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