Hemodynamics

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Hemodynamic or hÃÆ'Â|modynamics is the dynamics of blood flow . The circulatory system is controlled by a homeostatic mechanism, just like a controlled hydraulic circuit. The haemodynamic response continually monitors and adapts to conditions in the body and environment. Thus hemodynamics explains the physical laws that regulate the flow of blood in the blood vessels.

Blood flow ensures the transport of nutrients, hormones, metabolic wastes, O ₂ and CO ₂ throughout the body to maintain cell metabolism, pH regulation, osmotic pressure and body temperature, and protection from microbial and mechanical hazards.

Blood is a non-Newtonian fluid, best studied using rheology rather than hydrodynamics. Blood vessels are not rigid tubes, so classical hydrodynamics and fluid mechanics based on the use of classical viscometer are unable to explain hemodynamics.

The study of blood flow is called hemodynamics. The study of the properties of blood flow is called hemorheology.

Video Hemodynamics

Darah

Blood is a complex liquid. Blood consists of plasma and the elements that are formed. Plasma contains 91.5% water, 7% protein and 1.5% other solute. The elements formed are platelets, white blood cells and red blood cells, the presence of the formed elements and their interactions with plasma molecules is the main reason why blood is so different from Newton's ideal fluid.

Plasma viscosity

Normal blood plasma behaves like Newton's fluid at the physiological level of shear. The typical values ​​for normal plasma plasma viscosity at 37 ° C are 1.4 mNÃ/s/m ² . Normal plasma viscosity varies with temperature in the same way as water of the solvent; an increase in temperature of 5 Â ° C in the physiological range reduces plasma viscosity by about 10%.

plasma osmotic pressure

The osmotic pressure of the solution is determined by the number of particles present and by the temperature. For example, a molar solution of a substance containing a molecule of 6.022 ÃÆ' - 10 ²³ per liter of that substance and at a temperature of 0 Â ° C has an osmotic pressure 2.27 MPa (22.4 atm). Plasma osmotic pressure affects the mechanism of circulation in several ways. Changes in osmotic pressure differences across blood cell membranes cause water shifts and changes in cell volume. Changes in shape and elasticity affect the mechanical properties of the whole blood. Changes in plasma osmotic pressure alter hematocrit, which is the concentration of red blood cell volume throughout the blood by redistributing water between intravascular and extravascular spaces. This in turn affects the whole blood mechanism.

Red blood cells

The red blood cells are very flexible and the bikoncave is in shape. The membrane has a Young's modulus in the 106 Pa region. Deformation in red blood cells is induced by shear stress. When the suspension is shaved, the red blood cells change shape and rotate due to the velocity gradient, with the rate of deformation and spin dependent on the shear rate and concentration. This may affect the circulatory mechanism and may complicate the measurement of blood viscosity. It is true that in steady-state viscous fluid through a rigid round body immersed in a liquid, where we assume inertia is neglected in such a stream, it is believed that the downward force of gravity of the particles is balanced by the thickness of the viscous forces. Of this power, the balance of falling speed can be indicated by Stokes' law

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Where a is the radius of the particle, ? _p , ? _f are the respective particle and liquid density ? is the viscosity of the liquid, g is the acceleration of gravity. From the above equation we can see that the particle sedimentation rate depends on the square of the radius. If the particles are released from the residue in the liquid, the sedimentation rate U _s increases until it reaches a stable value called terminal velocity (U), as shown above.

We have seen blood flow and blood composition. Before we look at the main problem, hemodilution, let's take a brief history about the use of blood. The use of therapy is not a modern phenomenon. Egyptian writings dating back at least 2000 years suggest the consumption of oral blood as a 'sovereign remedy' for leprosy. Experiments with first intravenous blood transfusion began in the early 16th century, and in the last 50 years, the field of transfusion treatment has grown remarkably, bringing with it an increase in the use of blood and blood products. However, the therapeutic use of blood comes with significant risks. As a result, many people are looking for alternatives to whole blood transfusions. Currently, a program of bloodless treatment and surgery (BMS) has been developed not only for people with certain religious beliefs, but also for patients who fear the risks of blood transfusion and the desire to take the best medical precautions.

