Hypoxia

Question 1

hypoxia

Answer 1

hypoxia is defined as deficiency of o2 at the tissue level. tissues suffer from hypoxia when supply of adequate o2 to them is decreased or when they fail to utilise the available o2.

types of hypoxia

• hypoxic hypoxia
• anemic hypoxia
• stagnant hypoxia
• histotoxic Hypoxia

hypoxic hypoxia
- when po2 of arterial blood is reduced
- it occurs either due to decreased o2 in the inspired air or due to diseases of the respiratory apparatus – dec o2 to tissue
- seen in
• low po2 in inspired air eg at high altitude , 10000 ft above 15000 severe
• hypoventilation - airway obstruction, paralysis of resp muscles, depression of respiratory centers, scoliosis etc
• diffusion defect - eg pulmonary edema, pulmonary fibrosis, lung collapse
• ventilation perfusion mismatch - large arteriovenous shunts, atelectasis, lung collapse, cyanotic congenital heart disease.

anemic hypoxia
- when po2 is normal but hb to carry o2 is not adequate.
conditions
- anemia
- co poisoning
- altered hb
mechanism
-concomitant increase in 2,3- diphosphoglycerate (2,3-DPG)
such patients develop severe hypoxia during exercise

stagnant Hypoxia
hypoperfusion hypoxia
when hypoxia occurs due to dec blood flow to the tissues
sometimes also called ischemic hypoxia
also called as circulatory hypoxia

causes: seen in
1) heart failure
2) shock
3) vascular obstruction

mechanism

• o2 content of arterial blood is normal
• in chronic or complete stagnant hypoxia, local acidosis develops due to accumulation of lactate that inhibits cellular metabolism

histotoxic Hypoxia

• when tissue cannot utilize oxygen in spite of normal o2 supply
• as tissue is unable to utilise o2 the venous tension of o2 is high
• usually hypoxia occurs in tissue poisoning as produced by cyanides or similar poisons
• cyanide poisoning: cyanide inhibits cytochrome oxidase. therefore, tissue oxidation is paralysed
• diphtheria - in severe - diphtheria toxin inhibits the synthesis of one of the cytochromes and therefore prevents o2 utilisation.

Question 2

cyanosis

Answer 2

• bluish discoloration of the skin and mucous membranes of the body due to the presence of reduced hemoglobin or deoxyhaemoglobin in more than 5 g% in the blood.
• detected when oxygen saturation is less than 85%
• in excess of abnormal hemoglobin derivatives.

physiological basis.
-cyanosis is not seen jn severe anemia and co poisoning.

types of cyanosis
- peripheral cyanosis: occurs due to slowing of the flow of blood

• central cyanosis - due to admixture of venous and arterial blood or due to inadequate oxygenation of arterial blood
• mixed cyanosis - both central and peripheral mechanisms operate.

Question 3

periodic breathing

Answer 3

It is an abnormal type of cyclical breathing is which there are alternate phases of hyperpnoea and apnea.

one type of periodic breathing, cheyne-stokes breathing is characterised by slowly waxing and waning Respiration occuring about every 40-60 seconds.

• though it occurs in deep sleep in some normal persons, it is more common in congestive cardiac failure, uremia, and brain diseases
• patients have increased sensitivity to co2 due to disruption of neural pathways
• accumulation of co2 causes hyperventilation that lowers pco2
• decreased pco2 removes the co2 drive on ventilation and produces apnea, which consequently increases the pco2 again
• the increased sensitivity of respiratory mechanism of pco2 produces hyperventilation and the cycle continues

causes

• premature infants
• unacclimatized people at high altitude
• during deep sleep in some people
• heart failure
• renal failure