exam 2 lecture 17 and 18 Flashcards
blue membranes
cyanosis
PaO2
pressure of oxygen gas ***dissolved*** in the arterial blood; in mmHg
PaCO2
–pressure of carbon dioxide gas ***dissolved*** in the arterial blood; in mmHg
SpO2
percentage ***saturation of hemoglobin (Hb) *** in the arterial blood; in %
PiO2
partial pressure of oxygen in inspired gas; mmHg
FiO2
–fraction of oxygen in inspired gas; in %
low PaO2 means
hypoxemia
PaO2 is pressure of oxygen dissolved in arterial blood.
Units: mmHg
PaO2 vs PAO2
a= arterial
A = alveolar
pressure of dissolved oxygen
dalton’s law
•In a gas mixture, the pressure exerted by each gas is independent of the pressure of the others, so all pressures will sum to the total measured pressure
Pair = PN2 + PO2 + P(other gases)
Pair = PN2 + PO2 + P(other gases)
daltons law
•In a gas mixture, the pressure exerted by each gas is independent of the pressure of the others, so all pressures will sum to the total measured pressure
•For dalton’s law. In a gas mixture, the pressure exerted by each gas is independent of the pressure of the others, so ___
all pressures will sum to the total measured pressure
Pair = PN2 + PO2 + P(other gases)
FIO2
fraction of inspired oxygen
=21% or 0.21
what happens to atmospheric pressure as you climb a mountain?
decreases
at sea level 760 mmHg
on everest: 235 mmHg
how to calculate PiO2
PiO2 pressure of oxygen in airways
PiO2= (Patm - 47 mmHg) x FiO2
Patm depends on elevation 760 mmHg at sea level
47 is water vapor evaporating in the body
FiO2= % inspired oxygen =0.21 at room air, 1.0 on 100% O2
PiO2 is the the oxygen pressure in the ___, NOT in the ___
airways
alveolus
what is the FiO2 at room air and on oxygen?
room air= 21% or 0.21
oxygen= 100% or 1
-Atmospheric pressure at 9000m (Everest summit) is 253 mmHg. What is the partial pressure of oxygen in the air?
253 x FiO2
253x 0.21
53.13
what is the PiO2 in Amsterdam (760mmHg)?
Philly (749 mmHg)?
Everest (220 mmHg)?
PiO2= (PATM - 47 mmHg) x FiO2
(760-47) x 0.21 = 149.73 mmHg
(749-47) x 0.21= 147.42 mmHg
(220-47) x 0.21= 36.33 mmHg
what is the PiO2(1 atm) on
100% oxygen
Amsterdam (760mmHg)?
Philly (749 mmHg)?
Everest (220 mmHg)?
PiO2= (PATM - 47 mmHg) x FiO2
(760 -47) x 1= 713 mmHg
(749-47)x 1= 702 mmHg
(220-47) x 1= 173 mmHg
what is the FiO2 needed to get a PiO2 of 200 mmHg at sea level?
PiO2= (PATM - 47 mmHg) x FiO2
200= (760-47) x F
FiO2= 0.28
What FiO2 would you need to supply to get a PiO2 of 50 mmHg at seas level
PiO2= (PATM - 47 mmHg) x FiO2
50= (760-47) x F
FiO2= 0.07
PaO2 in arterial vs venous blood
150 in airways
100 in alveoli
100 in arterial
40 in venous
Gas exchange across blood-gas barrier in the lung is by ___
passive diffusion
Passive movement of gas down a partial pressure gradient (difference in PO2, PCO2) are influenced by:
Gas diffusivity (D; solubility)
- Surface area (A)
- B-G barrier thickness (T)
- Driving pressure gradient between alveolar-capillary blood (PA – Pcap)
Fick’s law
The amount of gas that moves across a sheet is:
- Proportional to the area of the sheet
- Inversely proportional to its thickness
the bigger the sheet the more things can diffuse, the thicker the sheet the less things can diffuse
Flow of gas= Area/thickness x diffusion constant (P1-P2)
why is PaCO2=PACO2
CO2 is 20 times more soluble than O2
will diffuse willingly across membrane and balance itself out
what is more soluble CO2 or O2
CO2 is 20x more soluble then O2
what happens to pleural pressure when you breathe very hard
more negative!!