Hemodilusi

Hemodilution is the dilution of the concentration of red blood cells and plasma constituents by replacing some of the blood with colloids or crystalloids. This is a strategy to avoid exposure of patients to the danger of homologous blood transfusions.

Hemodilution can become normovolemic which, as we say, implies the dilution of normal blood constituents by using an expander. During acute normovolemic hemodilution, (ANH) of blood lost during surgery contains fewer red blood cells per millimeter, thus minimizing intraoperative loss of whole blood. Therefore, blood loss by the patient during surgery is actually not lost by the patient, because this volume is purified and transferred to the patient.

However there is a hypervolemic hemodilution (HVH). Here, instead of simultaneously exchanging the patient's blood as in ANH, hypervolemic techniques are performed using acute, preoperative volume expansion without blood loss. In choosing a liquid, however, be sure that when mixing the rest of the blood behaves in microcirculation as in the original blood fluid, it retains all its viscosity properties.

In presenting ANH volumes what should be applied one study shows an ANH mathematical model that calculates the maximum RCM savings that might use ANH, given the patient's weight H _i and H < sub> m . (See below for a glossary of terms used.)

To maintain normovolemia, autologous blood withdrawal should be simultaneously replaced by the appropriate hemodilute. Ideally, this is achieved by the transfer of isovolemia transfusions from plasma substitutes with colloid osmotic pressure (OP). The colloid is a liquid containing particles that are large enough to release oncotic pressure across the micro-vascular membrane. When debating the use of colloidal or crystalloid, it is important to think about all the components of the star equation: $xmlns\; =\; "http://www.w3.org/1998/Math/MathML"\; alttext\; =\; "\{\backslash \; displaystyle\; \backslash \; Q\; =\; K\; ([P\_\; \{c\}\; ->$

P_ {i}] S- [P_ {c} -P_ {i}])} ">                    Ã,         Q         =         K ()         [                   P                      c                           -                   P                      me                   ]         S         -         [                   P                      c                           -                   P                      me                   ]         )           {Annotation encoding = "application/x-tex"> {\ displaystyle \ Q = K ([P_ {c} -P_ {i}] S- [P_ {c} -P_ {i}])}  Â

Untuk mengidentifikasi hematokrit aman minimal yang diinginkan untuk pasien tertentu, persamaan berikut berguna:

${\ displaystyle \ BL_ {s} = EBV \ ln {\ frac {H_ {i}} {H_ {m}}}}  ÂÂ$

where EBV is the approximate volume of blood; 70 mL/kg is used in this model and H _i (initial hematocrit) is the initial hematocrit of the patient. From the above equation it is clear that the volume of blood released during ANH to H _m equals BL _s . How much blood to be disposed of is usually based on weight, not volumes. Number of units to be removed for hemodilute to maximum safe hematocrit (ANH) can be found by

$Â\; ÂÂ\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂAÂ\; Â\; Â\; Â\; Â\; Â\; Â\; ÂNÂ\; Â\; Â\; Â\; Â\; Â\; Â\; ÂHÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â=Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\frac{Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂBÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂL_{Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂsÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â}Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â}{450}Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â}Â\; Â\; Â\; ÂAnnotation\; encoding\; =\; "application/x-tex">\; \{\backslash \; displaystyle\; ANH\; =\; \{\backslash \; frac\; \{BL\_\; \{s\}\}\; \{450\}\}\}\; Â\; Â$

This is based on the assumption that each unit removed by hemodilution has a volume of 450 mL (the actual volume of the unit will vary somewhat because the collection settlement depends on the weight and not the volume). The model assumes that the hemodilute value is equal to H _m before surgery, therefore, the reciprocal blood transfusions obtained through hemodilution should begin when the SBL is started. RCM available for retransfusion after ANH (RCMm) can be calculated from patients H _i and the final hematocrit after hemodilution ( H _m )

$Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂRÂ\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; ÂMÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â=Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂEÂ\; Â\; Â\; Â\; Â\; Â\; Â\; ÂVÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂBÂ\; Â\; Â\; Â\; Â\; Â\; ÂÃ\AE \text{'}\; -Â\; Â\; Â\; Â\; Â\; Â\; Â(Â\; Â\; Â\; Â\; Â\; Â\; Â}$ _{                        me                          -                       Â                          )           {\ displaystyle RCM = EVB \ times (H_ {i} -H_ {m})}  Â}

The maximum SBL that is possible when ANH is used without falling below Hm (BLH) is found assuming that all blood released during ANH is returned to the patient at sufficient level to maintain hematocrit at a minimum safe level

${\ displaystyle BL_ {H} = {\ frac {RCM_ {H}} {H_ {m}}}} < Â Â$

If ANH is used for SBL does not exceed BL _H then there is no need for blood transfusion. We can conclude from earlier that H should not exceed s . The difference between BL _H and BL _s is therefore an additional surgical blood loss ( BL < > i ) may be when using ANH. $xmlns\; =\; "http://www.w3.org/1998/Math/MathML"\; alttext\; =\; "\{\backslash \; displaystyle\; \backslash \; \{BL\_\; \{i\}\}\; =\; \{BL\_\; \{\; H\}\}\; -\; \{BL\_\; \{s\}\}\}\; ">\; Â\; ÂÂ\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\text{Ã,}Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂBÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂL_{Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\mathrm{me}Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â}Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â=Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂBÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂL_{Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂHÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â}Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â-Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂBÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂL_{Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂsÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â}Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â}Â\; Â\; Â\; Â\{Annotation\; encoding\; =\; "application/x-tex">\; \{\backslash \; displaystyle\; \backslash \; \{BL\_\; \{i\}\}\; =\; \{BL\_\; \{H\}\}\; -\; \{BL\_\; \{s\}\}\}\; Â\; Â$

Ketika dinyatakan dalam bentuk RCM

${\ displaystyle {RCM_ {i}} = {BL_ {i}} \ kali {H_ {m}}}  ÂÂ$

Where RCM _i is the red blood cell mass to be given using homologous blood to maintain H _m used and blood loss equal to BLH.

The model used assumed ANH was used for 70 kg patients with an estimated blood volume of 70 ml/kg (4900 ml). Various H _i and H _m are evaluated to understand the conditions under which hemodilution is necessary to benefit the patient.

Results

The results of the model calculations are presented in the table given in the appendix for the range H _i from 0.30 to 0.50 with ANH performed on minimum hematocrits of 0.30 to 0.15. Given H _i of 0.40, if H _m is assumed to be 0.25.then of the equation above the sum RCM is still high and ANH is not required if BL _s does not exceed 2303 ml, since hemotocrit will not fall below H _m , even though five units of blood should be removed during hemodilution. In this condition, to achieve the maximum benefit of the technique if ANH is used, no homologous blood will be required to maintain H _m if the blood loss does not exceed 2940 ml. In such cases ANH can store a maximum of 1.1 units equivalent to red blood cells, and homologous blood transfusions are required to maintain H _m , even if ANH is used. This model can be used to identify when ANH can be used for the given patient and the required ANH level to maximize the benefit.

For example, if H _i is 0.30 or less was not possible to save the red blood cell mass equivalent to two units of PRBC homologous even if the patient hemodiluted to H _m of 0.15. That's because of the RCM equation the RCM patient falls short of the above giving equation. If H _i was 0.40 person should remove at least 7.5 units of blood during ANH, yielding H _m 0.20 to save two equality units. Obviously, the greater the H _i and the greater the number of units removed during hemodilution, the more effective the ANH to avoid homologous blood transfusion. The model here is designed to enable physicians to determine where ANH can benefit patients based on their knowledge of H _i , potential for SBL, and forecast H _m . Although the model uses a 70 kg patient, the results can be applied to any patient. To apply this result to any weight, any BL, BLH and ANHH or PRBC values ​​given in the table need to be multiplied by the factor we will call T

${\ displaystyle T = {\ frac {\ text {patient's weight in kg}} {70}}}$

Basically, the model considered above is designed to predict the maximum RCM that can save ANH.

