Hemodynamics

Question 1

What factors affect the distribution of blood flow (cardiac output)?

Answer 1

• resistance: greater resistance will impede the distribution of blood flow
• pressure: blood moves from high to low pressure
• heart rate
• stroke volume

Question 2

What is blood pressure?

Answer 2

• pressure exerted on the walls of a vessel
• generated by ventricular contraction
• presence of water in blood puts outward stretch on arteries

Question 3

How does blood pressure change during the cardiac cycle?

Answer 3

• blood pressure is highest in the aorta
• diastolic and systolic pressures vary from 80-120mmHg
• pressure waves dampen as you move towards capillary system
• as you get further from the left ventricle, pressure drops
• pressure is almost 0 when entering the right atrium
• pressure is about 35mmHg entering the capillaries
• with decrease in blood volume over 10% BP drops
• water retention increases BP

Question 4

How do cross sectional area and velocity of blood movement relate?

Answer 4

• as you move away from LV, cross sectional area increases as more branches, etc. of the vasculature occur
• speed of blood movement decreases with increased cross sectional area
• slow movement in the capillaries to allow for gas exchange

Question 5

What are the systolic, diastolic, pulse, and mean pressures?

Answer 5

• systolic: highest pressure, ventricular systole
• diastolic: related to ventricular diastole
• pulse pressure: difference between systolic and diastolic, is a good indicator of CV health, small changes in systolic and diastolic pressures can increase pulse pressure
• mean arterial pressure: want to maintain this pressure, average pressure during entire cardiac cycle

Question 6

What are Korotkoff sounds?

Answer 6

• when taking a blood pressure, cuff compresses brahcial artery
• when cuff is released, Korotkoff sounds are produced from the initial blood coming back into the artery
• this is measured as systolic pressure
• more blood will flow through and flow will become laminar
• when sounds are no longer heard, that is measured as diastolic pressure

Question 7

What are pulse points?

Answer 7

• areas where we can compress the vessel against a bone or another structure
• dorsalis pedis often checked during surgery to make sure there is adequate perfusion to lower extremities

Question 8

What equation represents mean arterial pressure?

Answer 8

-mean ABP= diastolic pressure +1/3 pulse pressure

or

-mean ABP= cardiac output x total peripheral resistance

Question 9

What factors affect blood pressure?

Answer 9

• cardiac output (HR, SV)
• blood volume (blood loss- affects cardiac output and BP because this decreases venous return which affects afterload/preload, water retention)
• peripheral vascular resistance

Question 10

What is an equation representing peripheral vascular resistance?

Answer 10

• pressure=flow x resistance
• flow=pressure/resistance

Question 11

What is vascular resistance?

Answer 11

• blood close to wall of vessel causes friction
• friction can be influenced by blood vessel radius, blood viscosity, blood vessel length
• smaller vessel=increase in vascular resistance
• blood viscosity dependent on % of RBCs and lower water volume
• increase in viscosity=increase in resistance
• increase in BV length=increase in resistance
• arterioles control BP by changing diameter
• systemic vascular resistance aka total peripheral resistance

Question 12

What factors can increase BP?

Answer 12

Question 13

How is BP regulated?

Answer 13

Short term:

• neural: baroreceptor reflexes, chemoreceptor reflexes located in internal carotid arteries in carotid sinus/carotid bodies and aortic arch
• hormonal: EP, NE, ADH, ANP (atrial natriuretic peptide), renin-angiotensin-aldosterone system (longer term)

Question 14

Describe the chemoreceptor/baroreceptor reflexes

Answer 14

• measuring changes in chemistry of blood (eg. oxygen, CO2, acidotic)
• stimulates cardiovascular centre to increase sympathetic stimulation which increases vasoconstriction and BP
• baroreceptors get stretched with increase in pressure which then signal through CNs to medulla oblongata (carotid signals through CN9, aorta signal goes through CN10)
• stimulates parasympathetics to decrease BP

Question 15

Describe baroreceptor reflex for low blood pressure

Answer 15

Question 16

What is orthostatic hypotension?

Answer 16

• fainting (syncope) when standing quickly
• baroreceptors work slower in the elderly or others where this might be a problem

Question 17

Describe the baroreceptor reflex to an increase in BP

Answer 17

Question 18

Describe short term hormonal regulation of BP

Answer 18

• with sympathetic stimulation, nerve impulses fire and get stimulation of adrenal glands
• increase of EP and NE in blood
• increase HR and force of contraction
• vasoconstriction doesn’t happen everywhere; may occur in skin and abdominal region
• may still have vasodilation in cardiac and skeletal tissue

Question 19

Describe long term hormonal regulation of BP

Answer 19

• ADH (vasopressin): released from posterior pituitary, released in response to dehydration/decrease in blood volume, increases renal water retention and systemic vasoconstriction ->increases BP
• ANP: released by cells in atria, causes vasodilation, promotes renal loss of salt and water, lowers BP
• RAA system:

Question 20

Michael was in a car accident and sustained a severe injury to his left leg. While waiting for the paramedics to arrive he lost a lot of blood. Paramedics noted: rapid resting heart rate, weak pulse, cool/clammy skin, sweating. What is the diagnosis?

Answer 20

-hypovolemic shock

• sympathetic stimulation causes increase in HR
• blood loss causes decrease in venous return and increase in HR causes short filling time leading to a decrease in end diastolic volume–> weak pulse

-cool/clammy skin: vasoconstriction of vessels towards skin, clamminess is from sweat glands

Question 21

What is shock?

Answer 21

• failure of CV system to deliver enough O2 and nutrients
• inadequate perfusion
• cells forced to switch to anaerobic respiration
• lactic acid builds up
• cells and tissues become damaged and die
• system is designed to maintain mean arteriole BP
• compensation mechanisms: activation of RAA, secrete antidiuretic hormone, activate sympathetic nervous system, release of local vasodilators

Question 22

What can occur from left sided heart failure? Right sided heart failure?

Answer 22

• left side of heart can’t function properly
• can get fluid accumulation in the lungs
• right sided: accumulation in feet

Question 23

What is blood flow?

Answer 23

• volume of blood that flows through any tissue in a given period of time (mL/min)
• CO=HRx SV (total blood flow)

Question 24

Consider the baroreceptor reflex. Which of the following will increase in response to a rise in arterial blood pressure?

a) parasympathetic activity to the heart
b) cardiac output
c) vasoconstriction of blood vessels
d) heart rate
e) adrenal secretion of EP

Answer 24

a) parasympathetic activity to the heart

Question 25

Alex, a 21 year old university student, feels dizzy and almost faints after he jumps quickly from his bed on the morning of his final exam. What caused Alex to feel dizzy and almost faint after he jumped out of bed quickly?

Answer 25

• orthostatic hypotension
• very quick drop in BP so as a result there is inadequate supply of blood to the brain
• decreased oxygen to brain as a result which causes dizziness and almost fainting

decrease in BP–> decrease in baroreceptor stretch –> decrease rate of nerve impulses–> increase sympathetic, decrease parasympathetic, increase of EP and NE–> increase in CO from increase in SV and HR and increase in TPR from vasoconstriction of blood vessels

-this acts to restore mean arterial BP