physiology week 3 reading

variations between PAO2 and PaO2

due to right to left shunts in the pulmonary and cardiac circulation and regional differences in pulmonary ventilation and blood flow

anatomical shunt

portion of the cardiac output that returns to the left heart without being oxygenated by exposure to ventilated alveoli (R-L), reduces O2 content of arterial blood by dilution

V/Q ratio

ideal ratio is 1 (.8), high indicated more ventilation or less perfusion is present → pulmonary blood flow decreased but ventilation is normal (PE) conversely can indicated atelectasis

alveolar shunts

causes venous admixture, venous blood entering areas with V/Q of 0 cannot pick up O2 or unload CO2 so it returns to the left side of the blood and gets mixed with oxygenated arterial blood diluting O2 contents (perfusion, no ventilation, COPD, hypoventilation) the extreme form of V/Q mismatch

alveolar dead space

portion of the tidal volume that enters into alveoli that are without any perfusion or adequate perfusion (pulmonary emboli, destroyed pulmonary vasculature in COPD, reduced cardiac output)

physiologic dead space

the sum of alveolar and anatomical dead space (VD)

alveolar ventilation

= (VT - VD) X RR

lung apex

higher V/1 ratio, higher PAO2, lower PaCO2, lowest blood flow

oxygen storage

dissolved in a blood in the plasma and intracellular fluid or bound to Hb inside the RBC (gaseous O2 diffuses into blood and immediately dissolves in the plasma)

fully saturated Hb

oxyhemoglobin, 1g of normal Hb can carry approximately 1.34mL of