Acclimatization by Pandian M.

This PPT for all Medicos and Non medical Students for better understanding of Acclimatization

1. Acclimatization
(to low Oxygen at high altitude)
Pandian M
Dept. of Physiology

2. •Introduction to Physiology of High Altitude
•Fall in barometric pressure
•Hazards of rapid ascent.
•‘Safe Zone’ of ascent.
•Upto 12,000 feet-CVS & RS involvement.

3. Definition:-Readjustments&compensatory
mechanismwhichtakesplaceinthebodyto
reducetheeffectsofhypoxiainthosepersons
(permanentresidents)athighaltitudeiscalled
acclimatizationathighaltitude.
Thismakespossibleforthepermanent
residentstheretoleadanormal&prolonged
life,workharderwithouthypoxiceffectsor
toascendtostillhigheraltitude.

4. Acclimatization is possible by following
process
1.Increase in pulmonary ventilation.
2.Decrease affinity of Hb for O
2under hypoxic
condition.
3.Rise in Hb Conc.
4.Increases vascularity of hypoxic tissues.
5.Increased diffusion capacity of lungs for O
2
6.Changes at tissue level to reduced the effect
of hypoxia

5. unacclimatized
•At sea level, normal arterial pO
2and pCO
2are 100 to
40 mmHg.
•When rapid ascend in unacclimatizedsubjects, upto
10,000 ft ↓sesarterial pO
2to 60 mmHg while pCO
2is
kept normal.
•So, no ↑s in pul.vent.
•But, after 10,000ft art.pCO
2 falls rapidly due to ↑s in
pul.ventilation.

6. Acclimatized
•Sensitivity of Resp.center ↑sed.(hypoxia)
•even, slightly ↓se of art.pO
2,causes pulm.
Vent. ↑ses and alveolar pCO
2falls.
•This ↑ se in pul.vent is maintained by active
regulation of pH of CSF & blood to normal
levels.??

7. •Active transport of HCO
-
3out of CSF or
•Active transport of H
+
into CSF or
•Hypoxia causes LA formation this ↑ses H
+
Conc.

8. CHANGES DURING ACCLIMATIZATION
•Various changes that take place during
acclimatization
•help the body to cope with adverse effects
of hypoxia at high altitude.
1.Changes in Blood
2.Changes in Cardiovascular System
3.Changes in Respiratory System
4. Changes in Tissues

9. Compensatory mechanisms
1) ↑ in pulmonary ventilation.
2)↑ in red blood cell count.
3)↑ in hemoglobin concentration.
4)↑ in blood volume.
5)↓ affinity of the hemoglobin for O
2.
6)↑ diffusing capacity.
7)↑ capillarity.
8)Cellular acclimatization (change at tissue level).
9)Natural acclimatization of natives living at high altitude.

10. 1)↑ in pulmonary ventilation
At high altitude barometric pressure ↓
↓
↓ partial pressure of O
2
↓
↓ alveolar Po
2
↓
↓ arterial Po
2
↓
Stimulation of arterial chemoreceptors

11. Immediate effect i.e. in sec there is ↑
alveolar ventilation by 1.65 times normal.
But after acclimatization it ↑ by 5 times
normal (400% above normal).
Basic cause for ↑ pulmonary ventilation is
regulation of PHof CSF & blood by kidneys.

12. ↑ pulmonary ventilation → CO
2wash out →
alkalosis which inhibits respiration.
But kidneys actively excretes large amount of
HCO
3
-
in urine & maintains blood PHto normal.
So the inhibitory effect due to CO
2wash out
fades away
This effect of Co
2on resp. cent. Is potent for 1
st
few hours (1 to 2 days)
Respiratory centers responds to full force to the
peripheral chemoreceptors stimuli due to hypoxia.

13. 2) ↑RBC count
•Hypoxia acts as powerful stimulant for erythropoietin
secretion → erythropoisis starts in 2 weeks.
•↑ in RBC count from 5.5 millions/ cumm to 7-8
millions/ cumm of blood.
•↑ in Hb concentration from 15gm % to 20 gm %.
•↑ in Haematocrit value from 45 % to 60 %.
•↑ in blood volume by 20 to 30 %→↑ in circulating Hb
to 50 %.
•This results in ↑ O
2carrying capacity of blood.

14. 3) ↓ affinity of the Hb forO
2
-Hypoxia leads to ↑ 2-3 DPG in RBCs.
-2-3 DPG has high affinity for Hb.
-It shifts the O
2Hb dissociation curve to right
by displacing O
2from its sites.
-So more release of O
2from Hb to the tissues.

15. 4) ↑ Diffusing capacity through pulmonary membrane
•Normal diffusing capacity of O
2 is 21ml/mm of Hg/min.
It ↑ by three fold, cause are;
i)↑ pulmonary capillary blood volume → expands
the capillaries → ↑ surface area for diffusion.
ii)↑ in lung volume → ↑ surface area of the
alveolar membrane.
iii)↑ pulmonary arterial pressure → more blood
into more number of alveolar capillaries
(opening of more pulmonary capillaries)
especially in upper parts of lungs. So ideal
ventilation perfusion ratio.

16. 5)↑ Capillarity
•Immediately after ascending high altitude there is ↑
cardiac output. But as blood haematocrit value ↑
cardiac output becomes normal.
•Another change is ↑ in number of systemic
capillaries (i.e. in non pulmonary tissues).
•This effect seen much in the tissues of animals born
& breed at high altitude, but to less extent in those
who are exposed to high altitude later in life.
•↑ capillarity seen in Rt ventricle muscle due to
combined effect of hypoxia & excess work load on Rt
ventricle caused by pulmonary hypertension.

17. 6) Cellular acclimatization
•In natives changes occur at tissue level to reduce
the effect of hypoxia.
1)↑ Cell mitochondria (sites of oxidative reactions).
2)↑ in Oxidative enzyme systems e.g. cytochrome
oxidase.
3)↑ in synthesis of myoglobin (O
2storing pigment).
Thus the cells of acclimatized humans can use O
2
more effectively.

18. 7) Natural acclimatization
Those persons born & live at high altitude all their
life shows certain changes in their bodies which
begin at infancy.
i)Chest size is greatly ↑ where as body size some
what ↓. This gives high ratio of ventilatory capacity
to body mass.
ii)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.

19. iii)Delivery of O
2by the blood to the tissues is
highly facilitated. Arterial Po
2is only 40 mm of Hg
but due to ↑ conc. of Hb, the O
2content of blood is
more.
Venous Po
2is 25mm of Hg i.e. only 15 mm of
Hg less than low landers (40 mm of Hg).
This indicates O
2transport to the tissues is
exceedingly effective in the naturally acclimatized
persons. Thus natives are superior than best
acclimatized low landers.

20. Applied
Acute mountain sickness
Chronic mountain sickness

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

22. Chronic mountain sickness
•Develop in a person who remains at high altitude for
too long duration.
•Effects are;
-RBC and haematocrit becomes very high.
-Pulm. 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.

23. THANK YOU . . .