B4.036 - Gas Exchange and Transport Flashcards
what is the equation for pressure of a gas
P = nTR/V
what do you need to calculated partial pressure
Total pressure and concentration of a gas species
what is FO2
fraction of O2
how do you calculate PIO2
PIO2 = (760-47) * .21
in kansas city what should the sum of partial pressures of all gases add up to
PB aka 747
how do you change partial pressure of a gas
changing the concentration or the total pressure
what is the physical solution of gas in the liquid
the fraction of gas molecules that enters the liquid and does not undergo any chemical combination
does O2 combined with Hb contribute to PO2?
No, any gas molecule that combines with a substance in the liquid does not contribute to the partial pressure of the gas
in order for partial pressures of gas not to fall what must occur
the gas molecules must be replaced by additional molecules entering the liquid from the gas phase
what does hyperventilation do
high PAO2, low PACO2
what does hypoventilation do
low PAO2, high PACO2
what is the alveolar gas
the result of a balance between the rate of delivery and the rate of removal of each individual gas
describe air in the conduction system and respiration system at the end of expiration
the alveoli and airways are filled with alveolar air, volume of air in the lungs at that time is FRC
how much air remains in dead space during inspiration
1/3
what does this graph represent
gas composition pattern during breathing
during expiration PCO2 initially is low because of O2 left in the dead space, then once the air from the alveoli is exhaled you see a rise in PCO2. The opposite is true for PO2 for the same reason
how do you calculate VD/VE
VD/VE = (FACO2 - FECO2)/FACO2
what key differences does this graph demonstrate
- in the physiologic range, the blood CO2 content is about 2x the blood O2 content
- the curve for CO2 is fairly linear (changes in CO2 yeild proportionate changes in blood CO2 over a wide range of PCO2)
- teh non linearity of the ODC means the changes in O2 content produced by a given change in PO2 will depend on the initial PO2 level
- the CO2 curve is much steeper, note the v-a difference and its implications on PCO2 and PO2
what is the alveolar gas equation
PAO2 = PIO2 - (PaCO2 x 1.2)
what is the alveolar gas equation used for
PAO2 = PIO2 - (PaCO2 x 1.2)
to compare the measured arterial blood PO2 and the calculated one. In the normal lung PaO2 should be only 5-10 mmHg lower than calculated PAO2
what is normal inspired PIO2?
147 (PB in kansas city)
what is inspired PCO2?
always 0
why is alveolar PO2 lower than PIO2?
because the second it hits the alveoli gas exchange happens
goes from 147-100
what is normal aveolar PCO2?
40
how do you get the PIO2
(760-47) * .21
760 - atmospheric P
47 - subract H20 Pressure
.21 - fraction of inhaled air that is PO2
= 147