Oxygen diffuses into ___ and CO2 diffuses into ___
tissues
blood
anatomic dead space
volume of conducting airways- O2 here will never get to the blood
alveolar dead space
gas in alveoli not participating in gas exchange
if an blood clot blocks blood flow to some alveoli
physiologic dead space
alveolar + anatomic dead space(conducting airway deadspace)
•We measure hemoglobin-associated oxygen using __
SaO2
pulse ox → % of oxygen on hemoglobin
how is O2 carried in the blood
98% is carried on hemoglobin
1-2% is dissolved in plasma
normal SaO2
95-100%
% saturation of O2 = pulse ox= % of oxygen on hemoglobin
how to measure amount of oxygen dissolved in plasma?
arterial blood gas PaO2
•A very small quantity of O2 is carried dissolved in plasm. The amount dissolved is based on the ___of the air in the alveolus. Oxygen molecules are pushed down a gradient
PiO2
units of PaO2
mmHg
(partial pressure of O2 in arterial blood)
normal PaO2
85-95 mmHg
partial pressure of O2 in arterial blood= measured by blood gas machine
how to calculate CaO2
- Oxygen carrying capacity of hemoglobin is 1.34 ml/g
- Oxygen carrying capacity of plasma 0.003 ml O2/dl plasma per mmHg PaO2
CaO2 = (SaO2 x Hb x 1.34) + .003(PaO2)
= (98% x 19 g/dL x 1.34) + 0.003(92)
=(24.95) + 0.276
=25.226 ml/dL O2
CaO2= total oxygen content in the blood
what does CaO2 measure
total Oxygen in the blood
=(amount of O2 on hemoglobin) + (amount of O2 dissolved in plasma)
CaO2 = (SaO2 x Hb x 1.34) + .003(PaO2)
normal = 16-20 ml/dl O2
on admission on room air:
–What is the FiO2?
–PaO2: 39 mmHg
–SaO2: 71%
–Hb: 12 g/dL
CaO2? ________________________________
FiO2= 0.21 on room air
CaO2 = (SaO2 x Hb x 1.34) + .003(PaO2)
=(0.71 x 12 x 1.34) + 0.003 (39)
=11.42+0.117
=11.537 ml/dL O2
normal = 16-20 ml/dl O2
•On nasal oxygen at 4L/min
–PaO2: 58 mmHg
–SaO2: 85%
–Hb: 12 g/dL
CaO2? ______________
CaO2 = (SaO2 x Hb x 1.34) + .003(PaO2)
CaO2 = (SaO2 x Hb x 1.34) + .003(PaO2)
= (0.85 x 12 x 1.34) + 0.003 (58)
=13.842 ml/dl O2
normal = 16-20 ml/dl O2
CaO2 = (SaO2 x Hb x 1.34) + .003(PaO2)
•On the ventilator, on pure O2
–What is the FiO2?
–PaO2: 124 mmHg
–SaO2: 99%
–Hb: 12 g/dL
CaO2? ___________________________
CaO2 = (SaO2 x Hb x 1.34) + .003(PaO2)
FiO2 on pure O2= 100%
(0.99 x 12 x 1.34) + 0.003 (124)
=16.29 ml/dl O2
normal = 16-20 ml/dl O2
•On admission, on room air
–What is the FiO2?
–PaO2: 96 mmHg
–SaO2: 98%
–Hb: 3.5 g/dL
CaO2? ____________________
CaO2 = (SaO2 x Hb x 1.34) + .003(PaO2)
FiO2= 0.21
(.98 x 3.5 x 1.34) + (0.003 x 96)
=4.88 ml/dl O2
normal = 16-20 ml/dl O2
•In surgery to ligate the artery, on pure O2
–What is the FiO2?
–PaO2: 496 mmHg–SaO2: 99%–Hb: 3.5 g/dL
CaO2? __________
CaO2 = (SaO2 x Hb x 1.34) + .003(PaO2)
FiO2 on oxygen = 1
CaO2 = (SaO2 x Hb x 1.34) + .003(PaO2)
= (.99 x 3.5 x 1.34) + (0.003 x 496)
=6.13 ml/dl O2
normal 16-20 - need hemoglobin to fix the horse
Gas exchange influenced by
- ventilation (delivery of atmospheric O2 to alveoli);
- perfusion (transport of O2 from lungs in the blood);
- gas exchange at level of alveoli (influenced by amount of gas, properties of gas, tissue properties). Amount of gas available for transport (partial pressure) changes as move from atmosphere to alveolus
Driving pressure (ΔP) = PAO2 – PVO2
100-40
60 mmHg
arterial blood - venous blood
this will pull O2 into the blood from the alveolus until PAO2 and PaO2 are equal
how long does it take for a RBC to get fully loaded with O2?
