When pressure levels are too low

Answer: The term arterial hypotension defines the opposite condition to that of excess pressure values described in the previous section. Its definition of arterial hypotension applies to all conditions characterised by pressure values below 100 mmHg. In the definition of hypotension, the minimum blood pressure value is irrelevant, although in clinical terms an excessive reduction in it may play a potentially negative role. The diagnosis of hypotension is based on the same principles that commonly apply to blood pressure measurement, although in this situation the limitations of measurement are inherent in the instrumentation that is more accurate in measuring normal or elevated values.

The development of hypotension can have a multiple origin involving mechanisms that are part of both normal blood pressure control and the pathological realm of disease. The occurrence of reduced blood pressure values is frequent in adolescents of both sexes, but especially in the female sex in which the occurrence of systolic blood pressure values below 100 mmHg is very common and usually well tolerated due to an adaptation of the characteristics of the cardiovascular system that tend to diminish after the menopause leading to a progressive increase in blood pressure values. Hypotension often develops when the subject assumes the upright position, leading to the condition known as orthostatic hypotension, which can be diagnosed by making the subject assume the upright position for a period of 1 to 3 minutes and checking the blood pressure values at regular intervals and the possible appearance of symptoms correlated with the fall in pressure. When assessing blood pressure on an outpatient basis, the search for orthostatic hypotension should always be considered, especially when first assessing any subject whose medical history is unknown. In some patients the development of orthostatic hypotension depends on the functional insufficiency of the reflex arc that controls the relationship between pressure reduction and heart rate increase, a mechanism that underlies the stability of blood pressure levels when standing upright. The same basic mechanism is also responsible for the development of hypotension in emotional situations or after copious libations that cause a failure of the nerve reflex to adapt and the fall in blood pressure sometimes complicated by a real transient loss of consciousness.

However, the most common form of hypotension with clinical relevance is that induced by drugs, especially anti-hypertensives, which can lead to an excessive reduction in blood pressure, especially when administered in excessive doses or in inappropriate combinations in qualitative and quantitative terms. The latter phenomenon is nowadays relatively frequent due to the high percentage of patients taking polypharmacotherapies due to the need to treat several concomitant clinical conditions that involve the use of drugs capable of influencing blood pressure values without qualifying as anti-hypertensives.

From a diagnostic point of view, identifying the presence of arterial hypotension is relatively simple using a traditional manual or automatic instrument, especially if it is associated with specific symptoms such as dizziness, excessive tiredness, visual disturbances, increased heart rate, skin pallor, cold and sweaty skin. In some cases, the use of ambulatory 24-hour blood pressure monitoring (ABPM) is necessary, especially for patients in whom the symptoms compatible with the presence of arterial hypotension develop during the day in an unpredictable manner, while the blood pressure values measured in the baseline condition are perfectly controlled. This implies that pressure monitoring can be taken into consideration not only for the diagnosis of hypertension and its forms characterised by asymmetry of blood pressure values, but also in all those situations in which unexplained symptoms develop on the basis of the blood pressure values measured in outpatient clinical practice or home evaluation. A last mention of the fact that arterial hypotension can be the prevalent symptom of certain cardiac and vascular diseases such as heart failure, septic shock, severe anaemia, dehydration, myocardial infarction and many others in which, however, the reduction in blood pressure values is only one of the manifestations of a complex clinical picture in which the problem of blood pressure control appears to be an epiphenomenon rather than a primary and autonomous mechanism