1. Respiration under unusual conditions

2. birth

3. Birth Breathing initiated by :
Peripheral chemoreceptors responding to O2.
Central chemoreceptors responding to CO2.
First breath:
Important for development of residual volume
If some air is not retained after first breath, respiratory distress syndrome develops, making each subsequent breath as hard. (More common in premature infants)

4. Birth After few breaths: Functional residual capacity developed
pulmonary circulation
O2 causes vasodilatation of blood vessels in lungs
amniotic fluid absorbed.
Continuous breathing:
Maintained by neural feedback loops
Activated lung stretch receptors set up rhythm with respiratory centre.

5. Birth Summary First breath Few minutes Continuous breathing
Intiated by
chemoreceptors
Some air MUST be retained for development of
Residual volume
Pulmonary circulation increased
Vasodilation (response to O2) leads to absorption of amniotic fluid.
Maintained by neural lung reflexes
Stretch receptors

7. exercise

8. Exercise
Start:
Propioceptors trigger an in ventilation, beyond what is expected from O2 and CO2 levels, anticipating the requirement.
Moderate:
Ventilation closely matched to the extra demand of increasing O2 supply and removing CO2.
Controlled by central chemoreceptors responding to CO2 levels.

9. Severe:
Body temperature and acid leads to hyperventilation beyond expected for the CO2 levels being produced.
Hence PaCO2
Important to try and maintain blood PH

10. Exercise Summary Start Moderate Severe
Increase in ventilation via propioceptors
Ventilation matched via chemoreceptor response to CO2
Hyperventilation, PaCO2 decreases

11. diving

12. Diving Fear of being unable to expand thorax
Water pressure increases with depth
Gas must be of equal or greater pressure than surrounding water to allow for chest expansion otherwise unable to force chest out against the water with high pressure.
Middle ear
risk of ear drum implosion from pressure.
Valsalva

13. Diving
Nitrogen
N2 dissolved on descent, impair nerve conduction, narcosis
N2 less dissolved on ascent, bubbles out from solution in tissues Decompression sickness (joints, sensory organs, cerebral vessels)
O2- Helium mix

14. Diving Shallow water blackout Free diving hyperventilate before diving
Body relies on CO2 to control breathing
hyperventilation depletes CO2 without increasing O2 storage.
Reduces respiratory drive, low O2 leads to loss of consciousness
Risk of drowning

15. Diving summary Chest expansion Ear drum implosion N2
Single breath diving
Gas must be of equal or greater pressure
Water pressure increases with depth
Valsalva
Descent : narcosis
Ascent : Decompression sickness
Shallow water blackout
Hyperventilation

16. Spaceflight

17. Spaceflight During take off and landing: V/Q mismatch
Blood cannot effectively reach lung apices and bases likely to collapse upright position.
Lie horizontal and wear pressurised G suits to push circulation up to thorax.

18. Spaceflight Lack of gravity in space: Greater effect on circulation.
Lack of gravitational pull on movement on blood
no baroreceptor stimulation when posture changes.
Baroreceptors desensitise over time
Back to earth: when change from lying down to standing up, no stimulation of vasomotor tone and lack of increase in BP faint (orthostatic hypotension)

19. Spaceflight Summary Take off In space Blood to apices decreases
Horizontal
G suits
Bases collapse
No gravity
Baroreceptors densensitise
Orthostatic hypotension