Blood Pressure

Question 1

Where is maximum BP?

Answer 1

Aorta during systolic ejection

Question 2

When is minimum aortic blood pressure?

Answer 2

During isovolumetric contraction - diastole

Question 3

What is blood pressure a function of?

Answer 3

Stroke volume and arterial compliance

Question 4

What is the trend of arterial compliance over a life time?

Answer 4

Compliance decreases as age increases

Question 5

What are physiological values for blood pressure at ages:

1) Up to 45 years
2) 45-60 years
3) above 60 years

Answer 5

1) Up to 45 years
Diastolic = 60-90mmHg
Systolic = 100-140mmHg

2) 45-60 years
Systolic = 150mmHg

3) 60+ years
Systolic = 160mmHg

Question 6

What is hypotension and its results?

Answer 6

Low blood pressure

Degradation of tissues

Question 7

What is hypertension and its results?

Answer 7

High blood pressure and damaged vessels

Question 8

What is the trend of blood pressure values from the aorta to the right atrium?

Answer 8

Mean blood pressure falls as it leaves the aorta to the arteries, but the pressure is higher in the greater arteries due to less compliance.

Question 9

What is compliance?

Answer 9

The tendency of the arteries and veins to stretch in response to pressure has a large effect on perfusion and blood pressure.
Veins have a much higher compliance than arteries (largely due to their thinner walls).

Question 10

What is the systemic circulation?

Answer 10

Greater circulation.
From left ventricle to the peripheral capillaries via the arteries.
Returns to the right atrium via the veins.

Question 11

What is the pulmonary circulation?

Answer 11

Lesser circulation.
From right ventricle to the lungs.
Returns to the left atrium.

Question 12

Explain the total blood volume.

Answer 12

4-5L
80% of this is in the veins, right heart and pulmonary vessels.
This is the low pressure system.
This is the blood reservoir and can be released by vasoconstriction is necessary.

Question 13

What is the central venous pressure (CVP)?

Answer 13

Normally 4-12mmH2O.
Measured by the right atrium.
A good indicator of blood volume.
If the blood volume increases (transfusion) 99% of the blood goes to the low pressure system.
If the blood volume decreases, this will be a decrease almost entirely in the low pressure system.

Question 14

Explain the cardiac output (CO).

Answer 14

5.6L/minute at rest.
CO = Heart Rate * Stroke Volume
With an increase of HR the output can be increased to 15-20L/minute.
Stroke Volume = volume of blood ejected from ventricles during systole = 0.08L
Heart Rate = During rest = 70bpm

Question 15

What is the average oxygen consumption at rest?

Answer 15

250mL/minute

Question 16

Explain the flow resistance.

What are its values in the right and left ventricles?

Answer 16

The flow resistance is much lower in the pulmonary circulation than in the systemic.
Depends greatly on the radius of the tube (r^4).
The lesser arteries and arterioles account for 50% of the total peripheral resistance.
Right ventricle = 15mmHg (2kPa)
Left ventricle = 100mmHg (13kPa)

Question 17

What is the equation from blood pressure?

Answer 17

P = Q * R 
P = blood pressure 
Q = blood flow 
R = resistance of vessels

Question 18

Explain how arteries convert the alternating flow of the contracting heart to a steady flow in the vessels.

Answer 18

The greater arteries convert the alternating flow of the heart to a steady flow though the arteries.
This is possible due to their great compliance (elasticity).
The blood is ‘stored’ in the artery’s dilated lumen when the heart contracts, therefore offsetting the change in BP.
When the aortic valves close the arteries constrict.
The end result is an almost steady flow.

Question 19

Explain how a false reading can be gained from a blood pressure measurement.

Answer 19

If readying multiple times in a row without rest, the diastolic pressure will be elevated due to blood pooling.
If the cuff is too loose or too tight, this will give a false reading.

Question 20

Explain the palpation method of taking blood pressure.

Answer 20

Minimum systole value can roughly be measured without any equipment.
Used for emergency situations.
Radial artery gives a minimum of 80mmHg.
This method is not accurate.
With the use of a sphygmomanometer a more exact systolic value can be obtained.
Diastolic pressure cannot be measured in this way.

Question 21

Explain the auscultatory method of taking blood pressure.

Answer 21

Stethoscope and sphygmomanometer are used.
Gives absolute results.
Measured externally at the level of the heart using the brachial artery.
The first sound heard (Korotkoff sound) indicates systolic pressure.
When the sounds stop, this indicates diastolic pressure.

Question 22

Explain the oscillometric method of taking blood pressure.

Answer 22

Functionally similar to the auscultatory method.
An electronic pressure sensor is used.
Can be used at home, or by untrained staff.
But does NOT give exact values.