Cardiorespiratory Mechanics

Question 1

What are the mechanics of ventilation?

Answer 1

Inspiration - chest inflates —> Valv inc —> Palv dec —>
stretch —> air in
- need Palv < Patm
Expiration - chest deflates —> Valv dec —> Palv inc —>
squeeze —> air out
- need Palv > Patm

Question 2

How do airways react to an increased lung volume?

Answer 2

Dilate —> inc radius —> dec resistance —> inc conductance
∵ R = 8ηl / πr^4 (Poiseuille’s Law)

Question 3

How does pressure change throughout circulation?

Answer 3

Arteries —> higher pressure + v. pulsatile
Arterioles —> pressure dec + steadier flow
- smaller r —> inc R
Capillaries to veins —> pressure dec + steady flow

Question 4

How does exercise affect minute ventilation?

Answer 4

5L/min —> 100L/min
- inc breathing rate

Question 5

What is laminar vs turbulent blood flow?

Answer 5

Laminar —> flows in layers
- all blood at constant velocity
- fastest flow
- blood closest to centre of lumen

Turbulent —> erratic flow
- forms eddys (fluid spirals)
- prone to pooling
- sign of pathophysiological change in
vasculature endothelial lining

Question 6

How do you calculate pulse pressure?

Answer 6

PP = SBP - DBP (systolic - diastolic)

Question 7

How do you calculate MAP?

Answer 7

MAP = CO x PVR
= cardiac output x total peripheral resistance
- assumptions —> always steady flow
—> vessels rigid
—> right atrial pressure negligible
MAP = DBP + 1/3 PP
= DBP + DBP + SBP

Question 8

Why is cartilage needed to support extrapulmonary airways?

Answer 8

Prevent collapse of thoracic cavity during hard expiration
∵ high pressure in airways vs 0 pleural pressure
—> -ve gradient

Question 9

What is tissue compliance vs elastance?

Answer 9

Compliance —> tendency to distort under pressure
(opposite of rigidity)
- arterial dilation
- inc —> dec blood pressure
= ΔV / ΔP
Elastance —> tendency to recoil back to original vol
- arterial recoil
- inc —> inc blood pressure
= ΔP / ΔV
- lost in COPD

Question 10

Which 2 processes facilitate venous return?

Answer 10

1. Skeletal muscle pump
   
   • muscles contract —> push blood through veins
2. Respiratory pump
   
   • -ve pressure in thorax —> pull open veins

Question 11

Why how does diastolic pressure in the aorta change?

Answer 11

Flow intermittent —> continuous ∵ compliance

Question 12

What causes varicosity?

Answer 12

Incompetent vein valves —> veins dilate

Question 13

What causes oedema? (veins)

Answer 13

Prolonged high venous pressure —> fluid build up

Question 14

What is an aneurysmal disease?

Answer 14

Vessel walls weaken —> ballooning
- inc radius —> not enough force (LaPlace) ∵ weaker
muscle fibres —> aneurysm expands —> rupture
- expand over 4.5cm —> dangerous
- eg. diverticuli (abdominal aorta)

Question 15

What is the difference between arterial and venous compliance?

Answer 15

Venous compliance > arterial compliance
- 10-20 times
- inc smooth muscle contraction —> dec Vveins —> inc
Pveins —> veins store blood