Respiration under unusual conditions

birth

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)

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.

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

exercise

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.

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

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

diving

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

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

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

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

Spaceflight

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.

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)

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