Upper Respiratory Tract

Acute Inflammation

Infections of the nose, nasal sinuses, pharynx and larynx are common. They are usually mild and self-limiting. Most cases are due to viral infection, but this is often followed by bacterial superinfection.

1. Viral infection

This phase is characterised by features of acute inflammation but without the exudation of neutrophils.

Viruses involved

A wide variety, of which the major types are:

2. Bacterial phase Many bacteria are commensal in the respiratory tract (e.g. Streptococcus mutans, Haemophilus influenzae) and can superinfect the damaged tissue, which then exhibits the typical features of acute inflammation including exudation of neutrophils.

The wide variety of different viruses involved prevents protective immunity.

Rhinitis

Common Cold (Acute Coryza)

This common respiratory inflammation usually involves the nose and adjacent structures.

The 2 phases, viral and bacterial, are typically seen in this disease.

The drainage from the sinuses, especially the maxillary, is often blocked by swelling of the mucosa — giving rise to sinusitis.

The infection is acquired by droplet spread of viruses by sneezing.

Allergic Rhinitis ‘Hay Fever’

An allergic (immediate type hyper-sensitivity) type of inflammation (2. p.101) is often seen. Patients develop immediate symptoms of sneezing, itching and watery rhinorrhoea.

The repeated attacks frequently lead to chronic changes in the mucosa with polyp formation.

Nasal Polyps

These form particularly on the middle turbinate bones and within the maxillary sinuses.

In the nasopharynx, the lymphoid tissue may be greatly enlarged (adenoids) and contribute to the nasal obstruction.

Allergies

Seasonal Allergy

This is due to pollens liberated from trees and grass.

Non-Seasonal Allergy

The main cause is the house dust mite, Dermatophagoides pteronyssinus. Allergy to pets is common, e.g. cats – the allergens are usually glycoproteins secreted by sebaceous glands and found in cat skin and saliva.

Vasomotor Rhinitis

This is a clinical diagnosis. The pathological changes are, to some extent, similar to those of allergic rhinitis, but the condition is more continuous, less spasmodic. Although the cause is unknown, viral infections in a polluted atmosphere (usually an urban setting) are thought to initiate the ‘sensitivity’ and non-specific stimuli such as bright light and smells precipitate an attack.

Acute Pharyngitis, Tracheitis and Laryngitis

Acute Pharyngitis and Tracheitis

Most sore throats are caused by viruses – including adenovirus and Epstein–Barr virus.

Bacteria include Streptococcus pyogenes, Haemophilus parainfluenzae and Corynbacterium diphtheriae.

Tonsillitis is a common acute inflammation, historically due to streptococcal infection but, with the introduction of antibiotics, viruses are the initiating infective agents in most cases.

Diphtheria, now uncommon in countries where vaccination is widespread, is a serious infection.

The formation of a pseudomembrane is striking.

This pseudomembrane may spread to block the larynx, causing respiratory obstruction.

The exotoxin of diphtheria is encoded by a bacteriophage (a virus which infects the bacterium). It can cause myocarditis (p.212) and neuropathy (p.569).

In Acute epiglottitis, typically due to Haemophilus influenzae, there is severe inflammation and oedema. In young children, the larynx becomes obstructed necessitating tracheostomy and administration of antibiotics.

Acute laryngitis is often due to parainfluenza viruses. Acute oedema of the glottis is seen in some cases of anaphylaxis (p.101) and angioneurotic oedema.

Other Disorders of the Larynx

Chronic Laryngitis

Cigarette smoking, repeated attacks of infection and atmospheric pollution may lead to chronic inflammation of the larynx.

Two main features are (a) changes in the lining epithelium and (b) increase in mucus secretion.

The following sequence of events tends to take place:

Tuberculosis – this can cause severe ulceration of the larynx and is usually secondary to pulmonary tuberculosis.

Vocal Cord Nodule (Singer’s Node)

They consist of squamous epithelium overlying fibrin-rich and myxoid stroma.

Tumours of the Upper Respiratory Tract

Benign Tumours

(a) Epithelial

Papillomas may be single but are often multiple and due to infection by papilloma virus. The epithelium may be one of two types:

(b) Connective tissue

Haemangiomas, especially of the nasal septum, can cause persistent nose bleeds. A special form, angiofibroma, affects male children and grows throughout childhood but typically regresses.

Malignant Tumours

These are mainly squamous carcinomas and are commonly seen in the larynx. Intraepithelial neoplasia (carcinoma-in-situ) is a frequent precursor.

