The respiratory system

Anatomy and physiology

An understanding of the surface anatomy of the lungs ( Fig. 5.1 ) and their relation to closely adjacent structures is essential for the practice of respiratory medicine. At the end of tidal expiration the dome of the diaphragm extends high into the thorax to around the level of the anterior end of the fifth rib, slightly lower on the left. The lower anterior ribs therefore overlie the liver on the right and the stomach and spleen on the left, with the parietal pleura extending lower than the lungs on the lateral chest wall. Posteriorly, the lungs extend much lower, approaching the 12th rib on full inspiration.

Fig. 5.1

Surface anatomy of the thorax.

A Anterior view. B Right lateral view. C Lobar anatomy of the lung surfaces: anterior view (upper), lateral view (lower).

The lung apex lies immediately beneath the brachial plexus, so apical lung tumours commonly disrupt T1 root fibres, causing pain and numbness in the inner aspect of the upper arm and wasting of the small hand muscles. The upper thoracic sympathetic outflow to the eye may also be compromised, leading to a constricted pupil and ptosis. In the mid- and lower mediastinum, tumours can invade and compromise the pericardium, atria and oesophagus.

In health, the lungs optimise gas exchange by close matching of regional ventilation and perfusion. Airway and parenchymal lung diseases disrupt this matching, causing hypoxia and cyanosis, and commonly stimulate breathing through lung afferent nerves, leading to a history of breathlessness, and tachypnoea on examination.

The history

Patients use a wide range of terms to describe respiratory symptoms (such as infection, phlegm, catarrh, pleurisy and wheeze). These can be ambiguous and require careful definition to avoid misunderstanding. ‘Wheeze’ may be used when describing breathlessness, or ‘I had a chest infection’ may denote a breathless episode actually due to pulmonary embolism.

As with other systems, the respiratory history should start with open questions but should also specifically cover all the areas outlined in Box 5.1 .


Respiratory history taking/documentation framework

History of presenting symptoms

Specific respiratory symptoms

  • Breathlessness

  • Wheeze

  • Cough

  • Sputum/haemoptysis

  • Chest pain

  • Fever/rigors/night sweats

  • Weight loss

  • Sleepiness

Past medical history

  • Respiratory disease

  • Other illness/hospital encounters

Drug and allergy history

  • Drugs causing or relieving respiratory symptoms

  • Allergies to pollens/pets/dust; anaphylaxis

Social and family history

  • Family history of respiratory disease

  • Home circumstances/effect of and on disease

  • Smoking

  • Occupational history

Systematic review

  • Systemic diseases involving the lung

  • Risk factors for lung disease

Common presenting symptoms


Breathlessness (or dyspnoea) denotes the feeling of an ‘uncomfortable need to breathe’ and is the most commonly reported respiratory symptom. It is also one of the most challenging to quantify, being inherently subjective. Breathlessness may originate from respiratory or cardiac dysfunction, or be a manifestation of psychological distress.

Respiratory disease can cause breathlessness through a range of mechanisms:

  • stimulation of intrapulmonary afferent nerves by interstitial inflammation or thromboembolism

  • mechanical loading of respiratory muscles by airflow obstruction or reduced lung compliance in fibrosis

  • hypoxia due to ventilation/perfusion mismatch, stimulating chemoreceptors.

The Medical Research Council (MRC) breathlessness scale ( Box 5.2 ) is a useful and validated way to document the patient’s level of dyspnoea formally.


Used with the permission of the Medical Research Council.

Medical Research Council (MRC) breathlessness scale

Grade Degree of breathlessness related to activities
1 Not troubled by breathlessness except on strenuous exercise
2 Short of breath when hurrying on the level or walking up a slight hill
3 Walks slower than most people on the level, stops after a mile or so, or stops after 15 minutes walking at own pace
4 Stops for breath after walking about 100 yds or after a few minutes on level ground
5 Too breathless to leave the house, or breathless when undressing

Specific questions may help to distinguish the causes of breathlessness. Ask in particular:

  • How did the breathlessness come on? If the onset was instantaneous, think of pneumothorax, pulmonary embolus or acute allergy. Onset over hours is typical in asthma, acute pulmonary oedema or acute infections, while insidious onset occurs with developing effusions, interstitial diseases and tumours.

