CVS Session 5 (Lecture 5.2) Flashcards
What is the formula for cardiac output?
CO = SV . HR
What is the normal SV and HR for a 70kg man?
80ml and 60bpm
Describe the flow of blood as the heart pumps?
Heart ejects blood intermittently - pulsatile flow
Describe the flow of blood though arteries with distensible walls.
In systole, arteries stretch
More blood flows in than out
Pressure does not rise so much
Arteries recoil in diastole, flow continues through the arterioles
What factors affect the systolic pressure?
Force of contraction
TPR
Stretchiness of the arteries (increased stiffness increases peak pressure)
What factors affect the diastolic pressure?
Systolic pressure
TPR
Which pressure is the better indicator of TPR?
Diastolic pressure
What is a pulse pressure?
Difference between systolic and diastolic (around 40 mmHg)
What is the formula to calculate average pressure?
AVP = DP + 1/3 (PP) becasue diastole is 2/3 of heartbeat
What are the resistance vessels?
Arterioles and pre-capillary sphincters
What is vasomotor tone?
Tonic contraction of VSMCs
What do vasoconstriction and vasodilatation do to resistance?
VC - increases resistance to flow
VD - decreases resistance to flow
What factors affect the contraction of VSMCs?
Sympathetic branch of ANS controls vasomotor tone
Tone is antagonised by vasodilator factors e.g. H+, K+, adenosine
What is reactive hyperaemia?
Increase in blood flow to a part of the body.
How is reactive hyperaemia brought about?
Regulatory process mostly e.g. blood supply cut off to arm.
Metabolically active produce vasodilator metabolites e.g. H+, K+, Adenosine which accumulate in vessels due to no blood flow.
These act to relax VSMCs to cause vasodilatation of blood vessels. This decreases the resistance of these vessels to a very low level such that upon reuturn of blood flow, flow is very high through the vessels.
How is reactive hyperaemia resolved?
High flow of blood through low resistance vessels that have been dilated by metabolites washes them away causing VSMCs to contract.
What is the relationship between metabolism and blood flow?
Metabolism increases, more metabolites produced
Concentration increases of metabolites, vasodilatation occurs
Washes away metabolites from increased blood flow from low resistance
More metabolism = more blood flow
Describe autoregulation for local blood pressure and flow.
If supply pressure changes, blood flow to a tissue will change.
Which will change [metabolite]
Alter the resistance of arterioles so blood flow returns to an appropriate level for metabolism
What is the relationship between the TPR and blood flow?
TPR is inversely proportional to the body’s need for blood flow.
What determines the volume of blood in veins?
Pressure
The pressure in veins depends on…?
Balance between flows in from the body and out from the heart (increase heart pumping decreases venous pressure))
What is central venous pressure? What does it fill and what does it depends on?
1) Pressure in great veins
2) Fills heart in diastole
3) Depends on: return of blood from the body
pumping of the heart
gravity & muscle pumping
What affects superficial veins?
Gravity