Smoking and alcohol consumption are aetiologically important. The rate of growth and spread is influenced by the site within the larynx.

Nasopharyngeal carcinoma is common in Eastern countries and is associated with Epstein–Barr virus infection.

Adenocarcinoma of the nose is a rare tumour, sometimes seen in woodworkers.

Lungs – Anatomy

Acinus

This is the functional unit of the lung, where gas transfer takes place. It consists of the respiratory bronchiole and associated alveolar ducts and sacs supplied by one terminal bronchiole. There are approximately 25 000 acini in the normal adult male lung.

Lobule

This is served by one preterminal bronchiole and is the smallest anatomic compartment of lung that is grossly apparent. It contains 3 to 30 acini and is bound by connective tissue septa. These connective tissue septa may be accentuated in smokers.

The total area for air exchange is very large (equivalent to a tennis court) allowing considerable reserve capacity.

Histology of the Alveolus

Two types of cell (pneumocytes) line the alveoli:

Macrophages and mast cells are also present in the alveoli.

Pulmonary Vasculature

Respiration

The normal intake of air is around 7 litres per minute; of this, after allowing for nonfunctioning dead space (trachea, bronchi, etc.), approximately 5 litres per minute are available for alveolar ventilation. A definite flow of air is maintained as far as the terminal bronchiole. Beyond this point the actual flow ceases and gas exchange is effected by diffusion.

Three factors are involved in the maintenance of adequate respiration:

Interference with any of these factors will result in respiratory embarrassment (dyspnoea) and even respiratory failure.

Acute Bronchitis

This is an inflammation of the large and medium bronchi. The condition may be serious if associated with pre-existing respiratory disease. Mucous and serous glands in the walls of the bronchi provide abundant mucoid secretion during the inflammation. Ciliated epithelia lining the bronchi aid passage of the exudate upward and help prevent spread down to the bronchioles.

In most cases, the process is initiated by a viral or mycoplasmal infection. It is a common complication of influenza and measles. This initial phase is followed by bacterial invasion. Streptococcus pneumoniae and Haemophilus influenzae are commonest, but Staphylococcus aureus and Streptococcus pyogenes may be found, especially in infants.

The condition is usually mild, and spread to the bronchioles is unusual in healthy adults due to the effective ciliary action of the bronchial epithelium. Spread may occur however in debilitated people. Bronchiolitis and bronchopneumonia result and can prove fatal. Equally important is the serious effect of repeated attacks of acute infection in patients with chronic bronchitis (p.258).

In children:

1. Whooping cough (due to Bordetella pertussis) may cause permanent damage due to the severity of the infection and the stress on the airways during the coughing and whooping attacks.

2. Bronchiolitis in the very young (<2 years), in the majority of cases, is due to Respiratory Syncytial Virus and the risk of progression to bronchopneumonia is high.

Bronchial Asthma

In asthma, there are spasmodic attacks of reversible bronchial obstruction with wheezing and dyspnoea and often a dry cough. The prevalence has markedly increased in recent years, although has now plateaued. There are 2 main patterns:

1. Atopic asthma (p.102)

– typically starts in childhood.

– often a strong family history of asthma or atopic conditions (e.g. eczema).

– attacks provoked by predominantly IgE type I hypersensitivity reaction to inhaled allergens, e.g. pollen, cats, house mite dust.

2. Non-atopic asthma

– usually in middle age.

– usually no history of atopy: family history uncommon.

– no particular antigens incriminated.

Other varieties include occupational asthma and aspirin-induced asthma.

The basic mechanism is as follows:

ACUTE ASTHMA

Recurrent episodes of inflammation lead to irreversible damage

The histological changes are a combination of allergic reaction and muscular hypertrophy, the result of prolonged spasm.

Sputum

In some cases the following may be seen:

1. Curschmann’s spirals – appear as small white granules in sputum.

2. Charcot–Leyden crystals – in association with eosinophils.

Chronic Obstructive Pulmonary Disease (COPD)

This term describes three entities that show considerable clinical overlap:

1. Chronic bronchitis

2. Emphysema

3. Small airways disease

COPD is common and is the fourth leading cause of death worldwide.

Aetiology The main factors are:

1. SMOKING – by far the major risk factor and dose related.

2. α₁-antitrypsin deficiency. Reduced levels of this protease inhibitor correlate with lung damage, especially in smokers.

3. OCCUPATION, especially exposure to dusts, e.g. coal mining.

Chronic Bronchitis

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