Pulmonary Circulation

Question 1

Compare the systemic to pulmonary circulation

Answer 1

artery wall thick vs thin
Smaller lumen vs larger lumen
Ventricle thicker vs ventricle thinner
Greater length and distance vs smaller length and distance
High pressure vs low pressure
Greater volume vs lower volume
More resistance vs less

Question 2

Describe the pulmonary circulation using the following properties: 
artery wall thickness
Lumen size
Ventricular thickness
Length and distance
Pressure
Volume
Resistance

Answer 2

artery wall thickness - thinner
Lumen size - larger
Ventricular thickness - thinner (right)
Length and distance - smaller
Pressure - lower (15% of systemic)
Volume - less (10% of systemic)
Resistance - smaller

Question 3

What is the difference in output for the two circulations

Answer 3

CO is the same in both

Question 4

What are the functions of the pulmonary circulation

Answer 4

Perfusion of the respiratory airways for gas exchange
Gas exchange (O2, CO2, N2, CO)
Metabolism of vasoactive substances e.g. ACE for vasoconstriction 
Filtration of blood i.e. filtration for embolus before blood enters the systemic arteries

Question 5

Define embolus

Answer 5

Mass within the circulation that can cause obstruction

Question 6

Define embolism

Answer 6

Event characterised by obstruction of a major artery

Question 7

What can an embolus be a result of

Answer 7

Venous thrombosis
Ruptured fatty plaques
Air bubbles

Question 8

What is the fate of a small embolus vs large embolus

Answer 8

Eliminated in the pulmonary microcirculation

Trapped in the pulmonary microcirculation, leading to local perfusion obstruction

Question 9

What is a shunt

Answer 9

Circumstances associated with bypassing the respiratory exchange surface

Question 10

Where can pulmonary shunts arise

Answer 10

Bronchial circulation (blood from left leaks into the pulmonary trunk)
Foetal circulation
Congenital defect

Question 11

Where are the pulmonary shunts in the foetal circulation

Answer 11

Ductus arterioles between pulmonary artery and aorta

Foramen oval between atrial walls

Question 12

How can congenital defects cause pulmonary shunts

Answer 12

Atrial septal defect or ventricular septal defect
Blood is able to flow from left to right
Right side becomes dominant and de-oxygenated blood flow from right to left

Question 13

What is the effect on the systemic circulation of an increase in CO

Answer 13

1. increase CO
2. increased resistance
3. Increase MAP
4. Increase fluid leakage
5. Increased pulmonary oedema
6. Decreased pulmonary function

Question 14

What is the effect on the pulmonary circulation of an increase in CO

Answer 14

1. Increased CO
2. Increased resistance
3. Increased pulmonary artery distension
4. Increased perfusion of hypo perfused beds
5. Little change in MAP, minimal leakage, little pulmonary oedema

Fluid throughput increases but pressure does not

Question 15

Describe the pulmonary circulation in terms of resistance and capacity

Answer 15

Pulmonary circulation is a low resistance high capacity circuit at a resting Q̇ of 5 L/min

Question 16

What is the effect on the pulmonary circulation of an increase in ventilation

Answer 16

1. Expiration decreases the alveolar volume
2. Capillaries become compressed
3. Resistance increases
4. Expiration compresses extra-alveolar vessels
5. Inhalation
6. Capillaries expand and resistance decreases
7. Inspiration compresses alveolar vessels

Question 17

Describe the lung volume resistance graph

Answer 17

Vascular resistance is proportional to lung volume

High resistance at RV due to expiration compressing the extra-alveolar vessels

Resistance decreases to functional residual capacity where there is no compression

Resistance increases at tidal volume as inspiration compresses the alveolar vessels

Question 18

What is the systemic and pulmonary responses to hypoxia

Answer 18

systemic - vasodilation

Pulmonary - vasoconstriction

Question 19

Explain the pulmonary response to hypoxia

Answer 19

1. Hypoxia
2. Closure of oxygen sensitive K+ channels
3. Decrease in K+ efflux
4. Increase in membrane potential
5. Membrane depolarisation
6. Opening of voltage-gated calcium channels
7. Vascular smooth muscle constriction

Question 20

When is the pulmonary response to hypoxia beneficial

Answer 20

Foetal development
Blood flows in the path of least resistance
High-resistanc pulmonary circuit -> blood flows between shunts
Breathing increases alveolar PO2 and dilates the vessels

Question 21

When is the pulmonary response to hypoxia detrimental

Answer 21

COPD
Reduced alveolar ventilation and air trapping
Increased resistance in the pulmonary circuit
Pulmonary hypertension
Right ventricular hypertrophy
Congestive heart failure

Question 22

What factors articulate the behaviours of fluid accumulation

Answer 22

Hydrostatic pressure of the capillary
Hydrostatic pressure in the interstitium
Oncotic pressure in the capillary
Oncotic pressure in the interstitium

Question 23

What controls steady fluid accumulation

Answer 23

Lymphatic system

If production exceeds the max. rate of clearance/lymph system fails, fluid accumulates to cause oedema

Question 24

What is starling’s equation

Answer 24

permeability(hydrostatic Pressure in capillary - interstitium) - reflection coefficient(oncotic pressure in capillary - interstitium)