Ventilation Perfusion Relationship Flashcards
(32 cards)
Reason why alveolar PO2 has fallen to 100mmHg (1/3)
Removal of oxygen by pulmonary capillary blood
Continual replenishment by alveolar ventilation
Fluctuation in alveolar PO2 each breath
3 mmHg
Tidal volume is small
Alveolar PO2 is largely determined by the level of
Alveolar ventilation
Decrease in alveolar ventilation
Decrease in alveolar PO2
Accumulation of PCO2
Hypoventilation
In alveolar gas equation, if R (respiratory exchange ratio is normal), 0.8,
Fall in alveolar PO2 is __________ than rise in PCO2
Slightly greater
CO2 stores are much greater than O2 stores because
Large CO2 amount in the form of bicarbonate (blood and interstitial fluid)
Alveolar gas equation
Alveolar Ventilation equation
PO2 difference between alveolar gas and end capillary blood from incomplete diffusion is
SMALL
*can become larger during exercise, BG barrier thickened
Low O2 mixture is inhaled
Diffusion limitation RARELY causes hypoxemia because
Rbc spend enough time in pulmonary capillary to allow complete equilibration
Examples of diffusion limitation
Blood that enters the arterial system without going through ventilated areas of the lung
SHUNT
Examples of SHUNT
Bronchial Artery blood collected by pulmonary veins
Small amount of coronary VENOUS blood draining to
CAVITY of left ventricle thru Thebesian veins
——————
Pulmonary arteriovenous malformation
CHD
The ratio of SHUNT flow to TOTAL flow is
SHUNT FRACTION
Term used on what shunt would be if depression of arterial O2 concentration were caused by mixed venous blood
AS IF shunt
O2 supplementation no effect on shunt but some elevation in arterial PO2 because of
O2 added to the capillary blood of ventilated lungs
100% fio2 in shunt will cause a relatively large fall in PO2 from small depression of arterial o2 concentration because of
Almost flat slope of o2 dissociation curve
Regional differences in gas exchange. INCREASED
V/Q ratio (0.6)
PO2
O2 concentration
PH
Variation in PN2 is because of
Total pressure in the alveolar gas
Large difference in ph down the lung
Reflects considerable variation in PCO2 of the blood
Minimal contribution to overall O2 uptake made by the apex can be attributed
Low blood flow at the base
*during exercise, apex assumes larger share of O2 uptake
Difference in CO2 uptake is MUCH LESS because
Related to ventilation
Respiratory exchange ratio (CO2 output/O2 uptake) is HIGHER at the
APEX
Oxygen dissociated curve is NON LINEAR hence
Units with high V/Q ratio will not increase o2 concentration
