Alveolar Gas Exchange Flashcards
Alveolar ventilation equation
PAo2 = PIo2 - (PaCO2 / R)
PIo2 how to calculate it and what is it
PIo2 = (760 - 47) x 0.21 0.21 = percent o2 47= water vapor P
R is usually what
(200ml/min) / (250ml/min) = 0.8
how to know if alveolus is damaged
difference between the alveolar and arterial P PAo2 - Pao2 = should be less then 20 if over 20 there is alveolar damage if normal and dyspnea = low O2 in atm. or impaired RR breathing ability
what is the normal alveolar ventilation what is the normal alveolar perfusion
- 4L/min (air that reaches the alveoli) 2. 5 Blood/min (CO, from RV)
how do you calculate the diffusion rate
diffusion Rate = J (exchange between air and blood)
normal J for O2 and CO2
O2 : 250mL/min CO2 : 200mL/min *change independently of eachother*
what 2 factors depend on the ALVEOLAR STRUCTURE
SA of air exchange distance (for exchange, alveolar wall)
what changes the SA
- number of avleoli taking part in gas exchnage 2. number of open pulmonary capillaries
normal amount of blood in pulmonary capillaries
70ml
normal amount of blood in pulmonary capillaries during exercise
up to 200ml, more capillaries open
what influences distance of exchange
- thickness of alveoli wall (fluid) 2. BV (capillary) wall 3. alveolar endothelium 4. interstitial fluid (should be very thin)
pulmonary fibrosis and interstitial fluid
collagen is deposited in the interstitial fluid increasing thickness alot Also called interstitial lung disease
average distance for gas exchange
0.6 microns
the diffusion coefficient for each gas depends on what 2 things
- solubility of gas (CO2 is 20x more soluble) 2. molecular weight of gas (CO2 is heavier)
P1-P2 is what and what is it normally for O2
pressure across alveolar membrane (inside alv to outside blood) =PAo2 - Pvo2 = 104 - 40 = 60mmHg
normal P1-P2 for CO2
PACO2 - PvCO2 = 40 - 45 = -5 (interpleural P)
how long does if take for blood to get through one entire pulmonary capillary
0.75 sec
how long does O2 need to diffuse across from alv to blood how long does CO2 need
O2 : 0.25sec CO2 : almost immediately
how long does if take for blood to get through one entire pulmonary capillary during exercise
0.25sec, just enough time for all O2 to diffuse from alv to blood * someone with lung disease will first have Sx during exercise
what happens in COPD/emphysema and diffusion rate
diffusion rate is lowered and O2 needs more time to diffuse (more then 0.25sec)
how to calculate Diffusion Capacity in O2
V(dot)O2 x (P1-P2) = 250mL/min x 60mmHg = 21mL/min/mmHg at rest
how to quickly calculate Diffusion capacity for O2
* use CO, PaCO= 0mmHg* DLo2 = 1.23 (DLco)
normal DLco2 is what
DLco2 = 400mL/min/mmHg (20x more then 21 which is for O2)
reason in pnemonia or COPD there is found to be a NORMAL O2 and lowered CO2
as O2 gas diffusion rate decreases 1. PaO2 drops 2. peripheral chemoreceptors activated and increase RR + TV + f 3. PaO2 goes back to normal however the increases TV and RR causes a bunch of CO2 loss since its diffusion rate did not get effected from the start
in pnemonia or COPD there is found to be a NORMAL O2 and lowered CO2 Eventually what happens
low CO2 = high pH peripheral chemoreceptors responds only cant all the way becuz it will hinder body from getting adequate O2
normal baby HR is what
120 or higher
reason you need surfactant
the air (in alv) and tissue/wall (water in this case) cause the alv wall to bubble up like water = alveoli collapse surfactant reduces the surface tension b/w water(tissue) and air
LaPlace’s Law on P in alv
P = 2T/r T = surface tension r= radius * higher radius –> decrease P * higher surface tension –> increase P
reason you need surfactant
Surfactant LOWERS surface tension in SMALL ALVEOLI —-> so their P is lowered and equal to the big alveoli
what happens if you have no surfactant
the small alveoli have high P the large alveoli have low P AIR DIFFUSES —-> large alveoli (that makes the small alveoli smaller = collapse of small alveoli) = LOWERS SA
how does surfactant only effect the small alveoli
the closer the drops of surfactant are to one another the stronger it works , the drops are closer together the smaller alveoli
what can you give the baby if you know they dont have developed type 2 cells to make surfactant in time of delivery
Steroids that increase surfactant
what is surfactant composed of
phospholipid Dipalmitosphatidylcholine + Surfactant Proteins : SPB is the one lowering ST**** SPB is stored in the lamellar bodies and secreted
