Dyspnoea – Difficulty in breathing: Causes, Pathophysiology, Diagnosis

Article by Dr Raghuram Y.S. MD (Ay)
Dyspnoea is a medical term used for ‘shortness of breath’.
A feeling of ‘I am not able to breathe well enough’ is called shortness of breath. You feel as if your breathing or breath mechanism is suddenly cut short in the middle. This gives you a feeling of discomfort and loss of air, leads to gasping and many problems.

Definition

Definition (American Thoracic Society) – ‘A subjective experience of breathing discomfort that consists of qualitative distinct sensations that vary in intensity is called shortness of breath or dyspnoea’

The distinct sensations found during dyspnoea are –
– Effort / work to breath
– Chest tightness
– Air hunger (feeling of not having enough oxygen in our body)

Thus Dyspnoea is a condition of breathing discomfort associated with varied intensities of ‘effort to breath’, ‘chest tightness’ and ‘air hunger’

Other definitions describe dyspnea as –
Difficulty in breathing
Disordered or inadequate breathing|
Uncomfortable awareness of breathing
Experience of breathlessness (acute or chronic)

The American Thoracic Society also recommends evaluating dyspnoea by assessing the intensity of the distinct sensations, the degree of distress involved and its burden or impact on activities of daily living.

It is quite normal for dyspnoea to be associated with heavy exertion. Whenever we do a lot of work that causes exertion, we feel shortness of breath, which will settle by itself after rest. It is for shorter duration and do not bother us. In this condition, dyspnoea is normal.

Dyspnea occurring in unexpected situations or after light exertion or minimum exercise will be considered pathological and should be addressed immediately.

In 85% of cases it is due one or more of the below mentioned conditions –

• Asthma
• Pneumonia
• Cardiac ischemia
• Congestive heart failure
• Chronic Obstructive Pulmonary Disease (COPD)
• Interstitial Lung Disease
• Panic disorder
• Anxiety

Treatment typically depends on the underlying causes or diseases which are causing the shortness of breathe

Causes

Causes / Differential Diagnosis of Dyspnoea
Shortness of breath is generally caused by disorders of heart (cardiac) or lungs (respiratory system). Other systems involved could be –

• Neurological
• Musculoskeletal
• Endocrine
• Haematological
• Psychiatric

In October 2010, an online medical expert system called ‘DiagnosisPro’ listed 497 distinct causes for dyspnoea
The most common cardiovascular causes are – acute myocardial infarction and congestive heart failure

Common pulmonary causes are:

• Chronic obstructive pulmonary disease (COPD),
• Asthma,
• Pneumo-thorax,
• Pulmonary oedema and
• Pneumonia

The causes (on patho-physiological basis) can be divided into:
– An increased awareness of normal breathing such as during an anxiety attack
– An increase in the work of breathing
– An abnormality in the ventilation system

Below mentioned are some conditions which commonly present with dyspnoea –
Acute coronary syndrome
This condition presents with difficulty in breathing (shortness of breath may be the lone symptom) and retro-sternal chest discomfort (discomfort behind the central part of the chest).

Risk factors include:

• Old age
• Smoking
• Hypertension
• Hyper-lipidemia
• Diabetes

It can be diagnosed on the basis of electrocardiogram and analysis of cardiac enzymes
Treatment involves measures to decrease the oxygen requirement of the heart and efforts to increase blood flow

CHF (Congestive Heart Failure) –
Symptoms include:
– Shortness of breath on exertion
– Orthopnoea
– Paroxysmal nocturnal dyspnoea

Risk factors include:

• High dietary salt
• Medication non-compliance
• Cardiac ischemia
• Dysrhythmias
• Renal failure
• Pulmonary emboli
• Hupertension
• Infections

