Exam 2 - Topic 4 - Gas Exchange Flashcards
Three types of back flow possible
- X clamp the Aorta ON
- X clamp the aorta OFF
- Coming off bypass
Pressure formula
P = Force / unit area
How does gas exert pressure
- Colliding with walls of container
- will fill space of container and exert uniform force on all sides
Ideal gas law
PV = nRT
R = 0.082 P = atm V = Liters T = Kelvins
Bowles Law
P1V1 = P2V2
- Constant Temp
Charles Law
V1/T1 = V2/T2
- constant pressure
Gay-Lussacs Law
P1/T1 = P2/T2
- constant volume
Partial pressure of main gases in room air
- N2 = 79%
- O2 = 21%
- CO2 = 0.04%
Partial pressure of H2O in humidified air
- 47 mmHg
- Always true regardless of total partial pressure
- Take total PP….subtract the 47…. Then use % of other gases to find their individual PPs
PP of O2 and CO2 in alveolar air -> expired air
- O2 = 104 mmHg –> 120 mmHg
- CO2 = 40 mmHg –> 27 mmHg
- Change due to mixing with dead space air
- Dead space air = mix of atm air and alveolar air
O2 and CO2 PP in venous blood
O2 = 40 mmHg CO2 = 45 mmHg
Respiration and [CO2] relationship
- Increase in respiration will decrease [CO2]
Respiratory Quotient
- Tells us that consumption of 1 unit of O2 yields 0.8 CO2
- 10:8 ration
Gas/Liquid Equilibrium
- # molecules entering liquid phase = # molecules leaving
Henry’s Law
[gas] = PP of gas * solubility coefficient
0.003 ml O2/100ml solution/mmHg (example of solub. Coefficient)
How is blood carried in O2
- dissolved in plasma (2%)
- bound to hemoglobin (98%)
-Can ignore plasma O2 unless told otherwise
Solubility of O2
0.003 ml O2 / mmHg PO2 / 100 ml blood
Amount of O2 carried by hemoglobin
- Need 1.34 ml O2/gm Hgb (physiological max)
- Need [hemoglobin] in blood (gm Hgb/100 ml blood)
- % saturation of Hgb (if PO2 > 100mmHg….O2 sat is 100%)
So…. 1.34 * Ven or Art sat / 100
Total O2 presented to tissues (Delivery)
Same equation as O2 content but * by ml blood/min
(1.34 * Art or Ven sat / 100) * ml blood/min
Add O2 dissolved (0.003*PO2) only if asked
Equation for O2 Consumption
(1.34 * (Art sat-Ven sat) / 100) * ml blood/min
AV difference
Arterial sat - Venous sat
PP (pulse pressure)
PP = P systolic - P diastolic
MAP (Mean arterial Pressure)
MAP = P diastolic + (PP/3)
SVR (systemic vascular resistance)
SVR = ((MAP) - (CVP) / CO) * 80
CVP = central venous pressure (aka right atrial pressure) UNITS = dyne sec/cm^5
PVR (pulmonary vascular resistance)
PVR = ((MPP) - (LAP) / CO) * 80
MPP = mean pulmonary pressure LAP = Left atrial pressure UNITS = dyne sec/cm^5
Diffusability
Diffusion = (P)(Area)(Solubility) / (Distance)(sqrt of MW)
Area and Distance tend to be constant for a gas so…..
Diffusion = (P)(Solubility) / (sqrt of MW)
How to change surface area and distance in real lung?
Disease state or some other condition
Relative O2 and CO2 movement
- CO2 much more soluble than O2
- Pressure gradient much greater for O2 at lungs
- Overall…CO2 is removed 1.6 x faster than O2 is consumed
- > we only need to blow off 0.8…so we are good!
Respiratory membrane
- Normal SA is 70m^2 (tennis court)
- > if caused by edema
P50
- Partial pressure of O2 at which hemoglobin is 50% saturated with O2….normally around 27mmHg
Bohr effect
How changes in [CO2] affects O2 and hemoglobin affinity
….increased [CO2] lowers hemoglobin affinity for O2
Speed at which gases diffuse across alveoli
- Very fast and efficiently!
- All done by 1/3 of the way through the capillary
Arterial PO2 and Intracellular PO2
- If O2A increases…then Intracellular PO2 will increase too
ADP and O2 affect on energy production
- Need at least 1 mmHg PO2 to produce energy
- if true….energy production depends on [ADP]
