CVS

Question 1

What is the function of the CVS?

Answer 1

To transport through its pump and vessels by joining the pulmonary and systemic circulations, to work in series.

Question 2

What may be the cause for a difference in the R CO compared to the L CO?

Answer 2

Blood loss or pooling

Question 3

What are the pressures with the systemic, pulmonary and venous circulations?

Answer 3

Systemic - 90mmHg
Pulmonary - 25mmHg
Venous - 0mmHg

Question 4

Why do vascular beds run in parallel?

Answer 4

To ensure that all the capillaries receive blood with the same level of oxygenation. It also allows changes in flow to one organ without affecting the others.

Question 5

What is the value of Pao2 and Paco2 on leaving the LV given normal alveolar ventilation?

Answer 5

Pao2 = 13kPa
Paco2 = 5kPa

Question 6

What is absolute pressure?

Answer 6

As all the pressures in the body are higher than atmospheric pressure, but the measures used absolute is the total of atmopheric + mean BP

Question 7

What is the function of the heart’s pumping action?

Answer 7

To receive blood from the venous system at low pressures of 0mmHg due to resistance and to IMPART PRESSURE onto the blood in order to eject it into the systemic circulation.

Question 8

What stages occur during systole?

Answer 8

Ventricular contraction and ejection

Question 9

What stages occur during diastole?

Answer 9

Ventricular relaxation and filling

Question 10

What is CO?

Answer 10

The volume of blood ejected per minute = 5L/min.
CO = HR x SV
LCO=RCO

Question 11

What is the average SV and HR?

Answer 11

SV = 70ml
HR = 70bpm

Question 12

What is the pulse pressure?

Answer 12

The difference between the pressures during diastole and systole within the aorta = 30-50mmHg
PP=SP-DP

Question 13

What does PP show?

Answer 13

The force that the heart generates on contraction. The larger the PP, the greater the force.

Question 14

How can PP be measured?

Answer 14

Via BP or arterial line. It varies with each beat.

Question 15

How is mean ABP calculated and what does it show?

Answer 15

Indicates oxygenation to the brain. Should be >60mmHg.

mean ABP = (SP-DP)/3 + DP

Question 16

Why is PP divided by three in mean ABP?

Answer 16

During a cardiac cycle, the heart is in diastole 2/3 of the time and in systole for 1/3.

Question 17

What determines ABP?

Answer 17

Resistance to flow
Blood volume in the arterial system
ABP = CO x TPR

Question 18

What is TPR?

Answer 18

The resistance to flow in all systemic vasculature

Question 19

Why does the pressure fall throughout the system?

Answer 19

Due to increased resistance in the arteries and capillaries.

Question 20

What effect does vasodilation and vasoconstriction have on TPR?

Answer 20

Vasodilation = decreases TPR = increased flow
Vasoconstriction = increased TPR = decreased flow

Question 21

What controls vasoconstriction/dilation?

Answer 21

Sympathetic N and local factors

Question 22

Which organs have an autoregulatory range that is not affected by systemic vasodialtion/constriction?

Answer 22

Brain, Kidney and Heart

Question 23

How much blood is in a 70kg pt?

Answer 23

5L - All the blood passes through the heart once per minute (CO=5L.min)

Question 24

What happens if VR doesn’t equal CO?

Answer 24

A coordinated response is initiated to maintain ABP. If the response is too slow it causes light headedness.

Question 25

How can CO be increased and why is it needed?

Answer 25

To increase CO must increase VR:
-Increase HR via cardia stimulation
-Vasoconstrict to force more VR
-Increase water retention through kidneys
= increased BP