Lecture 13 - Altitude

Question 1

State the moderate altitude, high altitude and extreme altitude heights

Answer 1

• 1500m-3000m
• > 3000m
• > 5500m

Question 2

How does the following change as altitude changes?

• barometric pressure
• solar radiation
• chemical composition of air

Answer 2

• Barometric (air) pressure decreases as altitude increases (ie) as the weight of the column of air above the point of measurement decreases.
• Solar radiation: UV radiation is more intense at high altitude (sunburn, snow blindness)
• the chemical composition of the atmosphere is uniform up to 20,000 meters

Question 3

PO2 at:

• sea level
• 10000ft
• 29000ft Mt. Everest

Answer 3

• 160mmHg
• 107mmHg
• 52mmHg

Question 4

At what height can an unacclimatized person lose consciousness? (the height of Critical alveolar PO2)

Answer 4

7000m and within a few minutes due to hypoxia

Question 5

What is the relationship between altitude and air resistance/density/ gravity?

Answer 5

• Decreased density of air –> decreased external air resistance –> external work is decreased at altitude in sprint type activities where high velocities are involved. There will also be less air resistance encountered by projectiles.
• Force of gravity is decreased with distance from the earth’s center –> higher altitudes should have a favourable effect on jumping and throwing events.

Question 6

How does air temperature and moisture change as altitude changes?

Answer 6

• Air temperature decreases linearly by 6.5degC/ 1000 meters of altitude or 2degC/1000 ft.
• Air becomes increasingly dry with increasing altitude –> water loss via the respiratory tract is higher at high altitude.

Question 7

How does arterial oxygen and cardiac output change as altitude changes?
- State the equation for VO2 in terms of heart rate, stroke volume, arterial oxygen, and veinal oxygen

Answer 7

• With increasing altitude, CaO2 (arterial oxygen) progressively decreases. To compensate, cardiac output initially increases during rest and submaximal exercise due to an increase in heart rate.

VO2 = (HR X SV) X (CaO2 - CvO2)

Question 8

How does your body acclimate to higher altitudes?

Answer 8

• Over the first week at altitude, cardiac output falls to or below sea level values for the same VO2 and there is a progressive increases in O2 delivery efficiency

The most important long-term adaptation to altitude: blood’s oxygen carrying capacity.
Hemoglobin concentration starts to increase during the first two days at altitude due to a decrease in plasma volume and an increase in RBC production by bone marrow.
These hematological changes during acclimatization are dependent on an adequate iron intake

Even after several months of acclimatization, VO2 max. still remains significantly below sea- level values.

Question 9

In some high-altitude natives and well-acclimatized sojourners (trekkers), hemoglobin concentration may be increased _______ above normal.

Answer 9

40 - 50%

Question 10

How does the oxyhemoglobin curve shift at higher altitudes?

Answer 10

• to the right (more O2 is unloaded at the tissues for a given capillary PO2)

Question 11

What happens to the pulmonary system when alveolar PaO2 decreases

Answer 11

• increase in ventilation (hyperventilation) but drop in CO2, changing composition and increase in blood ph (respiratory alkalosis)
• After the acid-base balance is corrected, hyperventilation persists during acclimatization. Within a week at high altitude, a new level for VE is attained - 40 to 100% above sea level values.

Question 12

What decrements in performance occur at high altitude?

Answer 12

at high elevation:
decrease in visual acuity, 25% decrease in light sensitivity, 25% decrease in attention span

at extreme elevation:

• 15-20% decrease in cognition and recall
• 25% decrease in pursuit tracking ability
• 25% decrease in reaction time

Question 13

How much does VO2 max decrease as altitude increases? Why (2)?

Answer 13

VO2 max. decreases 3 - 3.5% per 1000 ft. above 5000 ft. At 14,000 ft. VO2 max. is decreased approximately 30%

• decreased oxygen content of arterial blood –> decreased a-vO2 difference in maximal exercise
• decrease in max. cardiac output (due to a decrease in heart rate and stroke volume) The decrease in max. stroke volume is due to the reduction in venous return caused by the decreased blood volume (Starling mechanism)

Question 14

How does the VO2 max reduction percentage differ in trained and untrained individuals?

Answer 14

The percentage reduction in VO2 max. is equal in both trained and untrained individuals.

Question 15

Explain the differences (if any) in the following variables if the 2 scenarios are 1. at sea level and 2. at high altitude:

• O2 requirements for working muscles
• heart rate
• minute ventilation

Answer 15

• Oxygen requirements for working muscle are the same at altitude as at sea level for the same submaximal workload.
• However, heart rate and minute ventilation will be greater, requiring slightly more O2 for the same workrate.

Question 16

At high altitude and during heavy exercise, muscle and blood lactase levels are higher for any given workload. Why (2)?

Answer 16

During heavy exercise, muscle and blood lactate levels are higher at altitude for any given workload for two reasons:

1. Since the VO2 max. is reduced, any given workload now requires a higher percentage of the
   VO2 max. to perform
2. There is a reduced blood buffering capacity due excretion of certain amount of bicarbonate via the kidneys.
   Higher level of perceived exertion for any workload.

Question 17

How does high altitude exposure impact body fat and lean body mass?

Answer 17

• significant reduction in body fat and lean body mass due to appetite depression

Question 18

How soon are the benefits of acclimaitzation lost after returning to sea level?

Answer 18

2-3weeks

Question 19

How many weeks may it take for endurance athletes to acclimitize before major competition at a high altitude? (6500ft)

Answer 19

2-3 weeks

- non endurance athletes can arrive close to time of competition

Question 20

What does the saying “sleep high, train low” mean?

