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BRS CVR > Cardiorespiratory Mechanics > Flashcards

Cardiorespiratory Mechanics Flashcards

1
Q

What drives pulmonary ventilation?

A

Pressure gradient
Inspiration - Atmospheric > intralveolar
Expiration - Intralveolar > atmospheric

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2
Q

What does 1 respiratory cycle include?

A

One sequence of inspiration and expiration.

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3
Q

Explain the mechanism behind inspiration + the muscles involved.

A

2 muscle groups are involved: Diaphragm + external IMs.

Diaphragm contracts → pulls inferiorly resulting in a larger thoracic cavity → Increased volume subsequently decreases the intrathoracic pressure.

External IMs contract → Ribs move outwards → Ribcage expansion ^ thoracic cavity volume → Lungs stretch and expand → Decreases intralveolar pressure → Pressure gradient enables air to move into the lungs.

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4
Q

Explain the mechanism behind expiration + the muscles involved.

A

Process of normal expiration is passive. Elasticity of lung tissues cause lung recoil → Diaphragm and intercostal muscles relax following inspiration.

Thoracic cavity and lungs decrease volume → Increases inter-pulmonary pressure > atm → pressure gradient causes air to leave lungs.

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5
Q

Equation for Poiseuille’s Law.

A

R = 8nL/pi.r^4

n=viscosity

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6
Q

What is Boyle’s Law (equation)?

A

Pressure of a gas is inversely proportional to the volume of the same gas.

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7
Q

What is resistance inversely proportional to?

A

4th power of the radius

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8
Q

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

A

Velocity of air moving down the airways slows.

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9
Q

In what generation of the airways is the resistance at its peak?

A

4th generation

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10
Q

What happens to resistance as radius decreases?

A

Increases

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11
Q

Do airways dilate as lung volume increases?

A

Yes

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12
Q

Define conductance in terms of the airways.

A

Ability for airways to conduct and enable air to pass through → increases, with increasing lung volume → Decreases resistance.

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13
Q

What happens to resistance as lung volume increases?

A

Decreases as airways dilate

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14
Q

What happens to conductance as lung volume increases?

A

Increases

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15
Q

What are the characteristics of the systemic circulation for arteries and veins respectively?

A

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

Veins and venules are highly compliant and act as a reservoir for blood volume.

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16
Q

Which blood vessels have the largest total surface area?

A

Capillaries

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17
Q

What type of blood vessels hold the largest proportion of systemic blood volume?

A

Veins

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18
Q

Why does pressure decline across the circulation?

A

Due to viscous (frictional) pressure losses → Small arteries and arterioles present majority of resistance to flow. Pulmonary artery presents a resistance to flow in addition.

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19
Q

List the order of blood vessels staring from ones with the highest mean pressure (mmHg).

A

Arteries, arterioles, capillaries, venules, veins

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20
Q

Physiologically, how is regulation of flow achieved?

A

VARIATION in RESISTANCE → BP remains relatively constant (relies on mechanisms to detect BP and feedback to maintain constant).

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21
Q

Equation relating BP, cardiac output and TPR?

Why is this relation an approximation?

A

Blood pressure (MAP) = CO x TPR

Assumes:
steady flow (which doesn’t occur due to intermittent pumping of the heart)
Rigid vessels
Right atrial pressure is negligible.

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22
Q

What 3 things does resistance to blood flow depend on?

A

Fluid viscosity (Eta)
Length of the tube
Inner radius of tube

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23
Q

What affect does halving the vessel radius have on resistance?

A

Halving the radius increases resistance by 16x hence also decreasing the flow 16x.

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24
Q

What does Poiseuille’s equation emphasise?

A

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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25
Q

How do exercise and therefore increased metabolic demand affect cardiac output and why?

A

Increase cardiac output - altering the radius of various vessels increases the blood flow to the working skeletal muscle → Constricting and dilating vessels to direct blood flow to highest priority.

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26
Q

Describe laminar flow.

A

Discrete current lines with minimal interference with each other. Laminar flow can’t be auscultated (heard).
Velocity of fluid is constant at any one point, flowing in layers. Blood flows fastest closes to the centre of the lumen.

