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BRS - Cardio > Respiratory Mechanics > Flashcards

Respiratory Mechanics Flashcards

1
Q

How is air flow generated?

A

by pressure gradients

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2
Q

What is Poiseuille’s Law equation? (using flow rate)

A 
Q = πPr^4 / 8ηl
Q = Flow rate
P = pressure
r = radius
η = fluid viscosity
l = length of tubing
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3
Q

What is Poiseuille’s Law equation? (using resistance)

A 
R = 8ηl / πPr^4
R = resistance
P = pressure
r = radius
η = fluid viscosity
l = length of tubing
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4
Q

What is Poiseuille’s Law?

A

describes factors that affect resistance

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5
Q

What does halving tube diameter do to resistance?

A

increases resistance by 16 times

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6
Q

What components is blood pressure a product of?

A

Blood pressure = Cardiac Output (blood entering system) x Total Peripheral Resistance (size of tubes in system)

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7
Q

What happens to the airways as lung volume increases?

A

conductivity + dilation of the airways increases

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8
Q

What are the characteristics of small arteries + arterioles?

A

extensive smooth muscle - to regulate diameters + resistance to blood flow

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9
Q

What are the characteristics of veins + venules?

A

highly compliant - act as a systemic blood reservoir

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10
Q

Why does pressure in blood vessels fall across circulation?

A

viscous (frictional) pressure losses

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11
Q

Which blood vessels present the most resistance to flow?

A

small arteries + arterioles

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12
Q

Why is the relationship between blood pressure, cardiac output + resistance an approximation?

A 
3 assumptions:
• steady flow (which does not occur due to the intermittent
pumping of the heart)
• rigid vessels
• right atrial pressure is negligible
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13
Q

What is regulation of flow achieved by?

A

variation in resistance in the vessels while blood pressure remains constant

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14
Q

What is MAP?

A

mean arterial pressure, also blood pressure

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15
Q

How is MAP calculated?

A
  • MAP = diastolic BP + (systolic - diastolic BP)/3

* MAP = diastolic BP + (pulse pressure/3)

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16
Q

What 3 variables does resistance of a tube to flow depend on?

A
  • fluid viscosity
  • length of tube
  • inner radius of tube
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17
Q

What does Poiseuille’s equation emphasise?

A

importance of arterial diameter as a determinant of resistance

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18
Q

How do small changes in vascular tone affect flow?

A

small changes in vascular tone = large changes in flow rate

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19
Q

What are the 2 types of fluid flow?

A
  • laminar

* turbulent

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20
Q

What is laminar fluid flow?

A
  • velocity is constant at any point
  • flows in layers
  • blood flows fastest closest to the centre of the lumen
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21
Q

What is turbulent fluid flow?

A
  • erratic blood flow
  • forms eddys
  • prone to pooling
  • associated w pathophysiological changes to endothelial lining of blood vessels
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22
Q

Where is blood pressure usually measured + why?

A
  • measured on upper arm

* easily accessible + at heart-level

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23
Q

How is blood pressure measured?

A

slow deflation of blood pressure cuff causes TURBULENT FLOW - heard with sthetoscope

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24
Q

How can pulse pressure be calculated using BP measurements?

A

systolic BP - diastolic BP = pulse pressure (PP)

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25
Q

What is the ratio of systole to diastole?

A

1 : 3

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26
Q

What happens to transmural pressure + the airways during inspiration?

A
  • transmural pressure is POSITIVE

* airways remain PATENT (open)

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27
Q

What effect does severe transmural pressure have on different sized airways?

A
  • collapse in small-to-medium airways

* no collapse in large airways due to cartilage rings

28
Q

What is compliance?

A
  • tendency for tissue to distort under pressure

* change in volume / change in pressure

29
Q

What is elastance?

A
  • tendency for tissue to recoil to its original volume

* change in pressure / change in volume

30
Q

Why do ventricular + aortic pressures differ?

A
  • aortic valve closing
  • ventricular pressure falls rapidly
  • aortic pressure falls slowly
31
Q

What explains the ventricular + aortic pressure differences?

A

elasticity of the aorta and large arteries which act to buffer the change in
pulse pressure

32
Q

What is arterial compliance?

A

ability of the arterial wall to distend + increase volume w/ increasing transmural pressure

33
Q

What happens to blood flow in the arteries during ejection?

