Lung Mechanisms And Ventilation Of The Lungs session2 Flashcards
Tidal volume
The volume of air being inhaled or exhaled at rest
Anatomical dead space + alveolar ventilation
How is air drawn in in quiet inspiration?
ACtIVE expansion of the thoracic cavity which in turn expands the lungs (pleural seal)
Ribs are drawn up laterally and superiorly by external ICM contracting
Diaphragm contracts (80% of volume increase)
Air is drawn in from high atmospheric to low intra-thoracic pressure
Muscles/ diaphragm contractions overcome the inward pull of the lung recoil
How is air expelled in quiet expiration?
PASSIVELY muscles of inspiration relax -> reduces volume of thoracic cavity & lungs
Air leaves from higher intra-thoracic pressure to lower atmospheric
Chest wall and diaphragm no longer overcome the inward pull of lung recoil
What keeps the lungs against the chest wall on inspiration and expiration
Lungs have elastic recoil so a tendency to want to collapse in
but pleural fluid between visceral and parietal pleura in intrapleural space forms a seal between the lung and thoracic wall (surface tension between the pleural surfaces)
so lungs expand with the thoracic cavity
When does the state of equilibrium occur and what is involved?
the resting expiration level- between quiet inspiration and quiet expiration
Lungs pull in and up (lung elasticity)
Chest wall pulls out (elastic recoil)
Diaphragm pulls down (passive stretch)
Forces are equal and opposite - tendency to want to return to this resting state
Definition of elasticity , what creates lung elasticity?
The ability of an object/ material to resume its normal shape after being stretched or compressed
In lungs: Primarily determined by elastin in the elastic fibres in Ct of lungs and surface tension of alveoli
Definition of compliance. What creates lung compliance?
Compliance - the ease with which an elastic structure can be stretched - distensibility
Lung compliance: also related to lung elastic fibres and alveoli surface tension
3 factors involved in ventilation
Lung elasticity
Lung compliance
Airways resistance (airway diameter and surface tension determine)
How do compliance and elastic recoil relate to one another?
Elastance= measure of elastic recoil
Compliance is inversely proportional to elastance e.g. compliance directly proportional to 1/elastance
Tissues with a high compliance have less elastic recoil
What is functional residual capacity? What does it depend on?
The volume of air in the lungs at the end of a quiet expiration
Depends on balance between lung elastic recoil inwards and chest wall elastic recoil outwards ( compliance )
So if lung elastic recoil is high (fibrosis) lower lung volume at rest
If lung elastic recoil is low (emphysema) greater lung volume at rest (hyper inflated)
What’s the main differences between a small bronchus and a bronchiole?
Small bronchus: small islands of cartilage and glands in submucosa
Bronchiole: no cartilage or glands, surrounding alveoli keep lumen open
Diameter 1mm or less
How do bronchioles stay open in expiration?
No cartilage
Radial traction (outward tugging force) from surrounding alveolar walls
Prevents collapse of bronchioles during expiration
What is surfactant, what is it made from and what is it’s function?
Lines alveoli
Mix of phospholipids and lipoproteins
Diminishes the surface tension of the water film that lines alveoli
Thereby decreasing the tendency of alveoli to collapse and the work required to inflate them
What is hypoventilation and what are some Causes?
Inability to expand chest
Sleep apnoea Duchenne muscular dystrophy COPD Opiates Head injury Myasthenia gravis Pneumothorax Respiratory distress
What is a pneumothorax? How do you treat it?
Air in the pleural space with a loss of pleural seal -> lung collapses
Chest injury
Lung disease
✅ drain air from pleural space, chest drain inserted, using an underwater seal (prevents fluid or air end Teri get pleural cavity)
What is interstitial lung disease? What are some causes? What are some clinical symptoms and signs?
