18 Flashcards
What is virtual capacity
Maximum volume of air you can shift in and out of your lungs
How much air do we breathe in and out
How much litres of air per minute in an adult
6
What is the dead space?
- some of the inhaled air never gets to the alveoli so channot gas exchange (VD) - about 150ml
- about 150mls of each breath just fills upper airways and is no use for gas exchange
Whats important is the amount of air that gets into the alveoli… Alveolar ventilation VA
What is alveolar ventilation
VA
The amount of air that gets into the alveoli
How to calculate Alveolar vetilation
- must suntract dead space
Why are tiny rapid breaths not helpful
- most of the air would just enter the dead space not the alveoli
Dalton’s law:
The pressure of any gas in a gas mixture is determined by its proportion
Gas diffusion depends on
Partial pressure
What is partial pressure
In a gas mixture, Each gas exerts its own individual pressure, called the partial pressure
The pressure of a minute of gasses =
The sum total of the pressure of each individual gas
Partial pressure on various conditions table
- higher water vapour pressure - water at body temp when inhaled
- lower oxygen as it’s given to the blood
Moving gas across the membranes (blood air barrier)
- the goal is to move gas back asn forth between the alveoli and the capillaries - until equilibrium
- transport inhaled oxygen into the capillaries
- transport carbon dioxide into the alveoli to be exhaled
How do gasses move across the membranes between alveoli and the apiliaareis ?
Difffusion
What determines the rate of diffusion?
- surface area of the membranes
- thickness of the membranes
- pressure difference between the two sides
Equation for rate of diffusion
What does the diffusion constant depend on?
Gas solubility (S) and its molecular weight
- on a per molecule basis, CO2 diffuses about 20x faster then O2 due to CO2 higher solubility
Why doesn’t nitrogen diffuse into circulation
Very low solubility
What does the bulbous structure of alveoli and the high density of capillarys create?
Lots of surface area for gas exchange
what creates the large surface area for gas exchange?
- bulbous structure of alveoli and the high density of capillaries
What is emphysema
A disease characterised by dilation of the alveolar spaces and destruction of the alveolar walls
- reduction in surface area means less contact between the air and capillaries, so oxygen exchange is greatly reduced
What is the result of reduction in surface area
Less contact between air and capillaries, so oxygen exchange is greatly reduced
What is emphysema an example of
Chronic obstructive lung disease
What is an example of chromic obstructive lung disease
Emphysema
What is the blood air barrier consisting of?
- alveolar
- capillary walls
Distance between the alveolar air and blood is very…
Small
Pulmonary fibrosis and consequences
- thickening and scaring of the alveolar membranes
- can arise from chronic inflammation or exposure to industrial chemicals
- thickness increases therefor rate of diffusion decreases
(People appear pale and blue as they are not getting enough oxygen)
3 factors that affect diffusion
- alveolar area for diffusion (emphysema)
- thickness of alveolar membrane (fibrosis)
- MAIN FACTOR IS: pressure difference
- must have pressure gradient across e membrane or gas will not move
Pressure difference drives
Diffusion
Alveolar - arterial
- high O2 in alveolar for flow to low
- high CO2 in arterial for flow to low
What does PAO2 depend on? Atmosphere?
- Partial pressure of oxygen in inspired air
- Alveolar consumption
- Oxygen consumption - blood oxygen
The atmospheric PO2 is usually constant, so it is the balance between oxygen consumption and alveolar ventilation that is most important
What pressure does equilibrium occur
100 mm mercury
Low activity - oxygen
- reduced oxygen consumption
- higher levels of oxygen in the venous blood
High activity - oxygen
- increased oxygen consumption
- lower levels of oxygen in the venous blood
(This means there is a greater pressure difference between alveoli and capillaries)
(High metabolism = more oxygen leaving the alveoli0
Gasses diffusing down their pressure gradient
- PO2 in venous system at beginning of diffusion = 40
- PCO2 in venous system at beginning of diffusion = 46
- PO2 in alveoli at beginning of diffusion = 100
- PCO2 in alveoli system at beginning of diffusion = 40
Breathing and metabolism control the difference in pressure thus the rate of diffusion?