In short, the efficacy of ANH has been described mathematically by measuring blood loss surgery and measuring blood volume flow. This form of analysis allows an accurate estimate of the potential efficiency of the technique and demonstrates the application of measurements in the medical field.

Maps Hemodynamics

Blood flow

Heart output

The heart is the propulsion of the circulatory system, pumping blood through rhythmic contractions and relaxation. The rate of blood flow out of the heart (often expressed in L/min) is known as cardiac output (CO).

The blood pumped out of the heart first enters the aorta, the largest artery of the body. It then develops into smaller and smaller arteries, then becomes arterioles, and finally capillaries, where oxygen displacement occurs. The capillary is connected to the venula, and the blood then moves back through the venous tissue to the right heart. Microcirculation - arterioles, capillaries, and venules - fills most areas of the vascular system and is where substrate transfer of O ₂ , glucose, and enzymes into cells. The venous system returns deoxygenated blood to the right heart where it is pumped into the lungs to become oxygen and CO ₂ and other gas wastes are exchanged and expelled during breathing. The 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 every minute is approximately equal to the volume pumped out every minute (cardiac output). Because of this, the speed of blood flow at each level of the circulatory system is primarily determined by the total cross-sectional area of ​​that level. This is mathematically expressed by the following equation:

v = Q/A

Where

• v = speed (cm/s)
• Q = blood flow (ml/s)
• A = cross sectional area (cm ² )

Turbulence

Blood flow is also affected by the smoothness of the blood vessels, resulting in turbulent flow (chaotic) or laminar (smooth). Fineness is reduced by the buildup of fat deposits in the artery walls.

The Reynolds number (denoted NR or Re) is the relationship that helps determine the behavior of the fluid in the tube, in this case the blood inside the vessels.

Persamaan untuk hubungan tanpa dimensi ini ditulis sebagai:

${\ displaystyle NR = {\ frac {\ rho vL} {\ mu}}}  ÂÂ$

• ? : kepadatan darah
• v : kecepatan rata-rata dari darah
• L : dimensi karakteristik kapal, dalam hal ini diameter
• ? : viskositas darah

Reynold numbers are directly proportional to the speed and diameter of the tube. Note that NR is proportional to the average speed and diameter. The Reynolds number of less than 2300 is a stream of laminar fluid, characterized by constant flow movement, while a value of more than 4000, is represented as a turbulent flow. Because of its smaller radius and the lowest speed compared to other vessels, the number of Reynolds in capillaries is very low, resulting in laminar instead of turbulent flow.

Velocity

Often expressed in cm/s. This value is inversely proportional to the total cross-sectional area of ​​the blood vessels and is also different per cross section, since under normal conditions blood flow has laminar characteristics. For this reason, the velocity of blood flow is the fastest in the middle of the ship and slowest in the walls of the blood vessels. In many cases, average speed is used. There are many ways to measure the velocity of blood flow, such as video microscope with frame-to-frame analysis, or Doppler laser anemometry. The blood velocity in the arteries is higher during systole than during diastole. One parameter to measure this difference is the pulsility index (PI), which is equal to the difference between peak systolic velocity and minimum diastolic speed divided by average velocity during the heart cycle. This value decreases with distance from the heart.

${\ displaystyle PI = {\ frac {v_ {systole} -v_ {diastole}} {v_ {mean}}}}$

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Blood vessels

Vascular Resistance

Resistance is also related to the radius of the blood vessels, the length of the blood vessels, and the viscosity of blood.

Dalam pendekatan pertama berdasarkan cairan, seperti yang ditunjukkan oleh persamaan Hagen-Poiseuille. Persamaannya adalah sebagai berikut:

${\ displaystyle \ Delta P = {\ frac {8 \ mu lQ} {\ pi r ^ {4}}}}  ÂÂ$

• ? P : penurunan tekanan/gradien
• µ : kekentalan
• l : panjang tabung. Dalam kasus kapal dengan panjang yang sangat panjang, l diganti dengan diameter kapal.
• Q : laju aliran darah di pembuluh darah
• r : radius kapal

In the second approach, more realistic than vascular resistance and derived from experimental observations on blood flow, according to Thurston, there is a plasma cell layer coating on the wall surrounding the flow attached. This is the liquid layer where distance, viscosity? is a function of? written as? (?), and the surrounding layers do not meet at the center of the blood vessels in the real bloodstream. Instead, there is a flow that is plugged into the hyperviscous because it holds a high concentration of red blood cells. Thurston string these layers into flow resistance to illustrate blood flow by using viscosity? (?) And thickness? of the wall layers.

