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What does matching ventilation and perfusion mean?

flow of blood and air into the lungs.
need enough time for it to take blace.


What do partial pressures of 02 and co2 at end pulmonary capillaries refelct?

the same as the alveolie! this determiens partial pressure of the blood and in the lungs.


Describe ventilation persfusion mismatch scenarios.

Normal V/Q: inside lung 02 100, co2 40, in blood initally o2 is 40 and co2 is 45, but then o2 is 100 and co2 is 40. Becomes the same.

Shunt like V/Q = zero. there is no exchange and everything is 40/45 Partial means that its between this and normal

Dead Space: blood clot, means no blood passing. V/Q= infinite


Describe barometric pressure and calculate individual partial pressures.

each gas has its own partial pressure, all indepedent. come together to form atmospheric pressure.
760 mmHG measured by mercury ometer
Individual pressure: baromentric x fraction in the air.


How do you determine partial pressure in the airways?

P(gas) = barometric pressure (760-47) x fraction of (gas)
47 is the partial pressure of water vapour (when inspired you need to subtract this from barometric pressure)


Why does the partial pressure of 02 decrease as you go into the lungs. what about co2?

1st it loses it to humidity, then it is diluted by FRC and drops to 40.
c02 is baseline at 40 as long as you keep breathing.


how does 02 work at high altitude?

barometric pressure is halved but still subtract same 47mmGg.


how do partial pressure work when dissolved in solution?

liquid and gases both dissolved, gas sits on top, gases move according to partial pressures. its NOT concentration because this is solubility affects concentration. Gases from from high partial pressure to lower partial pressure.
Tension: partial pressure of gas in the pocket above.


What are the driving pressures for gas exchange?

in lungs: oxygen is 60 driving, carbon is 6
in tissues: o2 is 60 and carbon is 6.


What's fick's law of diffusion?

Rate at which it diffuses across it.
Propertional to driving pressure of the gas x area of that surface (size of tennis court) x diffusivity of the given gas which is proportional to its solubility divided by square route of it's molecular weight.

The greater they are, the more gas will diffuse
The thicker, the less gas will diffuse.

Thin with huge surface area is ideal for gas exchange.
Gas that has good solubility/best solubility is ideal, and the greater the driving pressure, the greater the difference in pressures, the more gas will diffuse.

Compare diffusivity of oxygen compared to Co2, get equilibrium between air and lungs for diffusion (complete of both) within a similar time frame. But way more o2 diffuses. But that’s why not only partial pressure is important)
V(gas): rate at which gas is diffusing across.


What happens in exercise when surface area increases?

Increase in surface area?
- Exercise
1. increase tidal volume, stretch SA and decrease thickness)
2. Increase cardiac output, increase pressure, have more capillaries open, more surface area for gas exchange
All improves gas exchange.


what happens in emphysema to gas exchange? what about other factors?

Emphysema: loss of alveolar capillary walls
- Big bullae here.

- Increase lung compliance (fill easy but don't empty easy)
- Reduced area for gas exhange
Mechanical and gas exchange problems

Problematic for both carbon dioxide. Carbon dioxide RETENTION (cant breathe it out properly) .

Other factors for lost surface area?
Collapse of the lung (NRDS/ARDS (covid does this))
Surgical removal due to cancer :(


How does an increase in thickness impact gas exchange. Describe an example in detail.

Thickness impacts gas exchange
- Pulmonary fibrosis (collagen deposition and scar formation
○ Lung compliance (mechanical) stiff lung
○ Increase in thickness (gas exchange issue)

Mechanical and gas exhange issues.

PV: due to many things
- Industrial dust (asbestosis, silicosis)
- Spores from moldy hay (farmers lungs) , inflammation and scarring
- Antigens in avian feather/excreta (bird breedres lung), scar formation
- Therapeutic drugs, radiation, poisons, (weed killer, paraquat)


What are other things that impact gas exhange?

Pneumonia: inflammatory plus inside or outside of alveolar walls from viral, bacterial, injury etc.
- Common cause of death in ill, chronically ill, covid-19
- reach sepsis (blood) or pleural space (empyema)

Pulmonary Edema: fluid in interstitial or alveolar space, damage to lung tissue or inability to pump blood


how long does gas exchange take?

TIME: gas exchage happens in 0.25 seconds

At rest: 3/4 second transit time, after 1/4 gas exhange is done. You have extra time.

If you speed up movement of blood, PT time is less, but as long as its more than 1/4 second its okay!!
Normally you have time to spare!!

Pulmonary fibrosis: might not have enough time to complete gas exchange! (with exercise too)
Just fibrosis: its not a problem, you have enough time.

Elite athletes: CO are so high, PTT is less than 0.25 seconds, not enough time for gas exchange to take place. Low p02, so they have hypoxia