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 will affect arterial PO2 and PCO2. Define right-to-left shunts, anatomic and physiological shunts, and physiologic dead space (wasted ventilation). Describe the consequences of each for pulmonary gas exchange.

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

3. initially

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

5. The loss of CO2produces a respiratory alkalosis. To compensate, the kidney Loses bicarbonate to return arterial pH 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

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

7. Increased Diffusing Capacity After Acclimatization Increased tissue capillarity (or angiogenesis) Cellular Acclimatization -cell mitochondria and cellular oxidative enzyme systems are slightly more plentiful

9. Which of the following sets of changes best describes a Himalayan native living in the Himalayas, compared to a sea-level native living at sea level? Hematocrit Arterial Po2 Arterial O2 content A) Decreased Decreased Decreased B) Decreased Decreased No difference C) Decreased Increased Decreased D) Decreased Increased No difference E) Increased Decreased Decreased F) Increased Increased Decreased G) Increased Increased No difference H) Increased Decreased No difference

10. 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 PO 2 can be oxygen toxicity. The high PN 2 can cause nitrogen narcosis, but, more important, it can lead to the bends (caisson disease/decompression sickness). Bends, Chokes and strokes

11. 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.

12. Hypoxemia

14. NORMAL STATE

15. HYPO VENTILATION

16. 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.

17. DIFFUSION IMPAIRMENT

19. Perfusion limited situation

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

24. Hypoxia

26. 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.