1. ventilation moves air in and out of alveolar reservoir
2. diffuse across alveolar capillary membrane into solution in cell membranes and blood
3. react with hemoglobin
4. transport to periphery
5. extract oxygen by tissues through diffusion
6. use oxygen in cell metabolism
7. residual oxygen in venous blood transported back to lung

• at point of terminal bronchioles
• movement across alveolar capillary membrane

• gas diffuse into liquid phase, where they enter solution and exist in dissolved state
• diffusion takes place across membrane along pressure gradient
• at equilibrium:
  • atm gas P = dissolved gas P
  • ex: if alveolar air is 100 mm Hg, then after diffsusion, capillar blood would also be 100 mm Hg

Describe solubility of oxygen and carbon dioxide in water

• both are highly soluble and readily diffuse
• carbon dioxide is 20 times more soluble in water than oxygen, so dissolves 20 times faster

How gas transported in solution

• dissolved (dissolved gas P contribute to partial P)
• bound (Hb, plasma proteins)
• chemically modified (CO2 to HCO3)

1. fluid layer of alveoli
2. alveolar epithelial cell membrane (mainly type I cells)
3. epithelial cell basement membrane
4. interstitial space between basement membrane of epithelial cell and basement membrane of endothelial cell
5. capillary basement membrane
6. capillary endothelial cell membrane

• large surface area (70 meters squared)
• very thin (0.2-0.5 microns)
• small diameter (8 microns)
• not a lot of blood in capillary (60-140 mL)

• clinical measurement of diffusion characteristics of alveolar capillary membrane

1. use carbon monoxide to test diffusion capacity
2. combines diffusion coefficient, surface area, thickness of membrane, time for gas to combine with proteins (combines readily with Hb)
3. the person is asked take max inhalation, to hold their breath for 10 seconds, breath out (discard first part, but sample the second part of air)

• diffuse interstitial lung disease
• reduced lung volume
• parenchymal destruction (emphysema)
• pulmonary vascular disease
  • pulmonary embolism
  • primary pulmonary hypertension
• anemia
• resection of pulmonary parenchyma

Mean pressure of oxygen difference across membrane

Effect of oxygen diffusion on low alveolar O2 pressure

• diffusion time longer even with normal membrane
• if membrane diseased, diffusion may not be completed during time an RBC spends in capillary

21 mL/min/mm Hg

(11 mmHg x 21 mL/min/mm Hg = 230 mL/min)

CO2 diffuses very readily

• diffusion limited- total gas exchange limited by diffusion process
• perfusion limited- total gas exchange limted by blood flow through capillaries

• CO2
• oxygen during strenous exercise
• emphysema
• fibrosis
• high altitude

• O2 transfer at rest
• CO2
• blood flow

• 0.003 mL O2/100 mL of blood x 100 mm Hg = 0.3 mL O2/100mL

Define P50

Effect of there being significant amount of Partial pressure change in oxygen arterial pressure to have significant effects

O2 delivery = CaO2 x Q

• CaO2- includes both dissolved O2 and O2 combined with Hb
• Q = cardiac output

Pt at which somebody requires respirator

Define oxygen capacity

• normal arterial PO2
• Hb normal
• decrease O2 saturation and content

240 X greater affinity for Hb than oxygen

• changes in Hb affinity for oxygen
  • shift left- increase affinity
  • shift right- decrease affinity

• increase PCO2, leading to decrease pH
• increase temperature
• increase 2,3 BPG

Equation for CaO2

CaO2 = (0.003 x PaO2) + (1.34 x Hb x Sat.)

"a" is arterial

• increases and stays fairly high after going from venous to pulm. capillaries
• decreases in systemic capillaries and stays low in venous blood

Importance of PCO2 in cells

cells PCO2 is higher, so it wants to exit cell

• dissolved (10 % of CO2)
• carbamino compounds (Hb) (30% of CO2)
• HCO3 (60% of CO2)

• binding to Hb
• reacts with H20 and via carbonic anhydrase, forms HCO3
• HCO3 transported out of RBC via antiport with Cl
  • leads to slight rise in HCO3 in venous blood

• drive rxn with H20 in RBC
• determine PaCO2 and PvCO2

10% of CO2 in body is transported via dissolved state

• shows the effect of HbO2 content on CO2 concentration
  • decreases the amount of CO2 in blood

PaCO2 increases, signifies reduction in effective alveolar ventilation (Va) (Ve = Vd + Va)

• reduce minute ventilation
• increase dead space ventilation (alveoli with high V/Q ratios)

• depress respiratory center drive
• loss of neuromuscular coupling
  • impaired neuromuscular transmission
  • excessive resp. load, leading to resp. muscle fatigue

• direct relationship
• as ventilation rate continues to all, smaller decreases in minute ventilation lead to decreases in Vd/Vt

Henderson Hasselback for HCO3 and CO2

pH = pKa + log (HCO3/0.03 x PCO2)

• acidosis- rise in PaCO2 (hypoventilation)
• alkalosis- fall in PaCO2 (hyperventilation)

• increase HCO3
• decrease HCO3

for every rise of 10 mmHg in PaCO2, decrease in pH of 0.08

pH change = 0.08 x (PaCO2-40)/10

Cause of metabolic acidosis? alkalosis?

• acidosis- fall in HCO3
  • ketoacidosis
  • lactic acid
• alkalosis- rise in HCO3
  • volume contraction
  • hypokalemia

Purpose of Winter's formula and equation

• predict respiratory response of kidney to acidosis or alkalosis
• PaCO2 = (1.5 x HCO3) + (8 + 2)

• hyperventilation
• immediate
• linear correlation btw change in PaCO2 and change in HCO3

• hypoventilation
• response not easily predicted
• not linearly related to HCO3
• PaCO2 increases about 40 torr, but not greater than 50 to 55
• patient remain alkalemic in setting of compensatory elevation of PaCO2