0.25 seconds
at rest how fast does RBC go across alveoli?
0.75 seconds
what does this graph show?
how long is takes for RBC to get fully loaded with O2
in normal takes 0.25 seconds to reach full load. partial pressure of O2 in the arterial blood (PaO2) goes from 40→100 mmHg
in abnormal= takes 0.75 seconds, if exercising this is not enough cause blood is moving faster then it can pick up O2
in grossly abnormal= RBC never reaches normal even at rest and it barely gets any O2 with exercise
•Normal transit time for an RBC across the capillary:___
0.75 seconds
PAO2 a high altitude or hypoventilation
amount of O2 in your lungs can not be greater then the amount of O2 in the air, therefore max O2 is 50 at high altitude
that means any pulmonary disease or exercise would lead to even smaller amount of O2 in the blood
what is a pulmonary disease that can increase barrier thickness?
edema and fibrosis
what kind of pulmonary disease can lead to decrease in surface area?
capillary destruction and tumor
explain hemoglobin cooperativity
deoxygenated O2= tense
oxygenated = relaxed
(shy person drinking at a party)
Hb has different affinities for oxygen based on how much oxygen it’s already carrying. The first oxygen molecule is hard to bind, but when one oxygen attaches, the second binds more easily, and the third and fourth easier yet.
The same process works in reverse: once fully loaded hemoglobin lets go of one oxygen, it lets go of the next more easily, and so forth.
This is known as cooperativity
oxygen hemoglobin dissociation curve
x axis= Pa O2=partial pressure of O2 dissolved in the plasma= measured by total blood gas
y axis= SpO2= pulse ox
illustrates the % of hemoglobin that is chemically bound to O2 at each oxygen pressure
steep part of curve loose or gain O2 quickly
end of curve- max out at 100% no matter how much extra O2 you add
start of curve- hard to get started
why a sigmoid curve?
hemoglobin cooperativity
hard to get started, then very fast, then maxed out
steep slope between 10 and 60 mmHg
flat portion between 70 and 100 mmHg.
There are different oxygen levels in venous blood versus arterial. Why?
In venous blood, the PvO2 is about 40mmHg, which corresponds to an SaO2 of about 75%
tissues have used up O2 and it has dropped to 75%
The amount of oxygen in the arterial blood can be lower in patients with lung disease, or on the top of Everest. Why?
there is less O2 to begin with at the top of Everest= PiO2 is low
or lung disease: can’t get O2 into lungs or into blood so they drop even lower
arterial vs venous
SaO2
PAO2
PACO2
99%→75%
100 → 40
40→ 46
What happens if the oxygen-hemoglobin dissociation curve shifts to the RIGHT?
more O2 will be unloaded if shifted to the right instead of tissues using 25% they will use 50%
how to move oxygen hemoglobin dissociation curve to the right and left?
right- exercise= decrease pH (lactic acid- more acid), increase temp and DPG
left= increase pH, decrease temp and DPG
how does pH effect oxygen hemoglobin dissociation curve?
•↓pH–When you exercise, or in some forms of shock, blood pH goes down (acidemia)–This moves the curve to the RIGHT, so at a given PaO2, the SaO2 is LOWER so more O2 was delivered to the tissues–This is called the Bohr effect
Bohr effect
during exercise
pH decreases (more acid)
this shifts the curve to the right, this means more O2 is delivered to tissues so they can exercise more
What increases 2,3 DPG?
–High altitude, anemia, chronic hypoxia, hyperthyroidism, chronic alkalosis (high pH)
•Myoglobin is an oxygen-carrying protein in the muscles. Why is its curve so far to the left of Hb?
