Exam 2 - Topic 4 - Gas Exchange

Question 1

Three types of back flow possible

Answer 1

• X clamp the Aorta ON
• X clamp the aorta OFF
• Coming off bypass

Question 2

Pressure formula

Answer 2

P = Force / unit area

Question 3

How does gas exert pressure

Answer 3

• Colliding with walls of container

- will fill space of container and exert uniform force on all sides

Question 4

Ideal gas law

Answer 4

PV = nRT

R = 0.082
P = atm
V = Liters
T = Kelvins

Question 5

Bowles Law

Answer 5

P1V1 = P2V2

- Constant Temp

Question 6

Charles Law

Answer 6

V1/T1 = V2/T2

- constant pressure

Question 7

Gay-Lussacs Law

Answer 7

P1/T1 = P2/T2

- constant volume

Question 8

Partial pressure of main gases in room air

Answer 8

• N2 = 79%
• O2 = 21%
• CO2 = 0.04%

Question 9

Partial pressure of H2O in humidified air

Answer 9

• 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

Question 10

PP of O2 and CO2 in alveolar air -> expired air

Answer 10

• 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

Question 11

O2 and CO2 PP in venous blood

Answer 11

O2 = 40 mmHg
CO2 = 45 mmHg

Question 12

Respiration and [CO2] relationship

Answer 12

• Increase in respiration will decrease [CO2]

Question 13

Respiratory Quotient

Answer 13

• Tells us that consumption of 1 unit of O2 yields 0.8 CO2

- 10:8 ration

Question 14

Gas/Liquid Equilibrium

Answer 14

• # molecules entering liquid phase = # molecules leaving

Question 15

Henry’s Law

Answer 15

[gas] = PP of gas * solubility coefficient

0.003 ml O2/100ml solution/mmHg (example of solub. Coefficient)

Question 16

How is blood carried in O2

Answer 16

• dissolved in plasma (2%)
• bound to hemoglobin (98%)

-Can ignore plasma O2 unless told otherwise

Question 17

Solubility of O2

Answer 17

0.003 ml O2 / mmHg PO2 / 100 ml blood

Question 18

Amount of O2 carried by hemoglobin

Answer 18

• 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

Question 19

Total O2 presented to tissues (Delivery)

Answer 19

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

Question 20

Equation for O2 Consumption

Answer 20

(1.34 * (Art sat-Ven sat) / 100) * ml blood/min

Question 21

AV difference

Answer 21

Arterial sat - Venous sat

Question 22

PP (pulse pressure)

Answer 22

PP = P systolic - P diastolic

Question 23

MAP (Mean arterial Pressure)

Answer 23

MAP = P diastolic + (PP/3)

Question 24

SVR (systemic vascular resistance)

Answer 24

SVR = ((MAP) - (CVP) / CO) * 80

CVP = central venous pressure (aka right atrial pressure)
UNITS = dyne sec/cm^5

Question 25

PVR (pulmonary vascular resistance)

Answer 25

PVR = ((MPP) - (LAP) / CO) * 80

MPP = mean pulmonary pressure
LAP = Left atrial pressure
UNITS = dyne sec/cm^5

Question 26

Diffusability

Answer 26

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)

Question 27

How to change surface area and distance in real lung?

Answer 27

Disease state or some other condition

Question 28

Relative O2 and CO2 movement

Answer 28

• 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!

Question 29

Respiratory membrane

Answer 29

• Normal SA is 70m^2 (tennis court)

- > if caused by edema

Question 30

P50

Answer 30

• Partial pressure of O2 at which hemoglobin is 50% saturated with O2….normally around 27mmHg

Question 31

Bohr effect

Answer 31

How changes in [CO2] affects O2 and hemoglobin affinity

….increased [CO2] lowers hemoglobin affinity for O2

Question 32

Speed at which gases diffuse across alveoli

Answer 32

• Very fast and efficiently!

- All done by 1/3 of the way through the capillary

Question 33

Arterial PO2 and Intracellular PO2

Answer 33

• If O2A increases…then Intracellular PO2 will increase too

Question 34

ADP and O2 affect on energy production

Answer 34

• Need at least 1 mmHg PO2 to produce energy

- if true….energy production depends on [ADP]