Orthostatic intolerance: symptoms on standing, causes and tests

When a healthy person stands up, PoTS UK explains, blood vessels narrow and the heart rate increases slightly to maintain blood supply to the heart and brain. In orthostatic intolerance this automatic adjustment does not work smoothly, so symptoms appear when upright and ease on lying down.

The term describes a pattern, and several different conditions can produce it. PoTS UK uses it as a description of the symptoms of PoTS, which it says is an abnormality of the functioning of the autonomic nervous system, the system that controls things you do not have to think about, such as heart rate, blood pressure, digestion and sweating. The NHS describes a related picture, postural hypotension, in which blood pressure falls on standing.

PoTS UK lists the following symptoms, which can affect more than the heart and circulation because the autonomic nervous system regulates many body functions.

• Palpitations, a sensation of the heart pounding in the chest.

• Dizziness, light-headedness or near fainting, usually on standing but sometimes with prolonged sitting.

• Fainting or blackouts.

• Chest pain, shortness of breath, shakiness and sweating.

• Gut symptoms such as nausea, diarrhoea, constipation, bloating and abdominal pain.

• Visual problems such as glare, blurred or tunnel vision.

• Tiredness, weakness, headaches and exercise intolerance, with brain fog in many people.

• Purple discolouration of the hands and feet in around half of patients, which PoTS UK calls "PoTS feet".

There is no single cause. PoTS UK says PoTS has been reported to start after an infection (including COVID-19), a life stressor such as pregnancy or surgery, a traumatic event or an immunisation, although the exact link with some triggers is unclear. It describes subtypes including neuropathic, hypovolaemic (low blood volume) and hyperadrenergic PoTS, which can overlap in the same person.

PoTS UK stresses that some people meet the criteria but have a reversible cause, which it labels postural tachycardia of other cause. It lists dehydration or blood loss, hormonal causes, anaemia, anxiety and panic attacks, medication side effects, recreational drugs and prolonged bed rest or deconditioning. The NHS lists causes of low blood pressure such as pregnancy, some medical conditions including diabetes, and some medicines, and says it may be low because you are fit and healthy or inherited from your parents.

PoTS UK notes that symptoms may be worsened by heat, eating (especially refined carbohydrate), standing up quickly, dehydration, the morning, periods, deconditioning or prolonged bed rest, and alcohol.

The NHS says to get your blood pressure checked if you keep getting symptoms such as lightheadedness, dizziness, feeling sick, blurred vision, weakness, confusion or fainting, and to see a GP if you keep getting dizziness and fainting. If you faint, the NHS says to see a GP even if it seems minor.

The NHS says to call 999 if someone who has fainted is not breathing, cannot be woken within 1 minute, has not fully recovered, has chest pain or palpitations, has seriously hurt themselves, is having a seizure, fainted while exercising or fainted while lying down. It also says you must tell the DVLA if you are fainting regularly.

PoTS UK says detailed questioning is the key to accurate diagnosis, with examination and appropriate tests, and that alternative causes need to be considered. It says people are often diagnosed by a cardiologist, neurologist, geriatrician or paediatrician, although a GP can also diagnose PoTS.

The investigations it lists include an ECG, the active stand test (heart rate and blood pressure measured lying down, on standing and at intervals up to 10 minutes), a head-up tilt table test, 24-hour heart rate and ambulatory blood pressure monitoring, an echocardiogram, and blood tests to rule out other conditions such as anaemia, thyroid disease, adrenal problems and coeliac disease.

The NHS notes that low blood pressure is a reading of less than 90/60mmHg and can be checked by a pharmacist, practice nurse or GP, or at home with a monitor.

PoTS UK says many people's symptoms improve with lifestyle changes, although some need medication and some have significant symptoms over many years. The NHS gives self-help for low blood pressure symptoms: get up slowly from sitting or lying, eat small frequent meals, drink more water, and avoid standing for long periods, sudden posture changes and too much alcohol. Support stockings can improve circulation, and the NHS says medicine to raise blood pressure is rarely needed.

If you feel as if you might faint, the NHS suggests lying down with your legs raised, or sitting with your head between your knees, drinking water, crossing your legs while standing or rocking up and down on your toes, and clenching your fists.

PoTS UK notes that an occasional bout of exercise can make symptoms worse, but an ongoing exercise programme may improve them, and that exercise intolerance is common, so any programme should be built gradually and ideally with specialist advice.

On the NHS, assessment often starts with a GP, who can arrange an ECG, blood tests and a standing test, with referral to cardiology or neurology if needed. PoTS UK says many healthcare professionals do not know that PoTS exists, and that taking information with you can help.

Private cardiologists and syncope clinics can offer tilt-table testing and quicker appointments. The tests are the same, and the main differences are waiting times. Before any testing, ask your clinician whether medicines should be adjusted, as PoTS UK notes decisions about stopping medication before testing should be made with the clinician arranging the test.