At any given PaO2, it more saturated than Hb – this means it can “grab” the O2 off the Hb as the arterial blood passes by in capillaries to feed the tissues
myoglobin grabs really fast and really well to O2, only need very small amount of O2 to reach full capacity of myoglobin
P50
a way to measure how far the curve moves
at normal 27
left= 10
right =40
•When the O2/saturation curve shifts RIGHT, the oxygen affinity of hemoglobin ___ causing the hemoglobin to be ___saturated at a given PaO2
DECREASES,
LESS
right = 40 where normal = 27
•When the curve shifts LEFT the oxygen affinity of hemoglobin ___, causing the hemoglobin to be ___ saturated at a given PaO2
INCREASES,
MORE
left = 10 where normal =27
- On room air (FiO2 0.21), Hb is almost 100% saturated, and PaO2 is usually in the high 90s
- What happens to the amount oxygen carried in the blood when a patient receives 100% oxygen (FiO2 1.0) and their PaO2 goes up to ~500 mmHg?
will increase the amount of oxygen dissolved in the plasma which is 1-2% of all oxygen
will not make a big difference
how is CO2 transported in the blood?
10% dissolved in blood
22% carbamino compounds in hemoglobin
68% bicarbonate ion formation
explain how CO2 is transported on hemoglobin
22% of CO2 carried by Carbamino compounds in Hb
–CO2 joins reversibly with non-ionized terminal amino groups (-NH2) of Hb in RBC–Hb.NH2 + CO2 ↔ Hb.NH.COOH
explain bicarbonate ion formation for carrying CO2
68% of CO2
–most CO2 in the blood is transported in the bicarbonate ion form
–bicarbonate ion is from reversible reaction accelerated by enzyme, carbonic anhydrase, in RBC:
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-
–the first reaction is slow in plasma but fast in red cells due to carbonic anhydrase
–the second reaction (carbonic acid ionic dissociation) is fast even without an enzyme
how is most of CO2 transported in the blood?
as bicarbonate ion
carbonic anhydrase helps
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-
CO2 transport at the tissues
most into RBC: bicarbonate quickly with help of carbonic anhydrase
some into hemoglobin
Plasma: some dissolved
small amount into bicarbonate slowly cause no carbonic anhydrase in plasma
CO2 transport at the lung
reverse process
most out of RBC: bicarbonate quickly with help of carbonic anhydrase back into CO2
some from hemoglobin into CO2
Plasma: some dissolved
small amount from bicarbonate back into CO2 slowly cause no carbonic anhydrase in plasma
haldane effect
- Deoxygenation of blood increases its ability to carry carbon dioxide. Conversely, oxygenated blood has a reduced capacity for carbon dioxide
- This means it is easier for Hb to pick up CO2 at the tissues (where Hb is least O2 saturated), and release it in the lungs, where O2 is the most saturated. That’s really convenient, right?
1.What is the FiO2 of room air at sea level? What is the FiO2 in Denver, CO? What is the FiO2 of pure oxygen at sea level? In Denver?
- 21
- 0
????
1.If you were in a small room of 1000 L capacity and someone accidentally opened a helium canister that released 100L of helium into the room, what would be the FiO2 in that room? What principle of physics did you use to make this answer?
FiO2 would still be 21%, always 21%???
1.What is PiO2? What is the difference between FiO2 and PiO2, conceptually? Numerically? Give an example.
PiO2= partial pressure of inhaled O2= affected by elevation
PiO2= (PATM - 47 mmHg) x FiO2
FiO2= fraction of inhaled air that is O2= at room air always 0.21
1.What is normal PaO2 on room air at sea level? What is normal SaO2 on room air at sea level? Include the units.
PaO2 on room air at seas level: measure of dissolved O2 in arterial blood= measured by a blood gas machine
PiO2= (Patm - 47 mmHg) x FiO2
PO2 of inspired air = 150, PAO2= 100 PaO2= 100 mmHg ???
SaO2=95-100%
If you treating an animal with pneumonia, if the PaO2 is less than 60mmHg, that animal probably needs to be on oxygen. What will be the SaO2 at a PaO2 of 60mmHg?
use o2- saturation curve
90%
When the PaO2 is <40mmHg, the animal develops cyanosis (what’s that?). What SaO2 does that correspond to?
cyanosis- blue gums
SaO2 less then 75
If normal PaO2 and SpO2 are both the same approximate numerical value in the normal animal on room air, how come they are so different from each other in Q4 and 5? Draw a picture to illustrate.
ox sat curve is sigmoid
What is expected SaO2 on 100% oxygen at sea level? Include the units.
100%
