Cardiorespiratory mechanics (30)

Question 1

What happens to the flow-volume loop in variable extra thoracic obstruction?

Answer 1

• blunted inspiratory curve
• otherwise normal
• obstruction to inspiration, but not expiration

Question 2

What happens to the flow-volume loop in variable intrathoracic obstruction?

Answer 2

• blunted expiratory curve
• otherwise normal
• no obstruction to inspiration, but blocks air coming back/expiration

Question 3

What is the significance of Poiseuille’s Law?

Answer 3

if you decrease radius by half, the resistance goes up 16 fold
resistance=8.n.l/pi.r^4
fluid viscosity= n
length of tube= L
inner radius of tube= r

Question 4

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

Answer 4

• resistance increases up to airway generation 4, then decreases
• bc we are increasing the cumulative cross-sectional area (inc. numbers)

Question 5

What are some characteristics of systemic circulation?

Answer 5

• 60-70% of systemic blood is in venous system
• veins and venules are highly compliant
• small arteries and arterioles have extensive smooth muscle in their walls to regulate their diameters and resistance to blood flow

Question 6

Why does pressure fall across the circulation?

Answer 6

due to viscous/frictional pressure losses

Question 7

What is the equation for blood pressure/ mean arterial pressure?

Answer 7

MAP= cardiac output X resistance (TPR)
–> assumes steady flow, rigid vessels and that right atrial pressure is negligible
AND
MAP= diastolic blood pressure + 1/3 pulse pressure
(pulse pressure= SBP-DBP)

Question 8

What is laminar flow?

Answer 8

• velocity of fluid is constant at any one point and flows in layers
• blood flows fastest closest to the centre of the lumen

Question 9

What is turbulent flow?

Answer 9

• blood flows erratically, forming eddys, and is prone to pooling
• associated w/ pathophysiological changes to the endothelial lining of the blood vessels

Question 10

What is elastance in terms of lung tissue?

Answer 10

its tendency to resist force and return to original shape/volume

Question 11

What is compliance in terms of lung tissue?

Answer 11

willingness to distort its shape under pressure

Question 12

What is the equation for compliance?

Answer 12

change in volume/change in pressure

Question 13

What is the equation for elastance?

Answer 13

change in pressure/change in volume

Question 14

What is the relevance arterial compliance in the aorta?

Answer 14

• Windkessel effect
• aorta stretches during systole and recoils during diastole
• prevents intermittent flow–> continuous flow bc elastic aorta

Question 15

How does the body facilitate venous return?

Answer 15

• skeletal muscle pump e.g. when we walk, veins get squashed by muscles and pushes blood up
• respiratory pump e.g. when we breathe in, intrathoracic pressure decreases–> strethces open low pressure vena cava, increasing pressure gradient into right atrium–> improved venous return

Question 16

When does varicosity occur?

Answer 16

incompetent valves–> dilated superficial veins in the leg (varicose veins)

Question 17

When does oedema occur?

Answer 17

after prolonged elevation of venous pressure

Question 18

What is a pathological example of the law of Laplace?

Answer 18

• aneurysms
• vessel walls weaken–> balloon-like distension
• inc. radius of vessel, so inward force exerted by muscular wall must also increase for the same internal pressure
• if muscle fibres have weakened, the force needed cannot be produced, so aneurysm continues to expand until it ruptures

Question 19

Why is it easier to ventilate the base of the lung?

Answer 19

• lower transmural pressure
• tissue stretched by gravity
• more blood flows to base

Question 20

What can a flow-volume loop show in a pulmonary function test?

Answer 20

peak expiratory flow- the peak y-axis

vital capacity- difference between x points

Question 21

What does a COPD flow-volume loop look like?

Answer 21

• displaced to the left bc lungs fuller, but amount of air accessed is less
• decreased vital capacity and indented exhalation curve bc obstruction

Question 22

What does a flow-volume loop look like in restrictive disease?

Answer 22

restrict ability of chest to expand, so lungs cannot fill as much

• displaced to the right
• narrower curve

Question 23

What is conductance?

Answer 23

• willingness of airways to conduct air

- the conductivity of airways inc. w/ inc. volume