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Learning objectives

Learning objectives. Understand the Effect of low oxygen pressure on the body. Understand the Effect of high partial pressure of individual gases on the body Predict how the presence of abnormally low and high V/Q ratios in a person's lungs will affect arterial PO2 and PCO2 .

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Learning objectives

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  1. Learning objectives • Understand the Effect of low oxygen pressure on the body. • Understand the Effect of high partial pressure of individual gases on the body • Predict how the presence of abnormally low and high V/Q ratios in a person's lungs willaffect arterial PO2 and PCO2. • Define right-to-left shunts, anatomic and physiological shunts, and physiologic deadspace (wasted ventilation). Describe the consequences of each for pulmonary gas exchange.

  2. Understand Hypoxemia and Hypoxia: Be able to calculate the alveolar to arterial PO2 difference, (A-a)DO2. Describe thenormal value for (A-a) DO2and the significance of an elevated (A-a) DO 2.

  3. At high altitude, there is a permanent depression in alveolar and systemic arterial PO2. • The low PO2 stimulates the peripheral chemoreceptors, inducing a hyperventilation andadecreaseinalveolar and systemic arterial PCO2

  4. The loss of CO2produces a respiratory alkalosis. To compensate, the kidney Loses bicarbonate to return arterialpH close to normal. • Acutely, arterial oxygen content is depressed because of reduced hemoglobin saturation. • Acclimatization returns oxygen content toward normal because of an increase in hemoglobin concentration

  5. Acute Changes and Long-Term Adaptations (Acclimatization)

  6. High-Pressure Environment • The partial pressure of O2 and N2 will increase in the alveoli and systemic arterial blood. • The adverse effect of a high PO2can be oxygen toxicity. The high PN2can cause nitrogen narcosis, but, more important, it can lead to the bends (caisson disease/decompression sickness). • Bends , Chokes and strokes

  7. Hypoxemia and Hypoxia Hypoxemia is defined as a decrease in arterial PO2. Hypoxia is defined as a decrease in O2 delivery to, or utilization by, the tissues. Hypoxemia is one of the causes of tissue hypoxia.

  8. Hypoxemia

  9. NORMAL STATE

  10. HYPO VENTILATION

  11. There is no increase in the A–a oxygen gradient. • Supplemental oxygen can relieve the hypoxemia. • End-tidal air still reflects the systemic arterial compartment. • The problem is not within the lung itself.

  12. DIFFUSION IMPAIRMENT

  13. Perfusion limited situation

  14. Increase in A–a oxygen gradient • Supplemental oxygen ineffective at returning arterial PO2to normal • End-tidal air does not reflect the arterial values

  15. Hypoxia

  16. HYPERCAPNIA • Hypercapnia means excess carbon dioxide in body fluids. • Hypercapnia is not seen in hypoxia caused by hypoxemia, anemia or poisoning of the oxidative enzymes. • Hypercapnia occurs in association with hypoxia caused by hypoventilation. • At PCO2 of 80-100mmHg, the person is lethargic and at 120-150mmHg, death supervenes.

  17. Which of the following best shows the apex vs. the base of the lung in a standing subject?

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