Measuring Blood Pressure (BP)

Blood pressure (BP), the pressure of the circulating blood against the walls of the arteries, the veins, and the chambers of the heart. Overall blood pressure is kept by the complex interaction of the volume of the blood, the walls of the arteries and arterioles, and the force of the contraction of the heart. The pressure in the large artery of the heart (aorta) and the other large arteries of a healthy young adult is about 120 mm Hg during contraction (systole) and 70 mm Hg during relaxation (diastole) of the heart.

Measurement

The blood pressure is most often measured by using a device called a sphygmomanometer, a stethoscope, and a blood pressure cuff.

1. Allow the patient to sit for some time in a quite room before beginning blood pressure measurement.
2. Place the cuff around the upper arm and fill in air, tightening to stop the blood from flowing through the artery in the arm. The stethoscope is placed over the artery in front of the elbow and the pressure in the cuff is slowly released. The arm should always be kept straight with hands straight too (no fists).
3. No sound is heard until the cuff pressure falls below the systolic pressure in the artery; at that point a pulse is heard. As the cuff pressure continues to fall slowly, the pulse continues; first becoming louder, then dull and muffled. These sounds, called the sounds of Korotkoff, are caused by the disturbance of the blood flowing through the vessel.
4. The cuff pressure at which the first sound is heard is the systolic blood pressure, and the cuff pressure at which the sounds stop is the diastolic blood pressure.
5. Take at least two measurements spaced by 1-2 min, and additional measurements if the first two are quite different. The pressure in both arms is sometimes taken.

The blood pressure may also be taken using the thigh with the stethoscope held behind the knee. A larger cuff is used when taking the blood pressure of an overweight person or when using on the thigh. Any factor that increases resistance of the vessels to the flow of blood or that affects the amount of blood pumped by the heart will change the blood pressure. Strong emotion, for example, tends to do both; therefore the blood pressure reading is usually taken when the person is resting. 

Blood pressure increases with age, mainly because the veins do not expand as well. As a person grows older an increase in systolic pressure comes before an increase in diastolic pressure.

Self Measurement

Self measurement of blood pressure at home should be encouraged in order to:

• provide more information for doctor's decision
• improve patient's adherence to treatment regimen.

Self measurement of blood pressure at home should be discouraged whenever:

• it causes patient anxiety
• it induces self-modification of the treatment regimen.

Normal Blood Pressure

Age	Systolic Range			Diastolic Range			Pulse Pressure
Years	Minimum	Average	Maximum	Minimum	Average	Maximum
15-19	105	117	120	73	77	81	40
20-24	108	120	132	75	79	83	41
25-29	109	121	133	76	80	84	41
30-34	110	122	134	77	81	85	41
35-39	110	123	135	78	82	86	41
40-44	112	125	137	79	83	87	42
45-49	115	127	139	80	84	88	43
50-54	116	129	142	81	85	89	44
55-59	118	131	144	82	86	90	45
60-64	121	134	147	83	87	91	47

Rules for Calculating Arterial Pressure

Systolic: For ages 20 upto 60, standard systolic pressure equals 120 m.m. Hg., plus one-fifth of the age. At age 60, standard systolic pressure is 135 m.m. Hg. and for each year above this, upto and including age 80 add 1 m.m. Hg.

Diastolic: Taking standard Diastolic pressure at age 20 as 80 m.m. Hg., for each five years above 60 upto and including age 80 add 2 m.m. Hg.

Updated on: 01 Feb 2010