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Aparna wrote: The main parameter affected is diastolic BP. It decreases. Fall in TPR also means better compliance. Which means a fall in systolic BP. So pulse pressure either stays the same or decreases.
On Apr 23, - PM, doctorforever responded: i think since we have elastic tissue in b oth arteris and veins ofcource more in veins but still , so nomatter which vessel ,compliancy decrease in all.
Terms of Use. Privacy Policy. Author 18 Posts. Register To Remove Advertisement. The increased PP in anemia is not due to a fall in TPR even though fall in viscosity does reduce TPR, it matters very little but rather an increase in cardiac contractility as a compensation to low O2 delivery.
If by dr. Aparna, you meant the guy who teaches physiology on the Kaplan video lectures, then I'm sorry to tell you, he is an idiot. Are you telling me, if you were to give Phentolamine the preOp Rx for Pheo you are actually going to raise the SBP and kill the patient? It means increased compliance. Increased ability to accomodate changes. If a vessel is persistently constricted increased TPR , it is a stubborn one. It wont accomodate an increased cardiac output and systolic BP will increase.
If your cardiac output increases due to the fall in TPR which can also mean fall in afterload , the vessels are more capable of accomodating that increase remember increased compliance? So your systolic BP wont increase, it will decrease.
The cardiac cycle describes the path of the blood through the heart. It runs in the following order:. Vasculature plays a significant role in the regulation of blood flow throughout the body. In general, blood pressure decreases from arteries to veins, and this is because of the pressure overcoming the resistance of the vessels.
The greater the change in resistance at any point in the vasculature, the greater the loss of pressure at that point. Arterioles have the most increase in resistance and cause the largest decrease in blood pressure.
The constriction of arterioles increases resistance, which causes a decrease in blood flow to downstream capillaries and a larger decrease in blood pressure. Dilation of arterioles causes a decrease in resistance, increasing blood flow to downstream capillaries, and a smaller decrease in blood pressure. Diastolic blood pressure DP is the lowest pressure in an artery at the beginning of the cardiac cycle, while the ventricles are relaxing and filling.
DP is directly proportional to total peripheral resistance TPR. Also, the energy stored in the compliant aorta during systole is now released by the recoil of the aortic wall during diastole, thus increasing diastolic pressure. Systolic blood pressure SP is the peak pressure in an artery at the end of the cardiac cycle, while the ventricles are contracting.
Directly related to stroke volume, as stroke volume increases, SP also increases. SP is also affected by aortic compliance. Because the aorta is elastic, it stretches and stores the energy caused by ventricular contraction and decreases the systolic pressure.
Pulse pressure is the difference between SP and DP. Pulse pressure is proportional to SV and inversely proportional to arterial compliance. Thus the stiffer the artery, the larger the pulse pressure. Mean arterial pressure MAP is the average pressure in the arteries throughout the cardiac cycle.
This value is significant because whenever there is a decrease in CO, to maintain the MAP, the TPR will increase, which is relevant in many pathophysiology problems. Systemic veins have a lower decrease in pressure because it has low resistance. A small change in venous pressure can mobilize the blood stored in the venous system.
As the cross-sectional area increases, velocity decreases. Arteries and veins have smaller cross-sectional areas and the highest velocities, whereas capillaries have the most cross-sectional area and the lowest velocities.
The vasculature also gives resistance. Viscosity depends on hematocrit and increases in multiple myeloma or polycythemia. As tube length increases, the resistance increases. As tube radius increases, the resistance decreases.
The fact that the radius is to the power of 4 means that slight changes in the radius have a profound effect on resistance.
The Poiseuille equation measures the flow of blood through a vessel. Increasing resistance in a vessel, such as the constriction of an arteriole, causes a decrease in blood flow across the arteriole. At the same time, there is a larger decrease in pressure across this point because the pressure is lost by overcoming the resistance.
Increasing the resistance at any point increases upstream pressure but decreases downstream pressure. Its application is important, because in trauma situations with hemorrhage, there is also a decrease in cardiac output, but at times the blood pressure is near normal, this is because the TPR at the level of the arterioles has increased. This equation, as applied to the pulmonary vasculature, is used to determine the cause of pulmonary hypertension. The nervous system regulates the cardiovascular system with the help of baroreceptors and chemoreceptors.
Both receptors are located in the carotids and aortic arch. Also, both have afferent signals through the vagus nerve from the aortic arch and afferent signals through the glossopharyngeal nerve from the carotids.
Autoregulation is the method by which an organ or tissue maintains blood flow despite a change in perfusion pressure.
When blood flow becomes decreased to an organ, arterioles dilate to reduce resistance. The starling equation can explain the capillary fluid exchange. This equation describes the forces of oncotic and hydrostatic pressure on the movement of fluid across the capillary membrane.
