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Cardiology > Cardiorespiratory mechanics > Flashcards

Cardiorespiratory mechanics Flashcards

1
Q

Describe the mechanics of ventilation for one breath cycle

A 
As alveolar pressure decreases
A pressure gradient is created 
Causes air to flow in 
More gas particles in the lungs 
Diaphragm recoils and pressure returns to starting point
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2
Q

What is flow rate proportional to?

A

Flow rate is proportional to the pressure gradient

If airway radius is the same

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3
Q

Describe the protocol for performing pulmonary function tests

A

Patient wears noseclip
Patient wraps lips round mouthpiece
Patient completes at least one tidal breath
Patient inhales steadily to TLC
Patient exhales as hard and fast as possible
Exhalation continues until RV is reached
Patient immediately inhales to TLC
Visually inspect performance and volume time curve and repeat if necessary. Look out for:
- Inconsistencies with clinical picture
- Interrupted flow data

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4
Q

What are the key pieces of information that can be taken from flow-volume loops

A

Peak respiratory flow rate

Vital capacity

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5
Q

What would an abnormal flow-volume loop look like in a patient with COPD?

A

Lungs in COPD are fuller
Loops shift to the left
Air that is accessible is much less
Vital capacity decreases
Narrowing of the airways cause the peak to lower
Coving worsens- indented exhalation curve

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6
Q

What would an abnormal flow-volume loop look like in a patient with restrictive disease?

A

Displaced to the right

Narrower curve

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7
Q

What would a flow-volume loop look like in a patient with a variable intra-thoracic obstruction?

A

Blunted expiratory curve

Otherwise normal

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8
Q

What would a flow-volume loop look like in a patient with a variable extra-thoracic obstruction?

A

Blunted inspiratory curve

Otherwise normal

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9
Q

What would a flow-volume loop look like in a patient with a fixed airway obstruction?

A

Blunted inspiratory curve
Blunted expiratory curve
Otherwise normal

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10
Q

What is poiseuille’s law

A

𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒= 8ƞƖ/〖𝜋𝑟〗^4

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11
Q

What is resistance proportional to?

A

Inversely proportional to the fourth power of the radius

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12
Q

What is conductance?

A

Willingness of the airways to conduct fluid transpire (Air)

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13
Q

What happens to airways as lung volume increases?

A

They dilate

Conductivity increases

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14
Q

What is the role of smooth muscle in the walls of small arteries and arterioles?

A

to regulate their diameters and the resistance to blood flow

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15
Q

What is blood pressure equal to?

A

Cardiac output x Resistance

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16
Q

Why is the blood pressure relationship approximate?

A

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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17
Q

Physiologically, how is regulation of flow achieved?

A

Variation in resistance in the vessels

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18
Q

What is the importance of poiseuille’s equation?

A

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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19
Q

What does resistance of a tube to flow depend on?

A

Fluid viscosity (, eta)

  1. The length of the tube (L).
  2. Inner radius of the tube (r)
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20
Q

What would halving the radius to the flow?

A

Decrease it 16x

21
Q

At rest what is cardiac output?

A

5L/min

22
Q

During exercise what is cardiac output?

A

20L/min

23
Q

What is laminar flow?

A

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

24
Q

What is turbulent flow?

A

Blood flows erratically, forming eddys, and is prone to pooling

Associated with pathophysiological changes to the endothelial lining of the blood vessels..

25
Q

What is pulse pressure equal to?

A

SBP-DBP

26
Q

What is MAP equal to?

A

DBP + 1/3 pulse pressure

27
Q

What is compliance?

A

The tendency to distort under pressure

28
Q

What is elastance?

A

The tendency to recall to its original volume

Not the same as elasticity

29
Q

What is the elasticity of a vessel related to?

A

Compliance

30
Q

What happens one the aortic valve closes?

A

ventricular pressure falls rapidly but aortic pressure falls slowly

31
Q

What can explain the events that occur after the aortic valve closes?

A

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

32
Q

What occurs during ejection?

A

blood enters the aorta and other downstream elastic arteries faster than it leaves them (40% of SV is stored by the elastic arteries)

33
Q

What causes ejection to cease?

A

Aortic valve closes

Due to recoil of the elastic arteries, pressure falls slowly and there is diastolic flow in the downstream circulation

34
Q

What can cause arterial compliance to decrease?

A

arteries become stiffer; e.g. with age

35
Q

What happens when arterial compliance decreases?

A

the damping effect of the Windkessel effect is reduced and the pulse pressure increases.

36
Q

How can the failure of valves present?

A 
dilated superficial veins in 
the leg (varicose veins
37
Q

How can the prolonged elevation of venous pressure present?

A

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

38
Q

Define the law of Laplace

A

When the pressure within a cylinder is held constant the tension on its walls increases with increasing radius

39
Q

How does an aneurysm occur?

A

Over time, vessel walls can weaken causing a balloon-like distension

40
Q

What is a pathological example of the law of Laplace

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.

41
Q

What happens if the muscle fibres of the aneurysm weaken?

A

the force needed cannot be produced and so the aneurysm will continue to expand …
often until it ruptures.

42
Q

What is compliance?

A

The relationship between the transmural pressure and the vessel volume is called the compliance and depends on vessel elasticity

43
Q

What is the relationship between venous and arterial compliance?

A

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

44
Q

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

A

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

45
Q

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

A

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

46
Q

Why is there a lower flow rate at the top of the lungs?

A

Lower intravascular pressure (gravity effect)Less recruitment
Greater resistance
Lower flow rate

47
Q

Why is there higher intravascular pressure at the bottom of the lung?

A 
Higher intravascular pressure 
(gravity effect)
More recruitment
Less resistance
Higher flow rate
48
Q

What occurs to overcome variation in ventilation and perfusion?

A

Ventilation perfusion matching

Cardiology (16 decks)

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