is 90 mmHg plus yung gravitational pull pressure of 100 mmHg. Lahat na ng arterial system from the feet is about 190 mmHg. Subclavian vein pressure: +6 mm Hg ○ Because of the compression of the subclavian vein as it passes over the top rib Total arm venous pressure: +35 mm Hg ○ Obtained from the addition of the gravitational difference between the level of the rib and the hand which is +29 mm Hg to the +6 mm Hg pressure caused by the compression of the vein as it crosses the rib Effect of the Gravitational Factor on Arterial and Other Pressures A standing person who has a MAP of 100 mmHg at the level of the heart has an arterial pressure in the feet of about 190 mmHg. Therefore, when the arterial pressure is 100 mmHg ○ It means that 100 mmHg is the pressure at the gravitational level of the heart but not necessarily elsewhere in the arterial vessels. XI. VENOUS VALVES AND THE “VENOUS PUMP”: THEIR EFFECTS ON VENOUS PRESSURE Figure 16. Effect of gravitational pressure on the venous pressures throughout the body in the standing person. So pag nakahiga, what will happen to your lower extremity? Mababa ang pressure diba, kasi wala namang gravity that will cause an increase in pressure in the lower extremity. So once the patient is standing up from the heart to the column of blood in this area plus the gravitational pressure then the pressure in the lower extremity is about 90mmHg. STANDING POSITION Figure 17. Venous valves of the leg. Right atrium remains about 0 mmHg ○ In standing position, kahit anong gawin mo mapahiga or Aside from the valves of the venous system, meron din tayong mga mapastanding position, yung right atrium will still have a 0 venous pump. For example, this is the lower extremity; it will forward mmHg right atrial pressure. the column of blood to the heart. The valves here just like the valves because the heart pumps into the arteries any excess of blood that in the heart that they should be well coupdated. Pag nag pump yung attempts to accumulate at this point venous segment forwarding the blood flow of the heart during the ○ Kasi the heart will try to beat or to pump out any excess diastolic phase, dapat hindi bababa yung blood flow because of a fluid in the heart. So the heart will try to regulate as much very tight or closed valve in the venous segment so aakyat lang yan. as removing the excess fluid in the heart. What must The gravitational pressure effect would cause the venous pressure in come in must come out so that blood flow is regulated the feet to always be about +90 mmHg in a standing adult if with an absent venous valve. STANDING ABSOLUTELY STILL Page 9 of 12 [PHYSIOLOGY] 1.13 Vascular Distensibility and Functions of Arterial and Venous Systems - Dr. L. Viado ○ Kung walang valve, kung nakatayo ka, 90 ang pressure sa Therefore, there will be leaking of blood from the venous system to paa. the third space. So mawawalan ng volume ang venous segment, Leg movement: tightens the muscle and compresses the veins in or mapupunta siya sa interstitial space. adjacent to the muscles → which squeezes the blood out of the Legs swell and “apparent” blood loss veins. ○ Creating swelling in the lower extremity especially in the ○ However because of these other pumps which are afternoon. And also, the body will sense there will be present in our lower extremity 20 mmHg. Since the apparent blood loss because the fluid from the venous venous segment is found in between these muscles, the segment will go to the interstitium therefore there will be calf muscles, so as we move or extend or flex our foot around: what will happen is these calf muscles will contract and 10 to 20 percent of the blood volume can be lost from the circulatory try to squeeze the venous system in the lower extremity system within the 15 to 30 minutes of standing still so that blood can be forwarded to the heart. ○ Kung may apparent blood loss in our body, our heart will try to compensate. Before it will compensate, the heart As shown in Figure 17, the valves in the veins are arranged in a will sense that there will be decreasing pressure. Ang manner that the direction of venous blood flow can be toward the mangyayari is most of those patients who are standing heart only still for several minutes or hours will lead to pain. Diba Consequently, every time a person moves or tenses the leg muscles, pag nag CAT or ROTC, what will happen? Diba meron a certain amount of venous blood is propelled toward the heart, as tayong exercise wherein we stand still for several hours as seen in Figure 18 a punishment or exercise then it will lead to a fainting episode. Leads fainting Figure 18. Contraction of calf muscles pushes the blood towards the heart. Figure 20. Calf muscles are also called the “heart” of the lower extremity. “venous pump” or “muscle pump” ○ Efficient enough to maintain pressure less than (