L11: Ventilation And Perfusion Flashcards
What is PAo2 (alveolar partial pressure)
13
What is the pao2 (arterial partial pressure) when it leaves the left side of the heart
12
What are the 2 reasons for the 1kpa difference in alveolar and arterial partial pressure
Shunts
Ventilation perfusion mismatch
What is the shunting process
When deoxygnated blood reaches the lungs some alveoli do no oxygenate the blood this gives a mixture of deoxygenated and oxygenated blood leaving the left heart at 12kpa instead of 13kpa
What is the ventilation perfusion ratio (V/Q) mismatch
The flow of blood is greater than the alveolar ventilation
What is the fall in pao2 termed as
Hypoxia
From which side to side does blood move from in the heart
Right to left
Does the right side of the heart carry deoxygenated blood or oxygenated blood
Deoxygenated blood
After leaving the right side of the heart where does the deoxygenated go
To the lungs
What happens to the deoxygenated blood at the lungs
Blood becomes oxygenated
Where does oxygenated blood travel to after the lungs
Left side of the heart
After leaving the left side of the heart where does the oxygenated blood travel to
Rest of the body
What happens to the oxygenated blood after reaching to the rest of the body
Blood becomes deoxygenated
After the rest of the body where does deoxygenated blood go to
Right side of the heart
What is right-left shunted blood
Blood that contains a mixture of oxygenated and deoxygenated blood
Do we have natural right left shunts
Yes
What are the natural shunts in the heart
Thebesian veins
What are thebesian veins
Small valve-less venous channels that open directly into the heart
Arterial blood that has gone to supply the cardiac tissue but instead of draining back into the venous system it drains into the left ventricle
What are the other natural right-left shunts
Bronchial circulation
What is the bronchial circulation
Lungs has its only arterial supply from the thoracic aorta
What happens to the blood in the bronchopulmonary veins of the bronchial circulation
The blood join the pulmonary vein, mixes with the oxygenated blood to go into the left atrium
What are pathological right-left shunts
A greater alveolar-arterial pressure difference due to disease
Name pathological right-left shunts
Pulmonary disease
What does the pulmonary disease include
Airway blockage
Collapsed bronchi
How does pulmonary disease cause an increase in alveolar-arterial difference
Pulmonary artery cannot receive oxygen
What are left-right shunts
Cardiovascular anatomical abnormalities
How does cardiovascular anatomical abnormalities occur
Occur in neonates with septal defects
What happens in a left-right shunt
Oxygenated blood enters the deoxygenated areas
In a normal lung what is the ventilation/perfusion (V/Q) ratio
0.8
What are the main causes of ventilation in the lungs
Gravity
Compliance
What happens to the alveolar ventilation as you go down from apex to base
Increase
Why is there are greater ventilation at the base than apex
Base has a greater compliance and more negative intrapleural pressure
What are the main causes of change in perfusion
Gravity
What happens to the perfusion as you go down from apex to base
Increases
What happens to the ventilation/perfusion ratio as you go down from apex to base
Decreases
What are the 2 mechanisms that alter the ventilation/perfusion ratio (V/Q)
Bronchiole diameter
Arteriole diameter
What does the bronchiole diameter alter
Ventilation
What does arteriole diameter alter
Perfusion
What does a high V/Q lead to
Hyperoxia
Hypocapnia
What is hyperoxia
High oxygen in blood
What is hypocapnia
Low carbon dioxide
What does a low V/Q lead to
Hypoxia
Hypercapnia
What is hypoxia
Low oxygen in blood
What is hypercapnia
High carbon dioxide in blood
How does the body respond to a high V/Q
Vasodilation
Bronchoconstriction
How does the body respond to a low V/Q
Vasoconstriction
Bronchodilation
What is hypoxic pulmonary vasoconstriction
During hypoxia vascoconstriction occurs to divert the blood away
How does hypoxic pulmonary vasoconstriction occur
1) potassium channels of smooth muscle of bronchioles are inhibited by hypoxia
2) this leads to membrane depolarisation
3) voltage gated calcium channels open
4) calcium influx gives vasoconstriction
Name a lung disease which results in a high V/Q mismatch
Bronchitis
Emphysema
What equation do we use to find out hypoxia is due to alveolar ventilation
Alveolar gas equation
