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Flashcards in Test 2 (Gas Transport) Deck (24)
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1
Q

Alveolar Oxygen

A

Alveolar Oxygen = Oxygen Concentration in the Lungs - Oxygen used by Tissue

2
Q

Solubility of O2 in Plasma (or Water)

A

***0.3 mL O2/ dL Blood/ 100 mm Hg

  • So if the PaO2 is 100 mm Hg, each dL of blood will carry 0.3 mL O2!!!!!!
  • In order to meet our metabolic demands (250 mL O2/min), out hearts would have to pump at 83 LITERS OF BLOOD/ MIN!!!!! (Impossible)

IMPORTANT NOTE:
- When we refer to the PaO2 (the partial pressure of Oxygen in the Arterial Blood), we are referring to the DISSOLVED OXYGEN!!!!!!!!

3
Q

Hemoglobin

A
  • Helps carry the Oxygen instead of all of is having to be dissolved, which is impossible!
  • An EQUILIBRIUM is achieved between the Plasma and the Hb
4
Q

The Hb-O2 Dissociation Curve

A
  • Any PO2 above 60 mm Hg, we are at least at 85% Saturated with Oxygen. This is crucial where is we get sick, we can still meet the Oxygen Demand. This also means that our Oxygen content (using normal values we used before) is at least:
  • ** 20.1 mL O2/ dL Blood x 85% = 17 mL O2/ dL Blood!!!!!!!
  • There is a huge range of PO2 where we have a NORMAL AMOUNT of Oxygen being the same with Hb Saturation
  • Once we DROP BELOW 50 or 40, the amount of Oxygen Hb is holding DROPS DRAMATICALLY!!!
5
Q

Changing the Hb-O2 curve of HbA

A

LEFT SHIFT:
- Represents an INCREASE in the AFFINITY of Hb for O2

WHAT CAUSES THE CURVE TO SHIFT TO THE LEFT:
- LACTIC ACID

  • This left shift is associated with whats happening IN THE LUNGS!!!!!!!
  • A left shift means that there is a HIGHER AFFINITY for Oxygen on Hb

RIGHT SHIFT:
- Represents a DECREASE in the AFFINITY of Hb for O2

WHAT CAUSES THE CURVE TO SHIFT TO THE RIGHT:
- Associates with whats happening IN THE TISSUE!!!

  • What the O2 to leave the Hb and go to the Tissue
6
Q

Factors Which Produce Shifts in the Hb-O2 Curve

A

1) CO2 and/ or pH
- The Bohr Effect

  • High CO2 or Low pH: RIGHT SHIFT
  • Low CO2/ high pH: LEFT SHIFT

2) TEMPERATURE
- Increased: Right Shift

3) Certain Metabolites (2,3 DPG)
- Increased: Right Shift

7
Q

Benefits of altering the Hb-O2 Curve

A

When do we see INCREASES in:

  • CO2 and/ or H+
  • Temperature
  • 2,3 DPG

IN THE TISSUE!!!!!!!!!!*

8
Q

At the Tissue

A
  • Not all the Oxygen is taken up by the Tissue, ask indicated by the Venous PO2 of 40 mm Hg
    (PaO2: 95 ——> PvO2: 40)
  • The O2 Saturation of Venous Blood is about 75%

Giving us an O2 content of:
20.1 mL O2/ dL Blood x 75% = 15.2 mL O2/ dL Blood!!!!!!!

9
Q

a-v O2 Difference

A
  • The difference between the arterial O2 content and the venous O2 content

*****IMPORTANT: This represents HOW MUCH OXYGEN is USED by the Tissue being PERFUSED!!!

  1. 8 mL O2/ dL Blood - 15.2 mL O2/ dL Blood = 4.6 mL O2/ dL Blood!!!!!!!!!
    - This is whats used by the whole bodies Tissues!
  • The a-v O2 Difference varies substantially from Tissue to Tissue
    a) Adipose tissues removes VERY LITTLE O2 from the Blood

b) Skeletal Muscle removes much more O2
- The Reason: OXYGEN UTILIZATION by the two Tissues is very different!!!