Hukum resistensi darah muncul sebagai R disesuaikan dengan profil aliran darah:

${\ displaystyle R = cL \ eta (\ delta)/(\ pi \ delta r ^ {3})}  ÂÂ$

Where

• R = resistance to blood flow
• c = constant flow coefficient
• L = ship length
• ? (?) = blood viscosity in plasma wall cell coating
• r = blood vessel radius
• ? = distance in plasma release cell layer

Blood resistance varies depending on the viscosity of the blood and the clogged flow (or the sheath of the flow as they complement the entire part of the blood vessels) as well, and at the size of the blood vessels. Assuming a stable laminar flow in blood vessels, blood vessel behavior is similar to a pipe. For example if p1 and p2 are the pressure at the end of the tube, the pressure/gradient drop is:

$Â\; ÂÂ\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\frac{Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Âp_{Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â1Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â}Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â-Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Âp_{Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â2Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â}Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â}{l}Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â=Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\mathrm{?}Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂPÂ\; Â\; Â\; Â\; Â\; Â}Â\; Â\; Â\; ÂAnnotation\; encoding\; =\; "application/x-tex">\; \{\backslash \; displaystyle\; \{\backslash \; frac\; \{p\_\; \{1\}\; -p\_\; \{2\}\}\; \{l\}\}\; =\; \backslash \; Delta\; P\}\; Â\; Â$

Larger arteries, including all large enough to be seen without magnification, are channels with low vascular resistance (assuming no further atherosclerotic changes) with high flow rates that produce only a small decrease in pressure. The smaller arteries and arterioles have higher resistance, and provide a decrease in primary blood pressure throughout the major arteries for capillaries in the circulatory system.

Arteriolar blood pressure is lower than in the main artery. This is due to bifurcation, which causes a decrease in pressure. The more bifurcation, the higher the total cross-sectional area, therefore the pressure on the surface decreases. This is why arterioles have the highest pressure drops. The decrease in arteriolar pressure is a product of flow rate and resistance: P P = Q xresistance. The high resistance observed in arterioles, which is largely a factor in? P is the result of a smaller radius of about 30 Ã,Âμm. The smaller the radius of the tube, the greater the resistance to fluid flow.

Immediately following the arteriole is the capillary. Following the logic observed in arterioles, we expect lower blood pressure in the capillaries compared with arterioles. Since pressure is a function of force per unit area, ( P A ), the larger the surface area, the lower the pressure when external forces act on it. Although the capillary radius is very small, the capillary tissue has the largest surface area in the vascular tissue. They are known to have the largest surface area (485 mm) in human vascular tissue. The larger the total cross-sectional area, the lower the average speed and pressure.

Substances called vasoconstrictors can reduce the size of blood vessels, thereby increasing blood pressure. Vasodilators (such as nitroglycerin) increase the size of blood vessels, thereby reducing arterial pressure.

If the blood viscosity increases (the thicker), the result is an increase in arterial pressure. Certain medical conditions may alter the viscosity of the blood. For example, anemia (low red blood cell concentrations), reduces viscosity, whereas increased red blood cell concentrations increase viscosity. It has been thought that aspirin and lower blood-thinning drugs lower blood viscosity, but instead research has found that they act by reducing the blood's tendency to freeze.

Wall tension

Terlepas dari situs, tekanan darah berhubungan dengan tegangan dinding pembuluh menurut persamaan Young-Laplace (dengan asumsi bahwa ketebalan dinding pembuluh sangat kecil dibandingkan dengan diameter lumen):

${\ displaystyle \ sigma _ {\ theta} = {\ dfrac {Pr} {t}} \}  ÂÂ$

dimana

• P adalah tekanan darah
• t adalah ketebalan dinding
• r adalah radius dalam silinder.
• ${\ displaystyle \ sigma _ {\ theta} \!}  ÂÂ$ adalah tegangan silinder atau "lingkaran tegangan".

