PHYSIOLOGY OF HIGH ALTITUDE - PowerPoint Presentation

1. PHYSIOLOGY OF HIGH ALTITUDE DR RASHMI TIWARI

2. INTRODUCTIONHigh altitude is the region of earth located at an altitude of above 8,000 feet from mean sea level People can ascend up to this level, without any adverse effect

3. CATEGORISATION FOR DESCRIPTIVE CONVENIENCE: ALTITUDE TYPEFROM SEA-LEVEL (In feet)HIGH8,000 – 12,000VERY HIGH12,000 – 18,000EXTREMELY HIGHAbove 18,000

4. SIGNIFICANT ATMOSPHERIC PRESSURE VARIATION WITH ALTITUDE:ALTITUDE PRESSURE (FEET) ( mm of Hg) (ATMOSPHERIC UNIT) 0 760 1 18,000 380 1/2 34,000 190 1/4 48,000 95 1/8 63,000 47 1/16

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6. BAROMETRIC PRESSURE AND PARTIAL PRESSURE OF GASES. Barometric pressure at sea level is 760 mm Hg and it falls progressively with the increasing height . With decrease in total pressure of air at increasing altitude partial pressure of gases will change.

7. COMMON HYPOXIC EFFECTS WITH DIFFERENT ALTITUDES:ALTITUDE LEVELINSPIRED AIR PO2Hb-SATURATION EFFECTSIn feet (metre) In mm of Hg in % Stages (if any)0 (i.e.sea-level) 160 ~ 97 % NIL Upto 10,000(3,000) 110 ~ 90 %Usually none, +/- some nocturnal visual reduction ( of indifference)10,000 – 15,000(3,000 – 4,500) 98 ~ 80 %Mod. Hypoxic symptoms cardiorespiratory manifestaions & early CNS involvements ( of reaction)15,000 – 20,000(4,500 – 6,000) 70 < 70 %Severe hypoxic symp  aggravated CNS involvement (of disturbance)Above 20,000 & onwards Further falls below 60 % Unconsciousness & alarming deterioration survival impossible without supplemental O2 (critical survival altitude)

8. HYPOXIA AT HIGH ALTITUDEThe effects of hypoxic hypoxia produced by decreasing pO2 at high altitude depend upon:The level of altitude, The rate at which hypoxia develops, i.e. hypoxia occurs due to a rapid ascent (acute hypoxia) or slow ascent (subacute hypoxia) andDuration of exposure to hypoxia, i.e. whether shortterm stay or long-term stay (chronic hypoxia).

9. ALTITUDES & HEIGHTSNormally most people on earth stay at around the Mean Sea Level (MSL)However, groups of people stay at higher than normal attitudes.The Sherpas, a mountain tribe of Himalayas live at around 5500 Meters above MSL, normally.When people living around MSL go up to higher altitudes, changes occur in their physiology, especially in Respiration.

10. BAROMETRIC PRESSURE CHANGES IN HIGH ALTITUDEAs 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.

11. STAGES OF HYPOXIC HYPOXIA In a classical mould four stages of hypoxic hypoxia depending upon the value of pO2 are described 1. Stage of indifference is usually characterized by no symptoms of hypoxia as pO2 remains above 60 mm Hg. This occurs up to 10,000 ft altitude.

12. CONTD... Stage of reaction starts above 10,000 ft altitude and is characterized by development of moderate hypoxia up to 15,000 ft altitude at pO2 of 40–60 mm Hg. Hypoxic symptoms include:-Cardiovascular involvement in the form of tachycardia and hypertension.

13. CONTD....Respiratory symptoms in the form of increased pulmonary ventilation and Early central nervous system (CNS) involvement in the form of impaired judgement, feeling of overconfidence, talkativeness, reduction in visual acuity and emotional outburst of laughing or crying

14. CONTD...Stage of disturbance occurs when pO2 values fall between 30 and 40 mm Hg, usually between 15,000 and 20,000 ft altitude. It is characterized by the development of severe hypoxia. In addition to the symptoms described above, the CNS involvement is aggravated.

15. ACUTE EFFECTS OF HYPOXIAAs the altitude increases, the barometric pressure decreases.This causes a handicap which may be:AppreciableConsiderableSeriousCausing Imminent Collapse

16. High-altitude pulmonary oedemaHigh-altitude pulmonary oedema (HAPO) usually occurs as an effect of a rapid ascent at high altitude (above 10,000 ft). It is usually seen in individuals who engage in heavy physical work during first 3–4 days after a rapid ascent to high altitude due to sympathetic stimulation caused by hypoxia

17. Characteristics of HAPO It responds to rest and O2 therapy because it occurs due to aggravation of hypoxia and not due to cardiovascular or lung disease. It is associated with an increased pulmonary artery pressure, so it also responds to calcium channel blockers such as nifedipine, which lowers the pulmonary artery pressure

18. ACUTE MOUNTAIN SICKNESSThis occurs in a small number of lowlanders who ascend rapidly to high altitudes.Begins from a few hours up to 2 days after their ascent. The symptoms develop 8–24 hours after arrival at high altitude and last for 4–8 days. Is serious and results in their death unless they are given Oxygen or taken to a low altitude.

