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Respiratory Physiology 3, Revision
O2 and CO2 moves via diffusion
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Respiratory Physiology 3
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Factors affecting airway resistance, and how spirometry measures lung volumes and airflow in patients
Resistance increase due to
- Contraction of smooth muscle of bronchioles (bronchoconstriction)
- ↓ lung volume
- Mucus accumulation
↑ work of breathing (to draw air into lungs)
Bronchoconstriction
- Radius decrease, increase resistance
- Stimulated by irritants such as smoke or cold air
- Mediated by parasympathetic nerves
Bronchodilation
- Radius increase, decrease resistance
- Stimulated by drugs such as beta 2 adrenergic
agonists
- Mediated by sympathetic mediators
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Revision
- O2 and CO2 moves via diffusion
- Higher partial pressure to lower partial pressure
- Takes 0.25s for Hb to fully oxygenate
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Work of breathing is influenced by
- Compliance of lungs & chest wall Importance of surfactant in stabilising alveoli
- Airway resistance
- Altered by changes in airway caliber (constriction/dilation)
- FEV1: Forced Expiratory Volume of air exhaled in 1 sec after full inspiration, approx 80% (0.8) of Vital Capacity. Asthmatic patients has FEV1 of 0.6
- FVC: Forced Vital Capacity – total volume expired forcefully after full inspiration
Picks up changes in
- Resistance to airflow (airway resistance)
- Elasticity of lungs
↓ affinity for O2
- ↑ temperature
- ↑ PCO2 / H+ (↓ pH)
- ↑ 2,3-DPG in RBCs(2,3 diphosphoglycerate)
- High altitude areas or chronic lung disease
Revision
CO2 transport in blood
- CO2 transfer from tissue to blood
- In blood, 23% of CO2 gets attached to Hb
- CO2 + H20 > H2CO3 then disassociate to H+ and HCO3- (70% of CO2)
- H+ binds with Hb to maintain pH
- Erythrocyte expels HCO3 to tissue and receive Cl- (chloride), to maintain electrical neutrality of erythrocyte (you don't want them to repel/attract to one another)
