Gas Transfer and Diffusion Lecture 11

Question 1

Diffusion factors

Answer 1

Area, diffusion coefficient (solubility/root of Molecular weight), difference in pressure/distance to diffuse

Question 2

Diffusion barriers

Answer 2

alveoli->alveolar fluid->surfactant->alveolar epithelium->AV basement membrane->interstitium->capillary BM->capillary epithelium->plasma->RBC

Question 3

Restrictive lung disease effect on diffusion distance

Answer 3

edema is brought on by scoliosis or fibrosis which causes a buildup of interstitial fluid and alveolar fluid

Question 4

Pathological factors affecting surface area (2)

Answer 4

Emphysema - alveolar surface area decreased up to five fold

Alveolar edema or small airway constriction can cause decreased ventilation to some areas

Question 5

Diffusion stats related to oxygen demand being perfusion limited

Answer 5

complete absorption of oxygen happens in .3 seconds, or about 30% of the way down the capillary; at exercise speeds, it is totally diffused at 75% of the way down the capillary

Question 6

diffusion capacity definition and method used to determine

Answer 6

the amount of volume of a gas that diffuses in 1 min under a pressure gradient of 1 mmHg; normally CO is used to determine since it will not have a partial pressure in blood (since it is taken up so rapidly)

Question 7

reasons for O2 diffusion not reaching equilibrium

Answer 7

Thickening of the diffusion pathway, as in fibrosis, asbestosis, silicosis or edema
Decrease in surface area - emphysema or bronchial obstruction
Low lung compliance silicosis

Question 8

O2 in blood stats

Answer 8

0. 3 ml/dL dissolved

20. 1 ml/dL bound to Hb

Question 9

definitions for oxygen content, capacity, saturation

Answer 9

Capacity - what is 100% given the amount of Hb in the blood (20.1 ml/dL) (does not account for plasma oxygen)
Content - maximum amount, with the plasma included (20.4 ml/dL)
Saturation - percentage of oxygen actually in the blood given the statistical maximum
97% SO2 in the pulmonary vein, 75% in the pulmonary artery
Saturation can be affected by the Hb ability to bind or by the PO2, but not by the amount of Hb present

Question 10

Oxygen/Hb dissociation curve

Answer 10

At pressures of oxygen less than 70 mmHg, O2 releases from Hb dramatically. From 70 to higher, there is very little increase in O2 binding

Question 11

P50

Answer 11

the pressure at which half of the Hb are saturated, 26.5 mmHg normally; can be increased allosterically by increased H+ ion concentration, pCO2, BPG and temperature

Question 12

Bohr effect

Answer 12

H and CO2 cause a decrease in affinity for O2, this facilitates diffusion in lungs and resorption in the tissue

Question 13

DPG (BPG)

Answer 13

increases P50/Km, this is normal hypoxic response or can be the result of pathology. Normally high during elevated glycolysis

Question 14

Pathology of O2 capacity

Answer 14

Anemia/hypovolumic - decrease Hb means less O2 delivery
Mutant Hb
CO poisoning - 200 fold more binding to Hb than O2; decreases Hb carrying O2, and shifts ODC to the LEFT causing less offload at tissue sites; also not detected by the body

Question 15

Methods to increase oxygen delivery; fold increase

Answer 15

1) increase ventilation and perfusion - 3x increase
recruitment and distention of capillaries and increased tidal volume
2) shift the ODC to the right to extract more blood from the same volume

Question 16

Fick principle

Answer 16

Cardiac output = O2 consumption/(arterial O2 - venous O2)

Question 17

V CO2

Answer 17

200 ml/min resting

Question 18

Transport of CO2 in the blood (3)

Answer 18

• Dissolved (7%) - 20x more soluble than O2
• As bicarb (70%) - carbonic anhydrase in RBC turns out bicarb into the plasma, Cl into RBC (chloride shift)
• Carbaminohemoglobin (23%) competes with O2, knocks out O2 when pCO2 is high, part of Bohr

Question 19

What is the opposite of the Bohr effect experienced in the lungs?

Answer 19

Haldane effect

Question 20

In terms of acid/base hypoventilation leads to…

Answer 20

acidosis and hyperventilation is the opposite