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Z YEAR 1 BRS cardiology > Cardiorespiraotry mechanics > Flashcards

Cardiorespiraotry mechanics Flashcards

1
Q

How do you carry out a pulmonary function test?

A

1) Patient wears noseclip
2) Patient wraps lips round mouthpiece
3) Patient completes at least one tidal breath (A&B)
4) Patient inhales steadily to TLC (C)
5) Patient exhales as hard and fast as possible (D)
6) Exhalation continues until RV is reached (E)
7) Patient immediately inhales to TLC (F)
8) Visually inspect performance and volume time curve and repeat if necessary. Look out for:
a) Inconsistencies with clinical picture
b) Interrupted flow data

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2
Q

What happens as alveolar pressure decrease because intercostal muscles pull out and up?

A
  • Negative pressure in Thorax
  • Pressure gradient
  • So air flow
  • Air flows in
  • Then pressure goes back down
  • If excising the same cycle just magnitudes greater
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3
Q

What happens if alveolar pressure increases?

A
  • Gas molecules squished due to recoil forces
  • Positive pressure inside alveoli
  • Which if airways are open will squish it
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4
Q

What is flow rate proportional to?

A
  • Flow rate if airway same size if proportional to pressure gradient
  • Pleural pressure have weird line
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5
Q

What happens to the pressure volume loop in COPD?

A
  1. Shift to left (as lungs in COPD has more air in) as lungs are fuller and amount of isa gets access to is less
    - Residual volume increased
    - Vital capacity decreases
  2. Indented exhalation curve because force lungs can generate through narrow airways cause obstruction so peak Lowe r
    - If worse COPD, curve squished, peak lower and more indented
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6
Q

What happens in restrictive lung disease?

A
  • Reduce ability of chest to expand (bear hug)

1. Displaced to the right and narrower curve

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7
Q

What happens in variable extrathroacic obstruction for a flow volume loop?

A
  1. Blunted inspiratory curve

- Otherwise normal

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8
Q

What happens in variable intrathroacic obstruction for a flow volume loop?

A
  1. Blunted expiratory curve
    - Otherwise normal
    - Does not impeded inspiration but does impede expiration
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9
Q

What happens in fixed airway obstruction for a flow volume loop?

A
  1. Blunted inspiratory curve and blunted expiratory curve

- Otherwise normal

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10
Q

What happens when snorkelling?

A
  • Diameter: 2.2.cm length 30cm
  • Dead space is less than if deeper
  • if radius and halve it resistance to flow goes up 16 fold
  • Resistance is inversely proportional to the fourth power of the radius
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11
Q

What is airway generation?

A
  • A generation of an airway is every time it bioficates
    1. Trachea
    2. Primary bronchi
    3. Secondary bronchi etc
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12
Q

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

A
  • Capillaries have slow flow rate and low pressure
  • Increases the cumulative cross sectional area of airways as you go down the tipping point is generation four and beyond that goes down exponentially
  • Number of airways causes resistance to peak
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13
Q

What is conductance?

A

-The willingness of the airways to conduct fluid transfer

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14
Q

How does conductivity change?

A
  • Airways are not rigid pipes, they dilate as lung volume increases
  • The ‘conductivity’ of the airways increases with increasing volume
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15
Q

Describer small arteries and arterioles

A

Small arteries and arterioles have extensive smooth muscle in their walls to regulate their diameters and the resistance to blood flow

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16
Q

Describe veins and venules

A
  • Veins and venules are highly compliant and act as a reservoir for blood volume
  • Venous is reservoir
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17
Q

How does pressure change across the circulation

A
  1. Pressure falls across the circulation due to viscous (frictional) pressure losses.
  2. Small arteries and arterioles present most resistance to flow
    - Small arteries and arterioles are governing flow into capillary bed
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18
Q

How do you determine blood pressure?

A 
Change in pressure = Q x TPR (totally peripheral resistance)
Blood pressure (MAP) = cardiac output (CO) x resistance (Peripheral Vascular restiance )
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19
Q

Why is this relation an approximation?

A

This relation is an approximation because it assumes:

1) steady flow (which does not occur due to the intermittent pumping of the heart)
2) rigid vessels
3) right atrial pressure is negligible
- Physiologically, regulation of flow is achieved by variation in resistance in the vessels while blood pressure remains relatively constant.

