Hemodynamics (PDF)

Hemodynamics Hemo = Blood 18 - Hemodynamics Dynamic = Changing Hemodynamics = Ways that blood “changes”...

Hemodynamics Hemo = Blood 18 - Hemodynamics Dynamic = Changing Hemodynamics = Ways that blood “changes” Direction, speed, shape, etc. The study of blood moving through the circulatory system Flow Velocity X-Axis: Time Doppler is used to visualize “Velocity” Y-Axis: Velocity In this image, the Velocity Aka “Volumetric Flow Rate” information is displayed Speed + Direction (Speed + Direction) as a graph How much of a liquid is passing a Speed = How Fast certain point, per unit of time mph, 100 km/s, m/s, cm/s Ex: 20 mL/s or 100 L/hr. or Direction = Which way it’s going 25 mL/min Proximal, Distal (volume/time) Toward the Tx, Away from the Tx Velocity = 125 cm/s & Toward Tx Faster = Further away Toward Tx: Above baseline Away from Tx: Below Baseline from Baseline Types of Flow: Phasic Common Femoral Vein Blood moves with variable velocity Reduced acceleration and deceleration Mid Femoral Vein Looks like “waves on the ocean” Popliteal Seen in Venous Flow Vein Primarily influenced by Respiration (Pressure Differences due to Respiration) Posterior Tibial Vein Phasic flow visualized at different levels of the lower extremity Types of Flow: Pulsatile Pulsatile flow visualized at different levels of the Extracranial Arterial Blood moves with a variable velocity Circulation Profound acceleration and deceleration rates The most noticeable thing about this flow Capable of changing directions mid-flow Primarily influenced by the cardiac cycle By pressure changes within the Ventricles of the heart Just remember “Pulse” ; like taking someone’s “pulse” Represents Arterial Flow Types of Flow: Steady Laminar Flow When fluid moves at a constant When a fluid (blood) travels through a rate tube/cylinder (blood vessel; artery or vein) it tends to travel in discreet Layers. No variation in velocity Blood Vessel = an Artery or a Vein If seen in the body, it doesn’t last Discreet = Individual, unique; can be long (or isn’t normal) considered independently of its peers Layers = Think sheets of paper laid on In veins when respiration is ceased top of each other, cards in a deck, etc. (breath held) or partially occluded by a blood clot Laminar; like “Laminate” – Layers of Steady vein flow in a patient with plastic over paper a Deep Vein Thrombosis Secondary to particularly severe occluding much of the Common Laminate floorboards are Stenosis Femoral Vein in the Leg Laminar Flow is Normal made of layered material! Laminar Flow: Plug Plug Flow (Laminar) Laminar Flow: Parabolic Occurs when all the layers are Occurs when the layer velocities begin to differ as they travel travelling at roughly the same velocity The outer edges of the blood stream Parabolic Flow (Laminar) travel slower Happens at the “beginning” of a The inner core of the blood stream vessel or right after blood changes travels faster direction Creates a “Parabolic” curve ; a Turbulent Flow (non-Laminar) “Parabola” Bullet Shape This is the state of most flow within the body Turbulence Turbulence Pathologic Turbulence due to Mitral Valve Stenosis The opposite of Laminar Flow If seen in normal circulation, generally associated with areas of When the layers of flow separate, increased diameter / radius and the normal pattern of flow becomes disturbed / chaotic Note: Normal Turbulence due Flow separates into spirals: Stenosis = The abnormal to the diameter increase Eddies / Vortexes narrowing of an opening or of the Carotid Bulb Notice the spiral pathway Momentum and pressure differences “eddies” will maintain forward flow, but there is no uniform shape or pattern Aneurysm = The pathologic dilation (increase in diameter) of a Generally seen secondary to structure Pathology Stenosis, Aneurysm, etc. “Ballooning out” Turbulence: Reynold’s Number Reynold’s Number - Fluid Density Mathematical equation that determines Fluid Density = The chemical the probability that flow will become density of the fluid turbulent What it is composed of Reynolds # = (Fluid Density x Flow Speed x Tube Radius) / Fluid Viscosity In the body, this does not change. Blood, generally, is blood. If “Reynolds” ever exceeds 2000, turbulence will occur This number stays constant Reynold’s Number - Tube Radius Reynold’s Number - Fluid Viscosity Tube Radius = How