Respiration

1. Respiration

2. High altitude Changes • Atmosph. Pressure at sea level=760mmHg and PO2=160mmHg • As one ascends – Atmosph pressure keeps on decreasing • Composition or percentage of constituent gases remains same • At 10,000 feet = 523 mmHg PO2=110mmHg • At 50,000 feet = 87 mmHg PO2=18mmHg • Acclimatization – try to be normal at high altitude.

3. BAROMETRIC PRESSURE CHANGES IN HIGH ALTITUDE • As the altitude increases above the sea level, the corresponding atmospheric pressure decreases. • The partial pressure of Oxygen also decreases. • The arterial Oxygen saturation levels also decrease with increase in the altitude.

4. PARTIAL PRESSURES OF OXYGEN

6. ACCLIMATIZATION • “Getting used to…” • People remaining at high altitudes for days, weeks or years become more and more acclimatized to low PO2. • This causes the hypoxia to cause fewer deleterious effects on their bodies. • They can thus work harder at higher altitudes without hypoxic effects.

7. Acclimatization • At 10,000 feet, atmosph pressure = 523 and alveolar PO2 = 110mmHg • The changes in response to hypoxia if somebody stays at high altitude for sometime by • Great increase in pulmonary ventilation • Increases RBCs no • Increased diffusion capacity of lung • Increased vascularity of the tissue • Increased ability of tissue cells to use oxygen despite low PO2

8. Increased Pulmonary Ventilation • Hypoxic stimulation of resp. center by periph. Chemoreceptors • Immediate compensation to ↓PO2 by ↑ alveolar ventilation to →↑ CO2 exhaling →↑ PCO2 → inhibitory effect as resp. center opposes ↓ PO2 stimulatory effect • After a few days stimulatory effect overwhelms inhibitory effect b/c ↓ HCO3 ions in brain

9. Increased RBCs Count • Hypoxia → erythropoietin →↑ RBC production • Hct from normal (40-45) to 60-65 • Hb from normal (15mg/dl) to 20-22G/dl

10. Increased Diffusing Capacity • ↑ Pulmonary capillary blood vol. → capillaries expanding → ↑ surface area • Also inc in air vol → ↑ surface area • Inc in pulm art blood pressure– more perfusion • So diffusing capacity for O2 from normal (21 ml/mmHg/mint) to 65 ml/mmHg/mint

11. Increased Vascularity of Tissue (Circulatory Changes) • Initially ↑ cardiac out by 30% approx. • As Hct ↑ - C.O. becomes normal • ↑ in capillaries in non-pulmonary areas – called increased capillarity (angiogenesis) • Hypoxia → pulmonary vasoconstriction → Retrograde pressure on Rt heart → Rt ventricular hypertrophy • Pulmonary vasoconstriction → pulmonary hypertension

12. Cellular Acclimatization • More capillary formation in tissue → ↑ vascularity • Also ↑ Mitochondria, ↑ Myoglobin & Cytochromes oxidase enzyme

14. Acute Mountain Sickness • May be nausea, vomitting, headache, Irritability, Dyspnoea, at 1200ft • At 18000 ft - twitching, seizures • At 23000 ft – coma leading to death • Cerebral vasodilatation in response to hypoxia →fluid leakage into cerebral tissue → cerebral edema → Disorientation & other cerebral dysfunction • Pulmonary edema – exact cause not known

15. Vasocosntriction in pulmonary capillaries leads to increased blood pressure in open capillaries leading to edema • Breathing oxygen, especially under pressure, can reverse symptoms

16. Chronic Mountain Sickness • RBC count ↑ - so Hct ↑ • Pulmonary arterial pressure ↑ • Rt heart – hypertrophy • ↑ Hct → ↑ blood viscosity → sluggish circulation → ↑ O2 supply • Natives at high altitude – • Chest barrel shaped – chest longer • Aortic & carotid bodies of bigger size • Pulmonary hypertension & Rt ventricular hypertrophy • ↑ RBC count with ↑ Hct

17. Seen in people who reside for long at high altitudes. • Red cell number and mass increases exceptionally. • Pulmonary arterial pressure becomes very high. • The heart becomes enlarged in the right side. • The peripheral arterial pressure begins to fall • Congestive Cardiac failure & death follows • They need to be taken to low altitudes as soon as possible. • They recover in low altitudes within days or weeks.