Term 2 Life At Altitude Workshop

Question 1

Textbook definition of normal

Answer 1

Is a 70kg young, healthy, naked man.
In reality most of the population doesn’t fit this model.
Thus there are diff natural states relating to age & gender, life in utero/as a neonate, life whilst pregnant etc.

Illness is defined as a pathological state: conditions/diseases that cause changes away from normal.

Question 2

Basics of gas exchange

Answer 2

The diffusion of gases is a function of pp (partial pressure) difference of individual gases.

Can be measured by Henrys law and Ficks law.

Volume of gas = AsxDx∆P/ T
Diffusion coefficient D a solubility/✓(Mw)

Question 3

Hypobaric environment

Answer 3

Barometric pressure decreases exponentially as altitude increases.

Proportion of atmospheric O2 is constant so decrease in barometric pressure paralleled by decrease in ambient pO2

So alveolar & arterial pO2 fall causing a hypoxic hypoxia (hypobaric hypoxia)

Question 4

Altitudes compared to barometric pressure

Answer 4

13000m operational ceiling of commercial jets
11000m cruising altitude of “ “
8848m height of Mt Everest
5300m highest human habitation
4807m height of Mt Blanc
4300m Pikes peak
2000-2500 cabin pressure equivalent of commercial jets

Question 5

Hypobaric environment (cont.)

Answer 5

Decrease in alveolar and arterial pO2
Is greater than the decrease in ambient pO2 e.g. at Everest summit inspired pO2 is only 43mmHg (5.7kpa)

Question 6

Control of breathing and response to high altitude

Answer 6

Integrated changes in ventilation occur due to change in activity and environment e.g. exercise, resp illness, exposure to high altitude.

Hypoxia induced hyperventilation increasing minute ventilation in response to alveolar pO2 drop

Question 7

Adaptation and acclimatisation

Answer 7

Adaptation is a human phenomenon
Prolonged exposure to hypobaric conditions causes physiological changes allowing individuals to acclimatise to a hostile environment - however rapid exposure can be dangerous

Acclimatisation
Aerobic respiration depends on delivery of O2 to mitochondria, decrease in pO2 occurs at each stage of O2 transport - mountain dwellers show less loss of pO2 between these stages.

From atmosphere to respiring tissues:
Inspired gas to alveoli to artery to vein.

Question 8

LAN Vs HAN

Answer 8

Low altitude native (LAN) climbing a mountain will develop changes from first few hours or days which are ongoing over weeks and months. Acclimatisation may be seen long-term in a LAN but may be diff to a person born at altitude (a HAN)

Pulmonary ventilation:

HAN shows a decrease in slope of O2 cascade from inspired air to alveolar air
LAN shows increased minute ventilation and hyperventilation at above 3000m due to stimulation of peripheral chemoreceptors or carotid & aortic bodies

Bicarbonate buffer system
After several days at altitude LAN minute ventilation continues to increase over 1-2 weeks
LANs de-acclimatise on return to sea level

Question 9

HAN characteristics

Answer 9

Ventilation in HAN has higher asl than LAN

Relative decrease in ventilation is probably adaptive and instead less energy consuming methods are used e.g. more efficient pulmonary gas exchange

Pulmonary O2 transfer of HAN is 20-30% higher at rest than in LAN - probably due to increased alveolar SA (more or larger than in LAN) and the barrel shaped chest of HAN provided greater lung vol.

No significant change in pulmonary gas exchange has been observed in short term visitors however some reports if increased diffusion capacity in long term visitors reported (probably visitors arrived pre-pubescent allowing HAN-like development)

Question 10

Changes in RBC count and Hb

Answer 10

Increased hematopoiesis is stimulated by erythroprotein in response to low blood pO2
Rise in RBC seen after 3-5 days at altitude and trend continues for several weeks.

Question 11

Haemoglobin affinity for O2

Answer 11

In acclimatised visitors and HAN a shift in O2-Hb curve rightwards occurs to aid unloading of O2 from blood to tissues.

Shift ensures greater Hb desaturation for given pO2
Increase in P50 (So?) Attributed to increase in conc. Of 2,3-DPG favours stabilisation of deoxy form of Hb facilitating greater unloading

Question 12

Adaptive response to altitude summary

Answer 12

Increase ppO2

LAN- increase depth & rate of pulmonary ventilation
HAN- increase lung vol/alveoli/capillary/SA to increase diffusion capacity

Increase O2 delivery to tissues/cells/mitochondria

Both LAN & HAN
Increase blood O2 capacity by increasing RBC/Hb/hematocrit and increasing capilarisation decreasing intercapillary distance