Blood Pressure (BP) is the lateral force on the walls of artery by the pulsing blood under pressure from the heart. The heart' s contraction forces blood under high pressure into the aorta.
The peak of maximum pressure when ejection occurs is the systolic blood pressure. When the ventricles relax, the blood remaining in the arteries exerts a minimum a diastolic pressure.
Diastolic pressure is the minimal pressure exerted against the arterial walls at all times.
The standard unit for measuring blood pressure is millimeters of mercury (mmHg). The BP is recorded with the systolic reading before diastolic.
Eg. 120 / 80 mmHg. 120 is systolic pressure 80 is diastolic pressure
The difference between systolic and diastolic pressure is the pulse pressure.
Physiology of BP : BP reflects inter relationship of cardiac output, peripheral vascular resistance.
Cardiac output is the volume of blood pumped by the heart (stroke volume) during one minute.
o Cardiac output = Heart rate x stroke volume
The BP depends on the cardiac output and peripheral vascular resistance (R).
o BP = Cardiac output x R
Peripheral vascular resistance is the resistance to blood flow determined by the vascular wall and diameter of blood vessels when the diameter is less, the vascular resistance to blood flow is increased.
Blood volume the volume of blood circulating with in vascular system, affects BP. For adults, normal circulating blood volume is 5000 ml. If volume increases, BP elevates. Eg. rapid uncontrolled intravenous fluid. When circulating volume falls, blood pressure falls. Eg. haemorrhage, dehydration.
Elasticity : Normally the arterical walls are elastic and easily distensible. Contain diseases such as arteriosclerosis, lose their elasticity and cannot stretch wall. When the blood is forced into blood vessels, due to the rigid blood walls, the systolic pressure rises.
Table : Average normal BP
Age B P (mm Hg)
New Born 40 (mean)
1 month 85 / 54
1 year 95 / 65
6 years 105 / 65
10 - 13 years 110 / 65
14 - 17 years 120 / 75
Middle adult 120 / 80
Older adult 140 / 90
Factors influencing Variations in BP
Age : Normal BP levels vary through out life larger children have higher BP than smaller children of same age.
Stress: Anxiety, fear pain and emotional stress result in increase in heart rate resulting in
increasing in BP.
o Race : Certain race are more prone for high BP. Genetically and environmentally.
o Medication: Some medications can affect BP directly or indirectly.
Eg. Diuretics --- decreases BP
Nifedipine --- decreases BP
Dopamine --- increases BP
Diurnal variation : BP levels vary over the course of a day. BP is lowest in the early morning, gradually arises during morning and afternoon and
peaks in evening.
Gender : After puberty males tend to have higher BP. After, menopause, women tend to have high BP. BP is measured by sphygmomanometer.
Variation in BP
Hypertension : Elevated or high blood pressure is known as hyper tension. Hyper tension is a major factor causing deaths from strokes and myocardial infarction (Heart arrest)
Classification of hyper tension :
Category Systolic(mm Hg) Diastolic(mm Hg)
Normal < 130 < 85
Stage I (mild) 140 - 159 90 - 99
Stage II (moderate) 160 - 179 100 - 109
Stage III (Severe) 180 - 209 110 - 119
Stage IV (very severe) 210 120
Causes of Hypertension:
Family history of Hypertension .
high blood cholesterol level,
continued exposure to stress,
long - term follow up care and therapy.
When the systolic pressure falls to 90 mm Hg or below, that condition is known as hypo tension.
Causes of Hypotension:
Dilatation of the arteries.
Loss of blood, Due to haemorrhage.
Failure of heart muscle to pump adequately (Heart attack)
Signs symptoms of Hypotension :
cold and clammey
increased heart rate.
Decreased urine output.
To aid in the diagnosis of the patient' s condition
To guide in his treatment.
To evaluate the patient' s progress.
See that the patient is relaxed and is a comfortable position.
Help to take blood pressure for patients with the following conditions.
o New patients.
o Pre and post operative patients. o Antenatal and post natal patients.
o Patients with shock and haemorrhage.
o Patients with cardiac conditions and hypertension o Patients with neurological disorders.
Record pulse along with blood pressure.
Blood pressure is taken at the same arm, same time, same posture daily.
The sphygmomanometers generally used in clinical setting are mercury type. And aneroid type. The mercury type sphygmomanometers are more reliable than the aneroid type sphygmomanometers. The aneroid sphygmomanometers gives blood pressure reading on dial indicator.
Systolic pressure is increased in pressure induced by systolic contraction and diastolic pressure is decrease in pressure induced by diastolic relaxation of the left ventricle of heart.
Never take blood pressure when the patient is excited, exhausted and just after exercise, smoking or meals.
Allow the patient to rest for five minutes before taking blood pressure.
Do not use the extremity that is injured, diseased, paralysed, receiving intravenous infusion or when a female patient is with radical mastectomy on the same side.
When the arm cannot be used to measure the blood pressure, the thigh can be used being a good alternative site.
Always take the blood pressure reading on the same side and in the same position to maintain consistency.
Place the site (arm or leg) about the level of heart while taking blood pressure.
The apparatus should be in working order. The cuff should be of appropriate size (12-14 cm for arm and 18-20 cm for thigh) and deflated before wrapping around the patient' s site.
While taking blood pressure, certain sounds are heard in sequence. These are called as Korotkoff sounds and are described as under.
Tapping The faint clear sounds that gradually become louder, the first tapping sound may be followed by an absence of sound (auscultatory gap)and indicates systolic pressure reading.
· Murmuring The low swishing sounds that increase with cuff deflation.
Knocking The crisp, clear sounds that occur with each heart beat.
Muffling Abrupt change of sound indicates first diastolic pressure reading.
No sounds The sound disappears and indicates second diastolic pressure reading.
When deflating the cuff to take the readings, deflate the cuff to 0. Do not stop in between and start inflating again as this gives a false reading.
Note the variations in blood pressure.
Explain the procedure to patient. See patient is relaxed and is in a comfortable position. Support the arm.
Expose the arm and keep it extended.
Apply the end of the cuff with the rubber bag over the brachial artery two inches above the elbow.
Apply the end of the cuff smoothly and snugly around the upper arm. Tuck the end neatly.
Place the Sphygmomanometer in position.
Stay with the patient until the procedure is over.
Remove the cuff from the patient' s arm, roll neatly and replace in the box. See patient is comfortable.
The reading is recorded in the chart.
Systolic pressure is always written over the diastolic pressure Eg.120/80mm/Hg