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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.