Blood Pressure (With Detailed)

Blood pressure is the pressure exerted by Wood on the wall of a blood vessel.

Blood pressure may also be defined as the arterial blood pressure, which is the force exerted by circulating blood on the walls of systemic arteries.

Systolic blood pressure: This is the maximum pressure exerted by blood on the walls of blood vessels which develops at the peak of ventricular systole. Systolic blood pressure = 120 mm Hg

Diastolic blood pressure: This is the minimum pressure exerted by blood on the wall of blood vessels during ventricular diastole. Diastolic blood pressure = 80 mm Hg

Measurement of blood pressure

Blood pressure is measured clinically with a sphygmo-manometer which is either of mercury or aneroid type.
Advise the patient to rest at least 15-20 minutes. The patient should be in a sitting or lying position. There are two methods for taking blood pressure:
  • Palpatory method
  • Auscultatory method

Physiological variations of blood pressure

Diurnal variation

Blood pressure is lowest early in the morning and highest in the afternoon.


Blood pressure rises with age. The systolic blood pressure at different ages:
Infancy         =  80-90 mm Hg
Childhood    =  90-110 mm Hg
Adult             =  110-120 mm Hg
Elderly          =  140-150 mm Hg


Before the occurrence of menopause in females, both the systolic and diastolic blood pressures are slightly lower than males. After menopause blood pressure may be slightly higher than males of the same age.

Body build

Obese persons tend to have higher blood pressure.


In resting conditions as in sleep, blood pressure is decreased.


Light exercise such as walking increases the systolic blood pressure but decreases the diastolic blood pressure.
In severe exercise, the systolic blood pressure may rise up to 180 mm Hg.


Standing causes an increase in both systolic and diastolic blood pressure.

Excitement or Emotion

This may cause an increase in systolic blood pressure.

After digestion of blood

There is a slight rise in systolic blood pressure, but the diastolic blood pressure falls due to vasodilation in certain vessels of the body.

Regulation or control of Blood pressure

The following factors affect and regulate blood pressure. As we know:
Blood pressure= Cardiac output x Peripheral resistance.
Cardiac output = stroke volume x heart rate.
Blood pressure category                 Systolic mm Hg (upper #)             Diastolic mm Hg (lower #)
Normal                                                 less than 120                                   less than 80
Prehypertension                                   120-139                                           80-90
High Blood Pressure                            140-159                                           90-99
(Hypertension) Stage 1
High Blood Pressure                               160 or higher                                  100 or higher
(Hypertension) Stage 2

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