Acclimatisation and its Changes (With Graph) | Human Body | Biology

The term acclimatisation means the adjustment of the human body to suit the climate at a higher altitude. When the ascent is slow and to a moderate height (between 3000 and 4250 metres or 10,000 & 14,200 feet) as in mountaineering, various compensatory process are mobilised to combat the injurious effect and the subject is ultimately adapted to the rarefied atmosphere. Some of the changes are immediate and others are a little delayed.

Changes in Acclimatisation:

1. Changes in the Bone Marrow:

The red marrow proliferates as a result of anoxia. The yellow marrow may be transformed into red marrow.

2. Changes in Respiration:

Changes in pulmonary ventilation has shown that the respiratory centre becomes hypersensitive to Pco₂ due to long continued anoxia. It has further been shown that in chronic acclimatisation, e.g. in persons residing at high altitude the hypersensitiveness of the respiratory chemoreceptors are more marked than in acute acclimatisation.

Barometric pressure is 440 mm Hg at an altitude of 4260 metres, 14200 feet. So the O₂ pressure in the alveoli is 14% of (440 – 47 =) 393 mm Hg i.e., about 56 mm Hg.

Vital capacity of lungs increases in those people who live at higher altitude for long. Diffusing capacity for through the alveolo-capillary membrane increases.

The factors responsible for this change are:

i. Expansion and dilatation of pulmonary capillaries.

ii. Increased blood volume.

iii. Increased lung volume.

iv. Elevated pulmonary arterial pressure.

v. The apical part of the lungs which is normally under-perfused is adequately perfused during anoxic acclimatisation.

3. Changes in Circulation:

The right heart hypertrophies so that blood can be effectively pumped through the expanded capillary bed of the lung. There occurs temporary increase in cardic output. Blood flow through the heart, brain, muscles and other organs is increased at the expense of blood flow through the skin and kidneys. The blood capillaries of animals exposed to anoxia for a long time get dilated to accommodate the extra blood which is brought in more intimate contact with the tissues.

4. Changes in Blood:

2, 3-DPG content of RBC increases.

In acclimatisation the haemoglobin content of the blood increases due to anoxia, the PCV rises and also the blood volume increases often as much as 20 to 30 percent resulting in total increase of circulating haemo­globin by 50 to 90%

5. Cellular Acclimatisation:

Mitochondria and certain cellular oxidative enzyme systems increase in animals exposed to anoxia for a long time. It is presumed that in human beings too intracellular enzyme systems develop in such a way that oxygen can be utilised more effectively.

6. Changes in Urine:

Kidneys excrete alkaline urine. Urea content is more and ammonium salts, less. In other words, the ammonia coefficient falls. There is less excretion of acid in the urine. These are attempts to combat alkalosis resulting from hyperventilation.

Natural Acclimatisation of Natives Residing at High Altitude:

Natural acclimatisation occurs in natives born and brought up at high altitude. Highest altitude at which permanent acclimatisation is possible is perhaps about 5,500 metres or 18,000 feet (Peruvian Andes). The natives of these places have got a short body structure with a large-sized chest giving a high ratio to ventilatory capacity to body mass. The right heart is usually hypertrophied with rather high pressure in the pulmonary artery so as to fill up effectively the expanded pulmonary capillary system.

The mechanism of O₂ transfer in these natives is also highly officious and has been compared with that of an un-acclimatised subject in the accompanying diagram (Fig. 8.49):

The dissociation curve for the person residing at high altitude shows:

i. Low Po₂ (40 mm Hg) of the arterial blood compared to 100 mm Hg of the person at sea-level.

ii. In spite of the low pressure, the O₂ content of the arterial blood is higher than that of the person at sea-level because of high haemoglobin content.

iii. Venous Po₂ of the high altitude natives is only 10 mm Hg lower than those of the sea-level dwellers despite the low arterial Po₂. The fact is that the oxygen consumption of the high landers is usually higher in comparison to that of sea-level residents there cannot be any doubt the tissues of the naturally acclimatised person can utilise oxygen more effectively.

In Peruvian Andes coal mines are situated at an altitude of about 5800 metres or 19,000 feet whereas the workers in the mine live with their families in a township at an altitude of about 5,500 metres or 18,000 feet. It has not been possible to persuade the workers to live permanently at about 5,800 metres or 19,000 feet in neighbourhood of the mines.

They complain that at that altitude they do not keep good health and that they cannot sleep well at night, do not relish their food and that they develop also sexual weekness. About 5,500 metres or 18,000 feet altitude may be taken to be the limit of human tolerance and the altitude where perma­nent acclimatisation is possible.

The natives born and brought up here are superior to the best acclimatised low landers in the following respects:

(i) The chest-size is increased whereas body-size is somewhat decreased giving a high ration of ventilatory capacity to body mass.

(ii) The right heart of these persons is considerably hypertrophied to provide a high head of pressure in the pulmonary arteries so that blood can circulate through a greatly expanded pulmonary capillary system.

(iii) The RBC count and so the haemoglobin content and oxygen capacity of the blood is high so that even though the arterial Po₂ is low the O₂ content of the arterial blood is higher than those living at lower altitudes.

(iv) The O₂ content of the mixed venous blood is also higher though its percentage saturation is only slightly less than those living at lower altitude.

In all probability acclimatisation also occurs at cellular level the exact nature of which is not properly un­derstood. It is, however, known that the power to utilise oxygen in the natives of high altitude is higher and that the efficiency of muscular work of these persons is by no means less than those living at sea-level.

Acute Mountain Sickness:

Sometimes a well-acclimatised mountaineer may develop acute illness due to failure of compensatory adjust­ments to high altitude.

The following effects are noticed:

i. The red cell mass and PCV are elevated considerably.

ii. Pulmonary arterial pressure becomes very high and the right heart failure supervenes. The peripheral arte­rial pressure begins to fall and death occurs due to acute pulmonary oedema which aggravates the anoxic situation. Most of the patients recover if brought promptly to a lower altitude and oxygen is administered.

Maj. Joyal, a veteran mountaineer, and the founder principal of the Himalayan Mountaineering Institute at Darjeeling died of acute sickness described above.