Lung Ventilation Flashcards
Why are pO2 and pCO2s of capillaries around alveoli much more variable than alveolar gas?
pCO2 and pO2 that enters venous return is variable as tissues have varying metabolic rates - however, these areas are all mixed in the R atria
What 3 factors does diffusion depend on?
- area
- gradient
- diffusion resistance: nature of barrier, nature of gas
Name the 5 components of the ‘Diffusion Barrier’ that gases must travel through
- alveolar membrane/epithelial cell of alveolus
- Tissue fluid
- endothelial cel lining vessel
- plasma
- RBC membrane
Why is the diffusion of gases across the alveolar membrane into an RBC ‘low resistance’?
Oxygen diffusion takes 0.5 seconds but the single RBC is squashed against the endothelial cell for 1s, so there is double the necessary time for oxygen to diffuse
Explain the diffusion pattern of gases through gases, what does this mean in terms of O2 and CO2?
Gases diffuse through gases at a rate inversely proportional to molecular weight. Therefore CO2 diffuses slower as it is has a larger molecular weight
Explain the diffusion pattern of gases through liquids, what does this mean in terms of O2 and CO2?
Gases diffuse through liquids at a rate proportional to solubility. Therefore CO2 diffuses faster as it is more soluble than O2.
Why is the exchange of oxygen always limiting?
Because more of the diffusion barrier is liquid, and CO2 diffuses through liquid faster than O2 as it is more soluble. Therefore, the net diffusion of CO2 is much faster than O2 overall.
What determines the composition of arterial blood, O2 supply to tissues and CO2 removal from tissues?
The composition of alveolar air, as exchange is SO efficient that blood leaving the alveolar capillaries should be in equilibrium with alveolar air
Where does O2 immediately go once we’ve breathed in?
Down the resp tract and NEXT to the alveoli (not into) so it can diffuse in and CO2 can diffuse out and then be breathed out
Define the ____
a) tidal volume + it’s typical value
b) inspiratory reserve
c) expiratory reserve
a) Tidal volume: volume in and out of lungs with each breath - about 0.5L
b) Inspiratory reserve: extra volume that can be breathed in at rest
c) Expiratory reserve: extra volume that can be breathed out at rest
What is the residual volume?
The volume of air within the lungs that is never breathed out and therefore cannot be measured by a spirometer
What are the 3 points on the breathing cycle that don’t change without the presence of illness (or ageing)? What are they called?
Capacities are independent of breathing patterns and tell you when the lungs structurally change. (illness or ageing)
- Vital capacity: max inspiration – max expiration
- Inspiratory Capacity: from resting expiratory level – max inspiration
- Functional residual capacity: the amount of air in lungs at end of quiet expiration
What 2 factors regulate ‘ventilation rate’
What is pulmonary ventilation rate and how would you calculate it?
The Tidal volume and Resp rate
Pulmonary ventilation rate is the total rate of movement in and out of the lungs, calculated by multiplying the Tidal volume X resp rate
What is ‘Dead space’?
What are the 2 components that need to be considered when calculating the ‘Total Dead space volume’?
The air that never reaches the alveoli: the last air into the airways is the first air out
The 2 components are… (they must be added)
- Serial dead space: volume of air that doesn’t reach alveoli
- Distributive dead space: parts of the lungs that are filled but don’t support gas exchange (dead/damaged alveoli, alveoli with poor perfusion)
What is the Alveolar Ventilation rate and how would you calculate it?
AVR: The total amount of air that ACTUALLY reaches the alveoli
Calculated: Pulmonary ventilation rate - dead space ventilation rate
