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97-401: An embolism can cause partial or total blockage of blood flow in the affected vessel. Such a blockage ( vascular occlusion ) may affect a part of the body distant from the origin of the embolus. An embolism in which the embolus is a piece of thrombus is called a thromboembolism . An embolism is usually a pathological event, caused by illness or injury. Sometimes it is created intentionally for

194-399: A is the particle radius, ρ p , ρ f are the respectively particle and fluid density μ is the fluid viscosity, g is the gravitational acceleration. From the above equation we can see that the sedimentation velocity of the particle depends on the square of the radius. If the particle is released from rest in the fluid , its sedimentation velocity U s increases until it attains

291-415: A Newtonian fluid at physiological rates of shear. Typical values for the viscosity of normal human plasma at 37 °C is 1.4 mN·s/m . The viscosity of normal plasma varies with temperature in the same way as does that of its solvent water ;a 3°C change in temperature in the physiological range (36.5°C to 39.5°C)reduces plasma viscosity by about 10%. The osmotic pressure of solution is determined by

388-432: A blood cell causes a shift of water and a change of cell volume. The changes in shape and flexibility affect the mechanical properties of whole blood. A change in plasma osmotic pressure alters the hematocrit, that is, the volume concentration of red cells in the whole blood by redistributing water between the intravascular and extravascular spaces. This in turn affects the mechanics of the whole blood. The red blood cell

485-408: A fluid, however, it must be assured that when mixed, the remaining blood behaves in the microcirculation as in the original blood fluid, retaining all its properties of viscosity . In presenting what volume of ANH should be applied one study suggests a mathematical model of ANH which calculates the maximum possible RCM savings using ANH, given the patients weight H i and H m . To maintain

582-421: A jet of blood from the left atrium to the right atrium. If agitated saline is injected into a peripheral vein during echocardiography, small air bubbles can be seen on echocardiographic imaging. Bubbles traveling across an ASD may be seen either at rest or during a cough. (Bubbles only flow from right atrium to left atrium if the right atrial pressure is greater than left atrial). Because better visualization of

679-476: A more distal part of the systemic circulation . Sometimes, multiple classifications apply; for instance a pulmonary embolism is classified as an arterial embolism as well, because the clot follows the pulmonary artery carrying deoxygenated blood away from the heart. However, pulmonary embolism is generally classified as a form of venous embolism, because the embolus forms in veins, e.g. deep vein thrombosis . Arterial embolism can cause occlusion in any part of

776-407: A much rarer condition, which is also linked to cryptogenic (i.e., of unknown cause) stroke. PFO is more common in people with cryptogenic stroke than in those with a stroke of known cause. While PFO is present in 25% in the general population, the probability of someone having a PFO increases to about 40 to 50% in those who have had a cryptogenic stroke, and more so in those who have a stroke before

873-408: A portion of the body, including cerebrovascular accident (stroke), infarction of the spleen or intestines , or even a distal extremity (i.e., finger or toe). This is known as a paradoxical embolus because the clot material paradoxically enters the arterial system instead of going to the lungs. Some recent research has suggested that a proportion of cases of migraine may be caused by PFO. While

970-482: A systemic vein will always impact in the lungs, after passing through the right side of the heart. This will form a pulmonary embolism that will result in a blockage of the main artery of the lung and can be a complication of deep-vein thrombosis . The most common sites of origin of pulmonary emboli are the femoral veins . The deep veins of the calf are the most common sites of actual thrombi. In paradoxical embolism, also known as crossed embolism, an embolus from

1067-409: A therapeutic reason, such as to stop bleeding or to kill a cancerous tumor by stopping its blood supply. Such therapy is called embolization . There are different types of embolism, some of which are listed below. Embolism can be classified based on where it enters the circulation, either in arteries or in veins . Arterial embolism are those that follow and, if not dissolved on the way, lodge in

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1164-415: Is a non-Newtonian fluid , and is most efficiently studied using rheology rather than hydrodynamics. Because blood vessels are not rigid tubes, classic hydrodynamics and fluids mechanics based on the use of classical viscometers are not capable of explaining haemodynamics. The study of the blood flow is called hemodynamics, and the study of the properties of the blood flow is called hemorheology . Blood

1261-423: Is a complex liquid. Blood is composed of plasma and formed elements . The plasma contains 91.5% water, 7% proteins and 1.5% other solutes. The formed elements are platelets , white blood cells , and red blood cells . The presence of these formed elements and their interaction with plasma molecules are the main reasons why blood differs so much from ideal Newtonian fluids. Normal blood plasma behaves like

