Chapter 15: Altitude

what is Pb?

-barometric pressure

-absolute pressure exerted by the weight of the atmosphere

what is Pb at sea level vs mount everest?

-sea level: 760 mmHg

-everest: 250 mmHg

what is all affected by air PO2?

-lungs

-blood

-tissues

what happens to air temp at altitude?

-temp decreases 1 degrees celsius per 150 m ascent

-contributes to risk of cold-related disorders

what is humidity like at altitude?

-cold air holds very little water

-air at altitude is very cold and dry

-dry air leads to quick dehydration via skin and lungs

what is low altitude?

-500 to 2,000 m

what happens at low altitude?

-does not affect well-being

-performance may be decreased but restored by acclimation

what is moderate altitude?

-2,000 to 3,000 m

what happens at moderate altitude?

-affects well-being in unacclimated people

-performance and aerobic capacity decreases

-performance may or may not be restored by acclimation

what is high altitude?

-3,000 to 5,500 m

what happens at high altitude?

-acute mountain sickness

-performance decreases and not restored by acclimation

what is extreme high altitude?

-above 5,500m

what happens at extreme high altitude?

-severe hypoxic effects

-highest settlements found from 5,200 to 5,800 m

what happens to exercise performance at an altitude?

-VO2max decreases as altitude increases past 1,500 m

-anaerobic performance unaffected

-thinner air leads to less air resistance

why does VO2max decrease as altitude increases?

-due to an increase in arterial PO2 and max cardiac output

-atmospheric PO2 less than 131 mmHg

-8-11% drop per 1,000 m of ascent

why is anaerobic performance unaffected at altitude?

-ATP-PCr and anaerobic glycolytic metabolism

-minimal O2 requirements

what exercises are affected by the thinner air and less air resistance?

-improved swim and run times

-improved jump distances

-varied effects in throwing events

what is the mount everest ascent study?

-VO2max decreases from 62 to 15 mL

-if sea level VO2max <50 mL then climbing is not possible without supplemental oxygen

what is pulmonary ventilation response to acute altitude exposure?

-increases immediately

-occurs at rest and during submaximal exercise but not maximal

-decrease in PO2 stimulates chemoreceptors in aortic arch, carotids

-tidal volume increases for several hours, even days

what leads to hyperventilation as a response to acute altitude exposure?

-an increase in ventilation at altitude

-alveolar PCO2 decreases

-blowing off CO2 equals respiratory alkalosis

what happens to respiratory alkalosis as a response to acute altitude exposure?

-high blood pH

-oxyhemoglobin curve shifts left

-increased affinity for O2

-prevents further hypoxia-driven hyperventilation

what happens to the kidneys as a response to acute altitude exposure?

-excrete more bicarbonate

-minimizes blood suffering capacity

-reverses alkalosis

-blood pH decreases to normal

what is the short term response to acute altitude exposure?

-plasma volume decreases within a few hours

-respiratory water loss and increased urine production

-loss of up to 25% plasma volume

-short term increases in hematocrit and O2 density

what happens to cardiac output as a response to acute altitude exposure?

-increases at rest and submaximal exercise

-more O2 delivered to tissues per minute

-an increase in sympathetic nervous system activity leads to an increase in HR

-inefficient, short term adaptations

what does a decrease in max cardiac output mean?

-a decrease in max stroke volume times a decrease in max HR

what causes a decrease in max stroke volume?

-a decrease in plasma volume

what causes a decrease in max heart rate?

-a decrease in sympathetic nervous system responsiveness

what does a decreases in PO2 gradient added with a decrease in max cardiac output lead to?

-a decrease in VO2max

what happens to gas exchange at the muscles as a response to acute altitude exposure?

-decreases

-decreased PO2 gradient at muscle

-O2 diffusion into muscle significantly reduced

how does the body acclimate to chronic exposure to altitude?

-performance improved but may never match that at sea level

-pulmonary, cardiovascular, skeletal muscle changes

-3 weeks required at moderate altitude

what are the pulmonary adaptations to chronic exposure to altitude?

-an increase in ventilation at rest and submaximal exercise

-resting ventilation rate 40% higher than at sea level

-submaximal rate 50% higher

what are blood adaptations to chronic exposure to altitude?

-EPO release increases for 2 to 3 days

-stimulates polycythemia

-elevated red blood cell count for 3+ months

what is polycythemia?

-an increase in red blood cell count

-hematocrit

what are the consequences of polycythemia?

-hematocrit at sea level is about 45%

-hematocrit at 4,500 m is about 60%

-hemoglobin increases proportionally to elevation

what happens to plasma volume as a result to chronic exposure to altitude?

-decreases and then increases

-early loss leads to increase in hematocrit prior to polycythemia

-later increase leads to an increase in stroke volume and cardiac output

what are the muscle function and structure changes as a result of chronic exposure to altitude?

-cross sectional area decreases

-capillary density increases

-a decrease in muscle mass due to weight loss, possibly protein wasting

what is a potential consequence to muscle metabolism as a result of chronic exposure to altitude?

-potential decrease

-mitochondrial function and glycolytic enzymes decrease

-oxidative capacity decreases

what are the advantages of altitude training and performance acclimation?

-advantageous adaptations for competing

what does hypoxia at altitude lead to?

-prevents high-intensity aerobic training

what does living and training high lead to?

-dehydration

-low blood volume

-low muscle mass

what does living high and training low lead to?

-best of both worlds

-permits passive acclimation to altitude

-training intensity is not compromised by low PO2

what are the results of a 5K run time trial

-living high, training high: no improvement

-living low, training low: no improvement

-living high, training low: significant improvement