large the blood vessel or How “thick” a fluid is valve is Changes frequently Not constant How much that fluid resists Blood vessel radius changes with physiologic changes to its shape, dimension or changes Turbulence seen position in an Abdominal Different places in the body are differently sized Aortic Aneurysm Increased Viscosity = Increased Friction between the Laminar So, depending on where we evaluate for Layers turbulence, this changes as well Note: Radius = measured from center of Increased Viscosity = Thicker Fluid circle to the edge of the circle Diameter = 2x the Radius; Measured edge- Syrup is more Viscous than Water to-edge of a circle Turbulence Variables: Direct vs Inverse Turbulence Sounds Direct Relationship; More likely to As flow becomes turbulent, it creates vibrations that can be detected as sound be turbulent Audible by the human ear, detectable by Fluid Density (doesn’t change) human touch Flow Speed By Sound: Tube Radius Murmur Bruit (brew-y) Inverse Relationship; Less likely to By Touch: be turbulent Thrill Fluid Viscosity (doesn’t usually Echo Notes: change) “Murmur” is often used to describe any type of abnormal cardiac noise. Turbulence is seen in stenosis due to the In Stenosis; it’s the turbulence caused by the increased flow velocity and increased narrowed valve vessel diameter distal to the narrowing In Regurgitation; it’s the turbulence caused by the (usually narrow) leak in the valve Pressure Gradients Pressure Gradients Pressure = the relative density of a The greater the Pressure Gradient, fluid, how tightly compacted its the FASTER the fluid will flow particles are The greater the difference between Gradient = a difference in two values high and low, the faster it will attempt to equalize Pressure Gradient = The amount of difference between an area of High Note: In the physical world, all Pressure and an area of Low Pressure objects are attempting at all times to be set into a mode of “Equilibrium” Why is this important? Equal forces being exerted in all directions, at all times Fluid flows from areas of high pressure to areas of low pressure No exceptions This almost never happens, so things are always “Doing Something” Note: Fluid = Anything that Flows “Nature Abhors a Gradient” Abhor = Hates Liquids and Gases; Air and Blood Pressure Gradients: Example Types of Energy Pressure Gravity During the Cardiac Cycle, the Left Ventricle begins to contract (3) types of energy are associated This reduces the overall size of the ventricle, with blood flow: condensing the blood inside Kinetic The pressure within the blood begins to increase Pressure As soon as the pressure in the blood exceeds the Gravitational pressure outside the ventricle, the blood starts looking for a way to equalize the pressure Kinetic Looking for areas of lower pressure to go into Usually the only option is out of the ventricle, in the aorta Blood moves from the ventricle into the aorta, and continues searching for lower and lower pressure areas to extend into… Leading to blood going everywhere throughout the body Kinetic Energy Pressure Energy Associated with moving objects A type of Stored / Potential Energy The proximity of particles within a medium or object, and how much they want to Kinetic Energy is determined by: change that situation Object Mass (m) Proximity = How close things are to each other The Velocity of the object (v) Ex: During systole, a pressure gradient is Both have Direct Relationships formed between the High Pressure in the with Kinetic Energy Ventricle and the Low Pressure in the body. The greater the difference between these Ex: a heavy, fast-moving object will two, the greater the building Potential Energy have MORE Kinetic energy The Potential Energy of the Gradient wants to convert into the Kinetic Energy of moving. Gravitational Energy Energy Loss Another form of Stored / Potential Energy As blood flows through the Associated with the natural phenomenon of Gravity, circulation (the body), Kinetic and the pull of the Earth toward its center. energy is lost in (3) ways: Viscous Loss Closely associated with “Height” or distance from the ground and the Weight of the object travelling Frictional Loss We will deal with this particularly when we compare Inertial Loss the source of the Pressure Gradient (the heart) with its positional comparison to the other parts