For the assumption of thin-walled applicable, the vessel shall have a wall thickness of not more than one tenth (often referred to as a twentieth) of its fingers.

Tegangan silinder, pada gilirannya, adalah gaya rata-rata yang diberikan secara melingkar (tegak lurus terhadap sumbu dan radius benda) di dinding silinder, dan dapat digambarkan sebagai:

${\ displaystyle \ sigma _ {\ theta} = {\ dfrac {F} {tl}} \}  ÂÂ$

where:

• F is a circularly provided force on a cylinder wall area that has two lengths as the following side:
• t is a cylindrical radial thickness
• l is the axial length of the cylinder

Stress

When a force is applied to a material, it begins to change shape or move. Since the force required to damage a material (eg to make a fluid flow) increases with the surface size of material A., the magnitude of this force F is proportional to the area A of the surface portion. Therefore, the quantity (F/A) which is the force per unit area is called stress. The shear stress on the wall associated with blood flow through an artery depends on the size of the artery and the geometry and can range between 0.5 and 4 Pa.

${\ displaystyle \ sigma = {\ frac {F} {A}}}$ .

Under normal conditions, to avoid atherogenesis, thrombosis, smooth muscle proliferation and endothelial apoptosis, shear stress maintains its magnitude and direction within acceptable ranges. In some cases due to the blood hammer, the shear stress reaches a larger value. While the direction of stress can also change with backflow, depending on hemodynamic conditions. Therefore, this situation can cause atherosclerotic disease.

Capacitance

The vein is described as the "body capacitance" of the body because more than 70% of the blood volume is in the venous system. Veins are more suitable than arteries and thrive to accommodate volume changes.

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Blood pressure

Blood pressure in the circulation is mainly due to the action of the heart pump. Action pumping the heart produces pulsatile blood flow, which is carried into the arteries, across the microcirculation and finally, back through the venous system to the heart. During each heartbeat, systemic arterial blood pressure varies between maximum (systolic) and minimal (diastolic) pressure. In physiology, this is often simplified into one value, mean arterial pressure (MAP), which is calculated as follows:

MAP? ^{/ ₃} (BP _he ) ¹ / ₃ (BP _sys )

)

where:

• MAP = Means Arterial Pressure
• BP _he = Diastolic blood pressure
• BP _sys = = Systolic blood pressure

The difference in blood pressure means responsible for blood flow from one location to another in the circulation. The average blood flow rate depends on blood pressure and the flow resistance provided by the blood vessels. Means blood pressure decreases because circulating blood moves away from the heart through the arteries and capillaries due to loss of viscous energy. Mean blood pressure decreases throughout the circulation, although most of the fall occurs along small arteries and arterioles. Gravity affects blood pressure through hydrostatic forces (eg standing), and the valves in the blood vessels, breathing, and pumping of skeletal muscle contractions also affect blood pressure in the blood vessels.

The relationship between pressure, flow, and resistance is expressed in the following equation:

Flow = Pressure/Resistance

When applied to the circulatory system, we get:

CO = (MAP - RAP)/TPR

Where

• CO = cardiac output (in L/min)
• MAP = means arterial pressure (in mmHg), mean blood pressure when leaving the heart
• RAP = right atrial pressure (in mmHg), mean blood pressure on return to heart
• TPR = total peripheral resistance (in mmHg * mnt/L)

A simplified form of this equation assumes a right atrial pressure of about 0:

CO? MAP/TPR

The ideal blood pressure in the brachial artery, where the standard cuff blood pressure measuring pressure, is & lt; 120/80 mmHg. The other major arteries have the same level of blood pressure recordings that show very low disparities between the major arteries. In the innominate artery, the average reading is 110/70 mmHg, the right subclavian artery averaging 120/80 and the abdominal aorta is 110/70 mmHg. The relatively uniform pressure in the arteries indicates that this blood vessel acts as a pressure reservoir for the fluid transported therein.

