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Physiology
Blood Pressure
is a measure of the force blood exerts against blood vessel walls.
Systole: means contract.
Diastole: means dilate.
Atrail systole is contraction of the atrial myocardium and atrial
diastole is relaxation of the atrial myocardium.
Similarly ventricular systole is contraction of the ventricular
myocardium and ventricular diastole is relaxation of the ventricular
myocardium. When the terms systole and diastole are without
reference to specific chambers however the mean ventricular systole
or diastole.
Apparatus:
1-Sphygmomanometer.
2-Stethoscope.
Two method of measured blood pressure:
1-Blood pressure is measured directly by inserting a cannula (or tube)
into blood vessel and connecting a manometer or an electronic
pressure transducer to it.
Electronic transducers are very sensitive to changes in pressure and
can precisely detect rapid fluctuation in pressure.
Placing catheters in blood vessels or in chambers of the heart to
monitor pressure changes is possible but these procedures are not
appropriate for routine clinical determination of systemic blood
pressure.
2- The auscultatory method: can be used to measure blood pressure
without surgical procedures or causing discomfort so it is used under
most clinical conditions.
A blood pressure cuff connected to a sphygmomanomerer is placed
around the patients arm just above the elbow and a stethoscope is
placed over the brachial artery.
Some sphygmomanometers have mercury manometers and others
have digital manometers but they all measure pressure in terms of
millimeters of mercury. The blood pressure cuff is inflated until the
brachial artery is completely collapsed. Because no blood flows
through the constricted area no sounds can be heard.
The pressure in the cuff is gradually lowered. As soon as it declines
below the systolic pressure ,blood flows through the constricted area
during systole. The blood flow is turbulent and produces vibration in
the blood and surrounding tissues that can be heard through the
stethoscope. These sounds are called Korotkoff sounds and the
pressure at which a korotkoff sound is first heard represents the
systolic pressure.
As the pressure in the blood pressure cuff is lowered still more the
Korotkoff sounds change tone and loudness. When the pressure has
dropped until continuous laminar blood flow is reestablished the
sound disappears completely. The pressure at which continuous
laminar flow is reestablished is the diastolic pressure.
Normal value: 120/80 mm.Hg
The cause of low blood pressure is not always clear. It may be
associated with the following:
1-Pregnancy
2-Hormonal problems such as an underactive thyroid
(hypothyroidism). Overactive thyroid(hyperthyroidism).
3-Over dose of high blood pressure drugs.
4-Heart failure.
5-Liver disease.
6-Heat exhaustion or heat stroke.