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20
Q

What does resistance of a time to flow depend on?

A
  1. Fluid viscosity (h, eta)
  2. The length of the tube (L).
  3. Inner radius of the tube (r)
    - Halving the radius decrease the flow 16 times
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21
Q

What is Poiseuille’s equation?

A

-Poiseuille’s equation (Jean Poiseuille, 1797-1869) emphasises the importance of arterial diameter as a determinant of resistance. -Relatively small changes in vascular tone (vasoconstriction/vasodilation) can produce large changes in flow.

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22
Q

What is the cardiac output at rest?

A
  • Rest: cardiac output approx 5L/min
  • Stroke volume: 70ml/beat
  • Beats: 70beat/min
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23
Q

What is cardiac output in exercise?

A

-20 L/min

increased blood flow to muscle +hear, same to brain and gut sacrificed

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24
Q

What is Laminar flow?

A
  1. Velocity of the fluid is constant at any one point and flows in layers
  2. Blood flows fastest closest to the centre of the lumen.
25
Q

What is turbulent flow?

A
  1. Blood flows erratically, forming eddys, and is prone to pooling
  2. Associated with pathophysiological changes to the endothelial lining of the blood vessels
26
Q

How is blood pressure measured?

A
  • Blood pressure usually measured on upper arm as its easily accessed and at heart-level
  • Slow deflation of cuff causes turbulent flow which can be heard with a stethoscope
27
Q

How do you calculate pulse pressure (PP)?

A

SBP-DBP

28
Q

How do you calculate mean arterial pressure?

A

DBP + 1/3 PP

29
Q

What is a dichroic notch caused by?

A

Closure of the aortic valve

30
Q

What happens in normal flow in collapsible tube?

A
  • Normal inspiration
  • Airway transmural pressure -2–8+6 so positive
  • PATENT
31
Q

What happens in hard expiration in collapsible tube?

A
  • Airway transmural pressure 10-22 = -2
  • COLLAPSED
  • This is why our large extrapuomonary airways are supported with cartilage
32
Q

What is compliance?

A

The tendency to distort under pressure

33
Q

What is elastane?

A

Tendency to recoil to its original volume

34
Q

How do you calculation compliance?

A

Change V / Change in P

35
Q

How do you calculate elastance?

A

Change in P / Change in V

36
Q

Why do ventricular and aortic pressures differ?

A
  • Once the aortic valve closes (A) ventricular pressure falls rapidly but aortic pressure falls slowly
  • This can be explained by the elasticity of the aorta and large arteries which act to “buffer” the change in pulse pressure.
  • The elasticity of a vessel is related to its compliance.
37
Q

What is arterial compliance?

A
  • During ejection, blood enters the aorta and other downstream elastic arteries faster than it leaves them (40% of SV is stored by the elastic arteries)
  • Need continuous to stop intermittent flow as then rebase clotting factors etc
  • Aorta and its compliance allow this to happen continuous
38
Q

What happens when the aortic valve closes?

A

When the aortic valve closes, ejection ceases but due to recoil of the elastic arteries, pressure falls slowly and there is diastolic flow in the downstream circulation

39
Q

What happens if arterial compliance decreases?

A

If arterial compliance decreases (arteries become stiffer; e.g. with age), the damping effect of the Windkessel effect (start stop) is reduced and the pulse pressure increases.

40
Q

What is the skeletal muscle pump?

A
  • Low pressure system
  • Everytime move back of leg, muscle contract which squish vessel which pushes blood only in one way
  • When breath in interthroacic pressure decrease, which helps venous return because helps to stretch open low pressure inferior vena cava which increase pressure gradient between right atrium and vena cava so improve venous return
41
Q

What is the respiratory [ump?

A

-When breath in interthroacic pressure decrease, which helps venous return because helps to stretch open low pressure inferior vena cava which increase pressure gradient between right atrium and vena cava so increase venous return

42
Q

What happens if the valves fail?

A
  1. Varicose veins: Incompetent valves cause
    dilated superficial veins in
    the leg (varicose veins)
  2. Oedema: Prolonged elevation of venous pressure (even with intact compensatory mechanisms) causes oedema in feet
43
Q

What is the Law of LaPlace?