Treatment includes decreasing the lung congestion

COPD (Chronic Obstructive Pulmonary Disease)
COPD (emphysema or chronic bronchitis) presents with chronic shortness of breath and a chronic productive cough. It is a risk factor for pneumonia.
Treatment of acute exacerbation includes combination of anti-cholinergics, beta₂ adrenoceptor agonists, steroids and possibly positive pressure ventilation

Asthma –
Asthma is the most common reason for presenting shortness of breath in the form of emergency. It affects about 5% of the population. It is the most common lung disease in both developing and developed countries. Its symptoms are shortness of breath (dyspnoea), wheezing, tightness in the chest, and a non-productive cough.
Treatment includes inhalation of corticosteroids (children) and short acting bronchodilators (acute symptoms)

Pneumothorax
It presents with pleuritic chest pain of acute onset and shortness of breath. It doesn’t improve with oxygen. Physical findings include absence of breath sounds on one side of the chest (on auscultation), jugular venous distension and tracheal deviation

Pneumonia
Symptoms include shortness of breath (dyspnoea), fever, productive cough and pleuritic chest pain. On examination (auscultation) crackles can be heard on inspiration. A chest X-Ray helps in differentiating it from congestive heart failure.

Severity and prognosis of pneumonia can be estimated from CURB65, where C=Confusion, U=Uremia (>7), R=Respiratory rate (>30), B=BP (<90), 65=Age (>65)
Treatment includes administration of antibiotics since the cause is usually a bacterial infection

Pulmonary Embolism
This condition classically presents with an acute onset of shortness of breath. Other symptoms include fever, cough, haemoptysis and pleuritic chest pain. Risk factors include DVT (deep vein thrombosis), previous thrombo-embolism, cancer and recent surgery. Wells Score is often used to assess the condition.

Treatment includes administration of anti-coagulants, presence of low BP (ominous signs) may warrant use of thrombolytic drugs

Anaemia
Anaemia caused by low Hb levels (low haemoglobin levels) is often a cause for dyspnoea.
Anaemia presents with:

• Exertional dyspnoea
• Fatigue
• Weakness
• Tachycardia
• Headaches
• Numb sensation in their head
• Blurred vision
• Loss of concentration and focus
• Language faculty impairment
• Memory loss
• Heart failure

Excessive menstruation can contribute to anaemia leading to dyspnoea in women.

Other causes of Dyspnoea

• Cardiac tamponade – presents with dyspnoea, tachycardia, elevated JVP and pulsus paradoxus
• Anaphylaxis – typically begins over a few minutes in a person with a previous history of the same. Symptoms include urticaria, throat swelling and gastrointestinal upset.
• Interstitial lung disease – presents with gradual onset of shortness of breath, typically with a history of predisposing environmental exposure.
• Panic attacks – typically present with hyperventilation, sweating and numbness
• Pulmonary hypertension
• Empty nose syndrome
• Pregnancy – around 2/3 of women experience shortness of breath as a part of a normal pregnancy

Neurological conditions causing dyspnoea –

• Spinal cord injury
• Guillain-Barre Syndrome (GB Syndrome)
• Amyotrophic lateral sclerosis
• Multiple sclerosis
• Muscular dystrophy

Pathophysiology

Patho-physiology of Dyspnoea
Dyspnoea or shortness of breath occurs through different pathways. They include ASIC, chemo-receptors, mechanoreceptors and lung receptors.

3 main components contribute to dyspnoea. They are:
-Afferent signals
-Efferent signals and
-Central information processing

Both the afferent signals (need for ventilation) and efferent signals (physical breathing) reach the central processing unit located in the brain. This location compares and analyses both these signals. When there is a mismatch between both signals it leads to ‘shortness of breath’ or ‘dyspnoea’.

Afferent signals are the sensory neuronal signals that move towards the brain. Afferent neurons arise from large number of sources including the carotid bodies, medulla, lungs and chest wall. Chemo-receptors in carotid bodies and medulla supply information regarding the blood gas levels of oxygen, carbon dioxide and hydrogen ions.

