5 Blood Supply Flashcards
How do we denote alveolar air, arterial blood and mixed venous blood?
Alveolar air - A
Arterial blood - a
Mixed venous blood - ṽ (e.g. in pulmonary artery)
How do we denote the partial pressure of alveolar air?
PAO2 (A in subscript)
From what section of the heart do the L&R pulmonary arteries arise?
Right ventricle, carry entire cardiac output
What section of the heart does pulmonary circulation return to?
Left Atrium
Describe the pressure & flow of the pulmonary circulation?
High flow
Low pressure
What do systolic/diastolic mean?
Systolic is max blood pressure when heart is contracted
Diastolic is min blood pressure when heart is relaxed
What are the normal systolic pressures?
Pulmonary systolic pressure = 25mmHg
Systemic systolic pressure = 120mmHg
What is the difference between pressure of the pulmonary vein and artery that causes blood to flow?
Why is it clinically important?
About 10mmHg
Because its so small it only takes a little pathology to disrupt blood flow
(Systemic normally 100mmHg)
What causes gas to move between the blood and lungs?
Gases move down the partial pressure gradient
What effects the rate of diffusion of O2 across the membrane?
Directly proportional to:
- partial pressure gradient
- gas solubility
- surface area
Inversely proportional to membrane thickness
Most rapid over short distance
What happens in emphysema?
Destruction of Alveoli
Surface area reduced
Gas exchange decreases
PaO2 gets low
What happens in fibrotic lung disease?
Alveolar membrane thickens
Gas exchange slows
Loss of compliance may decrease alveolar ventilation
PAO2 may be reduced and reduce PaO2
How does pulmonary oedema affect gas exchange?
Interstitial fluid increases
Diffusion distance increases
PAO2 is normal but PaO2 is low
How does asthma affect gas exchange?
Bronchioles constrict
Airway resistance increases
Alveolar ventilation decreases
PAO2 & PaO2 are reduced
What is the ideal ventilation-perfusion relationship?
Alveolar ventilation matches perfusion in L/min
Where is pulmonary blood flow highest and why?
Base of lung
Arterial pressure exceeds alveolar pressure so vascular resistance is low
Where is pulmonary blood flow lowest and why?
Apex of lung
Alveolar pressure exceeds arterial pressure
Arterioles are compressed and vascular resistance increased
How much of the lung has an equal blood flow & ventilation?
Around 75% of lung height has 1:1 ratio of blood flow to ventilation
Where does most of the bloodflow to ventilation mismatch occur?
Apex
What is it called when blood flow to a section of lung tissue exceeds ventilation?
Shunt
(Blood gets shunted away)
Define shunt:
Passage of blood through areas of the lung that are poorly ventilated
In a shunt how do the Partial pressures alter in the alveoli?
- PA CO2 increases
- PA O2 decreases
What happens to blood flowing past a shunt?
It is deoxygenated
How does the body auto-regulate a shunt?
Hypoxia in alveoli detected
-> Relevant arterioles constrict
-> Less blood flows to under-ventilated parts of lung
-> Increased PA CO2 also causes bronchodilation
-> Ventilation increases
What normally happens to blood vessels when hypoxia is detected?
Systemic circulation - dilate to allow greater oxygen delivery
Pulmonary circulation - constrict to divert blood to better ventilated parts of lung
What do we call it when an area of lung tissue has a greater ventilation than blood flow?
Alveolar dead space
Define alveolar dead space?
Alveoli that are well ventilated but insufficiently perfused
What happens to PA during alveolar dead space?
PA O2 increases
PA CO2 decreases
How does the body regulate alveolar dead space?
- Increased PA O2 causes pulmonary vasodilation diverting blood to the highly ventilated areas
- Decreased PA CO2 causes bronchial constriction which reduces ventilation
What is physiological dead space?
Sum of Alveolar Dead Space + Anatomical Dead Space