  • How is your breathing at rest and overnight? Asthma commonly wakes patients, while most patients with chronic obstructive pulmonary disease (COPD) are comfortable at rest and when asleep but struggle with exertion. Breathlessness provoked by lying down (orthopnoea) is a feature of heart failure ( p. 42 ) but also occurs frequently in patients with severe airflow obstruction or diaphragmatic weakness because the weight of the abdominal contents displaces the diaphragm towards the head on lying down, compromising the vital capacity.

  • Is your breathing normal some days? Variable breathlessness is the hallmark of asthma, while consistent daily limitation is typical in COPD.

  • Tell me something you do that would make you breathless? How far can you walk on a good day? This is useful for quantification and assessment of disease impact and disability. Record restrictions on normal activity or work and the corresponding MRC breathlessness score ( Box 5.2 )

  • When does the breathlessness come on? Asthma induced by exercise frequently appears only after exercise, during early recovery, because sympathetic drive during exercise defends airway patency.

Certain phrases in the history strongly suggest a psychological aetiology of breathlessness, particularly ‘I feel I can’t get enough air (or oxygen) into my chest.’ In patients with hyperventilation due to anxiety, this symptom is frequently accompanied by a normal measured vital capacity. Associated symptoms induced by hypocapnia in hyperventilation include digital and perioral paraesthesiae, lightheadedness and sometimes chest tightness.

Fig. 5.2 summarises how to use the history and examination findings to distinguish some common causes of breathlessness. Remember that patients rarely report exactly what textbooks describe.

Fig. 5.2

Common causes of breathlessness: distinguishing features on history and examination.

COPD, chronic obstructive pulmonary disease; JVP, jugular venous pressure; MI, myocardial infarction.


Wheeze describes the high-pitched musical or ‘whistling’ sounds produced by turbulent air flow through small airways narrowed by bronchospasm and/or airway secretions. It is most commonly heard during expiration, when airway calibre is reduced. Wheeze must be distinguished from the rattling inspiratory and expiratory sounds caused by loose, mobile secretions in the upper airways, and from the louder, dramatic croak of stridor (see later) caused by obstruction in the trachea or large airways.

Identifying wheeze in the patient’s history is very important, as true wheeze is typical of small airways diseases. It is most commonly associated with asthma and COPD but can also occur with acute respiratory tract infection or with exacerbations of bronchiectasis (due to a combination of airway narrowing and excessive secretions).


  • Is the wheeze worse during or after exercise? If it occurs during exercise and limits it, this suggests COPD; in asthma, wheeze and tightness usually appear after exercise.

  • Do you wake with wheeze during the night? This suggests asthma.

  • Do you have hay fever or other allergies? Atopy is common in allergic asthma. A family history of wheeze or asthma is common in asthma.

  • Is it worse on waking in the morning and relieved by clearing sputum? This is common in COPD.

  • Do you smoke? Smoking is suggestive of COPD, though patients with asthma occasionally smoke.

  • Are there daily volumes of yellow or green sputum, sometimes with blood? This suggests possible bronchiectasis.


The cough reflex has evolved to dislodge foreign material and secretions from the central airways, and may be triggered by pathology at any level of the bronchial tree. Inspiration is followed by an expiratory effort against a closed glottis. Subsequent sudden opening of the glottis with rapid expiratory flow produces the characteristic sound.

Ask about:

  • Duration of the cough.

  • Whether it is present every day.

  • If it is intrusive/irresistible or whether the patient coughs deliberately to clear a perceived obstruction (throat clearing).

  • Whether it produces sputum. If so, how much and what colour?

  • Any triggers (such as during swallowing, in cold air, during exercise).

  • Smoking. This increases the likelihood of chronic bronchitis or lung cancer.

  • Associated clinical features:

    • Wheeze: may signal cough-variant asthma.

    • Heartburn or reflux: gastro-oesophageal reflux commonly triggers cough.

    • Altered voice or swallowing: consider laryngeal causes.

  • Drug history, especially angiotensin-converting enzyme (ACE) inhibitors.

