Systemic Circulaion Flashcards
. Elastic (Windkessel) vessels
. Contain abundant elastic fibers, smooth muscle, and collagen
Resistance vessels
. Arterioles and precapillary sphincter
. High thickness/lumen ration
. Have greatest ability to control blood flow
Exchange vessels
. Capillaries formed by single layer endothelial cells
. Allows efficient diffusion of substrates
Capacitance vessels
. Veins
. Contain abundant collagen fibers and some smooth muscle
. Have small wall thickness/lumen diameter ratio and therefore regulates volume more than pressure
. Velocity of blood flow vs cross sectional area of vascular bed
. Inverse relationship btw velocity of blood flow and the total cross-sectional area of the entire cardiovascular system
. Cross-sectional area in capillaries is greatest and velocity is slowest
Factors controlling arterial pressure
. Physical: arterial blood volume, arterial compliance
. Physiological: CO, peripheral resistance
Pulse pressure (PP)
. Systolic pressure - diastolic pressure
. Aortic bp is pulsatile due to oscillating output of pumping heart
. Arterial pressure rises during ventricular systole and falls during ventricular diastole
Peripheral runoff
. Transfer blood from arterial circulation into capillaries and veins during diastole
Systolic pressure
Peak aortic pressure
Diastolic pressure
. Lowest aortic pressure just prior to ventricular ejection
. Determined by the arterial compliance and residual arterial volume immediately before next cardiac ejection
Mean arterial pressure
. Average pressure of blood perfusing the capillaries during cardiac cycle
.results from area under the pulse curve divided by a time interval
. Approximated by adding 1/3 of the PP to the DP
.
Why does capillary flow continue during diastole even though heart output is cyclic?
. Part fo the energy of cardiac contraction is stored as potential energy by distensibility walls of the aorta and arteries during systole
Windkessel effect
. Elastic recoil of the arterial walls that converts the potential energy into capillary blood flow
What is responsible for generating a large diastolic pressure
. Aortic compliance
. Allows aorta to store as much as 50% of the SV during systole
. Elastic recoil of aorta propels this volume to the periphery generating continuous peripheral blood flow,, reduces ventricular afterload
Distortion of arterial pressure pulse
. Propagation of pressure pulse wave depends on elastic stiffness, radius, and thickness of vessel and density of the blood
. Arterial pulse changes shape and amplitude as it travels down the arterial tree
. Sharp incisura is lost, pulse pressure becomes larger, diastolic waves become apparent, mean pressure falls as pressure wave travels from aortic arch to femoral a.
. Changes result from heterogeneities in geometry and distensibility/elasticity of aa. And partial reflection of pressure waves occurring at any sharp discontinuity in arterial tree
. Reflecting waves interfere w/ upcoming pulse enhancing and dampening different components of pressure wave
Arterial pressure wave travels down aorta at ____ while blood flow wave travels at ____
.pressure: 5 m/s
. Blood: 1 m/s
. Explains why you can feel the peripheral pulse shortly after hearing the 1st heart sound in the precordial region
Measurement of arterial pressure
. Bp measured anywhere in circulation
. Most accurate w/ saline-filled catheter connects to a pressure transducer
. Both systolic and diastolic bp measured using sphygmomanometer
. High velocity blood flow is turbulent and produces korotkoff sounds
Determinants of arterial blood pressure
MAP = (HR X SV) TPR
. CO and total peripheral resistance are major determinants of MAP
. MAP and CO are measured, TPR is estimated
Peripheral runoff
. Qr
. Inversely determined by TPR
. Determines the change in arterial pressure as a direct result from changes in arterial blood volume
. Qh»_space; Qr = inc. arterial pressure
. Qh «_space;Qr = dec. arterial pressure
. These relationships are transient, in steady state Qh (CO) always equals to Qr
Determinants of pulse pressure and systolic pressure
. Determined by SV and aortic compliance and ventricular ejection velocity to a lesser degree
. DeltaP = DeltaV/C
.
Relationship between arterial pressure, TPR, and arterial compliance
. For given TPR, as compliance dec., the arterial pulse pressure widens (inc. in systolic, dec. in diastolic)
Relationship between pressure on SV and compliance
. When SV is dec. (hypovolemia, HF) the systolic pressure becomes smaller and pulse pressure is reduced
. Opposite when SV inc. (adrenergic stimulation, exercise)
. Dec. in arterial compliance causes an inc. in pulse pressure
Determinants of diastolic pressure
. Diastolic pressure is mainly influenced by HR and TPR
. HE determines interval for blood transfer from arterial system to venous system
. TPR determines rate of peripheral run-off
. Both affect volume of blood remaining in arterial system at the end of the diastolic period affecting diastolic pressure
Venus pressure
. Up to 65% of total blood volume is in venous system at one time
. High compliance, low resistance. Low pressure (0-6 mmHg)
. As veins fill, the cross-sectional area of veins inc. even though the perimeter measurement stays the same
Venous return
. Venous blood flow from peripheral veins to the RA
. Equal CO at steady-state
. Pressure gradient for venous return is determined by different btw peripheral venous pressure(pressure form flow of blood from capillaries to veins) and right atrial pressure (central venous pressure)
Effect of posture of venous pressure
. Supine: hydrostatic force form gravity insignificant
. Standing: hydrostatic force prominent and superimposes to other vascular pressures, inc. pressure below reference point
. Perfusion pressure does not change from head to toe or from supine to upright
Effect of posture on venous return
. Supine to standing there is rapid translocation of blood from thorax to lower extremities
. Blood pools in dependent peripheral veins and capillary hydrostatic pressure inc.
