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Module 103, Theme 3: Physiology of the CVS: principles of pathology, diagnosis and treatment of CV diseases. > Blood pressure > Flashcards

Blood pressure Flashcards

1
Q

Blood pressure measurements

A
  • mm Hg: amount of pressure required to push 1 mm of mercury.
  • kPa: 1 kPa= 1000 newton units/ m2
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2
Q

Normal blood pressure measurements

A

120/75 mm Hg

16/10 kPa

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3
Q

Pulse pressure

A

The difference between the maximum diastolic pressure and the minimum systolic pressure, in a given time.

Pulse pressure= Systolic max - Diastolic min

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4
Q

Blood flow circuits

A

In series: Blood flow goes through two paths in the same row. The pressure at the start of the row is higher that at the end- energy is lost.

In parallel- Branching of paths from one row into multiple rows. At the point of branching, the pressure is the same. If the resistance in each path is the same, the pressure at the end will also be the same.

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5
Q

Portal system

A

A type of in series blood vessel circuit where there are capillary beds in series.

A capillary bed converge into a venule/ arteriole before diverging into another capillary bed.

This allows conservation of the material in the blood and prevents diluting caused by mixing with other blood.

Example: Hepatic portal system.

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6
Q

Hepatic portal system- blood circuit

A

In series circuit:
Blood receives nutrients in the gut through the capillary beds.
Blood assembles into portal vein when it is carried to the liver.
Blood then diverges into another capillary bed whilst in the liver.

Allows nutritional content of the blood to be conserved.

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7
Q

Mean arterial pressure

A

Mean arterial pressure= Min diastole pressure + ( Pulse pressure/ 3)

A method of calculating blood pressure.

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8
Q

End diastolic volume

A

The volume of blood in the ventricle after filling, in diastole.

Greater volume = Ventricle is more stretched ( Starling’s law)

The average EDV is 120 ml.

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9
Q

End systolic volume

A

Volume of blood left in the ventricles after contraction. during systole.

The average ESV is 50 ml.

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10
Q

Stroke volume

A

The volume of blood pumped out of the ventricle after one heartbeat.

SV= EDV- ESV

Average SV is 70 ml.

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11
Q

Ejection fraction

A

Percentage of ventricular volume of blood pumped out during one heartbeat.

EF= SV/ EDV

Average ejection fraction is between 55-70%.
Heart failure occurs when EJ is too low.

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12
Q

Average HR and CO of an adult.

A

70 bpm

4.9L/min

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13
Q

What main factors cause an increase in blood pressure?

A

An increase in peripheral resistance.

An increase in cardiac output.

An increase in blood volume.

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14
Q

The vessel radius and blood pressure.

A

A decrease in the radius (vasoconstriction), causes more resistance and less flow= increased blood pressure.

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15
Q

What factors affect the size of the vessel radius.

A

Nervous control:
Autonomic control, CNS.

Hormonal control- endocrine

Local pressure regulation

Immune response

Haemostasis

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16
Q

Local vasomotor control

A

Release of NO- endothelial cells release NO which allows vasodilation, increasing vessel radius.

Blood flow- laminar flow allows shear force, which is atheroprotective. Sheer force is the stress on endothelial walls in the direction of blood flow.
Hydrostatic pressure pushes blood vessel walls outwards.

17
Q

Factors that control systemic blood pressure.

A

Locally- endothelial cells and release of NO.

Nervous control- autonomic NS
Release of noradrenaline causes vasoconstriction

Humoral (blood volume)- renal, pituitary and adrenal gland.

18
Q

Baroreceptors

A

Receptors that detects blood pressure.

Located:
Transverse aortic arch
Carotid sinuses

When pressure is high, receptors send impulses to the brain, to stimulate a decrease in pressure (parasympathetic system).

Low pressure= stimulation of sympathetic nervous system.

19
Q

Chemoreceptors

A

Receptors that detect mainly low O2, also high levels of CO2 and H+.

Location:
Aortic bodies
Carotid bodies

When O2 levels are low, impulses are sent to the brain to stimulate sympathetic nervous system.

20
Q

Nucleus tractus solitarius

A

Centre in the medulla oblongata that detects action potentials from baroreceptors,

Causes changes to cardiac output and systemic vascular resistance.

21
Q

Frank-Starling mechanism (Starling’s law)

A

This states that an increase in stroke volume arises from the increase in pressure of the ventricles.

The more cardiomyocytes are stretched, the greater they will contract.

22
Q

Preload

A

The initial stretching of cardiomyocytes before contraction.

The greater the venous return, the greater the preload.