1358-412: Is a relationship that helps determine the behavior of a fluid in a tube, in this case blood in the vessel. The equation for this dimensionless relationship is written as: The Reynolds number is directly proportional to the velocity and diameter of the tube. Note that NR is directly proportional to the mean velocity as well as the diameter. A Reynolds number of less than 2300 is laminar fluid flow, which

1455-429: Is a type of atrial septum defect in which the defect involves the venous inflow of either the superior vena cava or the inferior vena cava . A sinus venosus ASD that involves the superior vena cava makes up 2 to 3% of all interatrial communication. It is located at the junction of the superior vena cava and the right atrium. It is frequently associated with anomalous drainage of the right-sided pulmonary veins into

1552-436: Is as follows: In a second approach, more realistic of the vascular resistance and coming from experimental observations on blood flows, according to Thurston, there is a plasma release-cell layering at the walls surrounding a plugged flow. It is a fluid layer in which at a distance δ, viscosity η is a function of δ written as η(δ), and these surrounding layers do not meet at the vessel centre in real blood flow. Instead, there

1649-508: Is characterized by constant flow motion, whereas a value of over 4000, is represented as turbulent flow. Due to its smaller radius and lowest velocity compared to other vessels, the Reynolds number at the capillaries is very low, resulting in laminar instead of turbulent flow. Often expressed in cm/s. This value is inversely related to the total cross-sectional area of the blood vessel and also differs per cross-section, because in normal condition

1746-415: Is dependent on weight and not volume). The model assumes that the hemodilute value is equal to the H m prior to surgery, therefore, the re-transfusion of blood obtained by hemodilution must begin when SBL begins. The RCM available for retransfusion after ANH (RCMm) can be calculated from the patient's H i and the final hematocrit after hemodilution( H m ) The maximum SBL that is possible when ANH

1843-436: Is designed to allow doctors to determine where ANH may be beneficial for a patient based on their knowledge of the H i , the potential for SBL, and an estimate of the H m . Though the model used a 70 kg patient, the result can be applied to any patient. To apply these result to any body weight, any of the values BLs, BLH and ANHH or PRBC given in the table need to be multiplied by the factor we will call T Basically,

1940-412: Is established for a foramen ovale to remain open instead of closing, but heredity and genetics may play a role. In rats research showed a link to the amount of Cryptosporidium infestation and the number of newborn rats that failed to close their foramen ovale. PFO is not treated in the absence of other symptoms. The mechanism by which a PFO may play a role in stroke is called paradoxical embolism . In

2037-430: Is highly flexible and biconcave in shape. Its membrane has a Young's modulus in the region of 106  Pa . Deformation in red blood cells is induced by shear stress. When a suspension is sheared, the red blood cells deform and spin because of the velocity gradient, with the rate of deformation and spin depending on the shear rate and the concentration. This can influence the mechanics of the circulation and may complicate

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2134-409: Is imperative to think about all the components of the starling equation: To identify the minimum safe hematocrit desirable for a given patient the following equation is useful: where EBV is the estimated blood volume; 70 mL/kg was used in this model and H i (initial hematocrit) is the patient's initial hematocrit. From the equation above it is clear that the volume of blood removed during

2231-400: Is necessary to maintain H m , even if ANH is used. This model can be used to identify when ANH may be used for a given patient and the degree of ANH necessary to maximize that benefit. For example, if H i is 0.30 or less it is not possible to save a red cell mass equivalent to two units of homologous PRBC even if the patient is hemodiluted to an H m of 0.15. That is because from

2328-419: Is normally closed, but can open under increased right atrial pressure. On echocardiography, shunting of blood may not be noted except when the patient coughs. PFO is linked to stroke , sleep apnea , migraine with aura , cluster headache, decompression sickness , Raynaud's phenomenon, hyperventilation syndrome, transient global amnesia (TGA), and leftsided carcinoid heart disease (mitral valve). No cause

2425-487: Is not necessary, if BL s does not exceed 2303 ml, since the hemotocrit will not fall below H m , although five units of blood must be removed during hemodilution. Under these conditions, to achieve the maximum benefit from the technique if ANH is used, no homologous blood will be required to maintain the H m if blood loss does not exceed 2940 ml. In such a case, ANH can save a maximum of 1.1 packed red blood cell unit equivalent, and homologous blood transfusion

