MEASUREMENT OF BP

od is, mean BP = DBP + 1/3 pulse pressure. For example, in the above mentioned subject, the mean BP is about 93 mm. Hg. Fig. 5.9.1. Recording of BP in man by the usual method (Riva-Rocci manometer). MEASUREMENT OF BP I. In human subjects in routine clinical practice, BP is determined by the sphygmomanometer, an instrument devised by Riva - Rocci, and subsequently improved by Von Recklinghausen. The sphygmomanometer is essentially a mercury manometer. However, instead of the classical U tube of the manometer, only one of its limbs is long the othar is very short, and acts as a raservoir of mercury (figure 5.9.1). The reservoir is, via a rubber tube, connected with an arm 'cuff the cuff, in turn is, via rubber tube, connected with a hand pump. Air can be introduced into the cuff by pumping the hand pump, a process called 'inflation'. Air from the cuff can be driven out by unscrewing the pump ('deflation'). The determination. The subject lies flat on his back, the cuff is wrapped round his arm (preferably the left arm, as the left subclavian artery unlike the right one, is a direct branch of the aorta). The heart sphygmomanometer and the arm should be at same horizontal plane. Then inflation is started by pressing the pump and the radial arterial pulse palpated concomitantly. A time comes when the radial pulse disappears. 'The height of mercury column at this stage is noted in the side scale. Then the cuff is deflated fully. The ball of the stethoscope is placed lightly on the brachial artery near the elbow. The cuff is again inflated and inflation continued for sometime even after the column of mercury has attained the previous height where the radial arterial pulse disappeared. Then deflation is started, at a rate of 2-3 mm/sec, neither more nor less. At first there is no sound heard by the stethoscope ('grave yard silence), after the deflation has reached a particular stage. a 'tap' sound is heard and this marks the SBP the reading at the side scale (of the height of the mercury column) is noted, deflation continued, till all sounds disappear. Between the 'tap' sound and the, reappearance of silence, a series of sounds, called Korotkov sounds, are heard as follows: For a long time, there was a raging controversy, viz, which phase corresponds, to the true diastolic pressure. Some said it was phase IV ('muffled' sound), some others said, disappearance of all sounds., (phase V). The true diastolic pressure is between the phase IV and phase V, but nearer the phase V of Korotkov sounds. Therefore it is now the official policy to regard phase V as the diastolic BP* According to an American heart association subcommittee report in 1967, it is desirable to mention the readings of both the IVth and Vth phases. Thus, if the SBP is 120 and the readings at phases IV and V be 80 and 70 mm Hg,the BP should be expressed as 120/80/70 mm Hg. Dependability of the clinical method. The precautions. In the same subject, the BP can be measured simultaneously in one arm by the above mentioned clinical method and in the other arm by the direct method. It has been found that, usually the SBP, as measured by the clinical (spliygmamanometric) method, is considerably lower (the difference is usually between 10-25 mm Hg) than the value obtained by the direct method. Further, if the IVth phase (of the sphygmomanometric method) is regarded as the DBP, the clinical method gives about 8 mm higher figure than that obtained by the direct method whereas if the Vth phase is regarded as the DBP, the differences of the values obtained by the two methods is almost nil "Dollery, CT: Arterial Hypertension, in Wyngarden. J 3 dc Smith, LH (Ed), Cecil Text Book of Medicine. Chap. 47 Saunders, 1985. The above method is called, 'auscultatory method' BP can also be determined by palpatory method: inflate the cuff and simultaneously also continue to palpale the pulse. A time comes when the pulse can no longer be felt, continue to inflate for still some time, keeping the fingers an the radial artery. Now begin to deflate the cuff. A time comes when the pulse can again be felt. Note, the value (on the side scale of the mercury column) where the pulse reappears. This is the SBP as recorded by the palpatory method. But the SBP recorded by this method is a trifle lower than that obtained by the auscultatory method. Moreover, by palpatory method, only the SBP (but not the DBP) can be recorded. Auscultatory gap. This is seen sometimes in patients suffering from high blood pressure. A subject has a BP of say, 200/100 mm Hg. The first sound of Korotkov, the 'tap' sound, appears at 200 mm height as expected, but as deflation proceeds all sounds disappear. The sound reappears again at a lower pressure. Thus, in this example, the sound disappears, say, at 190 mm of Hg and reappears, again at 170 mm Hg, the Vth phase (disappearance) remaining at 100 mm Hg. Thus, if the inflation is made only upto say, 180 mm Hg, and a simultaneous palpation of pulse is not done, the clinician will record the BP as 170/100 mm Hg and rhe patient and the clinician may develop a false sense of security. The silent zone, mentioned above, viz. 190 mm Hg to 170 mm Hg is the auseutatory gap. The pulse however can be felt throughout the zone. Of auseultatory gap'. The BP, as will be shown later, is affected by many factors like, excitement, anxiety, exercise, meal and exposure to cold. It is expected that the clinician remembers these factors while determining the BP, and ensures that while recording BP, his subject is at rest (mentally and physically), in a comfortable climate and has not taken a heavy meal