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27
Q

Explain what happens to the laminar flow whilst taking BP measurements.

A

BP measurements involves pumping the cuff in order to obstruct flow → Releasing cuff slowly results in blood flowing through the cuff producing turbulent flow → Sounds of Korotkoff

28
Q

Describe turbulent flow.

A

Blood flows erratically, forming Eddys and is prone to pooling.
Characterised by whirlpool regions and velocity of fluid isn’t constant in turbulent flow.

Partial vascular occlusion results in turbulent flow → Soft tapping sound. Decreasing pressure significantly will result in reduced sounds considering that occlusion is removed, enabling blood to flow in a laminar fashion.

29
Q

Which type of flow is associated with pathophysiological changes to the endothelial lining of the blood vessels?

A

Turbulent flow

Can alter the shear stress on vessels.

30
Q

What causes dicrotic notch?

A

Closure of aortic valve → Ventricular pressure decreases → Aortic pressure falls slowly in diastole due to elasticity (buffers pressure changes).

31
Q

What is the dicrotic notch?

A

Blood enters the aorta faster than it leaves. Aortic valve closure causes blood recoil.

32
Q

How can you calculate pulse pressure?

A

PP = SBP - DBP

33
Q

How do you calculate MAP using DBP and PP?

A

MAP (mmHg) = DBP + 1/3PP

34
Q

Define airway patency.

A

Whether the airways are open and active, able to allow air through.

35
Q

Is airway transmural pressure negative or positive during preinspiration, mid-inspiration and end-inspiration?

A

It is positive.
Transmural pressure is Pinside-Poutside e.g. 0–5=+5

Airway is patent in a pre-inspiratory lung, mid-inspiration and post-inspiration.

36
Q

Explain the pressure and volume changes during forced expiration.

A

Forced expiration → TLC to RV, significant increase in intrapleural pressure (+30). Pleural pressure > internal pressure of collapsable tubes → Airways close making forced expiration difficult.

During forced expiration the intrapleural pressure is significant, exerting a pressure inwards on the collapsible tube. Inwards pressure > outward pressure exerted by individual tubes → Collapse

37
Q

Use 1 word to describe the airways during forced/hard expiration.

A

Collapsed

38
Q

Define compliance

A

Willingness of a structure to change shape when pressure is applied/tendency to distort under pressure.

Compliance = Delta V/Delta P

39
Q

Define elastance

A

Tendency for structure to recoil to original volume (OPPOSITE) → Resistant to permeant structural change, reduced exhibition of plastic behaviour.

Elastance = Delta P/Delta V

40
Q

Does a condom have a greater compliance than a balloon?

A

Yes

41
Q

Does a condom have a greater elastance than a balloon?

A

No

42
Q

Why do ventricular and aortic pressures differ?

A

Once the aortic valve closes ventricular pressure falls rapidly but aortic pressure falls slowly. This can be explained by the elasticity of the aorta and larger arteries which act to “buffer” the change in pulse pressure.

The elasticity of a vessel is related to its compliance.

43
Q

During ejection does blood enter the aorta and other downstream elastic arteries faster than it leaves them?

A

Yes

40% of SV is stored by the elastic arteries.

44
Q

Explain what arterial compliance means in terms of the aorta.

A

Compliance of aorta is the ability of the aorta to stretch during systole, and subsequently recoil under pressure.

45
Q

What happens after aortic valve closure?

A

Ejection from the LV ceases, however due to elastic recoil exhibited by elastic arteries, the pressure declines at a reduced rate → Diastolic flow in downstream circulation.

46
Q

How would you expect blood pressure measurements to change if arterial compliance decreases?

A

Arteries stiffen → The damping Windkessel effect is reduced, subsequently increasing pulse pressure as SBP increases and DBP decreases. (Pulsatile motion, reduces diastolic flow).

47
Q

Describe the relationship between elastance and compliance.

A

Inversely proportional

48
Q

Explain how the skeletal muscle pump facilitates venous return.

