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 a pulmonary artery)
So 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?
The right ventricle, they carry its 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 refers to max blood presssure when the heart is contracted
Diastolic refers to min blood pressure when the heart is relaxed
What are the normal systolic pressures?
Pulmonary systolic pressure = 25mmHg
Systemic systolic pressure = 120mmHg
Whats the diference between the pressure of the pulmonary vein and artery that causes blood to flow? And why is it clinically important?
About 10mmHg
Because its so small it only takes a little patholgy to disrupt the blood flow. (Systemic is 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
- Directly proportional to gas solubility
- Directly proportional to surface area
- Inversely proportional to membrane thickness
- Most rapid over short distance
What happens in emphysema?
- Destruction of Alveoli
- Surface area is reduced
- Gas exchange decreases
- PaO2 gets low
What happens in fibrotic lung disease?
- Alveolar membrane thickens
- Gas exchange slows
- Also loss of compliance may decrease alveolar ventilation
- PAO2 may be reduced and PaO2 is reduced.
How does pulmonary oedema affect gas exchange?
- Institial 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?
Ideally Alveolar ventilation with match perfusion in L/min
Where is pulmonary blood flow highest? whY?
The base of the lung
Arterial pressure exceeds alveolar pressure.so vascular resistance is low
Where is pulmonary blood flow lowest? Why?
The apex of the lung
Alveolar pressure exceeds arterial pressure so the arterioles are compressed and vascular resistance increased.
How much of the lung has an equal blood flow & ventilation?
Around 75% of the height of the lung has a 1:1 ratio of blood flow: ventilation
Where does most of the bloowflow:ventilation mismatch occur?
At the apex
When is it called when blood flow to a section of lung tissue exceeds ventilation?
A Shunt
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 isnt oxygenated
When detecting a shunt the body auto-regulates. How does it do this?
Hypoxia in alveoli detected
- > Relevant arterioles constrict
- > Less blood flows to underventilated parts of the lung
- > Increased PA CO2 also causes bronchodilation
- > Ventilation increases
What normally happens to blood vessels when hypoxia is detected?
They would usually dilate to allow greater oxygen delivery.
Only in the pulmonary circulation will they constrict on hypoxia.
