All About Health

General Information On Blood Pressure

The blood pressure is the pressure of blood in the streets. Also referred to as blood pressure because this pressure is the force exerted by blood against the walls of arteries, it stretches the artery wall (see article Mechanical tension), strictly speaking, the “tension” arises from ‘pressure’ and the ‘ elasticity of the wall.

The international unit for measuring pressure is the Pascal (Pa). However, the use that blood pressure is often measured in inches of mercury (cmHg), sometimes in millimeters of mercury (mm Hg).

It is expressed by two measures:

• The maximum pressure during the contraction of the heart ( systole )
• The minimum pressure at the time of “relaxation” of the heart (diastole).

If one sets the voltage in the form of a single figure, without unity, then this is the mean arterial pressure (MAP) expressed in mmHg. It is calculated as follows:

MAP = (systolic pressure + 2 × diastolic pressure) / 3

Note: in colloquial language (e.g. the doctor), the voltage is indicated by two numbers corresponding to the systolic pressure followed by diastolic pressure expressed in cmHg ; example “twelve / eight” is not 12.8 but pressure 12 cm Hg systolic and diastolic pressure of 8 cm Hg, and is usually displayed on a meter with the numbers 120 and 80 mmHg.

Changes in physiological

Blood pressure is the result of complex interactions between different systems. For simplicity, we can compare the fluid mechanics with the electric circuit and Ohm’s law: U = R × I:

• U corresponds to the difference in pressure between two places;
• I , electrical current can be compared to blood flow, it depends on the pump function of the heart and the total amount of blood in the body (called the blood volume ):
• Cardiac pump function depends directly on the frequency of contraction, but also the strength of the latter;
• Blood volume is the result of a balance between water intake and physiological losses (urine, feces, sweat, breath);
• R , resistance, actually corresponds to the resistance of small vessels to the flow of blood
• If they shrink ( vasoconstriction ), the resistance rise;
• Instead, they expand (vasodilation), the resistance decrease.
• Other physiological features: Pulse pressure and differential pressure, Poiseuille law.

The regulatory mechanisms are of type:

• Nervous vasodilation by the vagus nerve to slow the heart rate
• Humoral (that is to say, by producing chemicals that are spread throughout the body and act as distance):
• Adrenaline and noradrenalin (produced by the adrenal gland medulla) involving inter alia an acceleration of the heart.
• The renin-angiotensin-aldosterone system, causing vasoconstriction of the renal arteries, renin produced in the juxtaglomerular cells, allows the conversion of angiotensinogen (produced by the liver) to angiotensin.
• Anti-diuretic hormone (ADH or vasopressin peptide produced in the neurohypophysis).

Factors tissue vasodilators:

This explains the great variability of blood pressure values from one minute to another in the same individual: basically, the effort and stress are increasing blood pressure, lowers the rest.

The blood pressure measurement is subject to many artifacts , it should ideally be taken lying down, the patient is at rest, we must not ignore the “white coat effect” (the patient’s blood increases due to the nervousness induced by the measure). We should verify the adequacy of the size of the cuff and the arm, if the first is too small, we may have a false elevation of blood pressure values (effect “big arm”).

Measuring

Appliances

Sphygmomanometer classic stethoscope.

Automatic Blood Pressure Wrist indicating systolic and diastolic.

It is conventionally made by an inflatable cuff connected to a circular gauge, called sphygmomanometer or blood pressure cuff. The first aircraft of this type has been described by Dr. Scipione Riva-Rocci December 10, 1896 in the Medical Gazette of Turin.

The current instrument is placed in the arm. A stethoscope is placed at the elbow to listen to the brachial artery. Inflate the cuff to a pressure higher than the maximum pressure; the artery of the arm is then occluded. It then deflates it very gradually and when the air pressure equals the systolic pressure (or maximum), the artery opens intermittently as manifested by the appearance of a knocking noise in the stethoscope; these sounds, called “sounds Korotkoff “are due to turbulent blood flow, hampered by the pressure of the cuff. Pulses are also important perceptible by the patient and the examiner. When cuff pressure falls below the minimum pressure (diastolic), the artery is then permanently open: the laminar flow becomes turbulent and auscultatory sounds disappear.