Edema can result from an increase in capillary pressure heart failure , a decrease in plasma proteins liver failure , an increase in the interstitial fluid due to lymphatic blockage, or an increase in capillary permeability due to infections or burns. Swan-Ganz catheter is a thin tube that is inserted peripherally and passed to the right side of the heart and into the pulmonary artery.
This catheterization is to measure the pressures in the pulmonary vasculature and the left atrium. Pulmonary capillary wedge pressure PCWP is an estimate of the pressure in the left atrium given by the Swanz-Ganz catheter. It is significant because it helps to differentiate pathologies.
Chronic hypertension is a common pathological process related to the cardiovascular system. This condition is significant because, with hypertension, there is an increase in afterload. A long-term increase in afterload leads to concentric hypertrophy of the heart and eventual left-sided diastolic heart failure.
Also, an S4 heart sound will be audible at the apex of the heart. Another type of heart disease is alcoholic cardiomyopathy, which occurs in alcoholics and causes dilated cardiomyopathy, which means the ventricles become dilated, leading to systolic failure. It can be reversible if the patient stops drinking alcohol. Heart failure or cardiac tamponade can cause cardiogenic shock.
In cardiogenic shock, there is an increase in PCWP because there is a back up of blood; the heart is not able to pump blood forward because it is not able to overcome the afterload. Subsequently, there is a decrease in CO. In hemorrhagic shock, there is a loss of blood, thus a loss in total volume. Because there is a loss of volume, there is a decrease in pressure and, therefore, a decrease in PCWP. Also, there is an increase in cardiac output because there is a need for more blood in the periphery.
Blood pressure BP is an essential clinical value because it describes the status of the vasculature in acute and chronic states. If a patient has elevated blood pressure in the clinic on more than two occasions, the clinician can diagnose the patient with essential hypertension. BP can also be significant in acute settings such as in the emergency room after a patient is brought in by an ambulance due to a motor vehicle accident.
At this point, it is important to assess the patient's BP because if it is low, it might indicate the patient is bleeding somewhere, and the clinician must determine the location of the bleeding as soon as possible. S1 and S2 heart sounds are normal heart sounds heard on auscultation of the heart. S1 is the sounds made due to the closure of the mitral and tricuspid valves. This is followed by systole. Then the S2 sounds are heard, which are the closure of the aortic and pulmonary valves.
Diastole follows this. It is important to recognize these normal heart sounds on auscultation because abnormal heart sounds such as S3, S4, and murmurs can be signs of a pathological condition. This book is distributed under the terms of the Creative Commons Attribution 4.
Turn recording back on. National Center for Biotechnology Information , U. StatPearls [Internet]. Search term. Introduction The cardiovascular system provides blood supply throughout the body.
Organ Systems Involved The heart is the organ that pumps the blood through the vessels. Function The cardiovascular system consists of two main loops, the systemic circulation, and the pulmonary circulation. Mechanism It is important to understand the concept of cardiac output, stroke volume, preload, Frank-Starling law, afterload, and ejection fraction to understand the physiology of the heart.
It runs in the following order: Atrial contraction closure of the mitral valve. Baroreceptors are more specifically located in the carotid sinus and aortic arch. They respond quickly to changes in blood pressure. A decrease in blood pressure or blood volume causes hypotension, which leads to a decrease in arterial pressure, which creates a decrease in the stretch of the baroreceptors and decreases afferent baroreceptor signaling. This decrease in afferent signaling from the baroreceptor causes an increase in efferent sympathetic activity and a reduction in parasympathetic activity, which leads to vasoconstriction, increase heart rate, increase contractility, and an increase in BP.
An increase in blood pressure or blood volume causes hypertension which increases the stretch of the baroreceptors. Chemoreceptors come in 2 types: peripheral and central. Peripheral chemoreceptors are specifically located in the carotid body and aortic arch. They respond to oxygen levels, carbon dioxide levels, and pH of the blood.
They become stimulated when oxygen decreases, carbon dioxide increases, and the pH decreases. Central chemoreceptors are located in the medulla oblongata and measure the pH and carbon dioxide changes of the cerebral spinal fluid.
Myogenic theory: Myogenic regulation is intrinsic to the vascular smooth muscle. When there is an increase in perfusion, the vascular smooth muscle stretches, causing it to constrict the artery.
If there is a decrease in pressure to the arteriole, then there is decreased stretching of the smooth muscle, which would lead to the relaxation of the smooth muscles and dilation of the arteriole. Metabolic theory: Blood flow is closely related to metabolic activity. When there is an increase in metabolism to muscle or any tissue, there is an increase in blood flow to that location.
Metabolic activity creates substances that are vasoactive and stimulate vasodilation. The increase or decrease in metabolism leads to an increase or decrease in metabolic byproducts that cause vasodilation. Increased adenosine, carbon dioxide, potassium, hydrogen ion, lactic acid levels, and decreased oxygen levels, and increased oxygen demand all lead to vasodilation.
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