2522-630: Is required comparing of PFO closure with anticoagulation or anticoagulation with antiplatelet therapy. Once someone is found to have an atrial septal defect, a determination of whether it should be corrected is typically made. If the atrial septal defect is causing the right ventricle to enlarge a secundum atrial septal defect should generally be closed. If the ASD is not causing problems the defect may simply be checked every two or three years. Methods of closure of an ASD include surgical closure and percutaneous closure. Prior to correction of an ASD, an evaluation

2619-433: Is so characteristic that if it is absent, the diagnosis of ASD should be reconsidered. Most patients with a PFO are asymptomatic and do not require any specific treatment. However, those who develop a stroke require further workup to identify the etiology. In those where a comprehensive evaluation is performed and an obvious etiology is not identified, they are defined as having a cryptogenic stroke. The mechanism for stroke

2716-496: Is such individuals is likely embolic due to paradoxical emboli, a left atrial appendage clot, a clot on the inter-atrial septum, or within the PFO tunnel. Until recently, patients with PFO and cryptogenic stroke were treated with antiplatelet therapy only. Previous studies did not identify a clear benefit of PFO closure over antiplatelet therapy in reducing recurrent ischemic stroke. However, based on new evidence and systematic review in

2813-489: Is the pulsatility index ( PI ), which is equal to the difference between the peak systolic velocity and the minimum diastolic velocity divided by the mean velocity during the cardiac cycle . This value decreases with distance from the heart. Resistance is also related to vessel radius, vessel length, and blood viscosity. In a first approach based on fluids, as indicated by the Hagen–Poiseuille equation . The equation

2910-535: Is the driver of the circulatory system, pumping blood through rhythmic contraction and relaxation. The rate of blood flow out of the heart (often expressed in L/min) is known as the cardiac output (CO). Blood being pumped out of the heart first enters the aorta , the largest artery of the body. It then proceeds to divide into smaller and smaller arteries, then into arterioles , and eventually capillaries , where oxygen transfer occurs. The capillaries connect to venules , and

3007-440: Is the plugged flow which is hyperviscous because holding high concentration of RBCs. Thurston assembled this layer to the flow resistance to describe blood flow by means of a viscosity η(δ) and thickness δ from the wall layer. The blood resistance law appears as R adapted to blood flow profile : where Blood resistance varies depending on blood viscosity and its plugged flow (or sheath flow since they are complementary across

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3104-585: Is to sense the temperature change from a liquid injected in the proximal port of a Swan-Ganz to the distal port. Cardiac output is mathematically expressed by the following equation: where The normal human cardiac output is 5-6 L/min at rest. Not all blood that enters the left ventricle exits the heart. What is left at the end of diastole (EDV) minus the stroke volume make up the end systolic volume (ESV). Circulatory system of species subjected to orthostatic blood pressure (such as arboreal snakes) has evolved with physiological and morphological features to overcome

3201-399: Is unusual before 20 years of age, it is seen in 50% of individuals above the age of 40. Progression to Eisenmenger's syndrome occurs in 5 to 10% of individuals late in the disease process. A patent foramen ovale (PFO) is a remnant opening of the fetal foramen ovale , which often closes after a person's birth. This remnant opening is caused by the incomplete fusion of the septum primum and

3298-405: Is used without falling below Hm(BLH) is found by assuming that all the blood removed during ANH is returned to the patient at a rate sufficient to maintain the hematocrit at the minimum safe level If ANH is used as long as SBL does not exceed BL H there will not be any need for blood transfusion. We can conclude from the foregoing that H should therefore not exceed s . The difference between

3395-578: The BL H and the BL s therefore is the incremental surgical blood loss ( BL i ) possible when using ANH. When expressed in terms of the RCM Where RCM i is the red cell mass that would have to be administered using homologous blood to maintain the H m if ANH is not used and blood loss equals BLH. The model used assumes ANH used for a 70 kg patient with an estimated blood volume of 70 ml/kg (4900 ml). A range of H i and H m

3492-653: The SA node to the AV node . In addition to the PR prolongation, individuals with a primum ASD have a left axis deviation of the QRS complex, while those with a secundum ASD have a right axis deviation of the QRS complex. Individuals with a sinus venosus ASD exhibit a left axis deviation of the P wave (not the QRS complex). A common finding in the ECG is the presence of incomplete right bundle branch block , which