A

blood enters arteries FASTER than it leaves them

34
Q

How does pressure change when the aortic valve closes?

A

ejection ceases but due to elastic recoil of arteries, pressure falls slowly + there is diastolic flow in the downstream circulation

35
Q

What is the Windkessel effect?

A

large central arteries (e.g. aorta) are elastic = acts as a reservoir during systole + stores some ejected blood forced out during diastole

36
Q

What effect does reducing arterial compliance have on the Windkessel effect?

A

damping effect of Windkessel effect is reduced + pulse pressure increases

37
Q

What is venous return facilitated by?

A
  • skeletal muscle pumps in lower limbs

* respiratory muscle pumps in thorax

38
Q

What is varscosity?

A

incompetent valves cause dilated superficial veins in the leg

39
Q

What is oedema?

A

prolonged elevation of venous pressure (even with intact compensatory mechanisms) causes oedema in feet

40
Q

What is an aneurysmal disease?

A

vessel walls weakening causing balloon-like distention = aneurysm

41
Q

What effect do vascular aneurysms have on the radius of a blood vessel?

A

increases radius

42
Q

What effect do vascular aneurysms have on the forces acting on a blood vessel?

A

for the same internal pressure, the inward force exerted by muscular wall must INCREASE

43
Q

Why do aneurysms rupture?

A

force exerted by muscle wall must increase but muscle fibres have weakened - force needed can’t be produced so aneurysm will expand + rupture

44
Q

What is the difference between venous + arterial compliance?

A

venous compliance = arterial compliance x 10-20 times

45
Q

If arterial compliance decreases, what effect does this have on blood pressure?

A
  • systolic increases

* diastolic decreases

46
Q

What does increasing smooth muscle contraction do to venous volume + pressure?

A
  • decreases venous volume

* increases venous pressure

47
Q

How does ventilation differ across the lungs?

A
  • less ventilation at the top

* more ventilation at bottom

48
Q

Why is there less ventilation towards the top of the lungs?

A
  • intrapleural pressure is MORE negative
  • GREATER transmural pressure gradient
  • alveoli larger + less compliant
49
Q

Why is there more ventilation towards the bottom of the lungs?

A
  • intrapleural pressure is LESS negative
  • SMALLER transmural pressure gradient
  • alveoli smaller + more compliant
50
Q

How does perfusion differ across the lungs?

A
  • lower flow rate towards top

* higher flow rate towards bottom

51
Q

Why is there lower flow rate towards the top of the lungs?

A
  • Lower intravascular pressure (gravity effect)
  • Less recruitment
  • Greater resistance
52
Q

Why is there higher flow rate towards the bottom of the lungs?

A
  • Higher intravascular pressure (gravity effect)
  • More recruitment
  • Less resistance
53
Q

What varies more between base and apex; ventilation or perfusion?

A

perfusion

54
Q

What does V/Q ratio stand for?

A

ventilation/perfusion ratio

55
Q

What is V/Q ratio used for?

A

to assess to efficiency + adequacy of the matching of ventilation + perfusion

56
Q

What is a V/Q ratio?

A

ratio of:
• amount of air reaching the alveoli per minute :
• amount of blood reaching the alveoli per minute

57
Q

What are ventilation + perfusion the main determinants of?

A

blood O2 + CO2 concentration

58
Q

How is V/Q ratio measured?

A

ventilation/perfusion scan

59
Q

What can a V/Q mismatch cause?

A

type 1 respiratory failure

60
Q

What is a typical V/Q ratio value of the lung as a whole?

A

0.8

61
Q

How does V/Q ratio vary in the lung?

A

ratio value varies depending on position within lung

62
Q

How would COPD affect compliance?

A

emphysemic breakdown of structural lung tissue INCREASES compliance

63
Q

How does COPD affect resistance?

A

bronchitic swelling of the airways + mucus hyper-secretion INCREASES resistance to airflow

64
Q

Why doesn’t resistance continue to increase as airways get smaller?

A

resistance to airflow depends on no. of parallel pathways present - many many alveoli vs. two bronchi…

65
Q

What happens to airway resistance as lung volume increases?

A

airway resistance decreases

66
Q

Why does airways resistance decrease as lung volume increases?

A

airways distend as lungs inflate + wider airways have lower resistance

BRS - Cardio (15 decks)

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