CO2 Dissociation Curve, Hypoxia & Cyanosis

Question 1

Define tidal CO2 and its value

Answer 1

It is the amount of CO2 added from tissues to each 100 ml arterial blood to be changed to venous blood.
3.7 ml/100ml

Question 2

Describe forms and ratios of CO2 in arterial blood

Answer 2

• 5% physically dissolved
• 5% as carbamino compounds
• 90% as bicarbonate ions

Question 3

Describe the transport of tidal CO2 & its forms

Answer 3

10. 8% dissolved CO2
11. 6% as carbamino compounds
12. 6% as HCO3-

Question 4

GR: The pH doesn’t vary greatly between arterial (7.36) & venous (7.4) blood

Answer 4

Because CO2 added to blood at tissue is buffered as HCO3- and HbCO2.

Question 5

GR: Persesnce of CO2 in the form of HCO3- is beneficial

Answer 5

Beacuse HCO3- is more solubke in blood than CO2 is.

Question 6

Write a short note on the chloride shift phenomenon

Answer 6

HCO3-/Cl- exchanger facilitates the diffusion if these ions passively
At systemic level, carbonic anhydrase reaction results in HCO3- ion formation & its accumulation in RBCs, so it diffuses to plasma down its concentration gradient creating and electrical gradient. So, Cl- ion diffuses inside RBCs down its electrical gradient to preserve electrical neutrality.

Question 7

Comment on the following

Haldane & Bohr effects work in synchrony at tissue level

Answer 7

• Increased CO2 and H+ cause increased O2 release from Hb by Bohr effect
• Increased O2 release from Hb increased uptake of CO2 & H+ by haldane effect

Question 8

Describe the haldane effect

Answer 8

It is the effect of O2 on Hb CO2 and H+
AT tissue capillaries, O2 is released from Hb, increasing reduced Hb which has higher affinity to CO2 & H+ so inc their uptake by Hb.

Question 9

GR: hematocrit value is 3% higher in venous than arterial blood

Answer 9

Inc HCO3- in RBCS & plasma + increased Cl- in RBCs results in increased osmotic pressure leading to water entry to RBCs and increasing their volume.

Question 10

Describe the effects of administration of carbonic anhydrase inhibitors

Answer 10

Dec transport of CO2 from the tissue, inc PCO2 in tissue (may rise to 80 mmHg instead of 46 mmHg) as it is exerted by the physically dissolved form of CO2

Question 11

Compare hypoxia & hypoxemia

Answer 11

1, O2 deficinecy at the tissue level

2, is reduced arterial PO2

Question 12

Causes of hypoxic hypoxia

Answer 12

1. Inadequate blood oxygenation due to decreased PO2 in inspired air or hypoventilation (neuromuscular disorders, inc airway resistance or decreased pulmonary compliance)
2. Pulmonary disease: diminished respiratory membrane diffusion due to membrane thickening or decreased surface area
3. Abnormal V/Q ratio (inc physiological dead space, emphysema…etc)
4. Venous-to-arterial shunts, inter-atrial septal defect or pulmonary artery to pulmonary vein anastomosis

Question 13

Mention causes of anemic hypoxia

Answer 13

Anemia, abnormal Hb, CO poisoning

Question 14

Mentuon causes of stagnant hypoxia

Answer 14

1. Generalized as shock or congestive heart failure

2. Localizaed as local vascular spasm or block

Question 15

Mention causes of histotoxic hypoxia

Answer 15

1. Inhibition of cellular oxidative enzymes as in cyanide poisoning
2. Beriberi disease in which several steps in oxygen utilization is impaired

Question 16

What are the abnormal parameters in each type of hypoxia.

Answer 16

Hypoxic: decreased PO2, O2 content in both arterial and vebous blood.
Anemic:decraesed arterial O2 content and venous PO2 & O2 content.
Stagnant: decreased venous PO2 & O2 content
Histotoxic: increased venous PO2 & O2 content

Question 17

C/P of anemia

Answer 17

1. Headache, easy fatigability and drowsiness
2. Loss of appetite, nausea and vomiting
3. Tachycardia and tachypnea

Question 18

Agents used in tearting cyanide posoning

Answer 18

Nitrites and methylene blue

Question 19

Mention cases in which O2 therapy is beneficial

Answer 19

Hypoxic hypoxia due to hypoventilation, impaired gas diffusion, ascent to high altitudes.

Question 20

O2 therapy is of limited value in ….

Answer 20

Hypoxic hypoxia due to right to left shunts, anemic hypoxia and stagnant hypoxia.

Question 21

Hyperbaric oxygen therapy is used in

Answer 21

Histotoxic hypoxia and CO poisoning

Question 22

Mention conditions in which advrse effects hyperbaric oxygen can occur.

Answer 22

80-100% oxygen for 8 hours or more causes irritation to the respiratory passages (nasal conhgestion, sore throat & coughing)
4 atm for 30 min
6 atm for few minutes

Question 23

Mention side effects of O2 therapy in infacts with ARDS

Answer 23

Bronchopulmonary dysplasia (lung cysts)
Rertnopathy of prematurity: formation of opaque vascular tissue in retina

Question 24

Mention symptoms of oxygen toxicity

Answer 24

Tracheobronchial irritation
Muscle twitching
Dizziness, convulsions and coma

Question 25

When does cyanosis occur?

Answer 25

When the amount of reduced Hb in capillaries (or arteries) is increased above 5 gm/100 ml of blood

Question 26

Conditions for cyanosis to occur

Answer 26

Polycythemia, hypoxic hypoxia, stagnant hypoxia, moderate cold, asphyxia

Question 27

Cyanosis doesn’t appear in

Answer 27

Anaemic hypoxia, CO poisoning, histotoxic hypoxia, very cold weather.