What is dead space ?
Volume of inspired air playing no role in gas exchange
It is a proportion of your tidal volume and won’t do anything
What is tidal volume equation ?
Vt = VA + Vd
Tidal volume = alveolar volume + dead space volume
Types of dead space
Anatomical dead space
Alveolar dead space
Added together this makes physiological dead space
What is anatomical dead space ?
Some airways don’t have the option to transfer oxygen into alveoli because they don’t have alveoli
Ie trachea, bronchi, bronchioles
How much anatomical dead space does a normal person have
Normally about 2mg/kg
How is anatomical dead space increased or decreased
Increased by bronchodilation
Decreased by bronchoconstriction
What is alveolar dead space?
Some alveoli will not be perfused so will not have the ability of gas exchange therefore are dead space
Is alveolar dead space always an issue ?
No in health individuals should not be a problem
When would alveolar dead space be increased ?
Low ventricular cardiac output
Too much PEEP
PE
COPD
Why does too much PEEP cause alveolar dead space ?
Cause over distention of alveoli occluding pulmonary capillaries. This means there would be no gas exchange
Why would having COPD increase alveolar dead space ?
Break down of alveoli so not all alveoli get perfused
What is physiological dead space ?
Anatomical dead space + alveolar dead space
3 characteristics of red blood cells
No nucleus allowing for more oxygen binding
Concave shape to fit through capillaries
2 alpha and 2 beta chains
What is co-operative binding ?
As each oxygen binds the easier the next molecule of oxygen will bind due to the shape of the molecule changing.
This is why oxygen dissociation curve is a sigmoid shape
What is 2,3 DPG ?
A molecule that binds to red blood cells, regulates the haemoglobin oxygen affinity, controlling oxygen delivery to the cells
What would an increase in 2,3 DPG mean ?
More oxygen available for the cells
What conditions would an increase in 2,3 DPG benefit ?
Anaemia
High Altitude
Pregnancy
What would a right shift in the oxygen dissociation curve indicate ?
Oxygen is more readily available
What would cause a right shift if the oxygen dissociation curve
Increase in temperature (hyperthermia)
Decrease in pH (acidosis)
Increase in CO2
Increase in 2,3 DPG
What would a left shift in the oxygen dissociation curve mean ?
Oxygen is less readily available
What would cause a left shift in the oxygen dissociation curve
Decreased temp
Increased pH
Decreased CO2
Decreased 2,3 DPG
Why is the carbon dioxide transportation graph linear and not sigmoid ?
Because no association between molecules binding and then having more affinity to bind as with haemoglobin and oxygen
How is carbon dioxide transported ?
Bound to haemoglobin
Dissolved in plasma
Transported as part of bicarbonate (CO2 + H2O make carbonic acid which dissociates into HCO3 and H+)
