Non-respiratory causes of breathlessness – London & Surrey

Non-respiratory causes of shortness of breath include heart disease, anaemia, thyroid problems, obesity, reduced physical conditioning and anxiety. Breathlessness can therefore continue even when a chest X-ray or basic lung-function test is normal.

Breathing depends on more than the lungs. Your heart must circulate blood, the blood must carry enough oxygen, and your muscles need to use that oxygen efficiently. A problem at any stage can make everyday activity feel harder.

This article explains causes outside the lungs and how they are investigated. It also covers breathing pattern disorder, which affects how you breathe and can occur with or without lung disease.

When shortness of breath needs urgent help

Call 999 if you have:

• Severe breathing difficulty, including gasping, choking or being unable to get words out.
• A tight or heavy chest, or pain spreading to your arms, back, neck or jaw.
• Sudden confusion, or skin or lips becoming blue, grey or very pale.
• Heart palpitations happening now with shortness of breath, chest pain, feeling faint or fainting.
• Coughing up more than a few spots or streaks of blood, or coughing up blood with breathing difficulty, a very fast heartbeat, or chest or upper back pain.

Do not drive yourself to A&E.

Contact NHS 111 urgently for new or increased breathing difficulty without the emergency features above, pain or swelling in one leg, or a few small spots or streaks of blood in your phlegm. If palpitations with breathlessness, chest pain or faintness have now stopped, ask for an urgent GP appointment or contact NHS 111.

Follow the NHS advice on shortness of breath. Do not wait for a routine appointment if you are acutely unwell.

Common non-respiratory causes of breathlessness

Several conditions can affect oxygen delivery, the effort of breathing or how your body responds to activity. More than one contributor may be present, and a non-respiratory condition can coexist with lung disease.

Heart failure

Heart failure means the heart is not pumping blood as effectively as it should, or is not filling normally. It does not mean the heart has stopped. Pressure can build up in the circulation, sometimes causing fluid to collect in the lungs and legs.

Clues include breathlessness on exertion, swollen ankles, difficulty breathing when lying flat, needing extra pillows or waking during the night feeling short of breath. These symptoms can have other explanations, but they warrant assessment.

An NT-proBNP blood test helps guide investigation when heart failure is suspected. A raised result can lead to specialist assessment and an echocardiogram, an ultrasound scan of the heart. The result needs clinical interpretation because other conditions and treatments can affect it. A low level in an untreated person makes heart failure less likely, but does not settle every case. NICE guidance on diagnosing heart failure explains this pathway.

Coronary heart disease

Reduced blood supply to the heart muscle can cause breathlessness during activity, sometimes with chest pressure or discomfort. Some people have little obvious chest pain.

Symptoms may appear predictably with exertion and improve with rest. New symptoms, a change in the pattern or symptoms at rest can be more concerning. Do not push through breathlessness associated with chest discomfort; follow the urgent-help advice above.

Heart rhythm problems

Atrial fibrillation and other rhythm disturbances can make the heart beat too quickly, too slowly or irregularly. They may cause breathlessness with palpitations, dizziness, weakness or reduced exercise tolerance.

An electrocardiogram, or ECG, records the heart’s electrical activity. If episodes come and go, a normal ECG between symptoms may not identify the problem. Longer monitoring can sometimes capture an intermittent rhythm disturbance.

Our guide to heart tests for breathlessness explains what an ECG, echocardiogram and other investigations can show.

Anaemia and iron deficiency

Anaemia means there is less haemoglobin than expected in the blood. Haemoglobin carries oxygen, so anaemia can make you breathless when walking, climbing stairs or exercising, even when the lungs themselves work normally. Fatigue, palpitations, pallor or headaches may accompany it.

A full blood count checks for anaemia. Ferritin and other iron studies may help identify iron deficiency, but not every type of anaemia is caused by low iron. Other possibilities include vitamin deficiencies, chronic disease or kidney problems.

Finding the cause matters as well as replacing the missing iron. Heavy periods, gastrointestinal blood loss and difficulties absorbing iron are among the possibilities. Unexplained iron-deficiency anaemia in men and postmenopausal women needs investigation for an underlying cause, as set out in the British Society of Gastroenterology guidance.

Iron deficiency can also exist without anaemia. Its significance depends on the wider clinical picture, so taking supplements without appropriate testing may miss the reason for the symptoms.

Thyroid disease and other medical conditions

An overactive thyroid can increase metabolic demand and cause a fast or irregular heartbeat, making activity feel more difficult. An underactive thyroid may contribute through reduced muscle performance and other effects. Thyroid-function blood tests can be useful when breathlessness remains unexplained.

Kidney disease can contribute through anaemia, fluid retention or changes in blood chemistry. Less commonly, disorders affecting nerves or muscles can weaken the diaphragm and other breathing muscles. Difficulty breathing when lying flat, a weak cough or other muscle weakness should be mentioned during assessment.

These conditions are not identified by a chest X-ray alone. The history, examination and selected blood or physiological tests determine which possibilities need investigation.

Obesity and physical deconditioning

Excess body weight can increase the effort of breathing and reduce the space available for lung expansion, particularly when lying down. It can also coexist with asthma, sleep apnoea or heart disease.

Deconditioning means a reduction in physical fitness, sometimes after illness, surgery, injury or a long period of inactivity. Muscles become less efficient, so previously manageable tasks demand more effort and breathing feels harder.

