Cardiovascular System Design

Question 1

two systems in series

Answer 1

• pulmonary and systemic
• systemic blood flows entirely into and out of the pulmonary circulation driven by the right heart pump
• blood is driven into the systemic circulation by the left heart pump
• flow in the systemic circulation is divided between tissues in parallel
• internal environment is the distribution of body fluids between blood, intracellular compartments, interstitial compartment

Question 2

general scheme of ciculation

Answer 2

• distribution of blood volume
• different flow rates through tissue
• comparison of flow and oxygen usage- not always matching-excess capacity
• resistance
• capacitance (storage)
• high pressure/low pressure system (low is venous)
• supply and reservoir (50-60% in venous)
• concept of capillary beds, but still closed

Question 3

distribution of blood in the circulatory system

Answer 3

• pumped into the aorta and consecutively passes through many different vessels before it returns to the right heart
• at any one time, 84% of blood in systemic circulation with the remainder in heart (7%) and pulm vessels (9%)
• venous blood contains >50% total blood
• vessels are distinguished by physical dimensions, morphological characteristics, and function
• all are lined with contiguous sheet of endothelium, cells, including heart chambers and valve leaflets

Question 4

heart as a pump key concepts

Answer 4

• 4 chambered pump with valves, names/anatomy
• no direct connection normally between right and left heart pumps
• myogenic
• central control of BP and contractility
• systole/diastole
• starlings law of heart
• beating depends on external calcium
• electrophysiology

Question 5

requirements for effective cardiac fucntion

Answer 5

• efficient ventricular pumping
• contractions of individual cells must occur at regular intervals and be synchronized-not arrhythmic
• valves must be open fully-not stenotic
• valves must not leak- not insufficient or regurgitant
• muscle contractions must be forceful-not failing
• ventricles must fill adequately during diastole

Question 6

cardiac output

Answer 6

• quantity of blood per unit time pumped into aorta by heart
• also equals quantity of blood per unit time that flows through the circulation
• stroke volume times heart rate
• normal is 5L/min
• determinants:
• ventricular preload (length of muscle at onset of contraction)
• ventricular afterload (tension of muscle during contraction
• myocardial contractility

Question 7

effects of things on CO

Answer 7

• sleep, mod change in temp- no change
• anxiety/excitement- 50-100%
• eating-30%
• exercise- up to 700%
• high temo
• preg
• epi
• sitting or standing- down 20-30%
• rapid arrhythmias down
• heart disease down

Question 8

starlings law

Answer 8

• CO determined by rate of blood flow into the heart from the veins, so called venous return
• peripheral tissue controls local blood flow, all blood back via veins/right atrium
• the heart automatically pumps that blood into arteries
• heart stretches from increased volume of inflowing blood and contracts with greater force therefore pumping a greater quantity of blood
• the larger the end diastolic volume, the larger the stroke volume

Question 9

blood circulation occurs through arteries and veins

Answer 9

• artery >50 um
• ateriole 20-50 um
• metarteriole 10-15 um
• cap bed
• venous end of cap 9 um
• collecting venule
• small venule 20 um
• veins 0.5-3 cm
• arteriolar vasoconstriction via smooth muscle leads to increase in peripheral resistance
• venous vasoconstriction via smooth muscle leads to reduced venous volume and decrease in CO

Question 10

aorta

Answer 10

• 2.5 cm d
• 2 mm thick
• 1
• 4.5 cm2

Question 11

arteries

Answer 11

-0.4 cm d
-1 mm thick wall
-160 of them
20 cm2

Question 12

aterioles

Answer 12

30 um d
-20 um wall thickness
5 x 10^7 of them
200 cm2

Question 13

cap

Answer 13

• 5 um d
• 1 um wall thickness
• 10^10 of them
• 4500 cm2

Question 14

venules

Answer 14

70 um d
-7 um wall
10^8 of them
4000 cm2

Question 15

veins

Answer 15

-0.5 cm d
0.5 mm wall
200 of them
40 cm2

Question 16

veae cavea

Answer 16

3 cm d
1.5 mm wall
2 of them
18 cm2

Question 17

properties of flow throughout the circulation

Answer 17

• equal flow through each stage of the system
• heart acts as a generator of constant pressure head rather than as a generator of constant flow
• flow, pressure, resistance, volume
• see pictures!

Question 18

blood pressure vs air

Answer 18

• P=pxgxh
• force per unit area
• medical BP measured relative to atm pressure

Question 19

MAP

Answer 19

• average pressure over the entire cardiac cycle
• DP+1/3 (SP-DP)=DP+1/3PP
• PP=SP-DP=pulse pressure- systolic-diastolic

Question 20

systolic pressure

Answer 20

-peak reached during ejection

Question 21

diastolic pressure

Answer 21

lowest during diastole

Question 22

dichrotic notch

Answer 22

backfilling of aortic valve as it closes

Question 23

BP through circulatory system

Answer 23

• high in arteries and fluctuates with heart
• very little in caps and veins
• flow starts high, decreases in caps and rises again

Question 24

BP measurement

Answer 24

• external cuff pressure means no blood flow
• as pressure is lowered, flow is restored
• pulsatile pressure changes causes turbulence and generates sound
• as cuff pressure further reduced, higher turbulence and sounds
• below diastolic, flow silent and laminar

Question 25

direct method of BP measurement

Answer 25

• arterial pressure measured via catheter passed in a retrograde fashion for pressures in arteries, aorta and L vent
• venous catheter for veins, R atrium and R vent
• not possible to measure pulm venous and L atrium- need capillary wedge pressure

Question 26

wedge pressure

Answer 26

• pulm artery cath
• lumen is open at distal end
• balloon inflated and pressure falls downstream of balloon
• vascular pressure equilibrates beyond balloon and the wedge pressure at the cath tip is a measure of pulm venous and L atrium
• approximates L ven end diastolic pressure

Question 27

determinants of MAP

Answer 27

• average effective pressure driving blood through systemic organs
• MAP=COx TPR= HR x SV x TPR
• changes in MAP from changes in CO or TPR
• pulse pressure =stroke volume/compliance

Question 28

controlling MAP

Answer 28

• high enough to drive blood flow but not damage organs
• short term control alters CO and peripheral resistance- neurally and hormonally
• peripheral resistance counteracts most moment to moment fluctuations
• vasomotor activity regulates vasomotor tone and peripheral resistance
• baroreceptor reflex
• long term control by altering blood volume via kidneys