Arterial and venous pressure

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Arterial and venous blood Pressure

Arterial blood pressure

Arterial blood pressure: means the force exerted by the blood against any unit area of the vessel wall. Blood pressure almost always is measured in millimeters of mercury (mm Hg) because the mercury manometer has been used as the standard reference for measuring pressure. The pressure in the aorta and in the brachial and other large arteries in a young adult human rises to a peak value (systolic pressure) of about 120 mm Hg during each heart cycle and falls to a minimum (diastolic pressure) of about 70 mm Hg .
Systolic pressure is produced by ejection of blood into aorta during left ventricular systole while diastolic pressure is produced as a result of the elastic recoil of the aorta during ventricular diastole. The arterial pressure is conventionally written as systolic pressure over diastolic pressure, for example, 120/70 mm Hg.
arterial pressure is the product of the cardiac output and the peripheral resistance, it is affected by conditions that affect either or both of these factors.
BP=CO*PVR ( CO: cardiac output, PVR: peripheral vascular resistance).

The mean pressure equals the diastolic pressure plus one-third of the pulse pressure.
Mean BP=diastolic BP+1/3pulse pressure See figure 1.
The pulse pressure, the difference between the systolic and diastolic pressures, is normally about 40 mm Hg.

Figure(1):Arterial blood pressure curve (Guyton & Hall 2006).

Methods of Measuring Blood Pressure:
1-Invasive method: a cannula is inserted into an artery, the arterial pressure can be measured directly with a mercury manometer or a suitably calibrated strain gauge.
2-Non invasive methods: BP measured by sphygmomanometer. It includes :
I-palpatory method: The cuff is wrapped around the arm .the radial pulse is palpated then the cuff is inflated till the pulse disappears which indicate complete obstruction of brachial artery, then the cuff is slowly deflated till radial pulse becomes palpable.by this methods only systolic BP is measured.
II-Auscultatory method: The arterial blood pressure in human is routinely measured by the auscultatory method. An inflatable cuff attached to a mercury manometer (sphygmomanometer) is wrapped around the arm and a stethoscope is placed over the brachial artery at the elbow. The cuff is rapidly inflated until the pressure is well above the expected systolic pressure in the brachial artery. The artery is occluded by the cuff, and no sound is heard with the stethoscope. The pressure in the cuff is then lowered slowly. At the point at which systolic pressure in the artery just exceeds the cuff pressure, a spurt of blood passes and certain sounds called Korotkoff sounds are heard. The sounds of Korotkoff are produced by changing laminar blood flow into turbulent flow in the brachial artery.The first sound heard represent systolic pressure(phase1 of Korotkoff sound). Then the sound becomes louder,then dull, muffled and finally disappear. Diastolic pressure represented when the sound disappears.
Phases of Korotkoff sounds are:
- Phase1, tapping sound.
-Phase2, louder sound.
-Phase3,dull.
-Phase4, muffled sound.
-Phase5, disappeared.
In hyper dynamic conditions (e.g) pregnancy, children, and some disease conditions (e.g) hyperthyriodisim ,aortic insufficiency ,diastolic blood pressure represented by phase4.