Physiology #17: Resp physiology 3

• Pulmonary edema - alveoli become fluid filled, gas exchange cannot occur since the fluid displaces the air
• Interstitial fibrosis - alveoli become inflamed and scar tissue forms in interstitial layers of the alveolar walls. Thickens the diffusion membrane

CO2 is 20x more soluble

• <1% of O2 is "dissolved" directly into blood stream
• >995 is carried by hemoglobin in the RBC

• Hemoglobin is the red pigment of blood
• (mucous membranes tell us saturation)

RED (Hb + O2)

Purple (O2 released)

= % of all the Hb molecules that are bound to O2

4

• 4 heme protein subunits
• each has iron atom
• O2 binds loosely and reversibly to iron

NO its sigmoidal

• 'flat portion" 60-100mmHg PO2 = load O2 (for high carrying capacity so can carry to lungs)
• "steep portion" 30- 50mmHg PO2 = unload O2 (at tissues** because want to deliver O2)

No change in Hb saturation (stays at 100%)

Hb saturation across the normal range for O2 in the lungs is NOT significantly affected by PAO2

HUGE change in the % saturation (90% to 50%) - unload O2

when the surrounding O2 drops (ie in the tissue)

• Lungs: loading (where PO2 is high)
• Tissues: unloading (where PO2 is low)

(so veins are low in O2 and arteries are high in O2)

• "Right Shift": decreases the affinity of Hb for O2 (more O2 is released)
• occurs with increased Temp, decrease pH, increase CO2
• occurs at the level of the tissues

• "Left shift": increases the affinity for O2 (more O2 is loaded)
• occurs with decreased temp, increase pH, decreased CO2
• occurs at the level of the lungs

• Left shift
• hold onto O2 levels in tissue
• shock because not enough O2 in system

• Left shift: decreased temp, decreased 2-3 DPG, decreased H+ (increased pH), decreased CO2 : increased O2 affinity
• Right shift: increased temp, increased 2-3 DPG, increased H + (decreased pH), decreased CO2 : decreased O2 affinity

• 1. oxygen uptake: O2 taken up in alveolus, or arterial blood? (figure out through alveolar gas equation)
• 2. oxygen content: how much O2 is in the arterial blood (dissolved and bound to Hb)
• 3. oxygen delivery: blood flow (cardiac output)  is needed to actually move blood through the body to deliver oxygen.

• alveolar gas equation
• calculates max O2 pressure that can exist in the alveolus at a given time
• (room air is normally ~21% O2, but the partial P can change with altitude and weather)
• **********PaO2 (arterial) should be almost equal to PAO2 (alveolar) if everything is working properly

arterial should be ~=to alveolar partial pressure of O2 if everything is working properly

• CO2
• Nitrogen
• water vapor

• P_AO₂= FiO₂ x (P_{B -} P_H20) - (P_aCO2/0.8)
• FiO2 is the fraction of inspired oxygen
• P_B is barometric P ~760mmHg @sea level and ~670 in Calgary
• P_H2O  is the water vapor pressure which is 47 at normal body temp
• *If ventilation is normal P_aCO₂ is 40
• 0.8 is the respiratory quotient (related to metabolism)

PaO2 is 100mmHg

• Under anesthesia patients breath 100% O2
• so PAO2 and PaO2 should be 500mmHg

above 80mmHg maintain in anesthetics especially

• hypoxemia: refers to the condition when the oxygen saturation (%) of arterial blood is low. (need to measure this with an arterial blood gas sample or by using a pulse oximeter)-purple
• hypoxia: refers to when the oxygen levels are low at the level of the tissues themselves  

• A blood sample is collected "downstream" from a tissue bed ---analysis will reflect the metabolism and gas levels at that location only
• You need to think about what part you are interested in

• compares PaO2 vs PAO2 to decide if the oxygen levels are "acceptable" 
• -A-a gradient = PAO2 - PaO2
• Normal is 0 -15 mmHg
• assesses the difference between oxygen in the alveoli and the oxygen in the arteries
• Serves as a measure of the ability of the lungs to load O2 and the blood to pick it up***

• the inability of the lungs to oxygenate blood
• the presence of venous admixture

• FiO2- so increase inspired O2 to increase levels in the alveoli (cost effective)
• PaCO2- ventilate patient to remove CO2 (if CO2 is too high hypercarbia is a problem)

• The total amount of oxygen that is carried in the blood is a combo of its dissolved hb-bound components
• content = (1.34 x Hb x O2Sat%) + (PO2 x o.oo3)
• Need adequate oxygen pressure as well as adequate levels of Hb to carry the O2 or else the total content will be low

~20mL of oxygen/dL of arterial blood (nearly all is carried by Hb)

• DECREASE in oxygen content
• so Hb  amount decreases
• = ~11mL of O2/dL of blood (compared to the normal 15mL/dL in venous blood)

so if Hb drops by 50% so will the O2 content (because don't have the RBC to carry O2) 

• D(with dot ontop) = cardiac output x arterial O2 content
• -cardiac output is the V of blood pumped per min by heart beat