Pavlina Buckova M.D.12/2013Physiology of circulation II

Blood pressurePulse pressureMean arterial pressureBlood flowHemodynamic

pressureexerted by circulatingbloodupon the walls ofblood vesselsdue to the pumping action of the heart

maximum = systolic pressureminimum = diastolic pressure(ARTERIAL) BLOOD PRESSURE

Blood pressure values are generally reported inmillimetres of mercury(mmHg)InvasiveNoninvasive PalpationAuscultatoryOscilometric

Measurement

differences in mean blood pressure are responsible for blood flow from one location to another

physical factors that influence arterial pressure: P = Q. Rvolume of fluid (blood volume)resistance - related to vessel radius, vessel length, blood viscosity, smoothness of the blood vessel walls

mean blood pressure drops over the whole circulation (although most of the fall occurs along the small arteries andarterioles, because total cross sectional area increase = resistance decrease)

(arterial) Blood pressure

Pressure of blood decrases as blood flows to smaller vessels , because total cross sectional area increase = resistance decrease

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How Does Increased Fluid Volume Elevate the Arterial Pressure?Extracellular fluid volume Blood Volume Mean circulatory Filling pressure Venous return Cardiac output Arterial pressure

resistance to flow that must be overcome to pushbloodthrough thecirculatory systemsystemic circulation - systemic vascular resistance(SVR) = total peripheral resistancepulmonary circulation-pulmonary vascular resistance(PVR)

determinant of vascular resistance:small arteriolar(= resistancearterioles) tonepre-capillaryarterioles = autoregulatory vesselsviscosity of the blood

the vessel diameter controls resistance:vasoconstrictionincreases SVR vasodilation decreases SVR

Resistance

Another determinant of vascular resistance is thepre-capillaryarterioles. These arterioles are less than 100m in diameter. They are sometimes known as autoregulatory vessels since they can dynamically change in diameter to increase or reduce blood flow.8

is represented mathematically:R = P/QR is TPRP is the change in pressure across the systemic circulation from its beginning to its end(Mean Arterial Pressure-Mean Venous Pressure)Q is the flow through the vasculature (equal tocardiac output)

Resistance

is not completely understood

the following mechanisms of regulating arterial pressure have been well-characterized:Baroreceptorsin thehigh pressure receptor zonesBaroreceptorsinlow pressure receptor zoneRAAS

Regulation of arterial pressure

in the left and rightcarotid sinusesand in theaortic archdetect changes in arterial pressure

send signals ultimately to themedulla of the brain stem(Rostral ventrolateral medulla)by way of theautonomic nervous system adjusts the mean arterial pressure by altering:both the force and speed of the heart's contractionstotal peripheral resistance. Baroreceptors in thehigh pressure receptor zones

in thevenae cavae,pulmonary veins,atriaresult in feedback by regulating the secretion of ADH,reninandaldosterone

increase inblood volume

increasedcardiac outputby theFrankStarling law of the heart

increasing arterial blood pressureBaroreceptorsinlow pressure receptor zones

long-term adjustment of arterial pressureallows thekidneyto compensate for loss inblood volumeor drops in arterial pressure

activates an endogenousvasoconstrictor- angiotensin II

releases aldosteronin response to angiotensin II or high serumpotassiumlevels aldosterone stimulatessodiumretention and potassium excretion by the kidneyssodium determines the amount of fluid in vessels byosmosis

increase fluid retention indirectly arterial pressure

Renin-angiotensin - aldosteron system(RAAS):

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Renal-Body Fluid System for Arterial Pressure ControlToo much extracellular fluidThe blood volume & arterial pressure riseThe kidneys excrete thr excess extracellular fluidThe arterial pressure back toward normal

Pressure diuresis: An increase in arterial pressure only a few mm Hg can double the renal output of waterPressure natriuresis: An increase in arterial pressure only a few mm Hg can double the renal output of salt

Role of the Kidney in Long Term Regulation of Arterial Pressure?14

How Does Increased Fluid Volume Elevate the Arterial Pressure?Extracellular fluid volume Blood Volume Mean circulatory Filling pressure Venous return Cardiac output Auto-regulationTotal peripheral resistance Arterial pressure

Importance of Salt in the Renal-Body Fluid Schema for Arterial Pressure RegulationExcess salt in the body The osmolality of the body fluid increases Stimulate the thirst center Drink extra amounts of water Increases the extra-cellular fluid volumeThe increase in osmolality in the extracellular fluid Stimulate hypothalamus to secrete ADH The kidney reabsorb water from the renal tubular fluid Increasing the extracellular fluid volume.Increasing extracellular volume Elevation of the arterial pressure.