3589-401: The foramen ovale allows blood from the right atrium to enter the left atrium during fetal development. This opening allows blood to bypass the nonfunctional fetal lungs while the fetus obtains its oxygen from the placenta . A layer of tissue called the septum primum acts as a valve over the foramen ovale during fetal development. After birth, the pressure in the right side of the heart drops as

3686-414: The foramen ovale ; however, when this does not naturally close after birth it is referred to as a patent (open) foramen ovale (PFO). It is common in patients with a congenital atrial septal aneurysm (ASA). After PFO closure the atria normally are separated by a dividing wall, the interatrial septum . If this septum is defective or absent, then oxygen -rich blood can flow directly from the left side of

3783-439: The lungs to become oxygenated and CO 2 and other gaseous wastes exchanged and expelled during breathing. Blood then returns to the left side of the heart where it begins the process again. In a normal circulatory system, the volume of blood returning to the heart each minute is approximately equal to the volume that is pumped out each minute (the cardiac output). Because of this, the velocity of blood flow across each level of

3880-401: The physical laws that govern the flow of blood in the blood vessels . Blood flow ensures the transportation of nutrients , hormones , metabolic waste products, oxygen , and carbon dioxide throughout the body to maintain cell-level metabolism , the regulation of the pH , osmotic pressure and temperature of the whole body, and the protection from microbial and mechanical harm. Blood

3977-702: The septum secundum , or excessive absorption of the septum primum . About 10 to 20% of individuals with ostium secundum ASDs also have mitral valve prolapse . An ostium secundum ASD accompanied by an acquired mitral valve stenosis is called Lutembacher's syndrome . Most individuals with an uncorrected secundum ASD do not have significant symptoms through early adulthood. More than 70% develop symptoms by about 40 years of age. Symptoms are typically decreased exercise tolerance, easy fatigability, palpitations , and syncope . Complications of an uncorrected secundum ASD include pulmonary hypertension , right-sided congestive heart failure . While pulmonary hypertension

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4074-461: The splitting of the second heart sound (S 2 ). During respiratory inspiration, the negative intrathoracic pressure causes increased blood return into the right side of the heart. The increased blood volume in the right ventricle causes the pulmonic valve to stay open longer during ventricular systole. This causes a normal delay in the P 2 component of S 2 . During expiration, the positive intrathoracic pressure causes decreased blood return to

4171-462: The ventricles , and it occurs in approximately 30% of anterior-wall myocardial infarctions , compared with only 5% of inferior ones. Some other risk factors are poor ejection fraction (<35%), size of infarct, and the presence of AF. In the first three months after infarction, left-ventricle aneurysms have a 10% risk of emboli forming. Patients with prosthetic valves also carry a significant increase in risk of thromboembolism. Risk varies, based on

4268-470: The ANH to the H m is the same as the BL s . How much blood is to be removed is usually based on the weight, not the volume. The number of units that need to be removed to hemodilute to the maximum safe hematocrit (ANH) can be found by This is based on the assumption that each unit removed by hemodilution has a volume of 450 mL (the actual volume of a unit will vary somewhat since completion of collection

4365-427: The ASD causes a left-to-right shunt, the pulmonary vasculature in both lungs may appear dilated on chest X-ray, due to the increase in pulmonary blood flow. The physical findings in an adult with an ASD include those related directly to the intracardiac shunt and those that are secondary to the right heart failure that may be present in these individuals. In unaffected individuals, respiratory variations occur in

4462-471: The Greek ἐμβολισμός, meaning "interpressure". Blood flow Hemodynamics or haemodynamics are the dynamics of blood flow . The circulatory system is controlled by homeostatic mechanisms of autoregulation , just as hydraulic circuits are controlled by control systems . The hemodynamic response continuously monitors and adjusts to conditions in the body and its environment. Hemodynamics explains

4559-447: The RCM equation the patient RCM falls short from the equation giving above. If H i is 0.40 one must remove at least 7.5 units of blood during ANH, resulting in an H m of 0.20 to save two units equivalence. Clearly, the greater the H i and the greater the number of units removed during hemodilution, the more effective ANH is for preventing homologous blood transfusion. The model here

4656-431: The age of 55. Treatment with anticoagulant and antiplatelet medications in this group appear similar. A defect in the ostium primum is occasionally classified as an atrial septal defect, but it is more commonly classified as an atrioventricular septal defect . Ostium primum defects are less common than ostium secundum defects. This type of defect is usually associated with Down syndrome . A sinus venosus ASD

