High altitude ACCLIMATIZATION physiology

High altitude acclimatization

1. ACCLIMATIZATION Dr. Suman Inaniya Resident Physiology Department Contents

2. ACCLIMATIZATION Dr. Suman Inaniya Resident Physiology Department Contents Definition Respiratory changes Hematological changes Cardiovascular changes Tissue change Natural acclimatization in permanent residents of higher altitude Applied Uses of Acclimatization summary Acclimatization

3. ACCLIMATIZATION Dr. Suman Inaniya Resident Physiology Department Contents Definition When a person ascends to high altitude and stays there for longer periods, he slowly gets adapted to the new environment. This process of adaptation is called acclimatization. It starts within 12 hours and several days to weeks. Adaptation occurs till 18,000 feet. Beyond this needs O₂. Adaptive changes mainly occur in respiratory system, cardiovascular system, blood, and tissues. Primary objective:- ↑ O₂ supply to the tissues. Contents Respiratory Changes In case of Acute Hypoxia Peripheral chemoreceptor stimulate Increase ventilation ↑ CO2 & ↑ H+ in CSF central chemoreceptor stimulate Stimulation of medullary respiratory centers Arterial blood ↓ PO2 & ↑ PCO2 Definition Respiratory changes Hematological changes Cardiovascular changes Tissue change Natural acclimatization in permanent residents of higher altitude Applied Uses of Acclimatization summary

4. In case of Acute Hypoxia Peripheral chemoreceptor stimulate Increase ventilation ↑ CO2 & ↑ H+ in CSF central chemoreceptor stimulate Stimulation of medullary respiratory centers Respiratory Changes Arterial blood ↓ PO2 & ↑ PCO2 Acclimatization In case of Chronic Hypoxia ↑ pulmonary ventilation → CO2 wash out → alkalosis which inhibits respiration. But kidneys actively excretes large amount of HCO3 in urine & maintains blood PH to normal. So the inhibitory effect due to CO₂ wash out fades away. This effect of CO₂ on resp. cent. Is potent for 1st few hours (1 to 2 days). Respiratory centers responds to full force to the peripheral chemoreceptors stimuli due to hypoxia .

5. In case of Chronic Hypoxia Respiratory Changes ↑ pulmonary ventilation → CO2 wash out → alkalosis which inhibits respiration. But kidneys actively excretes large amount of HCO3 in urine & maintains blood PH to normal. So the inhibitory effect due to CO₂ wash out fades away. This effect of CO₂ on resp. cent. Is potent for 1st few hours (1 to 2 days). Respiratory centers responds to full force to the peripheral chemoreceptors stimuli due to hypoxia . Hematological Changes

6. Hematological Changes Hypoxia ↑ erythropoietin (Ep) ↑ red cell mass ↑ O₂ delivery to the tissues. 1.Increased red cell production Respiratory Changes Hypoxia ↑ 2,3-DPG in RBCs (high affinity for Hb) shifts O₂ -Hb dissociation curve to the right ↑ release of O₂ from Hb to the tissues. 2.Improved oxygen transport .

7. Hematological Changes Hypoxia ↑ 2,3-DPG in RBCs (high affinity for Hb) shifts O₂ -Hb dissociation curve to the right ↑ release of O₂ from Hb to the tissues. 2.Improved oxygen transport . Cardiovascular Changes

8. Cardiovascular Changes In the early phase, ↑ HR, ↑ CO, ↑ BP. Hypoxia → activation of sympathoadrenal axis → ↑ BP & ↑ HR → ↑ cardiac output → ↑ blood flow. Hypoxia → vasodilation → ↑ blood flow → ↑ O₂ supply to tissues. ↑ red cell mass → improves oxygenation of tissue, significant polycythemia ( ↑ hematocrit) → ↑ viscosity → ↑ workload on the heart → cardiac hypertrophy. Tissue Changes

9. Tissue Changes Following tissue changes occur, especially - skeletal muscles: 1. ↑ capillaries. 2. ↑ mitochondria in the cells(sites of oxidative reaction) 3. ↑ activity of oxidative enzymes like cytochrome oxidase. 4. ↑ myoglobin ( O₂ storage ↑ ) 5. Hypoxic tissue → chemicals → Angiogenesis. Natural Acclimatization in permanent residents of higher altitude

10. Natural acclimatization in permanent residents of higher altitude All they shows certain changes in their bodies which begin at infancy. Chest size ↑ where as body size some what ↓ . This gives high ratio of ventilatory capacity to body mass. Their hearts (particularly Rt side) provides high pulmonary arterial pressures to pump blood through greatly expanded pulmonary capillary system. Hence Rt side heart larger than that of low landers Delivery of O₂ by the blood to the tissues is highly facilitated. Less Arterial Po₂ 40 mm but high conc. of Hb so more O₂ content. Venous Po₂ is 25mm of Hg i.e. only 15 mm of Hg less than low landers (40 mm of Hg). This indicates O₂ transport to the tissues is exceedingly effective in the naturally acclimatized persons. Thus, natives are best acclimatized than low landers.. Applied Acute mountain sickness

11. Applied Due to rapid ascent & it leads to over reaction Acute cerebral edema -vasodilation due to hypoxia Acute pulmonary edema - increased pulmonary pressure leads to accumulation of fluid in some alveoli. Treatment:- Oxygen & remove to a low altitude. Acute mountain sickness Chronic mountain sickness

12. Applied Chronic mountain sickness Develop in a person who remains at high altitude for too long duration. Effects are:- RBC and haematocrit becomes very high. Pulmonary Arterial pressure becomes elevated. Right side of the heart becomes hypertrophied. Peripheral arterial pressure begins to fall. CCF occurs - Death. Treatment:- Move to a low altitude. Use of acclimatization

13. Use of acclimatization The Indian Army uses a multi-stage acclimatization schedule for troops deployed to high altitude areas, with the key altitude ranges being 2700m-3600m, 3600m-4500m, and above 4500m. Other use – by mountain trekkers, researchers etc Avoid direct flight journey to Leh. Summary :- Compensatory mechanisms

14. Summary :- Compensatory mechanisms ↑ in pulmonary ventilation. ↑ in red blood cell count. ↑ in hemoglobin concentration. ↑ in blood volume. ↓ affinity of the hemoglobin for O₂ . ↑ diffusing capacity. ↑ capillarity. Cellular acclimatization (change at tissue level). Natural acclimatization of natives living at high altitude