of the body… Ex: If a body part is above or below the heart Gravitational Potential Energy Above the Heart: The Heart works against Gravity being converted into Kinetic Below the Heart: Gravity helps the Heart work Energy is the primary motive force behind Roller Coasters! Note: When a body part is placed “below” the heart, IE; between the heart and the ground, it is called “Dependent Positioning” Viscous and Frictional Losses Inertial Loss Viscous Loss Relates to the tendency of a fluid Friction that happens within the fluid, to resist changes to its Velocity between the layers Occurs secondary to (3) events of Frictional Loss flow: Friction that happens along the edges Pulsatile Flow: the changing of blood of the vessel, creating parabolic flow velocity and direction Phasic Flow: the changing of blood velocity (less pronounced) Changes secondary to Stenosis Specifically, Turbulence Think of Inertia as Flow Attenuation Bernoulli’s Principal Bernoulli’s Principal The Bernoulli Principal: (1) The pressure within a fluid is Describes the relationship inversely related to the velocity of between Fluid Velocity and Fluid the fluid Pressures Read: WITHIN a fluid “With a steady flow, the sum of all Do not confuse this statement with forms of energy are the same pressure gradients that influence everywhere” fluid motion (Pressure Gradients describe the What does this mean, functionally? outside forces of pressure) Changes in one aspect of flow will result in equal, opposite changes What this means: to other aspects of the flow If a fluid increases its velocity, the We will be dealing specifically pressure within that fluid drops with changes to Velocity, Vessel This is also expressed in the Venturi Radius and Pressure Gradients. The Bernoulli in question Effect Bernoulli’s Principal 90 mmHg Poiseuille’s Principal A (2) The greater the difference of a “Flow within a closed system will pressure gradient, the greater the 120 mmHg remain constant, despite changes within the system” velocity of fluid motion B We’ve discussed this many times so The circulatory system is a closed far system, there is no normal external Fluids move from areas of high 140 mmHg outlet. pressure to low – and the greater the difference between them the faster C the fluid moves 180 mmHg Changes to the radius of a vessel will result in changes to the flow velocity Increases to vessel radius will decrease What are the Pressure Gradients for velocity the Red, Blue and Green systems? Decreases to vessel radius will increase Match each vessel with a corresponding velocity velocity at the purple mark: 1. = 1.2 m/s : Which would create the fastest flow? 50 mmHg Vessel Radius and Velocity are Inversely 2. > 1.2 m/s : 60 mmHg Related 3. < 1.2 m/s : Poiseuille’s Principal 2 cm2 Pressure Changes Due to Respiration Resistance describes the “ease” of Fluid responds to changes in pressure flow from areas of High Pressure into (pressure gradients) Areas of Low Pressure Blood and Air are both Fluids High Resistance = Difficult to flow Low Resistance = Easy to flow 1 cm2 When we breathe, a flat muscle (the Diaphragm) that stretches laterally (horizontal) across the body flexes Up The greatest determining factor of or Down. Resistance is Size (Radius, Area, etc.) Small Area = Higher Resistance Inspiration = Diaphragm flexes down Large Area = Lower Resistance (inhale) (breathe in) 3 cm2 The trunk of the The greater the resistance, the harder Expiration = Diaphragm flexes up body visualized as it is for blood to move from the Which of these Aortic Valves (exhale) (breathe out) a block schematic gradient source to the gradient’s would create the greatest destination Resistance against the The Diaphragm separates the Left Ventricle of the Heart? Thoracic and Abdominal Cavities Pressure Changes Due to Respiration Hydrostatic Pressure The Motion of the Diaphragm changes the The effect of gravity on a column, pressures within these cavities pool or container of fluid Inspiration = Decreased Thoracic Pressure = Increased Abdominal Pressure We will be discussing the effect of Expiration = Increased Thoracic Pressure gravity on blood, pushing against = Decreased Abdominal Pressure the walls of the vessels, particularly in the lower extremity The pressure effect on the Thoracic Cavity – or other “dependent” positions. creates pressure gradients that