the pressure difference between the systolic and diastolic pressurespressure that is felt when feeling the pulseproportional tostroke volumeinversely proportional to the compliance of the aorta

(120 80 = 40 mmHg)PULSE PRESSURE

abnormally low if it is less than 25% of the systolic valuethe most common cause of a low (narrow) pulse pressure is a drop in left ventricular stroke volume:significant blood lossshockaortic valve stenosiscardiac tamponadecongestive heart failure Low (Narrow) Pulse Pressure

increases with exercise due to increased stroke volume, simultaneously withtotal peripheral resistancedropshealthy values up to 100 mmHgmost individuals:systolicpressure progressively increasesdiastolicpressure remains about the samevery aerobically athletic individuals thediastolicpressure will progressively fallthis facilitates a much greater increase instroke volumeat a lowermean arterial pressure= enables much greater aerobic capacity and physical performancediastolic drop reflects a much greater fall in total peripheral resistance of the musclearteriolesHigh (Wide) Pulse Pressure

consistently greater than 100 mmHg

AtherosclerosisArteriovenous fistulaChronic aortic regurgitationThyrotoxicosisFeverAnemiaPregnancyEndocarditisRaised intracranial pressure..

Consistently high values

the average arterial pressure during a singlecardiac cycleconsidered to be theperfusion pressureseen byorgansin the bodynormally between 70 to 110mmHggreater than 60mmHgis enough to sustain the organsbelow this number for an appreciable time, vital organs will not get enough Oxygen perfusion, and will becomeischemic

MEAN ARTERIAL PRESSURE

Volume of fluid movement per unit time

F= v.A .F= flow, v= velocity, A= area

when fluid enters narrow section of tube, volume of fluid ( F2) that passes crosssection (A2) must be equal the volume (F1) that had passes cross section A1.The velocity (V2) in narrow section would increase. F1= F2 .. V1. A1 = v2. A2

Velocity of blood decrases as blood flows to smaller vessels , because total cross sectional area increaseAs blood continues toward bigger veins, velocity increase againBLOOD FLOW

Relationship between flow and pressure:Difference in blood pressure are responsible for blood flowPressure of blood decrases as blood flows to smaller vessels , because total cross sectional area increase = resistance decrease

F, Q = flow P = pressure R= resistance

HagenPoiseuille equation

BLOOD FLOW

Flow is influenced by: viscosity of blood, velocity (pressure) of blood and diameter of vesselsDiameter of vessels is influenced by neural (SY, PASY), hormonal (epinephrine, norepinephrin) and local mechanism24

tissues and organs are able to regulate their own blood supply in order to meet their metabolic and functional needslocal regulatory mechanisms act independently ofextrinsic(neural, hormonal) control mechanisms

main factor of local regulation is metabolic mechanism Others: myogenicandendothelial mechanisms

balance between local regulatory mechanisms and extrinsic factorsin vivodetermines the vascular toneand therefore the blood flowLocal Regulation of Blood Flow

Metabolic mechanism: release of vasodilator metabolites, if there is not enought O2Myogenic mechanism: vascular smooth muscle contracts to response to stretch, relaxes with reduction of stretchEndothelial mechanism: NO is released in response to increased shear stress, rapid blood flow

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Local Regulation of Blood Flow

if a vascular bed has a high degree of autoregulation, then the new steady-state flow may be very close to normalDifferent organs display varying degrees of autoregulatory behavior: The renal, cerebral,coronarycirculations - excellent autoregulation skeletal muscle and splanchnic circulations - moderate autoregulation cutaneous circulation - little or no autoregulatory capacity

Local Regulation of Blood Flow

lood flow is matched with the metabolic needsflow through exercising skeletal muscles can be 15 to 20 times greater than through resting musclesresting - 20% to 25% of the capillaries are openexercise - 100% of the capillaries are openlocal, nervous, and hormonal regulatory mechanismsBlood Flow Through Tissues During Exercise

local regulatory mechanism:release of vasodilator substances (lactic acid, carbon dioxide, potassium ions) dilation of precapillary sphincters

nervous regulatory mechanism:sympathetic stimulation hormonal regulatory mechanism:epinephrine released from the adrenal medulla vasoconstriction in the blood vessels of the skin and viscera vasodilation of blood vessels in skeletal muscleselevated heart rate and stroke volumeBlood Flow Through Tissues During Exercise

movement of skeletal muscles compresses veins great increase of venous return to the heart

