Respiratory anatomy and physiology faculty version

transcript

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

• Metabolic functions– Surfactant synthesis– Protein synthesis– Metabolism of vasoactive substances

• ACE/Bradykinins

• Blood reservoir– Volume = 450mls

• Allows phonation

• 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.

Muscles

Inspiration

Expiration

Diaphragm

External Intercostal Muscles

Accessory muscles

Abdominal Muscles

Internal Intercostal muscles assist

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

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

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

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

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 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

• 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.

• 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

• Common Problems – Chronic Obstructive Pulmonary Disease (COPD)– Past Medical History– Drug History– Social History– Review of systems.

• Common Problems – Chest Infection– History

• Cough• Sputum Production• Dyspnoea• Wheeze• Pleuritic chest pain• Fever.

– Drug History.

Respiratory anatomy and physiology faculty version

Health & Medicine