This is the method by “counter pulsation.

We can also estimate the pressure without a stethoscope, but less precise:

pulsation of the artery are reflected in the cuff, the cuff pressure oscillates between the systolic and diastolic pressure, when the cuff is deflated, it is therefore the pressure at which the gauge starts to oscillate (systolic pressure) and one to which the needle stops oscillating (diastolic pressure);

taking the pulse of the radial arm compressed when the cuff is compressed, it does not receive the pulse when the cuff deflates, the pressure at which the pulse appears is the systolic pressure (this method does not have diastolic pressure).

The association manual sphygmomanometer and stethoscope is increasingly being replaced by automated devices ( sphygmomanometers electronic ) with a cuff inflated by a motor and detection of noise or by a microphone (auscultatory method), or amplitude variations of pulse wave (oscillometric method). These devices allow for repeated measurements and monitoring in near real time blood pressure.

One can also measure blood pressure using the same techniques but this time the wrist and even finger. This is not however the reference method.

When a couple electronic sphygmomanometer to a battery and a memory, we can then take the blood pressure repeatedly during 24 h: the MAPA (= monitoring ambulatory blood pressure also falsely called Holter blood pressure ).

In some cases, blood pressure is measured by inserting into the artery, a catheter filled with liquid and connected to a pressure sensor . This more invasive (and therefore more risky) gives more accurate measurements and gives the blood pressure dynamics . Thus, the pressure at each moment of each cardiac cycle the patient is measured, not only the systolic and diastolic blood pressure over time.

Protocol use

The standard method is to measure the cuff with stethoscope (counterpulsation). She is a patient in a reclining position, arms along the body, after five to ten minutes of rest. The arm must be kept at heart level, if the arm is too low, the pressure will be overestimated. The size of the cuff should be appropriate to the size of the arm if the cuff is too small, the pressure will be overestimated. Initially, we measure the pressure in both arms. Sometimes the pressure is slightly higher in one arm than another: we consider the higher pressure as the reference value.

It is currently recommended, at a consultation, measure blood pressure at the beginning and the end of the consultation: the “white coat syndrome (anxiety in patients from the local medical staff) very often leads falsely high values early in the review.

Estimated unit without

In an emergency, lower systolic blood pressure can be estimated by simply taking the pulse , the latter resulting in the disappearance of a pulse distal to an adult:

• If the radial pulse is received, the systolic pressure exceeds 80 mmHg (T ≥ 8 cmHg);
• If the radial pulse is not seen but the carotid or femoral pulse is the systolic pressure is between 50 mmHg and 80 mmHg (8 cmHg ≥ T ≥ 5 cm Hg);
• If the carotid and femoral pulse disappeared, the voltage is less than 50 mmHg ( T ≤ 5 cm Hg).

According to people, distal pulses (radial and pedal) may be more or less well received, and on the other hand, the disappearance of a pulse may also be due to external compression (effect withers ) or internal (e.g. arteriosclerosis ). We must therefore identify the two Radial pulses. On the other hand, if the voltage is below 80 mmHg, we will not feel the radial pulse, but conversely, if we do not feel the radial pulse, this does not necessarily mean that the voltage is low.

We can also estimate the systolic pressure with the “capillary refill” putting pressure on a nail, it fades, and you look at the speed at which it recolors’s:

• Normal capillary refill (less than two seconds): systolic pressure above 100 mmHg ( T ≥ 10 cmHg);
• Delayed capillary refill (greater than two seconds): systolic pressure is between 85 and 100 mmHg (10 cmHg ≥ T ≥ 8.5 cmHg);
• No capillary refill: the systolic pressure below 85 mmHg (T ≤ 8.5 cmHg).