Cough productive of green or yellow sputum suggests bronchial infection. Large volumes of sputum over long periods suggest bronchiectasis. Haemoptysis is covered below.

Cough is most commonly a symptom of acute viral upper respiratory tract infections, which are usually self-limiting over days to weeks.

Cough that fails to settle over weeks may be the presenting feature of bronchial carcinoma. A history of smoking raises further suspicion of malignancy, although chronic cough is a non-specific symptom in smokers. Other investigations, including a chest X-ray, are often required to exclude early cancer. Chronic cough is defined as cough lasting more than 8 weeks and can be debilitating both physically and socially. Causes of chronic cough and features in the history that may indicate the underlying cause are summarised in Box 5.3 .


Causes of chronic cough and accompanying clues in the history

Pathophysiology Suggestive features in history/examination
Airways inflammation:
Asthma – ‘cough-variant asthma’ Affects children and some adults
Often present at night
Associated wheeze, atopy
Chronic obstructive pulmonary disease History of smoking and intermittent sputum
Persisting airway reactivity following acute bronchitis Recent acute-onset cough and sputum
Bronchiectasis Daily purulent sputum for long periods
Pneumonia or whooping cough in childhood
Recurrent haemoptysis
Lung cancer Persistent cough, especially in smokers
Any haemoptysis
Pneumonia that fails to clear in 4–6 weeks
Rhinitis with postnasal drip Chronic sneezing, nasal blockage/discharge
Oesophageal reflux Heartburn or regurgitation of acid after eating, bending or lying
Nocturnal as well as daytime cough
Drug effects Patient on angiotensin-converting enzyme inhibitors
Interstitial lung diseases Persistent dry cough
Fine inspiratory crackles at bases
Idiopathic cough Long history with no signs and negative investigations – diagnosis of exclusion

In patients with malignancy at the left hilum, damage to the left recurrent laryngeal nerve may paralyse the left vocal cord, making it impossible for the patient to close the glottis and generate a normal explosive cough. The resulting hoarse forced expiration without the initial explosive glottal opening is termed a ‘bovine cough’ and is an important symptom warning of possible hilar malignancy.


In health, the airway lining fluid coating the tracheobronchial tree ascends the mucociliary escalator to the larynx, where it mixes with upper respiratory tract secretions and saliva and is swallowed. In acute or chronic airways infection, accumulation of neutrophils, mucus and proteinaceous secretions in the airways results in cough with expectoration of sputum. Ask about the characteristics of sputum to clarify the pathology. A change in colour or consistency, or an increase in volume may indicate a new infection in chronic disease.


  • Clear (mucoid): COPD/bronchiectasis without current infection/rhinitis.

  • Yellow (mucopurulent): acute lower respiratory tract infection/asthma.

  • Green (purulent): current infection – acute disease or exacerbation of chronic disease, such as COPD.

  • Red/brown (rusty): pneumococcal pneumonia ( Fig. 5.3B ). Try to distinguish between rusty and frank red blood (see below).

    Fig. 5.3

    Sputum appearance in disease.

    A Colour chart of sputum purulence used in bronchiectasis. B Rusty red sputum of pneumococcal pneumonia. C Mucus plug from a patient with asthma.

    (A) Courtesy Medical Photography, NHS Lothian.

  • Pink (serous/frothy): acute pulmonary oedema.

In bronchiectasis, the colour of sputum may be used to guide the need for antibiotic treatment ( Fig. 5.3A ).


  • Establish the volume produced over 24 hours: small amounts into a tissue or enough to fill a spoon(s), eggcup(s) or cup(s).

  • Compare the current volume with the patient’s baseline or minimal volume.


  • An increase in stickiness (viscosity) may indicate exacerbation in bronchiectasis.

  • Large volumes of frothy secretions over weeks/months are a feature of the uncommon bronchoalveolar cell carcinoma.

  • Occasionally, sputum is produced as firm ‘plugs’ by patients with asthma ( Fig. 5.3C ), sometimes indicating underlying allergic bronchopulmonary aspergillosis.