19. ACUTE MOUNTAIN SICKNESS : SYMPTOMS & SIGNSAcute Cerebral Edema:Hypoxia causes cerebral vasodilatationIncreases capillary pressureCauses fluid to leak out into the tissuesThis leads to cerebral edema causing:Severe disorientationOther cerebral dysfunctions

20. TREATMENT. The symptoms of acute mountain sickness can be reduced by: Decreasing cerebral oedema by the administration of large doses of glucocorticoids, and by Decreasing alkalosis by administration of acetazolamide. Acetazolamide decreases H+ excretion through kidneys by inhibiting the enzyme carbonic anhydrase.

21. CHRONIC MOUNTAIN SICKNESSSeen 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 fallCongestive Cardiac failure & death followsThey need to be taken to low altitudes as soon as possible.They recover in low altitudes within days or weeks.

22. PHYSIOLOGICAL COMPENSATORY RESPONSES TO HIGH ALTITUDE HYPOXIATwo types of physiological compensatory responses known to occur in the individuals exposed to high-altitude hypoxia are accommodation and acclimatization

23. ACCOMMODATION AT HIGH ALTITUDEImmediate reflex responses of the body to acute hypoxic exposure.Hyperventilation: arterial PO2  stimulation of peripheral chemoreceptors  increased rate & depth of breathingB) Tachycardia:Also d/t peripheral chemo. Response  CO  oxygen delivery to the tissues

24. Contd…..Increased 2,3-DPG conc. in RBC:within hours, ↑deoxy-Hb conc.  locally ↑pH  ↑2,3-DPG  ↓oxygen affinity of Hb  tissue O2 tension maintained at higher than normal levelD) Neurological :Considered as “warning signs”Depression of CNS  feels lazy, sleepy ,headache‘Release Phenomena’ like effect of alcoholAt further height  cognitive impairment, twitching, convulsion & finally unconsciousness

25. 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.

26. HOW DOES ACCLIMATIZATION OCCUR?Increased :Pulmonary ventilation.Number of RBCs ( Hypoxia causes excess erythropoiesis).Diffusing capacity of the lungs.Vascularity of the peripheral tissuesAbility of the tissue cells to use Oxygen despite low PO2.

27. NATURAL ACCLIMATIZATIONThis occurs in people living from their birth at high altitudes.Those living in the Andes & Himalayan mountains, for instance.Acclimatization begins in them in infancy.The chest size is greatly increased.Their hearts are considerably larger than those of lowlanders

28. PHYSIOLOGICAL RESPONSES TO HIGH ALTITUDE HYPOXIA:Arbitrarily Divided into following two---Acute responses (aka accommodation)Long term responses ( aka acclimatization) “Arbitrary” because ----Acute are also beneficial for long-term coping up.ii) Acute are modified steadily & imperceptibly in such a way that after 2-3 days are considered as beginninng of acclimatization .iii) Sharpness of division depends on rate of ascent .

29. IMP. CONCEPTS IN ENVIRONMENTAL PHYSIOLOGY:

30. ACCLIMATIZATION AT HIGH ALTITUDE:Delivery of atmospheric O2 to the tissues normally involve 3 stages---with a drop in PO2 at each stage.When the starting PO2 is lower than normal, body undergoes acclimatization so as to—↓ pressure drop during transfer↑ oxygen carrying capacity of blood ↑ ability of tissues to utilize O2 With longer stay at high altitude ,body is able to adjust by certain physiological adaptations..

31. A)Sustained Hyperventilation:Prolonged hyperventilation  CO2 wash-out  respiratory alkalosis renal compensation alkaline urine normalization of pH of blood & CSF withdrawal of central chemo-mediated respiratory depression  net result is ↑resting pulmonary ventilation (by ~5 folds to 60L/min),primarily d/t ↑ in TV (upto 50% of VC)Such powerful ventilatory drive is also possible as-sensitivity of chemo- mechs to PO2 & PCO2Somewhat ↓ in work of breathing  make easy & less tiring

32. C)↑Vascularity of the Tissues:More capillaries open up in tissues than at sea-level (normal ~25 % at rest—remaining as ‘reserve’).This combined with systemic vasodilatation(also a hypoxic response) more O2 delivery to tissues.D) Cellular level changes:↑ intracellular mitochondrial density↑ conc. of cellular oxidative enzymes↑ synthesis of Mb( O2-storing pigment)→ all aimed to improve O2 utilization.

33. E) Physiological Polycythemia:

34. Cheyne-Stokes Respirations:Above 10,000 ft (3,000 m) most people experience a periodic breathing during sleep. The pattern begins with a few shallow breaths increases to deep sighing respirations  falls off rapidly. Respirations may cease entirely for a few secs & then shallow breaths begin again. During period of breathing-arrest, person often becomes restless & may wake with a sudden feeling of suffocation. Can disturb sleeping patterns exhausting the climber. Acetazolamide is helpful in relieving this. Not considered abnormal at high altitudes. But if occurs first during an illness (other than Altitude illnesses) or after an injury (particularly a head injury)  may be a sign of a serious disorder.

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