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Cardiovascular System > Haemodynamics > Flashcards

Haemodynamics Flashcards

1
Q

What is haemodynamics?

A

Physical factors that control blood flow

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2
Q

What is serum?

A

Plasma without the clotting factors

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3
Q

When can whole blood viscosity change?

A
  • Polycytheamia
  • Thrombocytopenia
  • Leukaemia

Leads to thick ‘sludgy’ blood and dry gangrene in peripheries

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4
Q

When do minor changes to plasma viscosity occur?

A

Typically from acute phase proteins (fibrinogen, compliment, c-reactive protein)
- Used to measure plasma viscocity as indicator of imflammation

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5
Q

What is flow?

A
  • Volume transferred per unit time (L/min, but for blood usually ml/min)
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6
Q

What is pressure?

A

Force per unit area (mmHg used for BP)

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7
Q

What is resistance in blood vessels known as?

A

Vascular resistance

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8
Q

How are flow and resistance related in the circulation?

A

Reciprocally related

Flow and pressure in the circulation pulsate

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9
Q

What is laminar flow?

A
  • The smooth, silent, maintaining energy and typical of most arteries, arterioles, venules and veins
  • Moves in stream lines
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10
Q

What is turbulent flow?

A
  • Disorganised, noisy flow where energy is lost
  • Pressure increases in the vessel beyond which flow can match it linearly (called Reynold’s number)
  • eg. after stenosis
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11
Q

Where does turbulent flow occur?

A
  • Changing directions of vessels (branching)
  • In stenosed arteries
  • Stenotic heart valves
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12
Q

What is stenosis?

A

Abnormal discrete narrowing of an artery or open area of a heart valve

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13
Q

What are the primary factors for resistance to flow?

A
  • Diameter
  • Length of vessel
  • Viscosity

Physiologically diameter is most important quantitatively as is Poiseuille’s law the radius is to the 4th power so it has a large impact on flow and/or resistance

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14
Q

What does a drop in vessel pressure indicate?

A
  • Drop in pressure indicative of a change in resistance across the vessel class
  • Resistance in the aorta is low (as they have a large diameter but are really short)
  • Smallest arteries and arterioles contribute greatest component if total peripheral resistance
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15
Q

What is the formula for pulse pressure?

A

Pulse pressure = Systolic Blood Pressure - Diastolic Blood Pressure

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16
Q

What is the formula for total peripheral pressure?

A

TPR = mean aortic pressure / cardiac output

17
Q

What is the formula for mean arterial pressure?

A

Mean arterial pressure = Cardiac output x total peripheral resistance

18
Q

What is the formula for cardiac output?

A

Cardiac output = Stroke volume x Heart rate

19
Q

What affects pulse pressure?

A
  • Volume of blood ejected and the compliance of the arterial system govern pulse pressure
    INCREASE:
  • Increase in stroke volume during exercise with the relative compliance of vessels will cause an increase
    DECREASE:
  • Haemorrhage causes a reduction due to reduction in blood return
  • Age, atherosclerosis leads to reduced compliance
20
Q

What is the pulse?

A

Shock wave that arrives slightly before the blood itself

21
Q

What increases pulse pressure and what is it called?

A
  • Described as a ‘bounding’ pulse
  • Bradycardia
  • Vasodilation causes a decrease in peripheral resistance (eg. hot bath, pregnancy)
  • Elite athletes; systolic increased and diastolic decreased
22
Q

How is blood pressure measured?

A
  • Indirect measurement used in modern times
  • Convenient, non-invasive, can be carried out with minimal training
  • Rely on changes in type of flow from laminar to turbulent to laminar
23
Q

How is blood flow affected by stenosis?

A
  • “Pathological turbulence”
    • Caused by atheroma or stenosed vessel
  • Velocity increases though the stenosis and turbulence occurs beyond the stenosis
24
Q

What can be detected in blood pressure readings (felt/heard)

A 
Thrill = felt
Bruit = heard
25
Q

What are the sounds heard in blood pressure readings?

A

Korotkoff sounds
- Changes in laminar to turbulent flow create sounds which can be heard and used to estimate blood pressure

  • First tapping sounds –> Auscultatory systolic sound
  • Then Korotkoff sounds (turbulent flow)
  • Then sound disappears as pressure decreases –> auscultatory diastolic
26
Q

What factors can affect blood pressure estimations by auscultation?

A
  • Cuff size (too small = overestimate blood pressure, too big = underestimate blood pressure)
  • Positioning of the cuff
  • Measure in both arms as there is often a difference (higher reference should be used)
  • Sat comfortably, upright with legs uncrossed and flat on the ground
  • Arm should be supported

Assume the measurement will be taken at the level of the heart and resting

27
Q

What are the effects of gravity on blood pressure?

A
  • Maintains a pressure gradient allowing blood flow from heart to the foot when standing
  • Pooling of blood occurs below the level of the heart upon standing in the venous system
28
Q

What happens to blood pressure when it is taken above/below the level of the heart?

A

Below the heart –> Pressure greater

Above the heart –> Pressure reduced

29
Q

What clinical condition is associated with pooling of blood when standing?

A

Postural hypotension

  • Dizziness upon standing
  • Due to reduced stroke volume causing transient arterial hypotension
30
Q

What is the formula for mean arterial pressure?

A

MAP = Diastolic Blood Pressure + ((Systolic Blood Pressure-Diastolic Blood Pressure)/3) = DBP + 1/3PP

Cardiovascular System (3 decks)

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