Cardiorespiratory mechanics

Question 1

Describe the mechanics of ventilation for one breath cycle

Answer 1

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

Question 2

What is flow rate proportional to?

Answer 2

Flow rate is proportional to the pressure gradient

If airway radius is the same

Question 3

Describe the protocol for performing pulmonary function tests

Answer 3

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

Question 4

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

Answer 4

Peak respiratory flow rate

Vital capacity

Question 5

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

Answer 5

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

Question 6

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

Answer 6

Displaced to the right

Narrower curve

Question 7

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

Answer 7

Blunted expiratory curve

Otherwise normal

Question 8

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

Answer 8

Blunted inspiratory curve

Otherwise normal

Question 9

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

Answer 9

Blunted inspiratory curve
Blunted expiratory curve
Otherwise normal

Question 10

What is poiseuille’s law

Answer 10

𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒= 8ƞƖ/〖𝜋𝑟〗^4

Question 11

What is resistance proportional to?

Answer 11

Inversely proportional to the fourth power of the radius

Question 12

What is conductance?

Answer 12

Willingness of the airways to conduct fluid transpire (Air)

Question 13

What happens to airways as lung volume increases?

Answer 13

They dilate

Conductivity increases

Question 14

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

Answer 14

to regulate their diameters and the resistance to blood flow

Question 15

What is blood pressure equal to?

Answer 15

Cardiac output x Resistance

Question 16

Why is the blood pressure relationship approximate?

Answer 16

steady flow (which does not occur due to the intermittent pumping of the heart)
rigid vessels
right atrial pressure is negligible

Question 17

Physiologically, how is regulation of flow achieved?

Answer 17

Variation in resistance in the vessels

Question 18

What is the importance of poiseuille’s equation?

Answer 18

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.

Question 19

What does resistance of a tube to flow depend on?

Answer 19

Fluid viscosity (, eta)

2. The length of the tube (L).
3. Inner radius of the tube (r)

Question 20

What would halving the radius to the flow?

Answer 20

Decrease it 16x

Question 21

At rest what is cardiac output?

Answer 21

5L/min

Question 22

During exercise what is cardiac output?

Answer 22

20L/min

Question 23

What is laminar flow?

Answer 23

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

Question 24

What is turbulent flow?

Answer 24

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

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

Question 25

What is pulse pressure equal to?

Answer 25

SBP-DBP

Question 26

What is MAP equal to?

Answer 26

DBP + 1/3 pulse pressure

Question 27

What is compliance?

Answer 27

The tendency to distort under pressure

Question 28

What is elastance?

Answer 28

The tendency to recall to its original volume | Not the same as elasticity

Question 29

What is the elasticity of a vessel related to?

Answer 29

Compliance

Question 30

What happens one the aortic valve closes?

Answer 30

ventricular pressure falls rapidly but aortic pressure falls slowly

Question 31

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

Answer 31

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

Question 32

What occurs during ejection?

Answer 32

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

Question 33

What causes ejection to cease?

Answer 33

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

Question 34

What can cause arterial compliance to decrease?

Answer 34

arteries become stiffer; e.g. with age

Question 35

What happens when arterial compliance decreases?

Answer 35

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

Question 36

How can the failure of valves present?

Answer 36

``` dilated superficial veins in the leg (varicose veins ```

Question 37

How can the prolonged elevation of venous pressure present?

Answer 37

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

Question 38

Define the law of Laplace

Answer 38

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

Question 39

How does an aneurysm occur?

Answer 39

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

Question 40

What is a pathological example of the law of Laplace

Answer 40

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.

Question 41

What happens if the muscle fibres of the aneurysm weaken?

Answer 41

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

Question 42

What is compliance?

Answer 42

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

Question 43

What is the relationship between venous and arterial compliance?

Answer 43

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

Question 44

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

Answer 44

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

Question 45

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

Answer 45

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

Question 46

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

Answer 46

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

Question 47

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

Answer 47

``` Higher intravascular pressure (gravity effect) More recruitment Less resistance Higher flow rate ```

Question 48

What occurs to overcome variation in ventilation and perfusion?

Answer 48

Ventilation perfusion matching