increased preload and increased sympathetic stimulation of heart

elevated heart rate and stroke volume elevated the cardiac output

blood pressure usually increases by 20 to 60 mm Hg (which helps sustain the increased blood flow through skeletal muscle blood vessels)Blood Flow Through Tissues During Exercise

increases with exercise due to increased stroke volume, simultaneously withtotal peripheral resistancedropshealthy values up to 100 mmHgmost individuals:systolicpressure progressively increasesdiastolicpressure remains about the samevery aerobically athletic individuals thediastolicpressure will progressively fallthis facilitates a much greater increase instroke volumeat a lowermean arterial pressure= enables much greater aerobic capacity and physical performancediastolic drop reflects a much greater fall in total peripheral resistance of the musclearteriolesPulse Pressure during exercise

sympathetic stimulation decrease in the blood flow through the skin at the beginning of exercise

as the body temperature increases - temperature receptors in the hypothalamus are stimulated

action potentials in sympathetic nerve fibers causing vasoconstriction decrease vasodilation of blood vessels in the skin

the skin turns a red or pinkish color

excess heat is lost as blood flows through the dilated blood vesselsBlood Flow Through Tissues During Exercise

CortexFormatio retikularisVMC (vasomotor center)Simpathetic activation of heartElevated heart rate and stroke volumeHigh blood pressureReaction to stress

SHOCK

SHOCKlife-threateningmedicalconditiondue to an inadequate tissue level ofoxygen

progresses by apositive feedbackmechanism

once shock begins, it tends to make itself worse

immediate treatment!!!!

signs of shock are:low blood pressurerapid heartbeat signs of poor end-organperfusion(peripheral shut down)

decreased urine output, and confusion35

SHOCKHypovolemicDistributive (septic,anaphylactic)CardiogenicObstructive

Hypovolemic: bleeding, burns, in children vomiting and diarrheaCardiogenic: MI, dysrithymias, myocarditis, contusio cordis, congestive heart failure, valve failureObstructive: pericarditis, cardiac tamponade, tension pneumotorax, pulmonary embolism36

Four stages of shock InitialCompensatoryProgressiveRefractory

Initial

cells performlactic acid fermentation

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Compensatoryemploying physiological mechanisms - neural, hormonal and bio-chemical mechanisms - in an attempt to reverse the conditionacidosis hyperventilationhypotension release of epinefrin, norepinefrinRAAS is activated and ADH is released to conserve fluid via the kidneysthese hormones cause the vasoconstriction of thekidneys,gastrointestinal tract and other organs divert blood to the heart,lungsandbrain The lack of blood to therenalsystem causes the characteristic lowurineproduction.

Progressive - compensatory mechanisms begin to fail

If the bowel becomes sufficientlyischemic, bacteria may enter the blood stream, resulting in the increased complication ofendotoxic shock41

Refractoryvital organs have failed and the shock can no longer be reversedcell death is occurring and death will occur imminently

much cellularATPhas been degraded intoadenosinein the absence of oxygenadenosine easily perfuses out of cellular membranes into extracellular fluidcells can only produce adenosine at a rate of about 2% of the cell's total need per hourrestoring oxygen is futile at this point because there is no adenosine tophosphorylateinto ATP

Circulation in organs

Circulation in heart

Circulation in brainRelies on continuous blood flow interruption of flow for 5-10s causes loss of consciousnesCerebral autoregulation is very effectiveFlow is determined by factors in brain itselfFlow remains constant in wide range of systemic pressureVasculature is very sensitive to changes in CO2 (increase CO2 vasodilatation)

Circulation in lungsBlood flow is controled locally by alveolar gas tensionO2 and CO2 in alveoli vasoconstriction

Low pressure, low resistance circulationPressure in heart influence pressure in pulmonary circulationHigh pressure in heart/ lungs - pulmonary oedema

Circulation in splanchnicArterial blood flow to liver +Portal system = vessels of inestine and spleen portal vein liver

In responds to incresed metabolic activity (after meal) blood flow doubls in intestine

Participates in regulation of circulating volume and systemic blood pressuref.e.hypovolemia reduced splanchnic circulation redistribution of blood to heart and brain

Liver cirhosis = obstruction of flow in liver congestion in splanchnic

Circulation in skinSkin has small nutrient requirements supply of nutrients is not chief factor in blood flow regulationThe primary function of cutaneous blood flow regulation maitnance of constant body temperature

Two types of resistance vessels:ArteriolesArteriovenous anastomoses

Circulation in skin

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