4753-418: The aortic valve during ventricular systole , and coronary artery disease which increases the stiffness of the left ventricle, thereby increasing the filling pressure of the left ventricle during ventricular diastole . The left-to-right shunt increases the filling pressure of the right heart ( preload ) and forces the right ventricle to pump out more blood than the left ventricle. This constant overloading of

4850-404: The arterioles is the product of flow rate and resistance: ∆P=Q xresistance. The high resistance observed in the arterioles, which factor largely in the ∆ P is a result of a smaller radius of about 30 μm. The smaller the radius of a tube, the larger the resistance to fluid flow. Immediately following the arterioles are the capillaries. Following the logic observed in the arterioles, we expect

4947-429: The atria is achieved with transesophageal echocardiography, this test may be performed in individuals with a suspected ASD which is not visualized on transthoracic imaging. Newer techniques to visualize these defects involve intracardiac imaging with special catheters typically placed in the venous system and advanced to the level of the heart. This type of imaging is becoming more common and involves only mild sedation for

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5044-496: The atrium occurs mainly in patients with mitral valve disease, and especially in those with mitral valve stenosis (narrowing), with atrial fibrillation (AF). In the absence of AF, pure mitral regurgitation has a low incidence of thromboembolism . The risk of emboli forming in AF depends on other risk factors such as age, hypertension , diabetes , recent heart failure, or previous stroke. Thrombus formation can also take place within

5141-441: The blood flowing in the opposite direction through the ASD is called Eisenmenger's syndrome, a rare and late complication of an ASD. Venous thrombus (clots in the veins) are quite common. Embolizations (dislodgement of thrombi) normally go to the lung and cause pulmonary emboli . In an individual with ASD, these emboli can potentially enter the arterial system, which can cause any phenomenon attributed to acute loss of blood to

5238-476: The blood flow has laminar characteristics . For this reason, the blood flow velocity is the fastest in the middle of the vessel and slowest at the vessel wall. In most cases, the mean velocity is used. There are many ways to measure blood flow velocity, like videocapillary microscoping with frame-to-frame analysis, or laser Doppler anemometry . Blood velocities in arteries are higher during systole than during diastole . One parameter to quantify this difference

5335-401: The blood pressure to be lower in the capillaries compared to the arterioles. Since pressure is a function of force per unit area, ( P  =  F / A ), the larger the surface area, the lesser the pressure when an external force acts on it. Though the radii of the capillaries are very small, the network of capillaries has the largest surface area in the vascular network. They are known to have

5432-406: The blood then travels back through the network of veins to the venae cavae into the right heart . The micro-circulation — the arterioles, capillaries, and venules —constitutes most of the area of the vascular system and is the site of the transfer of O 2 , glucose , and enzyme substrates into the cells. The venous system returns the de-oxygenated blood to the right heart where it is pumped into

5529-518: The body. It is a major cause of infarction (tissue death from blockage of the blood supply). An embolus lodging in the brain from either the heart or a carotid artery will most likely be the cause of a stroke due to ischemia . An arterial embolus might originate in the heart (from a thrombus in the left atrium , following atrial fibrillation or be a septic embolus resulting from endocarditis ). Emboli of cardiac origin are frequently encountered in clinical practice. Thrombus formation within

5626-414: The case of PFO, a blood clot from the venous circulatory system is able to pass from the right atrium directly into the left atrium via the PFO, rather than being filtered by the lungs, and thereupon into systemic circulation toward the brain. Also multiple substances -including the prothrombotic agent serotonin- are shunted bypassing the lungs. PFO is common in patients with an atrial septal aneurysm (ASA),

5723-512: The cerebral impact of the ASD or PFO. The ECG findings in atrial septal defect vary with the type of defect the individual has. Individuals with atrial septal defects may have a prolonged PR interval (a first-degree heart block ). The prolongation of the PR interval is probably due to the enlargement of the atria common in ASDs and the increased distance due to the defect itself. Both of these can cause an increased distance of internodal conduction from

5820-427: The circulatory disturbance. For instance, in arboreal snakes the heart is closer to the head, in comparison with aquatic snakes. This facilitates blood perfusion to the brain. Blood flow is also affected by the smoothness of the vessels, resulting in either turbulent (chaotic) or laminar (smooth) flow. Smoothness is reduced by the buildup of fatty deposits on the arterial walls. The Reynolds number (denoted NR or Re)