Haemoptysis means coughing up blood from the respiratory tract. It can complicate any severe forceful cough but is most commonly associated with acute or chronic respiratory tract infections. Haemoptysis may also indicate pulmonary embolism and lung cancer. Never assume haemoptysis has a benign cause until serious pathology has been considered and excluded.

Ask about how it appeared, how much blood there was, whether there are associated features and over what time period it came on:

  • Was the blood definitely coughed up from the chest? Blood in the mouth may be vomited, may have come from the nose in epistaxis, or may appear on chewing or tooth brushing in patients with gum disease.

  • A short history of streaks of blood with purulent sputum suggests acute bronchitis.

  • A sudden episode of a small volume of blood with pleuritic pain and breathlessness suggests pulmonary embolism.

  • Recurrent streaks of blood in clear sputum should prompt a search for lung cancer.

  • Recurrent blood streaks in purulent sputum over weeks suggest possible tuberculosis or cancer with infection; over years, they suggest bronchiectasis.

  • Larger volumes of haemoptysis (> 20 mL, for example) suggest specific causes:

    • lung cancer eroding a pulmonary vessel

    • bronchiectasis (such as in cystic fibrosis)

    • cavitatory disease (such as bleeding into an aspergilloma)

    • pulmonary vasculitis

    • pulmonary arteriovenous malformation.


This harsh, grating respiratory sound is caused by vibration of the walls of the trachea or major bronchi when the airway lumen is critically narrowed by compression, tumour or inhaled foreign material. Inspiration lowers the pressure inside the extrathoracic trachea, so critical narrowing here leads to inspiratory stridor. In contrast, the intrathoracic large airways are compressed during expiration by positive pressure in the surrounding lung, leading to fixed expiratory wheeze or stridor. Large airway narrowing at the thoracic inlet (for example, tracheal compression by a large goitre) may cause both inspiratory and expiratory stridor. Rapid investigation and treatment are vital when this sign is present.

Chest pain

Chest pain may originate from musculoskeletal, respiratory, cardiovascular and gastro-oesophageal disease.


  • Site and severity.

  • Character: sharp suggests pleural pain.

  • Onset: gradual or rapid?

  • Exacerbating or relieving factors: worsening with cough or deep breaths suggests pleural disease.

  • Associated symptoms: breathlessness, fever and cough suggest an infective cause.

A large pulmonary embolus can cause angina-like chest pain ( p. 40 ), due to increased right ventricular work together with reduced coronary oxygen delivery caused by hypotension and hypoxaemia, resulting in right ventricular ischaemia.

Besides myocardial ischaemia, chest pain can arise from the chest wall, parietal pleura, mediastinal structures, tracheobronchial tree, pericardium, oesophagus and subdiaphragmatic organs (liver and gallbladder). Pain does not originate in the lung parenchyma or visceral pleura, as they have only an autonomic nerve supply.

Pleuritic pain is worse on inspiration and coughing, and is usually described as sharp, stabbing or knife-like. It is usually sited away from the midline, and may be localised or affect a wide area of chest wall. Disease causes parietal pleural pain in several ways:

  • pneumonia and pulmonary infarcts: either direct pleural inflammation or adhesions with pleural traction on respiratory movement

  • pneumothorax: mechanical distortion of pleura with lung collapse

  • lung cancer: pleural distortion by infiltration, although constant pain is more typical.

Musculoskeletal chest pain is common and may occur with chest trauma, forceful coughing or connective tissue disease. The chest is characteristically tender to local palpation, and the pain can be reproduced by respiratory movements and/or movement of the spine or shoulder muscles. There may be associated soft tissue injury or rib fractures. A detailed history of events preceding the onset is vital, as injury is easily overlooked.

Two other uncommon conditions can cause acute chest pain. Bornholm disease is an infection with an enterovirus (Coxsackie B), which causes acute but self-limiting inflammation of intercostal muscles. Episodes of unilateral severe, stabbing myalgia develop over an intercostal space and settle after a few days. Costochondritis (called Tietze’s syndrome when costochondral swelling is present) is idiopathic inflammation of the costochondral cartilages adjoining the sternum and can cause acute localised pain and tenderness. The pain settles with simple analgesia and the passage of time in both of these conditions.