Answer 20

Since VO2 max. is decreased at altitude, intensity of training must be decreased. However, this problem can be solved by living at altitude, but going down to lower altitudes for few hours per day to train – “sleep high, train low”.

• The purpose of this procedure is to get the beneficial physiological altitude adaptations, while maintaining sea level training intensity.
  This method of training results in better sea level performance than is obtained by living and training at altitude for a number of weeks and then returning to sea level to perform.

Question 21

During the first few days at altitude, athletes may experience __________ which may hinder their training.

Answer 21

acute mountain sickness

Question 22

• does training at altitude improve sea level performance?

list benefits and cons

Answer 22

There is no consistent scientific evidence to support training at altitude to improve sea level performance.

• increased hemoglobin concentration
• increased number of mitochondria, oxidative enzymes, etc
• decreased maximum stroke vol and max heart rate
• increased Ve at given workload, extra oxygen goes to respiratory muscles during exercise
• decreased buffering capacity of blood for lactic acid
• specificity of training - while at altitude, the athlete isn’t able to train at close to sea level
  race pace. One must lower the absolute workload to perform aerobic exercise at the same relative intensity at altitude as at sea level.

Question 23

How can you prevent altitude sickness? (7)

Answer 23

1. staged ascent (climb slowly and wait to acclimatise); avoid flying or driving to high altitude; don’t go higher until altitude sickness symptoms go away; if temperature is extreme (cold or heat) ascend even more slowly
2. avoid alcohol or other depressant drugs; they decrease respiratory drive in sleep which can worsen symptoms
3. high carbohydrate diet (diet of 70% carb reduces mountain sickness by 30%; start 1-2 days prior to ascent)
4. exercise moderately, avoiding excessive breathlessness and fatigue until acclimatized
5. drugs (prophylaxis: prevents symptoms); drug of choice acetazolamide; don’t rely on them!
6. drink lots of water to produce diluted urine to avoid headaches
7. keep in mind everyone acclimatizes at different rates; make sure whole party is properly acclimatized before going higher

Question 24

Describe: acute mountain sickness

• is dependent on what factors?
• usually occurs at what altitude and how soon after? lasts how long?
• what can exacerbate
• symptoms
• treatment

Answer 24

• very common; occurs at over 2500m
• AMS occurs 12 - 36 hours after arriving at altitude and usually lasts 2 to 3 days. The occurrence of AMS is dependent on the elevation, the rate of ascent, and individual susceptibility. Many people will experience mild AMS during the acclimatization process. This condition is exacerbated by exercise during the first few hours of altitude exposure.

Symptoms - headache, fatigue, irritability, loss of appetite, nausea, vomiting, dizziness, insomnia, generalized weakness. The syndrome resembles an alcohol hangover.

Treatment – the only cure is either acclimatization or descent. Symptoms of mild AMS can be treated with pain medications for headache and Diamox. Moderate or severe AMS requires descent to lower altitudes.

Question 25

define: high altitude pulmonary edema (HAPE)
- occurs when?
- due to ?
- symptoms
- what can predispose someone to HAPE?
- treatment

Answer 25

• Pulmonary edema: accumulation of fluid in the alveoli –> decreased diffusing capacity for oxygen
• uncommon
• Occurs above 3000m (10,000 ft.) and takes 36 - 72 hrs. to become obvious. It can strike individuals of any age, particularly those who ascend rapidly. The occurrence rate is 1% to 2% of trekkers at altitudes over 3000m (10,000 ft.). Risk factors for HAPE include the altitude above sea level, the rate of ascent to that altitude, and individual susceptibility.
• Due to hypoxia in lungs; causes vasoconstriction, increasing pulmonary vascular resistance, causing hypertension and movement of fluid from the circulatory system to the pulmonary interstitial spaces and alveoli
• symptoms: shortness of breath, severe fatigue, cough which sometimes produces a frothy and/or bloody sputum, fast heart beat, severe headache, insomnia, chest tightness or congestion, blue or gray fingernails or lips, often a slight fever; may rapidly go on to unconsciousness and death. The symptoms often begin at night when shortness of breath at rest may occur.

The hypoventilation and associated hypoxemia that occur during sleep may further predispose persons to HAPE –> avoid sleeping medications, alcohol, and sedatives that further depress ventilation.

Treatment - descend to lower altitude immediately

• diuretics are quite effective if and only if fluids are replaced as rapidly as they are excreted.
• Diamox is effective for prevention and treatment
• Dexamethasone will improve symptoms

Question 26

Define: High altitude cerebral edema (HACE)

Answer 26

• Accumulation of excess fluid in the brain
  (Rare below 3600m (12,000 ft.) )

Symptoms – loss of coordination, confusion, hallucinations, severe headache, severe weakness and fatigue, coma Treatment - same as for HAPE

Question 27

What are some other medical problems at high altitude?

Answer 27

• Retinal hemorrhage: occurs in 50% of people going above 5500m (18,000 ft.) - reversible after return to sea level. However, irreversible visual defects can occur.
• Low temperatures –> hypothermia, frostbite
• Sunburn

Question 28

• Treatment of altitude illness is based on 4 principles. What are they?(4)

Answer 28

Treatment of altitude illness is based on four principles:

(1) stop ascent in presence of symptoms;
(2) descend if no improvement or if condition worsens;
(3) descend immediately if HAPE, loss of coordination, or changes in consciousness are present;
(4) ill persons must not be left behind alone or sent down alone.

Question 29

• differentiate between the effects of hypoxia on systemic arterioles and the lungs

Answer 29

The direct effect of hypoxia on systemic arterioles is vasodilation. In contrast, hypoxia in the lung causes vasoconstriction. See HAPE