Increased collagen in alveolar walls, lungs stiff makes lung expansion difficult -> reduced lung compliance, elastic recoil of lungs is increased
Increased diffusion distance
200 different types
Thickening of pulmonary interstitium (microscopic space between alveolar epithelium and capillary endothelium made from elastin fibres, collagen fibres, fibroblasts, matrix substance)-> common final pathway is lung fibrosis (sometimes irreversible)
Can follow specific exposure e.g. asbestos, drugs (methotrexate), radiation, mouldy hay or autoimmune (sarcoidosis) or idiopathic 20% (Cryptogenic alveolitis)
Clinical symptoms: dry cough, dyspnoea, fatigue, gradual progression
Signs: decreased lung excursion, bi-basal end inspiratory lung crepitations, finger clubbing, pleural effusions
What is respiratory distress in the newborn? Symptoms? Treatments? At what age will this no longer be a problem?
Often in premature babies when they can’t produce sufficient surfactant so increased surface tension of alveoli making lung expansion difficult, some alveoli remain collapsed
Symptoms: grunting, nasal flaring, intercostal and subcostal retractions, rapid respiratory rate (tachyonea), cyanosis
Surfactant made 24-28 weeks, sufficient amounts by 25-36 weeks
✅steroids encourage production or put on surfactant ventilator
When might quiet expiration be difficult? Why are problems with airflow typically worse in expiration compared with inspiration?
When airways resistance is high and elastic recoil is low e.g asthma, COPD (chronic bronchitis and emphysema) also have decreased elastic recoil of lungs
Intra pulmonary pressure is positive in expiration so exacerbates narrowing of intra thoracic airways
What is COPD? What’s the new term for someone likely to get COPD and what are the criteria?
Third leading cause of death
Smoking/ inhaled pollutants interact with genetic vulnerability
Chronic respiratory symptoms with associated pulmonary abnormalities - impaired airflow not fully reversible (chronic bronchitis and emphysema)
‘PRE-COPD’ no clinical symptoms but airflow impaired and normal spirometry, high risk developing in next 5yrs
What is chronic bronchitis? Possible causes? Diagnosis criteria
Bronchi-> bronchioles
Inflammatory cells/ oxidative stress/ infection -> Mucus hypersecretion, reduced cilia -> blocked lumen airways, epithelial remodelling, increased surface tension predisposing to collapse
Diagnosis: cough productive sputum >3months for > one year
What is emphysema? What is the disease pathology? What can develop in the anatomical chest with chronic emphysema?
Permanently enlarged air sacs distal to terminal bronchioles with destruction of alveolar walls
Inflammatory cells accumulate -> elastases + oxidants -> destroy alveolar walls and elastin (protease mediated)
Reduced elasticity (airway trapping) and reduced surface area for gas exchange
Bc the lungs are chronically overinflated the rib cage stays partially expanded all the time -> barrel chest (ratio of anteroposterior to transverse/ lateral diameter is 1:2 normally, becomes 1:1 as AP enlarges and diaphragm crosses 8th rib bc flattened rather than 5th)
what is atelectasis? Several causes and the main complication.
Lung collapse
Inadequate expansion of air spaces
- Neonatal- respiratory distress due to lack of surfactant
- compression collapse due to pneumothorax or pleural effusion
- compression from abdominal distension (compresses alveoli)
- resorption collapse due to obstruction (airway obstructed, air downstream of blockage slowly absorbed into blood stream & not replaced, alveoli collapse)
Can lead to pneumonia if not restored
Clinical sign: Crackles at base of lung
What is cough reflex? Where is it mediated? What occurs in order to cough?
Co-ordinated by cough centre in medulla oblongata
Initiated by irritation of me and and/or chemoreceptors in the respiratory epithelium
- deep inspiration
- Glottis closed by vocal cord adduction
- Strong contraction of expiration muscles (abdo, internal intercostal) builds up intrapulmonary pressure
- Sudden opening of glottis -> explosive discharge of air
What is anatomical dead space?
The volume of air in the conducting airways