A 
When the pressure within a cylinder is held constant the tension on its walls increases with increasing radius 
Wall tension (T) = pressure in vessel (P) x medius of vessel (R)
44
Q

What can happens overtime to vessel wall?

A

-vessel walls can weaken causing a balloon-like distension

45
Q

What are vascular aneurysms?

A

-Vascular aneurysms increase radius of the vessel
-This means that for the same internal pressure, the inward force exerted by the muscular wall must also increase.
-However, if the muscle fibres have weakened, the force needed cannot be produced and so the aneurysm will continue to expand …
often until it ruptures.
-This pathology and the underlying physical forces involved also holds for the formation of diverticuli in the gut.

46
Q

What is the relationship between the transmural pressure and vessel volume?

A
  • The compliance

- Depends on vessel elasticity

47
Q

Describe venous compliance and arterial compliance

A
  • Venous compliance is 10 to 20 times greater than arterial compliance at low pressures.
  • Venocontriction aid venous return (in hormonal and neuronal sympathetic) if loose loads of blood (less compliant)
48
Q

What happens in a vein if you increase smooth muscle contraction?

A
  • Increasing smooth muscle contraction (green arrow) decreases venous volume and increases venous pressure.
  • Most blood volume is stored in the veins (70% in venous)
  • Relatively small changes in venous pressure distend veins and increase the volume of blood stored in them
49
Q

What happens in ventilation?

A

-PPL is more negative (-8 cmH2O)
-Greater transmural pressure gradient (0 vs. -8)
-Alveoli larger and less compliant
-Less ventilation
-PPL is less negative (-2 cmH2O)
Smaller transmural pressure gradient (0 vs. -2)
-Alveoli smaller and more compliant
More ventilation

50
Q

What happens in perfusion?

A
  • Lower intravascular pressure (gravity effect)
  • Less recruitment
  • Greater resistance
  • Lower flow rate
Higher intravascular pressure 
(gravity effect)
More recruitment
Less resistance
Higher flow rate
51
Q

What happens in the lung?

A
  • Top of lung more stretched at rest as gravities pulling lung down
  • More pressure at top
  • Lung tissue at bottom is easier to ventilate , lower Transmural pressure
  • Blood flows to base of lung
52
Q

What happens at top of lung?

A

-Least amount of perfusion
-Least amount of ventilation
PA>Pa>Pv
-Wasted ventilation (want perfect ration between perfusion and ventilation)

53
Q

What happens at base of lung?

A
  • Blood preferential at base compared to apex at deeper relationship than air
  • More perfusion than you need
54
Q

Why is there more ventilation at base of lung?

A
  1. Gravity causes the base of the lungs to be compressed due to the natural ‘stretchiness’ of the lung tissue.
    2, This means the alveoli at the bottom of the lung are smaller in size and therefore more compliant (tendency to distort under pressure//are ready to be stretched)
  2. Additionally, the transmural pressure is greater at the apices so there is a greater Pa to overcome in order to have changes in volume occur.
  3. SO overall there is more ventilation at the base of the lungs due to less pressure to overcome and more compliant (stretch-ready) alveoli, all due to gravity.
55
Q

When does ventilation not match with perfusion?

A
  • V/Q mismatching is when the ventilation does not match the perfusion
  • occurs in certain conditions like COPD or pulmonary fibrosis where blood is being sent to alveoli that are not effectively undergoing gas exchange due to air trapping or lack of inflation ability (due to fibrosis)
  • so the ratio of amount of blood to amount of O2 that can be exchanged is mismatched and it can cause hypoxaemia w or w/o hypercapnia
56
Q

When does resistance to flow stop increasing?

A

Resistance to flow stops increasing after the 4th generation of the respiratory tree due to the shear number of respiratory branches

57
Q

Are arteries or veins more compliant?

A

Arteries and 10-20x LESS compliant than veins at low pressures

58
Q

How do veins act under a small amount of pressure?

A

-Veins when under small amounts of pressure will have greatly affect their volume (increased) and this is achieved by skeletal muscle pump where the muscles surrounding the veins literally push on the veins and increase transmural pressure thereby increasing volume

Z YEAR 1 BRS cardiology (10 decks)

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