A

Contraction of muscles to facilitate the movement of blood through the veins towards the heart, this decreases venous capacitance → Contraction and venous valves enables blood to flow unidirectionally.

49
Q

Explain how the respiratory pump facilitates venous return.

A

Intrathoracic pressure decreases during inspiration through increased intrathoracic volume → Reduction in pressure provides pressure potential for blood to return to the RA through the VC → increases venous return.

50
Q

Explain how gravity facilitates venous return.

A

Gradient of pressure from larger artery to capillary is maintained, providing flow to occur. Major effect of gravity is on distensible veins in the leg and the volume contained in them.

Standing causes activation of SNS → Vasoconstriction of veins → Increases TPR and maintains BP.
Standing increases HR in addition to increasing the force of contraction, enabling more blood to return to the brain. Dysfunctional return mechanism → Syncope

51
Q

What is varicosity?

A

Incompetent valves causes dilated superficial veins within the leg (Varicose veins).

52
Q

Explain how facilitated venous return can lead to oedema.

A

Prolonged elevation of venous pressure → Oedema in feet, despite intact compensatory mechanisms.

53
Q

Explain the pathophysiology of aneurysmal diseases.

A

Over time, vessel walls can weaken causing a balloon-like distension.
Pathological examples of Law of Laplace. Vascular aneurysms increase radius of the vessel → For the same internal pressure, the inward force exerted by the muscular wall increases.
Weakened muscle fibres, hence force can’t adequately be produced to withstand the internal pressure, therefore the aneurysm will continue to expansion until eruption.

(Pathology and underlying physical forces involved also responsible for DIVERTICULI formation within the gut wall.)

54
Q

Summary of Law of Laplace.

A

T= PR

Therefore increasing radius increases the tension (thickness of the wall must be thicker) → Prevents wall tension exceeding the tension capacity of vessel.

55
Q

What is compliance?

A

Relationship between the transmural pressure and the vessel volume.
Depends on vessel elasticity.

56
Q

Is venous compliance greater than arterial compliance?

A

Yes

Venous 10 to 20 times greater than arterial compliance at low pressures.

57
Q

What effect does increasing smooth muscle contraction have on venous volume and venous pressure?

A

Decreases venous volume and increases venous pressure.

58
Q

What type of blood vessel stores most blood volume?

A

Veins

59
Q

Do relatively small changes in venous distended veins increase the volume of blood stored in them?
Explain answer.

A

Yes

Relatively small changes in venous pressure distend veins and ^ volume of blood in them (Venous reservoir) → Gravity results in accumulation of blood in the legs due to venous capacitance → Reduced venous return → EDV/Preload decreases → Syncope

Thus, compensatory mechanism to overcome postural hypotension is to provide venous constriction, more blood returned to heart and CO is increased.

60
Q

What is syncope?

A

Medical term for fainting or passing out. It is caused by a temporary drop in the amount of blood that flows to the brain. Syncope can happen if you have a sudden drop in blood pressure, a drop in heart rate, or changes in the amount of blood in areas of your body.

61
Q

Explain how less ventilation occurs across the lung.

A

Pleural pressure is more negative therefore greater transmural pressure gradient. Alveoli larger and less compliant.

62
Q

Explain how more ventilation occurs across the lung.

A

Pleural pressure is less negative therefore smaller transmural pressure gradient. Alveoli smaller and more compliant.

63
Q

What effect does a low intravascular pressure have on recruitment, resistance and flow rate?

A

Less recruitment
Greater resistance
Lower flow rate

64
Q

What effect does a high intravascular pressure have on recruitment, resistance and flow rate?

A

More recruitment
Less resistance
Higher flow rate

65
Q

Define perfusion of a lung.

A

Refers to the flow of blood to alveolar capillaries.

66
Q

Does more ventilation occur at the top or bottom of an upright lung?

A

Bottom

67
Q

Does more perfusion occur at the bottom or top of an upright lung?

A

Bottom

More recruitment of vessels → Higher flow rate inferiorly → Greater perfusion.

BRS CVR (15 decks)

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