5917-450: The circulatory system is primarily determined by the total cross-sectional area of that level. Cardiac output is determined by two methods. One is to use the Fick equation: C O = V O 2 / C a O 2 − C v O 2 {\displaystyle CO=VO2/C_{a}O_{2}-C_{v}O_{2}} The other thermodilution method

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6014-427: The defect is small. Also, in terms of health risks, people who have had a cryptogenic stroke are more likely to have a PFO than the general population. A cardiac shunt is the presence of a net flow of blood through a defect, either from left to right or right to left. The amount of shunting present, if any, determines the hemodynamic significance of the ASD. A right-to-left-shunt results in venous blood entering

6111-484: The defect is termed a mixed atrial septal defect. Due to the communication between the atria that occurs in ASDs, disease entities or complications from the condition are possible. Patients with an uncorrected atrial septal defect may be at increased risk for developing a cardiac arrhythmia, as well as more frequent respiratory infections. ASDs, and particularly PFOs, are a predisposing venous blood carrying inert gases, such as helium or nitrogen does not pass through

6208-455: The exact mechanism remains unclear, closure of a PFO can reduce symptoms in certain cases. This remains controversial; 20% of the general population has a PFO, which for the most part, is asymptomatic. About 20% of the female population has migraines, and the placebo effect in migraine typically averages around 40%. The high frequency of these facts make finding statistically significant relationships between PFO and migraine difficult (i.e.,

6305-435: The field, percutaneous PFO closure in addition to antiplatelet therapy is suggested for all who meet all the following criteria: A variety of PFO closure devices may be implanted via catheter-based procedures. Based on the most up to date evidence, PFO closure is more effective at reducing recurrent ischemic stroke when compared to medical therapy. In most of these studies, antiplatelet and anticoagulation were combined in

6402-430: The heart and how they are formed during the developmental process during early fetal development. The ostium secundum atrial septal defect is the most common type of atrial septal defect and comprises 6–10% of all congenital heart diseases. It involves a patent ostium secundum (that is, a patent foramen secundum ). The secundum atrial septal defect usually arises from an enlarged foramen ovale , inadequate growth of

6499-443: The heart to mix with the oxygen-poor blood in the right side of the heart; or the opposite, depending on whether the left or right atrium has the higher blood pressure. In the absence of other heart defects, the left atrium has the higher pressure. This can lead to lower-than-normal oxygen levels in the arterial blood that supplies the brain, organs, and tissues. However, an ASD may not produce noticeable signs or symptoms, especially if

6596-489: The heart. Sometimes, for example if a patient coughs just when an embolus is passing, it might cross to the arterial system. The direction of the embolus can be one of two types: In anterograde embolism, the movement of emboli is in the direction of blood flow. In retrograde embolism, the emboli move in opposition to the blood flow direction; this is usually significant only in blood vessels with low pressure (veins) or with emboli of high weight. The word embolism comes from

6693-415: The largest surface area (485 mm^2) in the human vascular network. The larger the total cross-sectional area, the lower the mean velocity as well as the pressure. Patent foramen ovale Atrial septal defect ( ASD ) is a congenital heart defect in which blood flows between the atria (upper chambers) of the heart . Some flow is a normal condition both pre-birth and immediately post-birth via

6790-429: The left atrium may cause a volume overload of both the right atrium and the right ventricle. If untreated, this condition can result in enlargement of the right side of the heart and ultimately heart failure. Any process that increases the pressure in the left ventricle can cause worsening of the left-to-right shunt. This includes hypertension, which increases the pressure that the left ventricle has to generate to open

6887-415: The left side of the heart and into the arterial circulation without passing through the pulmonary circulation to be oxygenated . This may result in the clinical finding of cyanosis , the presence of bluish-colored skin, especially of the lips and under the nails. During development of the baby, the interatrial septum develops to separate the left and right atria . However, a hole in the septum called

6984-411: The left-to-right shunt, producing a widely split S2. Because the atria are linked via the atrial septal defect, inspiration produces no net pressure change between them, and has no effect on the splitting of S2. Thus, S2 is split to the same degree during inspiration as expiration, and is said to be "fixed". In transthoracic echocardiography , an atrial septal defect may be seen on color flow imaging as

7081-462: The lungs open and begin working, causing the foramen ovale to close entirely. In about 25% of adults, the foramen ovale does not entirely seal. In these cases, any elevation of the pressure in the pulmonary circulatory system (due to pulmonary hypertension , temporarily while coughing , etc.) can cause the foramen ovale to remain open. The six types of atrial septal defects are differentiated from each other by whether they involve other structures of

