Lecture 4 - ventilation, lung mechanisms and disorders Flashcards
Functional residual capacity in patient with emphysema
Increases - air filled alveolar spaces
Chest wall expansion has a greater force than lung elastic recoil
Functional residual capacity in patient with pulmonary fibrosis
Decreases
Elastic recoil greater than compliance
Therefore can’t stretch as much
Bronchus structure
Small islands of cartilage
Glands in submucosa
Bronchiole structure
No cartilage or glands in submucosa
Thin walls
Radial traction
Outward tugging force exerted by surrounding alveoli on the bronchioles to prevent collapse during expiration when the pressure increases.
What type of cells are type II pneumocytes?
Cuboidal
Type I is simple squamous
What can arise if there is an inability to expand the chest?
Hypoventilation
CO2 increases
O2 decreases - Type 2 respiratory failure
e.g. in Duchene’s muscular dystrophy
Pneumothorax
Air in pleural space with loss of pleural seal therefore lung collapse as loss of negative pressure
Conditions where there is decreased compliance
Restrictive
Interstitial lung disease - increased collagen in alveolar walls therefore stiffer
Respiratory distress syndrome - decrease in surfactant increases surface tension
Conditions where there is decreased elasticity
obstructive
Asthma - narrowed airways therefore increased resistance and loss of elastin
COPD - emphysema - loss of elastic recoil and alveoli are distended
Why are problems with air flow worse in expiration?
During expiration, pressure increases as airways decrease in volume as compressed.
Therefore more likely to collapse e.g. due to loss of radial traction
Passive so not controlled by muscles
Interstitial lung disease
Diffuse lung fibrosis - thicker pulmonary interstitium, increasing the diffusion pathway
- Stiffer lungs
- Reversible and irreversible fibrosis
Pathophysiology of interstital lung disease
- Deposition of fibrous tissue in the interstitium
- Lungs are less complaint
- Elastic tissue is replaced by collagen therefore decreased compliance as stretch less
- Elastic recoil increases therefore SA decreases
(airways are not narrowed as the alveolar still exert radial traction) - Restrictive ventilatory defect as chest expansion is reduced as greater elastic recoil force
- Thickening of the alveolar walls increases the diffusion pathway
What type of ventilation defect is interstitial lung disease
Restrictive
FVC decreased
FEV1/FVC - normal or greater than 70%
Symptoms of intersitial lung disease
Shortness of breath (dyspnea)
Dry cough
Reduced exercise tolerance
Fatigue
Signs of interstitial lung disease
Tachypnoea Tachycardia Coarse crackles Finger clubbing Reduced bilateral chest movement
Pleural effusions
What does the interstitium contain?
Fibroblasts
Elastin fibres
Collagen fibres
What can cause interstitial lung disease?
Exposure to:
- Asbestos
- Drugs - methotrexate
- Radiation
- Mouldy hay
Autoimmune- mediated inflammation - sarcoidosis
Connective tissue disorder:
SLE
Rheumatoid arthritis
Idiopathic pulmonary fibrosis
Neonatal respiratory distress syndrome
Do not produce surfactant in babies less than 30 weeks
Increased surface tension
Decreased lung expansion
Some alveoli collapse therefore no gas exchange
Impaired ventilation
Presentation of neonatal respiratory distress syndrom
Grunting Nasal flaring Intercostal and subcostal retractions Tachypnoea Central cyanosis
How to treat respiratory distress syndrome
Give steroid in utero
Give surfactant in ventilator when 34 weeks old
COPD
Chronic
Impaired airflow
Irreversible
Emphysema and chronic bronchitis
Mucus hypersecretion - mucous plugging
Reduced cilia - mucous not cleared
Obstructive ventilation
Clinical diagnosis of COPD
Productive cough for more than 3 months for more than once a year
Cause of COPD
Smoking
Inhaled pollutants
Pre COPD
Impaired airflow but no clinical symptoms yet with normal spirometry.
High risk of COPD in 5 years
Causes of mucous hypersecretion on COPD
Loss of cilia
Decreased PEF
Airway occlusion
Increased production: Oxidative stress Viral infection Inflammatory celss Bacterial infection
Chronic bronchitis
Increased mucus production in bronchi
Emphysema
Loss of elastin (destruction) in alveolar walls therefore loss of elastic recoil and radial traction. Increased compliance
Permanent enlargement of air spaces distal to the terminal bronchioles (air trapping)
Dried mucus plug block - Inflammatory cells accumulate which releases elastases and oxidants, destroying alveolar walls and elastin + protease-mediated destruction (alpha 1 antitrypsin deficiency)
Increased lung volume and takes longer to completely expel air
Barrel chest
Asthma
Reversible airway obstruction triggered by a stimulus
Smooth muscle hypertrophy - thicker airway walls
Bronchoconstriction
Mucosal oedema
In bronchi and bronchioles
Emphysema on CXR
Flattened diaphragm
Hyperinflated lungs - air trapping
Difference between emphysema and pulmonary fibrosis
Emphysema:
- Loss of elastin
- Decreased elastic recoil and increased compliance
- Hyperinflated lungs (Barrel chest)
- Small airways collapse during expiration due to loss of radial traction
- Air trapping
- Obstructive
Pulmonary fibrosis:
- Increased collagen deposition
- Increased elastic recoil and decreased compliance
- Lungs are stiffer and harder to expand
- Smaller lungs
- Decreased functional residual capacity
- Restrictive
Causes of atelectasis
Respiratory distress syndrome
Compression collapse:
- Pneumothorax
- Pleural effusion
Compression from abdominal distension - after major abdominal surgery don’t want to take deep breaths
Resorption collapse:
Tumour in bronchioles - obstructed airway
How to treat pneumothorax
Chest drain using an underwater seal - prevents fluid or air from entering the pleural seal
Resorption collapse
The airway is obstructed
Air downstream is slowly absorbed into the bloodstream but new air cannot enter distal to the site of blockage
- Alveoli collapse
Causes of hypoventilation
Duchene's muscular dystrophy RDS Opiates Head injury Guillain Barre syndrome Myasthenia gravis Pneumothorax Severe asthma End-stage COPD Foreign body Pulmonary fibrosis Kyphoscoliosis Severe obesity
Cough reflex
Coordinated by the cough centre in the medulla oblongata
- Deep inspiration
- Glottis is closed due to adduction of the vocal cords
- Strong contraction of expiratory muscles
- Increase in intra-pulmonary pressure
- Sudden opening of the glottis by abduction of the vocal cords causes an explosive discharge of air
