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The Arterial Blood Pressure ( ABP ).
DEFINITIONS: - Systolic blood pressure(SBP) : It is the maximum pressure in the aorta at the end of systole. Value: 100 -140 mm. Hg (Average= 120 mm. Hg). - Diastolic blood pressure (DBP): It is the minimum pressure in the aorta at the end of diastole. Value: 60 -90 mm. Hg (Average = 80 mm. Hg).
DEFINITIONS: - Pulse pressure(PP) : It is the difference between systolic and diastolic blood pressure values. PP = SBP – DBP = 120 -80 = 40 mm. Hg. - Mean arterial blood pressure : It is the average pressure throughout the cardic cycle. Mean ABP = DBP + 1/3 pulse pressure. Mean ABP = 80 + 13 = 93 mm. Hg.
Measurment of arterial blood pressure ABP : The apparatus used is the sphygmomanometer which consists of : a. The sphygmomanometer cuff : It is rubber bag enclosed in a cloth cuff. b. The cuff has two openings connected with rubber tubes : e first opening is connected to valved pump to control inflation and deflation. he second opening is connected to some kind of manometer to measure the pressure.
Technique : - The subject should be under the basal conditions of physical , mental and digestive rest and may be either in the recumbent position or comfortably seated. - The arm should be bared, slightly flexed, abducted and perfectly relaxed. - The center of completely deflated rubber bag is placed over the line of brachial artery, the lower end is kept 1 inch above the blend of the elbow. - Wrap the cloth bag which cover the rubber bag around the arm. - Put the manometer at the level of the heart and make sure that the mercury is at zero on the scale.
A- Palpation method : 1 - Feel the radial pulse with the tip of the fingers of the left hand. 2 - With the right hand raise the pressure in the sphygmomanometer till the pulse disappear. 3 - Raise the pressure 20 mm further. 4 - Now, start to deflate the bag slowly and take the reading on the manometer when the pulse is just palpable. Palpatory method measures only the systolic BP, which is 5 -10 mm. Hg less than that recorded by the auscultatory method.
B- Auscultation method : 1 - Feel the pulse of the brachial artery just medial to the biceps tendon in the cubital fossa. 2 - The diaphragm of the stethoscope is placed over the area of maximum pulsation. 3 - The bag is inflated 30 mm. Hg above the systolic blood pressure as determined by palpatory method.
4 - Deflate the bag slowly, then the following 5 sounds can be heard (Korotkoff's sounds) : i- Tapping sound ( systolic BP ). ii- Sound with adding murmur, called ( thudding sound ). iii- Increase intensity of tapping sounds ( but not so sharp as before ). iv- Sound muffling i. e. sudden lowering of intensity v- Silence: (diastolic BP).
Auscultatory gap (silent gap ) : Sometimes during measurement of the ABP by the auscultation method, the Korotkoff's sounds due to unkown cause disappear for a variable gap then reappear again ( found in some patients with hypertension ). If the sounds above the gap are missed this gives a false low systolic B. P. So the systolic B. P. is preferably determined first by the palpatory method because there is no palpatory gap.
Measurment of ABP by Auscultatory method.
Uses of sphygmomanometer : 1 - Measurment of ABP. 2 - Cold pressor test. 3 - Hiss test ( capillary fragility test ). 4 - Tournique in hemorrhage. 5 - Demonstration of reactive hyperemia. 6 - Demonstration of ischaemic pain. 7 - Diagnosis of latent tetany.