Other Factors Contributing to Non-Uniform Distribution of Perfusion
• Right pulmonary artery comes off at an acute angle. Therefore, there is more flow to the left lung.
Factors Contributing to Non-Uniform Distribution of Ventilation
• Diaphragm and ribcage association with lungs provides for• greater expansion at the base than at apex
• outer parencyma expands more than inner
• Weight of the lung and blood at the base• greater starting volume at apex (less ventilation upon
inhalation)
• results in less negative pleural pressure at base, favoring greater expansion at apex
• Net result: more ventilation at the base than at the apex.
Powder Dye (x mg)
Concentration (x mg / total ml)
V/Q Matching
Powder Dye (V)
Fluid Flow (Q)
Concentration (V/Q)
V/Q Matching
Powder Dye (V)
Fluid Flow (Q)
Concentration (V/Q)
Powder Dye (V)
Fluid Flow (Q)
Concentration (V/Q)
Powder Dye (V)
Fluid Flow (Q)
Concentration (V/Q)
V/Q Matching
Powder Dye (V)
Fluid Flow (Q)
Concentration (V/Q)
Powder Dye (V)
Fluid Flow (Q)
Concentration (V/Q)
2345 TOPBOTTOM
Rib Number
0.15
0.10
0.05
L/min or
% lung volume
Ventilation
Blood Flow
3
2
1
VA/QC
VA
/ Q
C
60
40
20
0
PC
O2
(mm
Hg
)
40 80 100 120 14060
PO2 (mmHg)
Low VA/QHigh V
A /Q
V/Q Matching
mixed venousblood
Tracheal air
VA
(L/min)Q
0.24 0.07
0.82 1.29
VA/Q
3.3
0.63
PO2 PCO2
mmHg
132 28
89 42
pH
7.51
7.39
V/Q Matching
Why is arterial PO2 lower than average (ideal) alveolar PO2?
• When pulmonary veins joins combining volumes of blood that have different oxygen concentrations, the final concentration of oxygen is a simple, linear function of• Oxygen content of each volume
• Sum of the volumes (final volume)
pv
V/Q=10/10
O2 Concentration inVol%
V/Q=1/10 V/Q=10/1
20.5
18.0 X 10 = 18020.0 X 10 = 20020.5 X 1 = 20.5
400.5 / 21 = 19.1
19.1
V/Q Matching
mv(pa)
2018
60 X 10 = 600100 X 10 = 1000150 X 1 = 150
1750 / 21 = 83.3
(60) (150)(100)(PO2)(70)
Hb
Sat
ura
tion
(%
)100
80
60
40
20
0
2
20 40 60 80 100 600
PO (mmHg)
O2 C
onten
t
(ml O
2 /dl b
lood)
2
6
10
14
18
22Total O2
OxygenTransport
Why is arterial PO2 lower than average (ideal) alveolar PO2?
• When pulmonary veins joins combining volumes of blood that have different oxygen concentrations, the final concentration of oxygen is a simple, linear function of• Oxygen content of each volume
• Sum of the volumes (final volume)
• PO2 is not a simple linear function of oxygen content or concentration.
• The PO2 of blood leaving the lungs of an upright individual will be slightly less than ideal (average) alveolar PO2 as a result of
• the largest quantity of blood coming from regions with the lowest V/Q ratios, coupled with the non-linear characteristics of the oxyhemoglobin dissociation curve, skews the PO2 of arterial blood toward the alveolar PO2 values at the base
• shunts
READ A BOOK!
cheesecheesech eesecheesecheeseche
esecheesecheese