Respiratory Diseases

Question 1

What are examples of obstructive lung diseases?

Answer 1

1. Chronic Bronchitis
2. Asthma
3. Emphysema

Question 2

What is CHRONIC BRONCHITIS?

Answer 2

Long term inflammatory condition of the lower respiratory airway

Question 3

What is the pathophysiology of chronic bronchitis?

Answer 3

• Airways become narrowed by prolonged edematous thickening of the airway linings
• Hypersecretion of mucus with chronic productive cough. The mucus cannot be satisfactorily removed, causing recurrent infections

Question 4

What is the pathophysiology of ASTHMA

Answer 4

• inflammation and histamine-induced oedema that causes thickening of airway walls
• increased mucus secretion
• Airway hyper-responsiveness as profound bronchoconstriction caused by trigger-induced spasm of the smooth muscle. This reduces airway radius in the bronchioles, increasing resistance to airflow

Question 5

Draw the vitalograph and flow volume loop and describe the effects of Asthma on the graphs

Answer 5

• Decrease in FVC and FEV1 due to early closure of small airways.
• The increased airway resistance results in reduced diameter of airways. This causes increased loss of pressure in small airways. Therefore, pressure between the small airways and pleural space reaches equilibrium at a larger lung volume. This results in early small airway closure, trapping more air in the alveoli, causing increase in residual volume.
• During inspiration, lung expands, resulting in bronchioles expanding, reducing airway resistance. This cancels out the effect of increased resistance, which results in the same PIV

Question 6

Why is there difficulty in expiration in obstructive lung diseases?

Answer 6

• Smaller airways do not have cartilaginous support. They are kept open by transmural pressure gradient
• During inspiration, the thoracic cavity expands, indirectly dilating the airways even more than expiratory dimensions like alveolar expansion. This decreases airway resistance during inspiration as compared to expiration
• Normally, small airways stay open during quiet breathing, even during active expiration when intrapleural pressure is increased. Therefore, there is low airway resistance and little frictional loss of pressure within the airways
• Airway pressure is the same as intra-alveolar pressure as air exits the alveoli and drops only slightly as air flows through airways. Airway pressure remains higher than intrapleural pressure throughout the length of the airways, so airways remain open
• Even though during active expiration, intrapleural pressure is elevated, the intra-alveolar pressure is elevated and airway resistance is still low.
• Pressure in small airways does not fall below elevated intrapleural pressure

Question 7

What are the symptoms of COPD

Answer 7

• Obstruction caused by bronchoconstriction: Excess mucus
• Difficulty during expiration due to early small airway closure and air trapping
• Reduced gas exchange as there is reduced surface area and increased diffusion distance
• Ventilation-perfusion mismatch as there is an imbalance between air in the alveolus and blood in the surrounding capillaries

Question 8

Draw the vitalograph and flow volume loop and describe the effects of COPD on the graphs

Answer 8

• Emphysema causes permanent enlargement of small airways and alveoli, resulting in reduced elastic recoil. This results in decreased FEV1 due to resistance to airflow
• Early airway closure in emphysema as there is loss of lung tissue which results in decreased lung recoil, causing intrapleural pressure to increase. This results in Decreased FVC, FEV1:FVC and increased residual volume
• Increased pressure in the pleural space cause the difference between the pressure in the small airways and pressure in intrapleural space to be smaller. Therefore, equilibrium is reached at an earlier point
• During inspiration, muscle activity is working against recoil of the lungs. In emphysema, lungs are able to inflate more easily due to decreased elastic recoil. Inspiration occurs easier and faster, causing PIF to increase

Question 9

Explain dynamic airway closure

Answer 9

• During maximal forced expiration, intra-alveolar and intrapleural pressure increases.
• This results in slight frictional loss of pressure as air exits through the airways, causing the airway pressure to fall below the surrounding elevated intrapleural pressure before the existing air reaches the level of which the airways are held open by cartilaginous rings.
• The small airways are compressed closed by the surrounding higher intrapleural pressure, blocking further expiration of air
• This occurs at low lung volumes during maximal forced expiration
• In COPD, small airways collapse at high lung volumes during expiratioin as there is magnification of pressure drop due to increased airway resistance
• Intrapleural pressure higher than normal due to emphysema and reduced elastic recoil. This causes excess air to be trapped in the alveoli behind the compressed bronchiolar segments in COPD, which reduces the amount of gas exchanged between alveoli and the atmosphere, resulting in increased residual volume

Question 10

Examples of restrictive lung disease

Answer 10

• Pulmonary Fibrosis
• Pleural effusion
• Pleurisy
• Atelectasis

Question 11

Draw the vitalograph and flow volume loop and describe the effects of asbestosis on the graphs

Answer 11

• Restrictive diseases reduces the lungs capacity to expand, affecting inspiration
• Vitalograph will show decreased FVC, Normal or increased FEV1,:FVC, no increased airway resistance
• Flow volume loop will show reduced FVC, normal PEF and decreased PIF

Question 12

What does the Vitalograph measure

Answer 12

Amount of air forcefully exhaled

Question 13

Effects of dynamic small airway closure on vitalograph

Answer 13

• During lung function test, small airways close
• The pressure in small airways fall below the intrapleural pressure. This results in slow airflow and frictional loss of pressure
• Higher pressure from pleura pushes onto the small airways, causing the small airways to collapse
• This occurs at low lung volumes in healthy people
• Remaining air that is trapped in lungs after closure is the residual volume

Question 14

What does flow volume loop measure?

Answer 14

Airflow rate during forced expiration and inspiration

Question 15

Why does PEF occur early in expiration?

Answer 15

• Elastic recoil contributes most to flow early in expiration
• Forceful expiration occurs through muscular effort and elastic recoil of the lungs
• With fully expanded lungs, elastic recoil increases, contributing most to flow early in expiration