7178-406: The lungs. The only way to release the excess inert gases from the body is to pass the blood carrying the inert gases through the lungs to be exhaled. If some of the inert gas-laden blood passes through the PFO, it avoids the lungs and the inert gas is more likely to form large bubbles in the arterial blood stream causing decompression sickness. If a net flow of blood exists from the left atrium to

7275-421: The main blood pressure drop across major arteries to capillaries in the circulatory system. In the arterioles blood pressure is lower than in the major arteries. This is due to bifurcations, which cause a drop in pressure. The more bifurcations, the higher the total cross-sectional area, therefore the pressure across the surface drops. This is why the arterioles have the highest pressure-drop. The pressure drop of

7372-413: The measurement of blood viscosity . It is true that in a steady state flow of a viscous fluid through a rigid spherical body immersed in the fluid, where we assume the inertia is negligible in such a flow, it is believed that the downward gravitational force of the particle is balanced by the viscous drag force. From this force balance the speed of fall can be shown to be given by Stokes' law Where

7469-486: The medical therapy arm. Although there is limited data on the effectiveness of anticoagulation in reducing stroke in this population, it is hypothesized that based on the embolic mechanism, that anticoagulation should be superior to antiplatelet therapy at reducing risk of recurrent stroke. A recent review of the literature supports this hypothesis recommending anticoagulation over the use of antiplatelet therapy in patients with PFO and cryptogenic stroke. However, more evidence

7566-408: The model considered above is designed to predict the maximum RCM that can save ANH. In summary, the efficacy of ANH has been described mathematically by means of measurements of surgical blood loss and blood volume flow measurement. This form of analysis permits accurate estimation of the potential efficiency of the techniques and shows the application of measurement in the medical field. The heart

7663-417: The normovolemia, the withdrawal of autologous blood must be simultaneously replaced by a suitable hemodilute. Ideally, this is achieved by isovolemia exchange transfusion of a plasma substitute with a colloid osmotic pressure (OP). A colloid is a fluid containing particles that are large enough to exert an oncotic pressure across the micro-vascular membrane. When debating the use of colloid or crystalloid, it

7760-410: The number of particles present and by the temperature . For example, a 1 molar solution of a substance contains 6.022 × 10 molecules per liter of that substance and at 0 °C it has an osmotic pressure of 2.27 MPa (22.4 atm). The osmotic pressure of the plasma affects the mechanics of the circulation in several ways. An alteration of the osmotic pressure difference across the membrane of

7857-501: The oxygen-poor blood gets shunted to the left side of the heart and ejected to the peripheral vascular system. This causes signs of cyanosis . Most individuals with a significant ASD are diagnosed in utero or in early childhood with the use of ultrasonography or auscultation of the heart sounds during physical examination . Some individuals with an ASD have surgical correction of their ASD during childhood. The development of signs and symptoms due to an ASD are related to

7954-448: The patient typically. If the individual has adequate echocardiographic windows, use of the echocardiogram to measure the cardiac output of the left ventricle and the right ventricle independently is possible. In this way, the shunt fraction can be estimated using echocardiography. A less invasive method for detecting a PFO or other ASDs than transesophagal ultrasound is transcranial Doppler with bubble contrast. This method reveals

8051-405: The relationship may just be chance or coincidence). In a large randomized controlled trial , the higher prevalence of PFO in migraine patients was confirmed, but migraine headache cessation was not more prevalent in the group of migraine patients who underwent closure of their PFOs. In unaffected individuals, the chambers of the left side of the heart are under higher pressure than the chambers of

8148-409: The right atrium (instead of the normal drainage of the pulmonary veins into the left atrium). Common (or single) atrium is a failure of development of the embryologic components that contribute to the atrial septal complex. It is frequently associated with heterotaxy syndrome . The interatrial septum can be divided into five septal zones. If the defect involves two or more of the septal zones, then

8245-419: The right atrium, called a left-to-right shunt, then an increase in the blood flow through the lungs happens. Initially, this increased blood flow is asymptomatic, but if it persists, the pulmonary blood vessels may stiffen, causing pulmonary hypertension, which increases the pressures in the right side of the heart, leading to the reversal of the shunt into a right-to-left shunt. Reversal of the shunt occurs, and

