Why do infants wheeze?

Question 1

How do the foetal lungs change over 36+ weeks in utero?

Answer 1

weeks 4-8: embryonic 
weeks 5-18: pseudoglandular 
weeks 16-27/28: canalicular 
weeks 24-38: saccular 
weeks 36+: alveolar

Question 2

At which week in utero does the surfactant system begin to kick in?

Answer 2

~26 weeks

Question 3

What is a common feature of bronchiectasis on a CT?

Answer 3

Signet ring sign = when the dilated bronchus and accompanying pulmonary artery branch are seen in cross-section.

Question 4

What is a wheeze? How can it indicate a mild or severe obstruction?

Answer 4

Musical lung sound
Frequency of a wheeze will depend on the degree of anrrowing, elasticity of airway wall and local airflow
Mild obstruction = wheeze during expiration
Severe obstruction = wheeze during inspiration AND expiration

Question 5

What causes a wheeze during expiration/inspiration?

Answer 5

Expiration = Intrathoracic airway obstruction
Inspiration = Intrathoracic airway expansion (wheeze is not usually heard) OR extrathoracic airway obstruction

Question 6

What are the risk factors for ‘preschool wheeze’

Answer 6

Smoking during pregnancy
Younger mother
Pollution

Question 7

What is a transient early wheeze? What is the cause? Does normal lung function return?

Answer 7

Wheeze only during first 3 years of life
Due to infant being born with low lung function and tendency to develop “twitchy”/hyperactive airways with colds
Normal lung function returns by the age of 11

Question 8

How many infants with atopic asthma will develop recurrent wheezing later in life?

Answer 8

1/3

Question 9

How does a non-atopic wheeze usually start? How does a non-atopic wheeze usually progress?

Answer 9

usually starts with symptomatic lower respiratory tract viral infections (e.g. RSV, bronchiolitis)
continue to wheeze beyond 3rd year
most will outgrow this condition; if not will progressively lose lung function over time

Question 10

What is the difference between an asthmatic person and non-asthmatic person at a cellular level?

Answer 10

Non-asthmatic:

• epithelium is intact
• no thickening of subbasement membrane
• no cellular infiltrate

Asthmatic:

• goblet cell hyperplasia
• thick subbasement membrane
• cellular infiltrate

Question 11

What steps are involved in ‘preschool wheeze’ treatment?

Answer 11

Step 1: inhaled short-acting beta-2 agonist
Step 2: inhaled steroid 200-400 mcg/day OR leukotriene receptor antagonist (LTRA) fi steroids cannot be sued
Step 3: consider LTRA or add in an inhaled steroids if on LTRA alone
Step 4: refer to respiratory paediatrician

Question 12

What are the differential diagnoses of a ‘preschool wheeze’?

Answer 12

1. Bronchogenic cysts: large cystic abnormality
   - thin walled with ciliated columnar lining
   - may contain cartilage, smooth muscle
   - some have gastro-oesophageal mucosa
   - air-filled or fluid-filled
   Presents:
   - early with resp. distress
   - late with infection OR
   - asymptomatic
2. Hyperinflation of entire left upper lobe:
3. Congenital lobar emphysema:
   - overdistension of lobe
   - partial bronchial obstruction
   - ball valve effect