allows Air to move in and out of the body (through the mouth) This is what is meant when This pattern also effects blood flow “columns of blood” are discussed Column = Vertically oriented cylinder Because blood is also a fluid, and pressure Imagine the Veins / Arteries of the applied to the cavities to move air also moves the blood abdomen, legs, etc. as vertical cylinders Hydrostatic Pressure Venous Hemodynamics Hydrostatic Pressure describes the Veins are thin-walled and collapsible force being exerted by the fluid on the walls of these columns They can change their size / shape The “weight” of the fluid depending on the amount of blood contained within Imagine the weight of fluid in an above-ground swimming pool, being Low Volume = Hourglass Shape exerted on the walls of that swimming pool High Volume = Circle / Oval The weight of water inside a glass, pushing against the walls This causes a paradox during high- volume flow The greater the Volume of blood in a Column, the greater the Hydrostatic Paradox = when it seems like one Pressure thing should happen, but the opposite happens instead Venous Hemodynamics Venous Hemodynamics The increase in blood volume dilates Blood always moves from an area of High the veins Pressure to Low Pressure. This is still true with Vein flow This increase in radius decreases the resistance in the vein It is required that there be an Increased Pressure Distal to the heart to move blood Decreased Resistance in the vein from the body back into the heart allows easier flow (back to the heart) This is accomplished in (3) ways: The Paradox Being: one would Reduced Pressure in the Right Ventricle assume that increased volume would increase Hydrostatic Pressure and Variations of Pressure due to Respiration make flow more difficult. It does the opposite. Flow becomes easier. Increased Pressure in the Calf Venous Hemodynamics Venous Hemodynamics Right Ventricular Pressure Decrease: Increased Pressure in the Calf: During the cardiac cycle, the heart moves through (2) main phases: The calf is oriented with 2 large muscle Systole = Time of Increased Pressure within the groups on either side (medial/lateral) Ventricle Diastole = Time of Reduced Pressure within the Ventricle Between them, several large veins run from the foot and other muscles (think of it like respiration) During Diastole, the ventricle expands. This The muscle groups are responsible for reduces the pressure within the ventricle flexing the toes forward Blood flows from outside the ventricle, to inside the ventricle When they flex forward, they squeeze the veins This has the same effect on the body’s veins as sipping from a straw This creates an area of high pressure, urging blood to move proximally Venous Hemodynamics Variations in Pressure due to Respiration: As the diaphragm flexes superiorly and inferiorly, it creates areas of high and low pressure Blood will move from areas of high pressure into areas of low pressure When the Thoracic Pressure Drops (during Inspiration) blood from the Upper Extremities (arms, head) will increase flow toward the heart When the Abdominal Pressure Drops (during Expiration) blood from the Lower Extremities (legs) will increase flow Notes about Respiration Supine vs Standing: Hydrostatic Pressure During inspiration, the diaphragm will Supine = Laying flat on your back press down on the Inferior Vena Cava (The Vein companion to the Abdominal When a patient is truly supine, the Hydrostatic Aorta) Expiration Pressure is equalized No portion of the Patient’s body is above or This will create a temporary stenosis below the heart in the vein, preventing much blood from travelling past Gravity’s effect on the patient is equal throughout the body This helps to further increase the This is primarily noticed when comparing effect of the increased pressure in pressures within the circulation the abdominal cavity during Arm vs Leg, etc. expiration Inspiration When a patient is standing, creating Dependent Positioning, blood pressures will vary between The increased volume of blood in the dependent and non-dependent segments. abdominal cavity increases the Above the Heart: Reduced pressure gradient, resulting in more Below the Heart: Increased flow  Notice the blood pressure increases as the Hydrostatic In the supine patient, the Pressure increases blood pressures are equalized