Gaseous Diffusion And Transport Flashcards
Definition of fractional concentration (FO2/%)
The proportion of air that is made up of O2
Definition of partial pressure (PO2)
The pressure at which a gas in the air exerts
Definition of barometric pressure (Pb)
Total pressure of gases in the atmosphere
Definition of inspired PiO2, FiO2
Partial pressure of O2/fractional concentration of O2 in moistened inspired air at the end of the trachea
Definition of alveolar PAO2,FAO2
Partial pressure of O2/fractional concentration of O2 in the alveoli
Definition of arterial PaO2/FAO2
Partial pressure of O2/fractional concentration of O2 in the arterial blood
Definition of dead space
Airway volume with no gas exchange
Definition of anatomic dead space (ADv)
All except alveoli and respiratory bronchioles
Definition of physiologic dead space (PDv)
Anatomic dead space and areas where gas exchange is dysfunctional
Definition of saturation
Depends on how much air has been in contact with the water
Definition of polycythaemia
Increase in no of RBCs in the blood
Definition of capacity
How much something is capable of carrying
What is Dalton’s Law
In a mixture of non reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases
What is Pb at sea level
What is FO2
What is PO2 as a result
Pb = 101kPa
FO2 - 0.209
PO2 = 101 x 0.209 =21kPa
How does Pb, FO2, PO2 change at altitude?
Pb falls
FO2 doesn’t change
PO2 falls
What is Henry’s Law
What happens when the partial pressure increases
How would you increase partial pressure
C = kp
C = conc of dissolved gas at equilibrium k = solubility p = partial pressure
Partial pressure increases = more dissolves
Change PP by changing volume
Describe the relative solubilities of N2, O2 and CO2
What is the bends?
O2 = 2x more soluble than N2 CO2 = 20x more soluble than O2
If Pb decreases too rapidly (rise to the surface too fast), N2 isn’t breathed out and gas accumulates in blood and joints
Causes severe pain
What factors affect PH2O
What is the value of PH2O
How does PH2O affect PAO2
Affected by temp and saturation, NOT BY PB
6.3kPa
As you breathe in, air comes into contact with moisture in lungs = 100% saturation
In atmospheric air, what is
PO2
PCO2
PH2O
PO2
-21
PCO2
-0
PH2O
-var
In expired air, what is
PO2
PCO2
PH2O
PO2
-16
PCO2
-3.5
PH2O
-var
In inspired tracheal air, what is
PO2
PCO2
PH2O
How would you calculate these values
PO2
-20
PCO2
-0
PH2O
-6.3
(Pb-PH2O) x FiO2
(101-6.3) x 0.209 =20 ish
In alveolar air, what is
PO2
PCO2
PH2O
How would you calculate these values
PO2
-13.5
PCO2
-5.3
PH2O
-6.3
PO2 = PiO2 - PACO2/R 13.5 = 20 - 5.3/0.8
How do you calculate PAO2 as you cannot measure it directly and why
What is the normal value for R
Can’t be measured directly as O2 input and CO2 output are not equal
PAO2 = PiO2 - PACO2/R
R=CO2 production/O2 consumption
R=0.8
Describe gas exchange of O2 and CO2 in the pulmonary arteries and veins
What are the PP values in the pulmonary arteries, alveoli, pulmonary vein
What can happen when flow is abnormal/too fast
O2 movement powered by PP grad
Pulmonary arteries PO2 = 5.3
Alveoli = 13.5
Pulmonary veins PO2 = 13.5
CO2 diffuses slower than O2 due to increased MW
Solubility is higher equilibrates rapidly
Pulmonary arteries PCO2 = 6.1
Alveoli = 5.3
Pulmonary veins = 5.3
Less time for gas diffusion => hypoxia/hypercapnia
Name the 3 capillary layers
Alveolar epithelium
Interstitial fluid
Endothelium
How would you measure the rate of gas diffusion across the capillary wall
Rate = c∆ x A/x∆ x sol/√MX Rate = Dlg (PA -Pc)
CO has a v high affinity for haem, none dissolved in blood
Patient inhales CO tracer gas, composition of exhaled gas examined
-If DlCO = 100% => efficient gas transfer
How do these factors affect the DlCO
- Surface area of barrier
- Thickness of barrier
- Anaemia
- Polycythaemia
- Increasd pulmonary BV in exercise
SA
- reduced in emphesyma, lung resection, reduced venous return
- Decreased DlCO
Thickness
- increased in fibrosis, congestive heart failure, vascular diseases
- decreased DlCO
Anaemia
- decreased Hb to pick up O2
- decreased DlCO
Polycythaemia
- increased Hb to pick up O2
- increased DlCO
Increased pulmonary BV in exercise
- Increased effective area
- increased DLCO
Describe how gas exchange occurs between the capillaries and tissues
What problems could occur at the venous end of the capillaries
O2 diffuses down the partial pressure gradient
Arterial end = 13.5
Venous end = 5.3
Venous end less likely to receive highly oxygenated blood, if PO2 too low => diffusion slows down => hypoxic tissue
Describe how O2 is loaded and unloaded from RBCs
What is the PO2, O2 content, SaO2 in venous blood and arterial blood
What is the Bohr effect?
Sigmoid relationship between O2 sats and PP
Venous blood
- PO2 = 5.3
- O2 content = 150ml/l
- SaO2 = 75%
Arterial
- PO2 = 13.5
- O2 content = 200ml/l
- SaO2 = 100%
Bohr effect
- decreased pH
- increased pCO2
- increased temp
- increased 2, 3 DPG => MORE O2 OFFLOADED
What PO2 is good in venous blood?
At what values should we be concerned and why?
PO2 in venous blood > 8 => good oxygenation of tissues
PO2 < 8 => O2 offloads too quickly (on steepest part of curve), tissue on venous side => hypoxic
Describe how altitude affects
- O2 capacity
- Pb
- PiO2
- PaO2
- SaO2
O2 capacity
-normal
Pb
-decreased
PiO2
-decreased
PaO2
-decreased
SaO2
-decreased
Describe how anaemia affects
- O2 capacity
- Pb
- PiO2
- PaO2
- SaO2
O2 capacity
-decreased due to less Hb
Pb
-normal
PiO2
-normal
PaO2
-normal
SaO2
- normal
What is the difference between capacity, content and saturation?
Capacity
-how much O2 a RBC can carry
Content
-How much O2 a RBC is carrying
Saturation
-Percentage of Hb carrying O2
