respiratory anatomy and physiology faculty version
DESCRIPTION
Presentation given by Jonathan Downham for Clinical History Taking and Examination course 2013TRANSCRIPT
Respiratory Anatomy and Physiology
Broncioles branch many times and each division produces tubules which are smaller
Terminal bronchioles have a diameter of 0.5-1mm in diameter.They are too thick for air exchange and considered to be the last of the conducting zone structures
Type I cells account for gas exchange.Type II cells secrete surfactant
Functions of the lung
• Main function is gas exchange– Allow passage of O2– Allow removal of CO2
Functions of the lung
• Metabolic functions– Surfactant synthesis– Protein synthesis– Metabolism of vasoactive substances
• ACE/Bradykinins
• Blood reservoir– Volume = 450mls
• Allows phonation
Functions of the lung
• Heat exchange• Immunological
– Alveolar macrophages– IgA production– Mucociliary escalator
Ventilation MechanicsHow air gets to the alveoli.
Gas ExchangeHow gas crosses the blood gas interface.
Gas TransportHow they are carried
around the body.
Ventilation MechanicsHow air gets to the alveoli.
Muscles
Inspiration
Expiration
Diaphragm
External Intercostal Muscles
Accessory muscles
Abdominal Muscles
Internal Intercostal muscles assist
Ventilation MechanicsHow air gets to the alveoli.
Forces acting on the lung
Elastic Tissue
Elastic tissue of lungs is stretched under normal conditions. Resulting tension acts as a force pulling inwards on visceral pleura
As chest wall and diaphragm pull on outwards on parietal pleura causing a negative pressure in interpleural space. This keeps the lungs inflated
Ventilation MechanicsHow air gets to the alveoli.
Airway Resistance
If radius halved then resistance increases 16 fold
Chief site of airway resistance is the medium sized bronchi.Peripheral airways contribute little resistance
Considerable small airway disease can be present before being detected in pressure changes.
Lung Compliance
Factors determiningLung volume
Bronchi supported by surrounding tissueTheir calibre is increased as the lung expandsSo as lung volume is reduced resistance is increased
Contraction of bronchial smooth muscle
the slope of the pressure-volume curve at a particular lung volume => i.e. volume change per unit of pressure change (mL/cmH2O) normal value = 200mLs/cmH2O Lower compliance = more effort of breathing
Posture affects lung volume, therefore complianceDisease states
Asthma leads to hyper-inflationFibrosis, collapse and consolidation all decrease distensibilityEmphysema increases compliance
Ventilation MechanicsHow air gets to the alveoli.
FRC- volume of gas remaining in lungs at end of normal expiration
Volume of lung at which elastic forces causing recoil = thoracic chest wall forces causing expansion
FRC = 30mls/kg = 2200 mls in supine 70kg adult
Functional Residual Capacity
FRC increases withHeightChanging from supine to erectEmphysema- gas trapping
FRC decreases withObesityMuscle paralysis and GAChanging from supine to erectRestrictive lung diseasePregnancyRaise intra-abdominal pressure
Gas ExchangeHow gas crosses the blood gas interface.
Rate of diffusion is: Directly proportional to cross sectional area across which diffusion occursInversely proportional to the thickness of the membraneDirectly proportional to the partial pressure of the gas across both sides
Gas ExchangeHow gas crosses the blood gas interface.
The amount of time that blood is in contact with the alveolus also influences gas exchange.The speed of blood flow past the alveolus is:
0.75 seconds under normal conditions0.25 seconds with heavy exercise
Ventilation-Pleural pressure are higher at the bases of the lungs.So they receive 4 times more ventilation than apices.Circulation-Low pressures in pulmonary circulation are affected by gravityBases of upright lungs receive 20 times more blood flow than apices.
Gas ExchangeHow gas crosses the blood gas interface.
Gas TransportHow they are carried
around the body.
Respiratory Examination
• Common Problems- Asthma.– Baseline control
• Usual exercise tolerance• Frequency of attacks• Best Peak expiratory flow rate• Usual precipitating factors• Medication• Usual response to therapy• Previous hospital/ITU admissions• Symptoms suggestive of poor baseline control
Jonathan Downham 2010
Respiratory Examination
• Common Problems – Asthma– Drug History
• Do they have a nebuliser at home?• Do they use a bronchodilator?• Do they take theophylline or aminophylline?
(bronchodilators).• Do they take steroids?• Are they on medication which aggravates the
symptoms... Beta blockers, aspirin.• Demonstrate inhaler technique.
Jonathan Downham 2010
Respiratory Examination
• Common Problems – Chronic Obstructive Pulmonary Disease (COPD)– Detailed history
• Time course• Treatment given and effects• Any hospital admissions in the last year• Baseline function• Chronically deteriorating exercise tolerance.• Quantify normal amounts of sputum
Jonathan Downham 2010
Respiratory Examination
• Common Problems – Chronic Obstructive Pulmonary Disease (COPD)– Past Medical History– Drug History– Social History– Review of systems.
Jonathan Downham 2010
Respiratory Examination
• Common Problems – Chest Infection– History
• Cough• Sputum Production• Dyspnoea• Wheeze• Pleuritic chest pain• Fever.
– Drug History.
Jonathan Downham 2010