In the lungs – J receptors (juxtacapillary receptors) are sensitive to pulmonary interstitial oedema, while the stretch receptors signal broncho-constriction. Muscle spindles in the chest wall signal the stretch and tension of the respiratory muscles. This leads to various events all of which could contribute to a feeling of dyspnoea. They are:

Poor ventilation – leading to hypercapnia
Left heart failure – leading to interstitial oedema leading to impairment of gas exchange process
Asthma – causing broncho-constriction which leads to limited airflow
Muscle fatigue – leading to ineffective respiratory muscle action

Efferent signals – these signals descend downwards from the brain and bring commands to the respiratory muscles suggesting them how to respond. The most important respiratory muscle is diaphragm. Other muscles include the external intercostals muscles, internal intercostals muscles, abdominal muscles and the accessory muscles of breathing.

When the brain receives afferent information relating to ventilation, it compares it to the current level of respiration as determined by the efferent signals. If the level of respiration is inappropriate for the body’s status then dyspnoea might occur.

Psychological dyspnoea – some people are aware of their breathing in such circumstances but do not experience the distress typical of dyspnoea.

Diagnosis, Evaluation

Diagnosis and Evaluation of Dyspnoea
Initial approach to dyspnoea evaluation –
Assessment of airway, breathing and circulation
Thorough medical history
Thorough physical examination

Evaluation of Dyspnoea according to mMRC breathlessness scale

Signs that represent significant severity –

• Hypotension
• Hypoxaemia
• Tracheal deviation
• Altered mental status
• Unstable dysrhythmia
• Stridor
• Intercostals in-drawing
• Cyanosis
• Tripod positioning
• Pronounced use of accessory muscles (sterno-cleido-mastoid and scalene muscles) of breathing and
• Absent breath sounds

Blood tests
D-dimer – used to rule out a pulmonary embolism
Brain natriuretic peptide – low levels used to rule out congestive heart failure (high levels also supportive of diagnosis, but it may also be due to advanced age, renal failure, acute coronary syndrome or large pulmonary embolism)

Imaging –
Chest X-ray – is useful to confirm or rule out pneumothorax, pulmonary oedema, or pneumonia. Spiral computed tomography with intravenous radio-contrast is the imaging study of choice to evaluate for pulmonary embolism.

Epidemiology

Shortness of breath is the primary reason 3.5% of people present to the emergency department in the United States
Among these, 51% are admitted to hospital and 13% are dead within a year
According to some studies, up to 27% of people suffer from dyspnoea while in dying patients 75% will experience dyspnoea
Acute shortness of breath is the most common reason people requiring palliative care visit an emergency department

Etymology

The English word ‘dyspnea’ comes from Latin word ‘Dyspnoea’, from Greek dyspnoea, from dyspnoos, which literally means ‘disordered breathing’.

Related terms –

• Eupnea – Good Breathing
• Dyspnea – Bad Breathing
• Tachypnea – Fast Breathing
• Bradypnea – Slow Breathing
• Orthopnea – Upright Breathing
• Platypnea – Supine Breathing
• Hyperpnea – Excessive Breathing
• Hypopnea – Insufficient Breathing
• Apnea – Absent Breathing

Treatment

The primary treatment is directed at addressing the underlying cause causing shortness of breath or dyspnoea
For those with hypoxia, administration of extra oxygen is essential and effective (not effective in those having normal blood oxygen saturations)

Physiotherapy – people with neurological and or neuromuscular abnormalities may have breathing difficulties due to weak or paralyzed muscles needed for breathing and ventilation. The physical therapy interventions include –

Active assisted cough techniques
Volume augmentation such as breath stacking
Education about body position and ventilation patterns
Movement strategies to facilitate breathing

Palliative treatment

• Immediate release opioids
• Long acting or sustained release opioids
• Midazolam
• Nebulised opioids
• Use of gas mixtures
• Cognitive behavioural therapies

Click to consult Dr Raghuram Y.S. MD (Ay)