Ventilation Flashcards
What happens during inspiration
Pressure difference is produced by increasing lung volume
Thoracic cage expands & lung volume increases
Expansion is brought about by inspiratory muscles
Diaphragm contracts – dome flattens & moves caudally
Ribs pulled cranially & outwards by contraction of external intercostal muscles
What happens during expiration
Caused by relaxation of inspiratory muscles
Ribs recoil back to original position
Fill in the table of airflow during inspiration
Fill in table of airflow during expiration
What is compliance in lungs
Ability of lungs chest wall to expand & stretch in response to changes in pressure during breathing
Reduced lung compliance causes scar tissue in lungs or pleura
Increased lung compliance can aid inspiration but if prolonged (due to excessive coughing) can reduce elasticity in lungs
What is alveolar surface tension
Occurs at interface between water & air
Inner surface of alveoli lined with fluid
Surface tension reduced with production of surfactant
Pressure higher in smaller spaces
How is ventilation regulated
Medulla is respiratory centre in brain
Generates action potentials, modulated by feedback from
Chemoreceptors
Mechanoreceptors
What mechanisms limit ventilation regionally & globally
Globally:
Resistance to flow in airways
Lung compliance
Alveolar surface tension
Regionally:
Lower portions of lung ventilated more than upper zones
Intra-pleural pressure higher at base of lung than apex due to weight of fluid
Lung easier to inflate at low volumes than high volumes
How do lung diseases & cardiac function affect perfusion
Lung diseases:
Asthma
Pneumonia
Mountain sickness
Cardiac function:
Congenital heart defects
Hypovolemia
Pulmonary oedema
What is ventilation/perfusion mismatch
Optimal gas exchange in lungs requires appropriate ratio between ventilation & blood flow in each alveolus
V/Q ratio should ideally be 1
Ventilation/perfusion mismatch = disturbance in O2 supply & blood supply to alveoli
What are the effects of V/Q mismatch on animals
Impaired oxygenation
In areas of lungs were ventilation is less than perfusion (V/Q < 1 ) oxygen uptake is reduced
Results in hypoxemia – decreased oxygen in arterial blood
Shunting
Blood bypasses poorly ventilated alveoli & directly moves from right side of heart to left without being oxygenated
Leads to decrease in arterial oxygen saturation
Alveolar dead space
In areas of lungs where ventilation higher than perfusion (V/Q > 1)
Resulting in decreased CO2 elimination leading to increased arterial CO2 levels (hypercapnia)
Fill in the graph
Define tidal volume
volume of air flowing through airways during each inspiration & expiration
(increases with exercise)
Define minute ventilation
volume of air inspired or expired per minute
Tidal volume X frequency of breathing
Define dead space ventilation
portion of minute ventilation that isn’t available for gas exchange
Dead space volume X frequency of breathing
What is the pathway of oxygen from outside in
- Atmosphere
- Into lungs by ventilation
- Into blood by diffusion
- Heart
- Circulated to tissues in blood
- Into tissues by diffusion
- Into mitochondria
CO2 is reverse
PO2 reduces as it travels through system
PCO2 increases as it travels through system
How is oxygen transported in blood
Dissolved in plasma (1.5%)
Bound to haemoglobin in erythrocytes (98.5%)
How do temperature and pH affect oxygen-haemoglobin curve
Both tend to be increased in respiring tissues
Tissues/cells doing metabolic work = right-ward shift in curve = unloading of O2
How is carbon dioxide transported
Dissolved in blood (10%)
Carboxyhaemoglobin on proteins (20%)
Bicarbonate ions in plasma (70%)
CO2 enters RBC where it reacts with water to form carbonic acid
Carbonic acid dissociates to:
Bicarbonate ions (transported to plasma)
Hydrogen ions (buffered by Hb)
What is Fick’s law of diffusion
Links together nature of membrane, surface area, partial pressure gradient, membrane thickness
Rate of diffusion is inversely proportional to distance over which diffusion occurs
What factors affect diffusion
Concentration gradient
Surface area
Membrane thickness
Diffusion distance
Solubility of gases
Blood flow
Metabolic rate
What does hyperventilation cause
Getting rid of too much CO2 = increased alveolar ventilation that leads to reduced arterial pCO2
Causes respiratory alkalosis
(Increased pH, decreased pCO2)
What does hypoventilation cause
Hypoventilation (not blowing off enough CO2) = reduced alveolar ventilation that leads to increased arterial pCO2
Causes respiratory acidosis
(decreased pH, increased pCO2)
Define inspiratory reserve volume
Amount of air a person can inhale forcefully after normal tidal volume inspiration
(decreases with exercise)
Define residual volume
Volume of air remaining in lungs after maximum forceful expiration
Define inspiratory capacity
Maximum volume of air that can be inspired after reaching end of normal, quiet expiration
Define vital capacity
Total amount of air exhaled after maximal inhalation
Define functional residual capacity
Volume remaining in lungs after normal passive exhalation
Define conditions under which ventilation perfusion mismatch would occur
Asthma, COPD, bronchiectasis, cystic fibrosis, interstitial lung diseases, pulmonary hypertension