Both can contribute to shortness of breath, but neither should be assumed to explain a new symptom without assessment. After the cause is understood, an individual plan may include rehabilitation, appropriate activity and weight-management support.

If exertion produces a delayed worsening of symptoms, especially after COVID-19, explain this before starting an exercise programme. That pattern needs a different approach from simply increasing activity to rebuild fitness.

Anxiety and panic attacks

Anxiety can change breathing rate, muscle tension and awareness of breathing. A panic attack may cause a racing heart, chest tightness, dizziness and the sensation of not getting enough air.

Breathlessness itself can also create anxiety, making the two reinforce each other. The symptoms are real. However, new, worsening or unexplained breathlessness should not automatically be attributed to anxiety, particularly when there are other symptoms or a clear decline in exercise capacity.

Breathing pattern disorder

Breathing pattern disorder, sometimes called dysfunctional breathing, involves a change in the rhythm or mechanics of breathing. It is a breathing problem rather than a disease of the lung tissue, and is considered alongside both respiratory and non-respiratory causes.

Symptoms may include frequent sighing, upper-chest breathing, an unsatisfying deep breath, chest tightness or episodes of tingling and light-headedness. It can follow illness or develop alongside asthma, stress or anxiety, but it does not necessarily mean someone has an anxiety disorder.

An appropriate assessment looks at the breathing pattern and checks for other explanations. Specialist respiratory physiotherapy and breathing retraining can help selected patients. UCLH explains breathing pattern disorder and its management.

When it coexists with asthma, both need attention. Increasing inhaler treatment alone may leave symptoms unresolved if the breathing pattern is also contributing.

Reflux and throat symptoms

Gastro-oesophageal reflux can irritate the throat and contribute to cough, throat clearing, a hoarse voice or an uncomfortable sensation around breathing. Reflux can also worsen airway symptoms in some people with asthma. Nasal blockage can make breathing feel harder and disturb sleep.

These symptoms deserve assessment in context. Reflux or nasal disease should not automatically be used to explain persistent breathlessness during exertion, and treating them may not address another coexisting condition.

Medicines

Some medicines can contribute to breathlessness by affecting heart rate, breathing control or the lungs. A medication review is particularly useful if symptoms began after starting treatment or changing a dose. Medication-related lung disease is a respiratory cause even when the medicine was prescribed for another condition.

Bring a list of prescribed medicines, inhalers, over-the-counter treatments and supplements to the review. Do not stop a prescribed medicine without advice from the prescriber.

Pregnancy

Pregnancy can increase awareness of breathing through hormonal and physical changes. Nevertheless, sudden, worsening or unusual breathlessness needs prompt assessment and should not simply be dismissed as a normal part of pregnancy.

Call 999 for severe breathing difficulty, or breathlessness with chest pain, fainting or swelling in one leg. For other concerning changes, contact your maternity team or NHS 111 promptly.

Breathlessness after COVID-19 or another illness

Persistent symptoms may have several contributors. These can include reduced conditioning, breathing pattern disorder, anaemia, heart or circulation problems, as well as respiratory causes.

Tell your clinician if standing brings on palpitations or dizziness, or if physical or mental effort causes symptoms to worsen later that day or over the following days. These details can change the investigation and rehabilitation plan. UCLH guidance on returning to activity after COVID-19 emphasises an approach based on individual symptoms and tolerance.

Normal initial tests do not make persistent symptoms unimportant. Equally, a previous COVID-19 infection should not prevent investigation for a new or treatable condition.

Clues that can guide assessment

Symptom pattern	Possibilities to consider
Worse lying flat, with swollen ankles or waking breathless	Heart failure, as well as some respiratory or muscle conditions.
Palpitations with dizziness or episodic breathlessness	A heart rhythm problem or another cause of a fast heartbeat.
Fatigue, pallor or heavy menstrual bleeding	Anaemia, including iron-deficiency anaemia.
Frequent sighing, tingling or an unsatisfying breath	Breathing pattern disorder or anxiety, after appropriate assessment.
Reduced activity following illness or injury	Deconditioning, potentially alongside other medical causes.

These patterns are clues, not diagnostic rules. Finding one contributor does not necessarily explain every symptom. If symptoms are happening now, the urgent-help advice above takes priority.

What happens during an assessment?

A clinician will ask about the onset, triggers and progression of symptoms, as well as smoking, medication, recent illness and relevant family history. Examination may include your heart and lungs, pulse, blood pressure, oxygen saturation and any ankle swelling.

Initial investigations can include:

• An ECG to assess the heart’s electrical activity.
• A full blood count to check for anaemia.
• Kidney-function and thyroid-function blood tests when appropriate.
• Ferritin or other iron studies if iron deficiency is suspected.
• An NT-proBNP blood test if heart failure is suspected.
• Chest imaging and lung-function testing because lung and non-lung conditions can coexist.

Further investigation may involve an echocardiogram, longer heart-rhythm monitoring or specialist review. Cardiopulmonary exercise testing, or CPET, can sometimes help when breathlessness remains unexplained after initial investigations by assessing the response of the heart, lungs and muscles during exercise.

The aim is to choose tests that answer a clinical question. You will not necessarily need every investigation. Our guide to tests for unexplained breathlessness explains the main options and what they can show.

Frequently asked questions