23
Q

Factors that increase preload

A
  1. Decrease in heart rate:
    The gives more time for the ventricles to fill with blood.
  2. Increased aortic pressure:
    This increases background pressure, increasing the venous return. Therefore more blood fills ventricles.
  3. Increased central venous pressure:
    Increases venous return, thus increasing preload.
  4. Decreased venous compliance:
    Lower blood volume in the veins, thus decreasing central venous pressure.
  5. Increased thoracic venous blood volume:
    Increased venous return and total blood volume.
  6. Increase atrial contractility:
    More blood pumped into ventricle, cardiomyocytes stretch more.
  7. Increase ventricular compliance:
    The ventricles are more stretchy, more blood can fill ventricles.
24
Q

Autonomic control of blood pressure

A
  1. Medulla oblongata receives signals from receptors, saying that blood pressure is too low.
  2. This triggers the sympathetic system, via the
Effects:
Vasoconstriction
Increased heart rate
Increased peripheral resistance
Increased cardiac output
Ultimately increases blood pressure.
25
Q

Afterload

A

The resistance in chambers during systole.

Factors that increase afterload:

  • Increased back pressure from the aorta and pulmonary artery= more resistance.
  • Failed valve: stenosis and regurgitation causes more resistance.
26
Q

Pressure overload

A

Pathological condition that occurs from elevated afterload.

Stress on the myocardial tissue that occurs during systole.
Myocardium generates force to contract but cannot contract (eg due to too much blood being in the heart or to the heart tissue being non-compliant)

27
Q

Venous return

A

The volume of blood flowing to the heart, in the veins.

This blood is pulled up by:
Thoracic pump
Muscle pump

28
Q

Thoracic pump

A

Method of pushing blood in the veins back to the heart.

This is achieved by the mechanical movement of inspiration.

During inspiration:
Intrathoracic pressure is negative as air goes in.
Abdominal pressure is positive as the diaphragm contracts.

This forms a pressure gradient:
blood is pulled from the infradiaphragmatic vena cava to the supradiaphragmatic vena cava.
This pulls blood into the atrium

29
Q

Muscle pump

A

Method of pushing blood in the veins, back to the heart.

Rhythmic contraction of limb muscles during locomotor activity (running, walking, swimming), squeezes nearby veins.

30
Q

Orthostatic hypotension

A

Drop in blood pressure when standing.

Whilst sitting, blood pools at the feet due to a decrease in venous return. This causes a temporary, insufficient perfusion to the upper body
This can causes dizziness or syncope when standing.

Causes:
Hypovolemia
Age
Drugs (diuretics, vasodilators)

31
Q

Features of pulmonary circulation

A
  1. Low vascular resistance:
    When O2 levels are low in a section of the lung, this causes vasoconstriction. This directs blood flow to areas that are better ventilated.
  2. Filtration of material:
    The mass network of microvessels allow foreign material to be trapped. This prevents emboli (clots), entering the systemic vessels.
  3. Angiotensin converting enzyme (ACE):
    Lungs contain ACE which convert Angiotensin I to II. This increases blood pressure.
  4. Blood reservoir:
    The lungs contain 10% of the total blood volume (500ml)
32
Q

Coronary circulation

A

Blood flow in the coronary arteries:
Most flow occurs during diastole. In systole, the vessels are squeezed shut due to great contraction.

Coronary arteries have little resistance as there is not a lot of back pressure so blood can flow in very low pressures.

33
Q

Cardiogenic shock

A

Low perfusion to tissues caused by heart dysfunctions.

Compensatory mechanisms:
Tachycardia
Tachypnea

Symptoms, due to failure to compensate:
Low urine output (Oliguria)
Hypotension
Confusion
Syncope
Acidosis
34
Q

Shock

A

Low perfusion of tissues, which can cause cellular injury and impaired tissue function.

Hypovolemic: low blood volume
Cardiogenic: dysfunctional heart
Distributive shock: blood vessel dilatation
Obstructive: obstruction of great blood vessels or the heart.

35
Q

Hypertension

A

Having high blood pressure; especially the diastolic pressure. Mismatch between blood volume and circulatory capacity

Causes:
Chronic kidney disease
Dysfunction in the nucleus tractus solitarius
Hormonal dysfunctions: angiotensin II
Idiopathic 
Consequences:
Aneurysm 
Stroke
Myocardial infarction 
Cardiac hypertrophy
Kidney and heart failure
36
Q

What happens to blood pressure during exercise?

A

Peripheral dilation occurs in skeletal muscles and the skin- to supply more O2/ nutrients.
Central vasoconstriction- less blood flow in splanchnic circulation.

This causes in increase in systolic pressure BUT diastolic pressure decreases.

Heart rate increases which causes a decrease in diastolic pressure.

Module 103, Theme 3: Physiology of the CVS: principles of pathology, diagnosis and treatment of CV diseases. (20 decks)

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