Herpes zoster infection (shingles) may start with superficial itch or burning pain in a thoracic dermatome, followed by the appearance of a vesicular rash. Pain and altered sensation may persist long after the rash has resolved, often with scarring in the dermatomal distribution.

Burning retrosternal pain may indicate oesophagitis but also occurs with myocardial ischaemia. Alteration of discomfort after eating or antacids helps to distinguish oesophageal pain; cardiac pain is described on page 40 .

Central, constant, progressive, non-pleuritic chest pain may represent mediastinal disease, particularly malignancy. Similarly, chest wall pain (without trauma) that is constant, progressive and non-pleuritic suggests chest wall invasion by malignancy. Pain-induced sleep disturbance is a feature of such malignant pains.

Fevers/rigors/night sweats

These symptoms are not specific to respiratory medicine but are commonly reported by patients with respiratory diseases. Infection (acute or chronic) is the usual cause but other aetiologies such as lung cancer, lymphoma or vasculitis should also be considered.

Patients use a range of terms to describe fever (such as shivers, chills, being ‘hot and bothered’, shakes), so ask for a detailed account of their symptoms using common terms.

Rigors are generalised, uncontrollable episodes of vigorous body shaking lasting a few minutes. Despite high fever, the patient may complain of feeling cold and seek extra clothing. Rigors usually indicate bacterial sepsis; lobar pneumonia and acute pyelonephritis are the most common causes. They can be misinterpreted as seizures but the retention of consciousness and associated pyrexia suggest rigors.

Night sweats are more closely associated with chronic infection (such as tuberculosis) and malignancy or lymphoma rather than acute infection. Occasional episodes of a sweaty head or pillow are inconclusive, but if patients report having to change their nightclothes or sheets frequently due to profuse nocturnal sweating over several weeks, this is more likely to indicate underlying disease.

Weight loss

Weight loss is a common feature of several important respiratory diseases:

  • lung cancers

  • chronic infective diseases (such as tuberculosis and bronchiectasis)

  • diseases causing chronic breathlessness (such as COPD and interstitial lung diseases).

The pathophysiology is complex; however, breathlessness is associated with diminished appetite, and the systemic inflammatory response is also thought to contribute to weight loss.

Small amounts of weight loss also occur in acute infection with consequent loss of appetite, particularly during hospitalisation. Ask the patient to estimate the extent and duration of weight loss, and enquire about appetite and dietary intake. Being underweight is a poor prognostic indicator in any chronic respiratory disease.


Excessive daytime sleepiness may be a symptom of an underlying sleep-related breathing disorder (obstructive sleep apnoea (OSA) or obstructive sleep apnoea/sleep hypopnoea (OSASH)). In these conditions, frequent episodes of upper airway obstruction at night cause repeated microarousals from sleep, leading to complete disruption of normal sleep. Daytime somnolence impairs work and driving performance, causing danger to the patient and others.

Ask about:

  • Normal sleeping habit: does the patient keep hours that allow reasonable rest?

  • Shift or night work: this can disrupt and prevent healthy sleep patterns.

  • Does the person wake refreshed or exhausted? Sleep apnoea patients are exhausted in the morning.

  • Have they struggled to stay awake in the day: for example, at work or when driving?

It is vital to advise cessation of driving pending investigation if OSA is suspected.

Ideally, seek a description of any night-time breathing disturbance from a bed partner. In OSA, the partner may observe periodic cessation of breathing, accompanied by increasing respiratory efforts, followed by a sudden and loud resumption of breathing, often with postural repositioning, then repetition of this cycle.

Validated sleepiness scores (such as the Epworth Sleepiness Scale: ) can be used to quantify daytime somnolence and are helpful if considering referral to a sleep disorder clinic.

Past medical history

Past illnesses relevant to respiratory disease are summarised in Box 5.4 . These include respiratory disease that may recur or cause long-term symptoms, and disease in other systems that may cause, complicate or present with respiratory symptoms, including thromboembolic, cardiovascular, haematological, malignant and connective tissue diseases.

Dec 29, 2019 | Posted by in GENERAL & FAMILY MEDICINE | Comments Off on The respiratory system

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