TAILIEUCHUNG - Chapter 035. Hypoxia and Cyanosis (Part 3)

Adaptation to Hypoxia An important component of the respiratory response to hypoxia originates in special chemosensitive cells in the carotid and aortic bodies and in the respiratory center in the brainstem. The stimulation of these cells by hypoxia increases ventilation, with a loss of CO2, and can lead to respiratory alkalosis. When combined with the metabolic acidosis resulting from the production of lactic acid, the serum bicarbonate level declines (Chap. 48). With the reduction of PaO2, cerebrovascular resistance decreases and cerebral blood flow increases in an attempt to maintain O 2 delivery to the brain. However, when the reduction of. | Chapter 035. Hypoxia and Cyanosis Part 3 Adaptation to Hypoxia An important component of the respiratory response to hypoxia originates in special chemosensitive cells in the carotid and aortic bodies and in the respiratory center in the brainstem. The stimulation of these cells by hypoxia increases ventilation with a loss of CO2 and can lead to respiratory alkalosis. When combined with the metabolic acidosis resulting from the production of lactic acid the serum bicarbonate level declines Chap. 48 . With the reduction of PaO2 cerebrovascular resistance decreases and cerebral blood flow increases in an attempt to maintain O2 delivery to the brain. However when the reduction of PaO2 is accompanied by hyperventilation and a reduction of PaCO2 cerebrovascular resistance rises cerebral blood flow falls and hypoxia is intensified. The diffuse systemic vasodilation that occurs in generalized hypoxia raises the cardiac output. In patients with underlying heart disease the requirements of peripheral tissues for an increase of cardiac output with hypoxia may precipitate congestive heart failure. In patients with ischemic heart disease a reduced PaO2 may intensify myocardial ischemia and further impair left ventricular function. One of the important mechanisms of compensation for chronic hypoxia is an increase in the hemoglobin concentration and in the number of red blood cells in the circulating blood . the development of polycythemia secondary to erythropoietin production Chap. 103 . In persons with chronic hypoxemia secondary to prolonged residence at a high altitude 13 000 ft 4200 m a condition termed chronic mountain sickness develops. It is characterized by a blunted respiratory drive reduced ventilation erythrocytosis cyanosis weakness right ventricular enlargement secondary to pulmonary hypertension and even stupor. CYANOSIS Cyanosis refers to a bluish color of the skin and mucous membranes resulting from an increased quantity of reduced hemoglobin or of .

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