. Translocation followed by capillary transduction moving fluid into interstitium of lower extremities
. Blood pools in lower extremities and venous return dec. so CO and MAP transiently dec.
. Mechanism then activated to return levels to normal
Skeletal muscle pump
. Upon standing, leg muscles begin rhythmic cycles of contraction/relaxation causing swaying motion of body’s
. Reflex initiated by stimulation of plantar surface of foot
. Mm. Contractions squeeze veins w/in mm. And drive blood centrally towards the heart
. Veins refill w/ blood during rhythmic relaxation of muscles
. Activity potentiated w/ walking/running
. Pump augments venous return that facilitates ventricular filling and inc. SV
. Pump enhances perfusion of m. Capillary bed by inc. arterial-venous pressure gradient in leg mm.
. Occurs c venous pressure falls during muscular contraction while arterial pressure remains constant
Respiratory pump
. During forced inspiration, intrathoracic pressure is more neg. and intra-abdominal pressure inc. from diaphragm contraction
. The more neg. the intrathoracic pressure causes inc. in venous transmural pressure so central vv. Dilate and central venous pressure dec. while pressure in intra-abdominal vv. Inc.
. Inc. the pressure gradient to favor venous return from peripheral vv.
. Inc. in venous return inc. ventricular filling and inc. SV
Enhanced w/ exercise
Mean circulatory pressure
. Equilibrium pressure when pressure in aa. And vv. Equilibrate during cardiac arrest
. Function of both blood volume and vessel compliance
. Normal is approx. 7 mmHg
Vascular function curve
. Defines the changes in CVP that are caused by changes in CO
. At a constant TPR, an inc. inc CO will dec. CVP, occurs bc of transfer of blood from venous circulation to arterial circulation
How CO affects vascular function curve
. Changes in CO changes arterial pressure and venous pressure
. Acute HF occurs occurs as result of an astute MI and is accompanied by dec. in arterial bp and an inc. in venous bp
How blood volume affects vascular function curve
. MCP will inc. as blood volume is expended
. MCP dec. as blood volume dec.
Venomotor tone affect on vascular function curve
. MCP will inc. as tension exerted by vascular smooth mm. Surrounding veins inc.
. MCP will dec. as tension exerted by smooth muscle surround the vv. Dec.
Affect of peripheral resistance on vascular function curve
. Gradual changes in contractile state of arterioles don’t significantly alter MCP
. Sudden inc. in TPR causes greater blood volume to be retained in arterial system
. Inc. in arterial blood volume is accompanied by equivalent dec. in venous blood volume
. At any CO, an inc. in TPR will dec. venous pressure w/ no change in MCP, the curve is rotated counter clockwise
. A dec. in TPR at any CO will inc. venous pressure and rotate the vascular function
Contractility affect on cardiac function curve
. Inc. in ventricular contractility shifts cardiac function curve upward
. Dec. in contractility will shift the curve downward
How afterload affects cardiac function curve
. Inc. in ventricular afterload (inc. TPR) shifts curve down
. Dec. in afterload shifts curve upward
.
Equilibrium point
. Intersection between vascular function curve and cardiac function curve
. Represent values of CO and CVP at which a system operates
. Only transient deviations possible
How myocardial contractility affects cardiovascular function curve
. Inc. in myocardial contractility shifts curve upward w/ no effect on vascular function curve
. During periods of inc. contractility CO will inc. slightly and CVP will dec. slightly
. Dec. in contractility will shift functions urve down, w/ no effects on function curve
. During periods of inc. contractility CO will dec. slightly and CVP will inc. slightly
How blood volume affects cardiovascular function curve
. Inc. in blood volume shifts function curve right w/ no direct effect on curve, inc. CO and CVP
. Dec. in blood volume shifts curve left w/ no direct effect on curve, dec. CO and CVP
Venootor tone effect on cardiovascular function curve
. Inc. in tone will shift curve right, inc. CO and CVP w/ no direct effect on curve
. Dec. in tone will shif curve left w/ no direct effect on curve, dec. CO and CVP
Peripheral resistance effect on cardiovascular function curve
. Inc. in resistance rotates vascular curve counterclockwise and shift CO curve downward dec. CO w/ no changes in CVP
. Dec. in resistance rotates vascular curve clockwise and shifts cardiac curve upward, inc. CO w/ no major changes in CVP
Heart failure affects on cardiovascular curve
. Pumping capability of heart is impaired and myocardial contractility is dec.
When acute: cardiac curve shifts down, blood volume changes do not occur immediately
. When chronic: cardiac curve shifts down and vascular curve is shifted right indicating inc. in blood volume
. Moderate degrees of Hf, CVP is inc. but CO may be normal
. Severe HF, CVP is inc. and CO is decreased
