Challenges to Normal Respiration

oxygen requirements

• gas exchange demands increased enormously by exercise

• resting oxygen consumption

• control of increases in ventilation

oxygen requirements at rest

• 4.8mL/kg/min

• 160mL/min/m²

• 200mL/min

VO₂ max

• as work rate increases, O₂ rate increases

• up until a certain point→ VO₂ max

• VO₂ max= individual’s maximum rate of oxygen consumption

how is O₂ consumption changes controlled

• quick onset required

  • psychological

  • neural input to inspiratory centre

  • proprioceptors

  • small changes in ABGs

  • cardiovascular changes

  • temperature regulation

effect of exercise on oxygen

• basal O₂ req. increases several-fold

• max. O₂ is a measure of how fit an individual is

changes in altitude

• atmospheric pressure decreases with distance above earth’s surface

• requires acclimatisation

how does O₂% change with altitude

remains constant at 21%

atmospheric pressure at sea level

101.3 kPa

partial pressure of water vapour breathed in at sea level

6.3kPa

effect of altitude on O₂ inhalation

• at sea level PO₂→ 21.3kPa

• decreases going up

• partial pressure of oxygen decreases→ less oxygen reaches alveoli

what happens to body at 60,000ft

• atmospheric pressure→ 6.3kPa

• at body temperature, atmospheric pressure and saturated water pressure are the same

• water will begin to boil→ body fluids begin to vaporise:

  • blood and eyes will boil

  • lungs will fill with steam

response to altitude and acclimatisation

• hyperventilation and respiratory alkalosis

• increased 2,3-DPG causes better unloading of oxygen

• polycythaemia→ slow to develop

• bicarbonate excretion from CSF and kidneys

• diuresis, hyponatraemia

• acetazolamide

how does hyperventilation help respond to increasing altitude

• double minute volume=half arterial and alveolar PO₂ = more space for O₂

how does increasing 2,3-DPG levels helps respond to increasing altitude

• over time, not instant

• promotes release of CO₂ from haemoglobin

polycythaemia

• increased RBC and Hb levels

• increases oxygen carrying ability of blood

symptoms of hypoxia

• nausea

• confusion

• headache

• blurred vision

• raised intracranial pressure

• pulmonary hypertension

• pulmonary oedema

symptoms of acute mountain sickness

• nausea

• amnesia

• breathlessness

• headache

• loss of appetite

• difficulty sleeping

symptoms fo severe mountain sickness

• cheyne stokes respiration

• pulmonary and cerebral oedemas

cheyne stokes breathing

periods of deep breathing that alternate with periods of apnoea

how does pressure change with depth under water

for ever 10m, pressure increases by 1 atm

how does chest change on descent under water and effect

• compressed by increasing pressure

• allows PO₂ to be maintained or to rise

how does chest change on ascent under water and effect

• expands due to decreasing pressure

• causes PO₂ to fall→ divers may become hypoxic

why can’t you snorkel below 1.6m

• pressure under 1.6m is 2.6atm

• intercostal muscles too weak to overcome pressure gradient

dangers of nitrogen and deep-diving

• nitrogen is very soluble in tissues

• has high densities at high pressures→ increases work of breathing

• at 40m→ nitrogen narcosis

decompression sickness when diving

• caused on ascent from deep diving die to nitrogen

• bends

• staggers

• creeps

what is used to remove nitrogen during deep diving

helium oxygen

dive reflex

• innate reflex in many mammals

• involves vasoconstriction→ O₂ conserved to heart, lungs, brain

• reflex vagal bradycardia

• suppressed ventilation drive

effects of hyperoxia

• cellular oxygen toxicity

• fitting, free radical generation

• retrolental fibroplasia

• pulmonary fibrosis/ARDS

retinal fibroplasia

• high PO₂ puts pressure on retinal fibres

• causes blindness