Hemodynamics 2 Flashcards

Question

What are the main functions of aorta and arteries?

Answer 1

Aorta (and arteries) develop and withstand high pressures. Stable resistance. Therefore changes in their diameter have minimal effect on blood flow. They convert the pulsatile flow from heart into steady flow through the vascular beds Decreased compliance in artery (stiffness) comes with an increase in pressure. Thus pressures higher in arteries

Answer 2

Aortic compliance is clinically important in the elderly Old artery less compliant/stiffer than young artery At a given MAP, old arteries hold less blood than young For an old artery to hold the same volume of blood as a young artery, the pressure in the old artery must be higher. Systolic BP and pulse pressure in elderly> young Systolic hypertension of the elderly (diastolic can be normal)

Answer 3

Normally, when about 70 ml of blood (I.e. typical SV value) is ejected into the aorta, the aortic pressure rises from about 80 mmHg to about 120 mmHg which is the systolic BP Ejection of 70 ml of blood into an aorta which is less compliant means that the systolic BP rises to much greater values e.g. up to 160 mmHg Diastolic BP MSY be normal (at about 80 mmHg) Therefore, elderly person BP = 160/80 mmHg Condition is called “systolic hypertension of the elderly”

Answer 4

Decreased ventricular compliance leads to increased LVEDPr and vice versa LV hypertrophy leads to decreased compliance and increased LVEDPr Dilated cardiomyopathies lead to increased compliance and decreased LVEDPr

Answer 5

LV hypertrophy—> increased wall thickness —> decreased compliance —> increased LV End diastolic Pr —> decreased filling —> decreased stroke volume —> decreased cardiac output

Answer 6

Sphygmomanometry Inflate cuff to > 180 mmHg Auscultate brachial artery Reduce cuff pressure slowly 1st korotkoff sound is when cuff pressure is just below systolic BP - due to transient spurt of blood into artery = systolic BP Korotkoff sounds grow louder As cuff pressure approaches diastolic BP - artery is open most of the time and sounds get quieter At diastolic BP- sounds disappear

Answer 7

Place cuff on upper arm Automatically inflated to above systolic BP Cuff pressure is released Arterial pulsation causes cuff to oscillate Oscillations Digital reading of systolic BP, diastolic BP and mean arterial pressure in the brachial artery

Answer 8

The ventricle ejects blood into aorta (during systole) faster than it can flow away into the periphery. This causes a steep rise in aortic pressure. About 70% of the stroke volume is stored initially in the elastic arteries during systole. Remaining 30% runs off through the runs off through the peripheral vessels. Max. Pressure in the aorta is the systolic BP = 120 mmHg As blood runs into the peripheral circulation the aortic BP falls. Minimum pressure in aorta is the diastolic = 80 mmHg Pulse pressure= SBP- DBP= 120-80= 40 mmHg

Answer 9

The MAP is the mean pressure in the aorta during a single cardiac cycle Rough approximation: MAP= P(Dias)+ 1/3P(sys-dias) More accurately, at the line where area A= area B Value is about 95 mmHg The MAP is a critical variable Because it is the average effective pressure that drives blood around the circulation

Answer 10

Apex beat is hard almost simultaneously with feeling the radial pulse! When blood is ejected at high pressure into the aorta- a pressure wave is set up which is transmitted along the walls of the arteries Shape of the pressure wave becomes narrower and taller as it proceeds down the arterial tree Pressure wave velocity is faster in stiffer (older) arteries Note: the velocity of blood flow itself is much SLOWER than the pressure pulse wave

Answer 11

1. Stroke volume (pulse pressure inversely proportional to SV) 2. Arterial compliance: pulse pressure inversely proportional to compliance Aorta becomes stiffer and less compliant in old age Elderly: BP 160/80 mmHg “Systolic hypertension of the elderly” Don’t confuse arteriosclerosis and atherosclerosis. Arteriosclerosis is a consequence of ageing. Atherosclerosis is plaque formation. Atherosclerosis = stiffness of the arteries

Answer 12

Age Sleep Exercise (dynamic- increase by 10-40 mmHg, isometric can increase by 100 mmHg) Emotion/stress (increase BO) Pregnancy (BP falls)

Answer 13

Pressure foot > heart Is this in defiance of Darcy’s law Q is inversely proportional to P? Blood flows against pressure gradient

Answer 14

In the supine position- the entire body is at the level of the heart Pressure drop of about 5 mmHg between aorta and dorsal is pedis artery in foot. Pressure in foot= 90 mmHg 🔼P = driving pressure Pressure in veins draining feet is 5 mmHg Pressure falls to 2 mm Hg at RA On standing: add the weight of the column of blood (hydrostatic pressure) to BOTH arterial supply of the feet AND to the veins draining the feet 130 cm (in a 1.8 m individual) of blood is = to an extra pressure of 95 mmHg. (This is a hydrostatic pressure) ``` Arterial pr (in foot)= 90+ 95= 185 mmHg Venous pr(in foot)= 5+95=100 ``` Driving pressure= 185-100=85(same as in feet of a supinevperson ) As long as there is a pressure difference between arteries and veins- blood will flow On standing: subtract the weight of the column of blood (hydrostatic pressure) from BOTH the arterial supply of the head AND from the veins draining the head Subtract 37 mm Hg from the arterial and the venous side The driving pressure is the same as when recumbent

Answer 15

Pressure in the venous compartment Central venous pressure= pressure in thoracic vena cava near RA CVP is important because it determines filling pressure if RV, and thereby SV through the Frank-Starling mechanism RA pr is just slightly below CVP

Answer 16

1. RV contraction is strong: RAP decreased 2. RV contraction weak: RAP increased 3. Increased venous return leads to increased RAP RAP depends on balance between ability of heart to pump blood out into circulation and tendency of blood to flow back into heart

Answer 17

Factors that affect CVP and VR -increased blood volume -increased venomotor tone Both increase RAP Decreased CVP & VR -hemorrhage $venidilation Both decrease Right atrial pressure

Answer 18

Sympathetically induced venoconstriction displaces blood from the peripheral veins into central veins and into RA, thus increased venous return

Answer 19

RAP increases (20- 30 mmHg). CVP then increases as well as capillary hydrostatic pressure. Favoring edema formation

Answer 20

1. Skeletal muscle pump- contraction of skeletal muscles compresses veins rhythmically This displaces blood forward toward heart CVP is maintained, maintaining venous return and EDV Venous Pr in feet is decreased, because blood drains quickly into the muscle veins (pumping action) Capillary Pr is decreased in feet and ankles and tendency to form edema is decreased Remember valves in veins prevent back flow of blood 2. Respiratory pump

Answer 21

Respiratory pump-like bellows Moves chest blood into thorax *physiologically splitting of S2 during deep inspiration During inspiration: venous return increase to right atrium On inspiration decreased intrathoracic pressure leads to thoracic veins being expanded. This causes blood from head fills the vena cava. This causes increased flow to vena cava and increased venous return Another way inspiration increases venous return would be contraction of the diaphragm, leading to increased abdominal pressure, increasing venous return During expiration: decreased venous return

Answer 22

Fick principle Oxygen extraction Law of conservation of mass= [O2] pulmonary flow in artery- [O2] pulmonary flow out (veins) come back for exampke

Hemodynamics 2 Flashcards

(46 cards)