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62 Cards in this Set

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What is diffusion
simple molecules moving freely and randomly among each other
What type of energy is associate with diffusion
kinetic
When does kinetic motion theoretically stop
0 K
Oxygen and CO2 move via
diffusion
Net diffusion is from
an area of high concentration to an area of low concentration
What is partial pressure
the pressure of a gas acting on respiratory passages and alveoli is proportional to the sum of all forces of all the molecules
Sum of all partial pressures equals
the atmospheric pressure
The pressure of a gas is ______ to the concentration
directly proportional
Does gas in a liquid exert a pressure
yes
Partial pressure of a gas is determined by what two things
concentration and solubility coefficient
Explain Henry's Law
if gas molecules are physically or chemically attracted to H2O far more of them can be dissolved without building up an excess partial pressure within the solution
Henry's law formula
partial pressure = % dissolved gas/solubility coefficient
Per Henry's law and given solubility coefficients: CO2 = 0.57, oxygen = 0.024 - explain the solubility and partial pressure differences between oxygen, CO2
If oxygen solubility coefficient = 0.024 and CO2 solubility coefficient = 0.57
...then CO2 is about 20x more soluble than oxygen and
...the partial pressure of CO2 is about 1/20th of that of oxygen
If the partial pressure of a gas is high in the alveoli, it tends to
push it into solution (interstitial fluid)
If the partial pressure of a gas is high in solution (interstitial fluid) it tends to
push it into the alveoli
Net movement depends on
difference in partial pressures
The partial pressure of H2O is dependent on
body temperature
Normal vapor of water at 37 deg C is
47torr
at 0 deg C vapor pressure is 5 torr
at 100 deg C vapor pressure is 760 torr
Factors other than partial pressure differences and solubility coefficients that determine diffusion
1. distance a gas must diffuse (thickness of membrane)
2. molecular weight of gas
3. temp of fluid
4. cross sectional area
All gases in the respiratory system are lipid soluble so the major limitation of gas in tissues is
through H2O
Why is composition of alveolar air and atmospheric air different
O2 leaving alveoli
CO2 entering alveoli
H20 vapor is higher
atmospheric air is mixed with deadspace air
Partial pressure of atmospheric air
159torr
Partial pressure of alveolar air
149 torr - water vapor has diluted out
If TV is 500ml - how much is dead space
150ml
How quickly does alveolar air turn over
16 breaths?
Alveolar concentration of alveoli is controlled by two things
rate of absorption of oxygen into the blood
rate of entry of new oxygen into the lungs
Without perfusion, the normal partial pressure gradients would be
slowed - thus oxygen from alveoli to interstitial fluid would be slowed
Rate of entry of new oxygen into lungs is dependent on
ventilation - rate, depth, deadspace
Normal oxygen consumption rate
250 ml/min
250 ml/min must be absorbed to maintain a PO2 of
104torr
With optimal ventilation at 250ml/min consumptive rate - PO2 can never exceed
149torr
With optimal ventilation at 250ml/min consumptive rate - the only way to exceed a PO2 of 149 is to
increase the FiO2
If consumptive rate falls below 100ml/min will have
anaerobic metabolism
Normal CO2 rate of excretion is
200ml/min
at normal ventilation, PCO2 is
40torr
The alveolar PCO2 increases directly in proportion to the rate of
CO2 production
The alveolar PCO2 decreases directly in proportion to the rate of
alveolar ventilation rate
With higher metabolic rate (temp) CO2 production
increases
How many alveoli are there in two lungs of an adult
300million
Diameter of each alveoli
0.2mm
Air exchange occurs between alveoli and
the respiratory zone
Layers of respiratory zone (thickness of 0.2mm)
1. surfactant and fluid layer
2. alveolar epithelium
3. epithelial basement membrane
4. interstitial space
5. capillary basement membrane
6. capillary epithelium
Four factors that affect rate of diffusion
1. thickness of membrane
2. surface area
3. diffusion coefficient
4. partial pressure difference
What would increase the thickness
pulmonary fibrosis or pulmonary edema
What would cause reduced surface area of lung
lobectomy, emphysema,
CO2 diffuses____ faster than oxygen
20x
oxygen diffuses___ faster than nitrogen
much
What is V:Q ratio
compares ventilation of lung area to perfusion - set up as ratio
Normal V:Q ratio
0.8-1
West zone I - describe Pa:PA:Pv and V:Q ratio
PA > Pa > Pv (no flow)
V:Q >1
West zone II - describe Pa:PA:Pv and V:Q ratio
Pa > PA >> Pv
V:Q ratio = waterfall effect
resistance set by Pa and PA
West zone III - describe Pa:PA:Pv and V:Q ratio
Pa > Pv > PA
V:Q 0.8-1 - ideal for perfusion/placement of swan ganz or PA catheter
West zone IV - describe Pa:PA:Pv and V:Q ratio
Pa >> Pv >>> PA
V:Q = shunt
No ventilation but alveoli perfused - what are the alveolar gas pressures
shunt - PO2 = 40torr, PCO2 = 45torr
ventilation but no perfusion - what are the alveolar gas pressures
dead apace - PO2 = 149torr, PCO2 = 0torr
V:Q normal - what are the alveolar gas pressures
PO2 = 104torr (mixing 149torr with inspired air), PCO2 = 40torr (mixing venous 45torr with 0torr inspired)
What is considered shunt blood
when venous blood passing through the pulmonary capillaries is not oxygenated
Why is physiological dead space bad
wasted energy due to the body's response to increase ventilation or wob
How can shunt trauma occur
ETCO2 = 12 drop vent rate send ABG (CO2 72) this is because of poor or no perfusion
Does physiological shunt normally occur
yes
When does normal physiological shunting occur
zone I - V and Q are both low but Q < V
zone IV - V and Q are both low but Q > V - still have physiologic shunt
COPD causes air trapping/overstretching of alveoli - what 2 V:Q problems exist
1. obstructed alveoli are not ventilated V:Q = 0 or dead space
2. intact alveoli may ventilate but perfusion through destroyed walls is inhibited = physiologic shunt