10
Q

There is a consistent relationship between the amount of O2 consumed and the CO2 produced

A
  • This relationship (ratio) is determined by the fuel being utilized by the cells:

1) If the fuel is CARBOHYDRATES:
- There is a 1: 1 ratio
- 1 CO2 produced for every 1 O2 consumed

2) If the fuel is FATS:
- The ratio is 7:10 or 0.7!!!!!!
- 7 CO2 produced for every 10 O2 consumed

3) Usually a MIX OF FUELS is being used:
- 200 mL CO2 produced for every 250 mL O2 consumed
- Ratio 8: 10 or 0.8!!!!!!!

11
Q

The Respiratory Quotient (RQ)

A
  • The ratio between CO2 PRODUCED and the O2 CONSUMED is called the RESPIRATORY QUOTIENT or RQ!!!!!!!!
  • It is calculated according to the equation:

RQ = (Volume of CO2 Produced)/ (Volume of O2 Consumed)

RQ = V(dot) CO2 / V(dot) O2

= (200 mL CO2 produced) / (250 mL O2 consumed)

= 0.8!!!!!!

12
Q

How much CO2 can dissolve in the Plasma?

A
  • CO2 has a much greater SOLUBILITY in Water (And therefore Plasma) than O2

The Solubility of CO2 is:
6 mL O2/ dL Blood/ 100 mm Hg

  • Since the PCO2 of the Venous Blood is 45 mm Hg, there is about 2.7 mL CO2 DISSOLVED in each dL of Blood!!!
  • Once again, we’ need a Cardiac Output considerably higher than 5 Liters/ min to deal with the volume of CO2 produced every minute (about 200 mL CO2)
13
Q

Carrying CO2 in the Blood: Carbamino Compounds

A
  • CO2 can combine with Plasma proteins or Hb to form CARBAMINO COMPOUNDS
  • It does not bind to the HEME GROUP of the Hb, but the AMINE GROUP of the Chains!!!!
  • The presence of O2 of the Heme reduced the AFFINITY of the Hb chain for the CO2!!!!
  • This is called the HALDANE SHIFT!!!!!!!

***The VOLUME of CO2 carried this way is also about 3 m:/ dL of Blood (About 7% of the Total)

14
Q

Carrying CO2 in the Blood: as HCO3

A
  • Most of the CO2 in the blood is carried as BICARBONATE (HCO3)

**86% of the Total

** 44 mL of CO2

15
Q

Carbonic Anhydrase

A
  • It is found in RBC and acts on CO2 and Water to form Carbonic Acid. Which dissociated quickly into H+ and Bicarbonate
  • Bicarbonate is shunted out of the Plasma and can be measured
  • Bicarbonate has a NEGATIVE CHARGE
  • CHLORINE gets pumped into the cells for EVERY BICARBONATE PUMPED OUT, to keep the NEGATIVE PRESSURE

**This process is occurring in the VENOUS BLOOD

16
Q

Back in the lungs, the CO2 will move into the Alveoli

A
  • Dissolved CO2 will go down GRADIENT into ALVEOLI
  • CO2 and H+ will leave the proteins as the DISSOLVED CO2 moves into the Alveoli!!!!!
  • ** And the HCO3 will be converted back to CO2
  • Many of the H+ are displaced from the Hb as Oxygen starts to Bind
  • The CO2 is free to DIFFUSE into the Alveoli!!!
17
Q

Summary of CO2 Transport

A

1) CO2 may be dissolved in the plasma, bound to Hb/ other proteins, or converted to HCO3 for Transport
2) HCO3 is the major form of Transport
3) Because H2CO3 is also produced, INCREASES in plasma Co2 are associated with INCREASED ACIDOSIS of the blood
4) The HCO3 produced in the Blood cell is pumped out of the cell in EXCHANGE for Chlorine, producing the CHLORIDE SHIFT
5) Once in the lungs, the Equilibrium shifts back to DISSOLVED CO2 and the CO2 is EXHALED