8342-402: The right side because the left ventricle has to produce enough pressure to pump blood throughout the entire body, while the right ventricle needs only to produce enough pressure to pump blood to the lungs . In the case of a large ASD (> 9 mm), which may result in a clinically remarkable left-to-right shunt , blood shunts from the left atrium to the right atrium. This extra blood from

8439-426: The right side of the heart causes an overload of the entire pulmonary vasculature. Eventually, pulmonary hypertension may develop. The pulmonary hypertension will cause the right ventricle to face increased afterload . The right ventricle is forced to generate higher pressures to try to overcome the pulmonary hypertension. This may lead to right ventricular failure (dilatation and decreased systolic function of

8536-506: The right side of the heart. The reduced volume in the right ventricle allows the pulmonic valve to close earlier at the end of ventricular systole, causing P 2 to occur earlier. In individuals with an ASD, a fixed splitting of S 2 occurs because the extra blood return during inspiration gets equalized between the left and right atria due to the communication that exists between the atria in individuals with ASD. The right ventricle can be thought of as continuously overloaded because of

8633-404: The right ventricle). If the ASD is left uncorrected, the pulmonary hypertension progresses and the pressure in the right side of the heart becomes greater than the left side of the heart. This reversal of the pressure gradient across the ASD causes the shunt to reverse – a right-to-left shunt. This phenomenon is known as Eisenmenger's syndrome . Once right-to-left shunting occurs, a portion of

8730-408: The septum secundum; in healthy hearts, this fusion form the fossa ovalis, a portion of the interatrial septum which corresponds to the location of the foramen ovale in the fetus. In medical use, the term "patent" means open or unobstructed. In about 25% of people, the foramen ovale does not close, leaving them with a PFO or at least with what some physicians classify as a "pro-PFO", which is a PFO that

8827-440: The size of the intracardiac shunt. Individuals with a larger shunt tend to present with symptoms at a younger age. Adults with an uncorrected ASD present with symptoms of dyspnea on exertion (shortness of breath with minimal exercise), congestive heart failure , or cerebrovascular accident (stroke). They may be noted on routine testing to have an abnormal chest X-ray or an abnormal ECG and may have atrial fibrillation . If

8924-438: The steady value called the terminal velocity (U), as shown above. Hemodilution is the dilution of the concentration of red blood cells and plasma constituents by partially substituting the blood with colloids or crystalloids . It is a strategy to avoid exposure of patients to the potential hazards of homologous blood transfusions. Hemodilution can be normovolemic, which implies the dilution of normal blood constituents by

9021-508: The use of expanders. During acute normovolemic hemodilution (ANH), blood subsequently lost during surgery contains proportionally fewer red blood cells per milliliter, thus minimizing intraoperative loss of the whole blood. Therefore, blood lost by the patient during surgery is not actually lost by the patient, for this volume is purified and redirected into the patient. On the other hand, hypervolemic hemodilution (HVH) uses acute preoperative volume expansion without any blood removal. In choosing

9118-413: The valve type (bioprosthetic or mechanical); the position (mitral or aortic); and the presence of other factors such as AF, left-ventricular dysfunction, and previous emboli. Emboli often have more serious consequences when they occur in the so-called "end circulation": areas of the body that have no redundant blood supply, such as the brain and heart . Assuming a normal circulation, an embolus formed in

9215-414: The veins crosses to the arterial blood system. This is generally found only with heart problems such as septal defects (holes in the cardiac septum) between the atria or ventricles. The most common such abnormality is patent foramen ovale , occurring in about 25% of the adult population, but here the defect functions as a valve which is normally closed, because pressure is slightly higher in the left side of

9312-577: The vessel section) size as well, and on the size of the vessels. Assuming steady, laminar flow in the vessel, the blood vessels behavior is similar to that of a pipe. For instance if p1 and p2 are pressures are at the ends of the tube, the pressure drop/gradient is: The larger arteries, including all large enough to see without magnification, are conduits with low vascular resistance (assuming no advanced atherosclerotic changes) with high flow rates that generate only small drops in pressure. The smaller arteries and arterioles have higher resistance, and confer

9409-414: Was evaluated to understand conditions where hemodilution is necessary to benefit the patient. The result of the model calculations are presented in a table given in the appendix for a range of H i from 0.30 to 0.50 with ANH performed to minimum hematocrits from 0.30 to 0.15. Given a H i of 0.40, if the H m is assumed to be 0.25.then from the equation above the RCM count is still high and ANH

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