Etiology

The major causes of cerebral hypoxia are (a) hypoxemia, (b) anemia, (c) histotoxicity, and (d) ischemia (stagnant cerebral blood flow).

Hypoxemic hypoxia develops when the blood oxygen tension falls below 40 mm Hg, which may occur in acute respiratory arrest, chronic obstructive pulmonary disease, alveolar hypoventilation, airway obstruction, near-drowning, diminished oxygen concentration in the air, weakness of respiratory muscles, and status epilepticus.

Anemic hypoxia develops when the oxygen-carrying hemoglobin falls to half its normal concentration, as occurs in severe blood loss and chronic anemia.

Histotoxic hypoxia is caused by toxic substances, such as carbon monoxide, cyanide, and sulfide, which prevent utilization of oxygen by the neural tissue.

Ischemic (stagnant) hypoxia develops when the blood flow falls below 18 mL/100 g tissue/min. This drop may be regional, confined to an arterial territory (see Chapter 4), or global, leading to generalized cerebral hypoperfu-sion. Global cerebral ischemia, transient or permanent, may occur in a variety of clinical settings: cardiac arrest, cardiac arrhythmias, sudden hypotension from myocar-dial infarct, and severe rise of intracranial pressure. Unlike in hypoxemic and anemic hypoxias, in ischemic hypoxia, the brain is deprived of all blood constituents, most importantly of glucose; moreover, the harmful metabolites such as lactic acid are not eliminated.

In certain clinical situations, different types of hyp-oxias are combined; in cardiopulmonary arrest ischemia and hypoxemia occur concurrently.

FIGURE 3.1

Ammon's horn (Cornu Ammonis CA) A. histologic section (LFB-CV). B. Schematic drawing showing the sections of CA.

FIGURE 3.1

Ammon's horn (Cornu Ammonis CA) A. histologic section (LFB-CV). B. Schematic drawing showing the sections of CA.

Unraveling Alzheimers Disease

Unraveling Alzheimers Disease

I leave absolutely nothing out! Everything that I learned about Alzheimer’s I share with you. This is the most comprehensive report on Alzheimer’s you will ever read. No stone is left unturned in this comprehensive report.

Get My Free Ebook


Post a comment