In absolute terms hypotension or low blood pressure can be defined as a blood pressure lower than 80/50 mmHg. The potential causes range from dehydration to serious medical disorders and the condition itself becomes clinically important when it is associated with symptoms. The diagnosis of hypotension is based on the medical history, a physical exam and test results.

Classification of symptoms

Different forms of hypotension can be clinically classified into three groups based on their symptoms: asymptomatic chronic hypotension, chronic hypotension with multiple symptoms and orthostatic dysregulation. In contrast to arterial hypertension, low blood pressure does not lead to cardiovascular damage.

Asymptomatic chronic hypotension is not considered a disease, therefore treatment is not required. It is seen as a normal, constitutionally determined variant of circulatory regulation, often observed in trained high-performance athletes when the resting circulation is in a parasympathetic state.

In chronically or occasionally decreased blood pressure, different subjective complaints can arise as a result of insufficient circulation to the organs, but also due to the unspecific disorders of general condition. The cardinal symptom is dizziness or lightheadedness, which accounts for approximately 5 percent of primary care clinic visits.

Other symptoms include rapid tiring, lack of concentration, irritability, vertigo, nausea, sleep disorders, tinnitus (ringing in the ears), sensitivity to cold, lack of appetite, dyspnea and painful sensation near the heart. It is often hard to differentiate these symptoms from psychovegetative disorders of general condition.

In orthostatic hypotension, or orthostatic dysregulation, changes in the position (especially standing up) can decrease venous blood return to the heart, resulting in a sudden drop in blood pressure. Symptoms include feelings of vertigo, empty feeling in the head, insecurity in walking, collapse and syncope. The condition is frequent in older people with disorders of the autonomic nervous system.

Diagnosis of hypotension

A diagnosis of this condition is made when repeated blood pressure measurements show a decrease in blood pressure associated with symptoms and subjective complaints. The goal of additional diagnostic procedures is to find and underlying cause in order to determine any systemic problems and to suggest the correct treatment.

The measurement of blood pressure and heart rate while supine for at least 5 minutes and then again after standing for 1 and 3 minutes is important in establishing a diagnosis of orthostatic hypotension. Measuring both seated and standing blood pressures represents an alternative in everyday clinical practice.

The tilt table test (also known as head upright tilt test or passive head-up tilt test) records the blood pressure and heart rate on a minute-by-minute basis while the table is tilted in a head-up position at different levels. The test is important in the differential diagnosis of unexplained syncope and it has proven pivotal in understanding the hemodynamic changes related to dysautonomia.

The Valsalva maneuver is another physical examination that can be used to assess autonomic function in hemodynamics by analyzing heart rate and blood pressure. The parameters are measured after several cycles of a type of deep breathing using a noninvasive blood pressure monitoring system.

Blood tests (which should include complete blood count, vitamin B12 levels, basic metabolic panel and morning cortisol), electrocardiogram (ECG) and echocardiogram can provide additional information and sometimes aid in finding the principal cause of hypotension. Magnetic resonance imaging (MRI) can be employed to assess possible etiologies of neurogenic orthostatic hypotension.