Blood pressure values

Arterial pressure represents the force exerted by the blood on the walls of the arteries in which it flows. The input is given by the "cardiac pump", during the left ventricular systole, at the end of which the support of the elastic return of the arteries intervenes. These vessels of greater caliber, thanks to the presence of elastic and muscular tissue, facilitate blood progression and contribute to regulating the flow. The pressure imparted by the heart to the blood mass relaxes the arterial walls, which accumulate elastic energy to be released in the next phase of diastole (ventricular relaxation). The energy accumulated during the systole is then slowly released to the blood column directed to the periphery; in this way the arteries contribute to transforming the intermittent blood fleets, coming from the heart, into a continuous (laminar) flow, essential for allowing normal exchanges at capillary level.

If the walls of the arteries were rigid, the systolic pressure would rise rapidly, then leaving room for an equally sharp drop in pressure in the diastolic phase. This is the reason why aging, and the different pathological states (such as atherosclerosis) that lead to loss of vasal elasticity, are accompanied by an increase in blood pressure (hypertension).

In large and medium-caliber arteries, however, arterial pressure preserves a pulsatile pattern, which varies with the phases of the cardiac cycle: it is maximum during systole, and minimum during diastole.

Systolic pressure = pressure in the vessels during the ventricular systole (max)

Diastolic pressure = pressure in the vessels during ventricular diastole (min)

Differential or pulsatory pressure = difference between systolic and diastolic pressure.

Factors that influence the pressure values

1) strength developed by myocardial contraction during systole

2) blood mass expelled from the ventricle during systole

3) vascular resistance that the blood mass must overcome

4) distensibility of the vessels in which blood flows

5) volume (blood volume).

Accordingly, the pressure values:

• they increase as the volume of circulating blood increases (hypernatremia), while they decrease before a reduction in the total plasma volume (hemorrhage, dehydration, orthostatic hypotension, edema);

• They increase as the hematocrit increases (because the blood is more viscous);

• They increase with increasing cardiac output, which in turn increases with increasing frequency and force of contraction of the heart. The cardiac output is in fact given by the amount of blood pumped by each ventricle in a minute; it is therefore expressed in liters / minute and is calculated with the formula Gs x f. Gs represents the systolic or pulsatory range, ie the volume of blood expelled at each heartbeat from a ventricle, and f the heart rate, ie the number of beats per minute. The systolic range Gs, in turn, is given by the end-diastolic ventricular volume (amount of blood present in the ventricle at the end of the diastole or filling) minus the end-systolic ventricular volume (quantity of blood that remains in the ventricle at the end of the systole or emptying);

• They increase if at the peripheral level there is an important obstacle to the free flow of blood in the vessels, for example due to the presence of atherosclerotic plaques or to the violent contraction of a muscle during a physical exercise;

• They increase in exposure to cold, which causes vasoconstriction, while they decrease when taking a hot bath, a sauna or a Turkish bath;

• They increase in situations of strong psychophysical stress, due to the massive release of catecholamines that restrict the caliber of many arterioles, such as those of the skin.

• They increase with increasing rigidity of the vessels in which blood flows;

• They decrease with increasing section and length of vessels in which blood flows (although the vessels of greater section are those close to the heart, such as the aorta, the total area is maximum at the peripheral level, given the myriad of very fine capillaries supplying the various tissues, consequently the arterial pressure is maximum at the aortic level and minimum at the capillary level). The most important factor that changes arterial pressure is given precisely by the radius of the vessels.

During aging the pressure values ​​tend to increase especially because there is a loss of elasticity of the arteries, due mainly to the formation of the so-called atherosclerotic plaques (dangerous deposits consisting essentially of lipids, platelets, smooth muscle cells and white blood cells, which are formed in the inner lumen of the arteries of medium and large caliber).

Why is high blood pressure dangerous?

When a person suffers from high blood pressure the vessel walls are forced to withstand strong stresses which, when they become particularly high, can cause them to break. During a hypertensive crisis, the pressure exerted by the blood on the vessel walls is so high that it can flatten them or even break them; it is a bit like when, watering the vegetable garden, we hinder the escape of water with a finger to increase the length of the jet. All of this puts into an important effort the motor that draws water from the well (in this case our heart), but also the walls of the conductor tube (in this case the blood vessels), which in extreme cases can give way and crack. The heart, which is forced to contract against such high resistance, may instead "give in" (heart attack) due to excessive effort.

There are various physiological conditions that modify blood pressure:

• sex, as the woman has a blood pressure 5-7 mmHg lower than that of man;

• age, because with age there are changes in arterial pressure as the walls of the arteries become less distensible;

• racial factors, for example black individuals have higher blood pressure than whites;

• physical activity, as the pressure increases during physical activity;

• changes in body position, since passing from the upright to orthostatism there is a mainly increase in diastolic (see orthostatic hypotension);

• digestion, during which it increases;

• sleep decreases during REM, while it increases during sleep;

• emotional states (fear, anger) lead to an increase due to orthosympathetic intervention.

Normal pressure

Normal range of blood pressure values ​​in the various age groups