VPB 121: Veterinary Physiology - II (2+1)

HYPOXIA

• It is a state of inadequate O₂ supply to tissue. Absence of O2 is referred as anoxia. The Cerebral effects seen will be mostly as excitement, hallucination, restlessness and unconsciousness. When blood O₂ below 13%, breathing is stimulated. The anoxia can be classified into the following types.

Anoxic hypoxia (Ambient hypoxia)

• This is due to reduced alveolar ventilation and reduced O₂ tension in blood caused due to obstruction of air passage, paralysis of respiratory muscle, pulmonary disease or congenital diseases of heart. Ambient anoxia is caused by low pO₂ in environmental air in high altitudes or closed space. Symptoms seen are dyspnoea, alkalemia, high cardiac output, increased pulse pressure, dilatation of peripheral vessels.

Anemic anoxia

• Decrease in O₂ carrying capacity of Hb due to low concentration of Hb seen in haemorrhages, anaemia, CO poisoning. In this case the partial pressure of O₂ is normal but insufficient O₂ delivery to tissue results in increased cardiac output and rapid circulation time.

Stagnant hypoxia

• The O₂ content of arterial blood is normal, but the tissues receive low O₂ supply because general or local circulation failure.

Histotoxic hypoxia

• The tissue oxidation is interfered due cyanide poisoning. Paralysis of cytochrome oxidase system is responsible for this condition. The amount of O₂ and pO₂ are normal in arterial blood and above normal in venous blood.