The pressure decreases gradually as blood flows from the main artery, through arterioles, capillaries until blood is pushed back to the heart through the venules, veins through the vena cava with the help of the muscles. At any given pressure drop, the flow rate is determined by resistance to blood flow. In the arteries, in the absence of disease, there is little or no resistance to blood. Vessel diameter is the main determinant for controlling resistance. Compared to other smaller vessels in the body, the arteries have a much larger diameter (4 mm), therefore the resistance is low.

gradient of the arms (blood pressure) is the difference between blood pressure measured in the arm and that measured in the leg. Usually less than 10 mmHg, but can be increased in eg. aortic coarcation.

src: www.onlinejacc.org

Clinical interests

Monitoring

Hemodynamic monitoring is the observation of hemodynamic parameters over time, such as blood pressure and heart rate. Blood pressure can be monitored either invasively through a blood pressure transducer inserted (providing continuous monitoring), or non-invasively by repeatedly measuring blood pressure with a blowing blood pressure cuff.

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Glossary

ANH

Normovolemic Acute Hododolysis

ANH _u

Total Unit During ANH

BL _H

Maximum Loss of Blood When AnH is Used Before the Homologic Blood Transfusion Needed

BL _I

Loss of Additional Blood Possible with ANH. (BL _H - BL _s )

BL _s

Maximum blood loss without ANH before homologous blood transfusion is required

EBV

Blood Volume Estimates (70Ã, mL/kg)

Hct

Hematocritics Always Stated Here As Fractions

H _i

Initial Hematocrit

H _m

Minimum Safe Hematocrine

PRBC

Packaged Red Blood Cell Equivalent Saved by ANH

RCM

Red cell mass.

RCM _H

Cell Mass Available For Transfusion after ANH

RCM _I

Red Cell Masses Saved by ANH

SBL

Loss of Surgical Blood

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Etymology and pronunciation

The word hemodynamic ( ) uses a combination of the form hemo - and dynamics , so "blood dynamics". The vowels of the syllable hemo - are written varying according to the ae/e variation.

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See also

• Blood hammer
• Blood pressure
• Heart output
• Community Dynamic Cardiovascular System
• Electrocardiometry
• Doppler Esophogeal
• Impedance cardiography
• Photoplethysmograph
• Windkessel effect

src: www.pnas.org

Notes and references

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Bibliography

• Berne RM, Levy MN. Cardiovascular physiology. 7th Ed Mosby 1997
• Rowell LB. Human Cardiovascular Control. Oxford University hit 1993
• Braunwald E (Editor). Heart Disease: Medical Cardiovascular Medicine Book. Ed 5th. W.B.Saunders 1997
• Siderman S, Beyar R, Kleber AG. Electrophysiology of the Heart, Circulation, and Transport. Kluwer Academic Publishers 1991
• American Heart Association
• Otto CM, Stoddard M, Wagoner A, Zoghbi WA. Recommendations for Quantification of Doppler Echocardiography: Reports from the Doppler Quantification Task Force of the Nomenclature and Standards Committee of the American Society of Echocardiography. J Am Soc Echocardiogr 2002; 15: 167-184
• Peterson LH, Pulsatil Dynamic Blood Dynamics, Circ. Res. 1954; 2; 127-139
• Hemodynamic monitoring, Bigatello LM, George E., Minerva Anestesiol, 2002 April; 68 (4): 219-25
• Claude Franceschi; Paolo Zamboni Principles of Venous Hemodynamics Nova Science Publishers 2009-01 ISBN No. 1606924850/9781606924853
• WR Milnor: Hemodynamics, Williams & amp; Wilkins, 1982
• B Bo Sramek: Systemic Hemodynamic and Hemodynamic Management, 4th Edition, ESBN 1-59196-046-0

External links

• The Hemodynamic Society
• Learn hemodynamics
• Velocimetry Image Particle Education (e-PIV) - resources and demonstrations

Source of the article : Wikipedia