18
Q

Summary of Oxygen Transportation

A

1) Oxygen may either be dissolved in the Plasma or bound to Hb for transport
2) Binding to Hb is the most important for getting us the Oxygen we need
3) O2, CO2, pH, Temperature, and the presence of certain metabolites can change the affinity of Hb for O2
4) In the tissue, Oxygen leaves the Hemoglobin and enters the tissue for Metabolic use
5) The a-v O2 difference tells us how much Oxygen was used for the tissue
6) The Respiratory Quotient (RQ) tells how much CO2 is produced for each molecule of O2 consumed. The ratio changes depending on what fuel is being burned (Glucose vs FFA vs Mixture)

19
Q

Compare and Contrast O2 and CO2 Transport

A

O2

1) Volume Carried in Blood:
- about 20 mL O2/ dL Blood

2) Major form Transported:
- Bound to Heme in Hb

3) Volume Dissolved:
- 0.3 mL O2/ dL Blood

4) Other Forms:
- None

CO2

1) Volume Carried in Blood:
- about 50 mL CO2/ dL Blood

2) Major form Transported:
- HCO3

3) Volume Dissolved:
- about 3 mL CO2/ dL Blood

4) Other Forms:
- Carbamino Compounds

20
Q

Alveolar Oxygen

A

Alveolar Oxygen = (Oxygen in Lungs - Oxygen used by Tissue)

PAO2 = PIO2 - (PaCO2/R)
**ALVEOLAR GAS EQUATION**

1) PAO2 = Alveolar Partial Pressure of Oxygen

2) PIO2 = Inspired Partial Pressure of Oxygen
- Must account for Water Vapor:
so PIO2 = (760-47) x Oxygen %

3) PaCO2 = Arterial CO2
4) R = [V(dot) CO2] / [V (Dot) O2] = 0.8!!!!!

21
Q

PIO2

A
  • Inspired Partial Pressure of Oxygen

Calculated as: (Barometric P- the water vapor P) x FiO2

1) Barometric (Atmospheric) Pressure
a) At sea level: 760

b) DECREASES with INCREASING ALTITUDE (will be given)

2) Water Vapor Pressure
a) Air is humidified as you inhale it (water is added)

b) At body temperature (amor anything close) it is 47 mm Hg

3) FiO2
a) Fraction of Inspired Oxygen (percent Oxygen Inhaled)

b) 21% is Normal (Regardless of Altitude)
c) Changes if you supplement Oxygen (will be given)

***AT SEA LEVEL PiO2 = (760 - 47) x Oxygen %

22
Q

**ALVEOLAR GAS EQUATION**

A

PAO2 = PIO2 - (PaCO2/R)

  • It is used to calculate what inspired O2 needs to be to produce a desired alveolar (and therefore arterial) O2 level
  • Often listed with a small correction factor. This is small and can be ignored

Look at Example:
SLIDE 50 and 51 of GAS TRANSPORT LECTURE!!!!

23
Q

A-a O2 Gradient

A
  • It is nice to have the PAO2 but it is not useful!!!
  • However, it allows us to calculate the A-a O2 Gradient, and that is very useful number for determining the “health” of the Alveoli!!!!

**NORMAL

24
Q

Summary of Alveolar Gas Exchange

A

1) The alveolar gas equation allows us to predict the oxygen concentration in the Alveoli (Very helpful since it is non-invasive)
2) Once you have the alveolar concentration of Oxygen (and you know the arterial concentration) - you can calculate the A-a O2 Gradient
3) If the A-a gradient is GREATER than NORMAL (Roughly > 20 mm Hg), you know there is a PROBLEM WITH THE ALVEOLI

4) If the A-a gradient is Normal, but the PaCO2 and the PAO2 are BOTH LOW, the problem is elsewhere (Ex: The patient may be HYPERVENTILATING)
- Like people living in ALTITUDE!!!!