10. Control of breathing Flashcards
Origin of respiratory drive
medulla
Negative feedback control of PaO2
Arterial chemoreceptors
• Increases discharge when PaO2 falls
• Little change until PaO2 falls below 8kPa (60 mmHg)
- Decreased discharge when PaO2 rises
- High blood flow
Peripheral chemoreceptors
arterial
Central chemoreceptors
brain
Response to metabolic acidosis
- Stimulation of peripheral
- Increase in ventilation
- Reduction in PaCO2
- Reduced stimulation of central chemoreceptors
- Peripheral chemoreceptors stimulated more
- Central chemoreceptors stimulated less
- Partial correction of arterial pH
Effects of altitude - Initial response
Reduced barometric pressure, reduced PaO2 Hyperventilation limited
Effects of altitude - Acclimatisation
Increased ventilation (4 days)
• Loss of HCO3- and H+ transported into CSF
• Bohr effect vs increase in 2,3 DPG: overall decrease in Hb affinity for O2
• Easier release of O2 into tissues but less effective pickup in lungs
• Later erythropoeisis (erythropoetin) and increase in red cells
Exercise - sources of ventilatory drive
- Psychological factors
- Higher centres
- Proprioreceptors
- Adrenaline and noradrenaline
- Body temperature
- K+ acting on chemoreceptors
- Changes in sensitivity of central chemoreceptors
Hering-Breuer reflex
- Slowly adapting mechanoreceptors in smooth muscle of upper airways
- Termination of inspiration
- important at elevated tidal volume e.g. during exercise
Respiratory minute volume
VT x f
tidal vol x resp rate
Coughing
- Trachea
- Bronchoconstriction
- Deep inspiration
- Forced expiration against closed glottis
- Increased intrapleural pressure to 100 mmHg
- Sudden opening of glottis and explosive outflow of air
Sneezing
- Nasal mucosa
- Deep inspiration
- Forced expiration
- Increased intrapleural pressure
- Sudden opening of glottis and explosive outflow of air
