Protests continue, March 1947 to August 1947

The auscultatory method has been the main stay of clinical blood pressure measurement for as long as blood pressure has been measured but is gradually being replaced by other techniques those are more suited to automated measurement.⁹⁵

1)THE AUSCULTATORY METHOD:

It is surprising that nearly 100 years after it was first discovered, and the subsequent recognition of its limited accuracy, the korotkoff technique for measuring blood pressure has continued to be used without any substantial improvement. The brachialartery is occluded by a cuff placed around the upper arm andinflated to above systolic pressure. As it is gradually deflated, pulsatile blood flow is re-established and accompanied by sounds that can be detected by a stethoscope held over the artery justbelow the cuff. Traditionally, the sounds have been classifiedinto 5 phases: phase I, appearance of clear tapping sounds corresponding to the appearance of a palpable pulse; phase II, sounds becomesofter and longer; phase III, sounds become crisper and louder;phase IV, sounds become muffled and softer; and phase V, soundsdisappear completely. The fifth phase is thus recorded as thelast audible sound.⁹⁵

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The sounds are thought to originate from a combination of turbulent blood flow and oscillations of the arterial wall. There is agreementthat the onset of phase I corresponds to systolic pressure but tends to underestimate the systolic pressure recorded by direct intra-arterial measurement.⁹⁶The disappearance of sounds (phase V) corresponds to diastolic pressure but tends to occur before diastolic pressure determined by direct intra-arterial measurement. ⁹⁶No clinical significance has been attached to phases II andIII. There are three types of sphygmomanometers under auscultatory method:

i)Mercury sphygmomanometers

The Mercury sphygmomanometer has always been regarded as the gold standard for clinical measurement of blood pressure.⁹⁵It has been in widespread use in clinical and epidemiological studies for several decades.⁹⁷

Strengths: Much ofwhat we know about the relations of blood pressure with stroke,coronary heart disease, and other outcomes is built on studies,such as the Framingham Study, that used this device.⁹⁸ Because standard mercury readings are the main basis for blood pressure–

disease associations, one might go so far as to say that they are the epidemiological gold standard for measurement. By extension, studies relating childhood with adulthood blood pressure or examining blood pressure within childhood might benefit from the use of this instrument. Because this is the instrument generally used in doctors' offices, findings from epidemiological studies with standard mercury readings are directly applicable to clinical practice. Furthermore, the standard mercury sphygmomanometer is relatively inexpensive, easy to transport, and easy to maintain, when compared with the random-zero instrument.

Study personnel can be trained easily to use it.⁹⁷

Weaknesses: The standard mercury sphygmomanometer is subject to digit preference and observer bias resulting from knowledge of previous readings. The latter, especially, may

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severely compromise results in childhood studies because of the importance of accurately characterizingintraperson variability in children.^99,100 Additionally, because of the difficulty of hearing Korotkoffsounds in young children, using this device is problematic in this age group.¹⁰¹

ii) Anaeroid sphygmomanometers

In these devices, the pressure is registered by a mechanical system of metal bellows that expands as the cuff pressure increasesand a series of levers that register the pressure on a circular scale. This type of system does not maintain itsstability over time, particularly if handled roughly. They therefore are inherently less accurate than mercury sphygmomanometersand require calibrating at regular intervals. Recent developmentsin the design of anaeroid devices may make them less susceptible to mechanical damage when dropped. Wall-mounted devices maybe less susceptible to trauma and, hence, more accurate thanmobile devices.¹⁰²

The accuracy of the manometers varies greatly from one manufacturerto another. Thus, 4 surveys conducted in hospitals in the past 10 years have examined the accuracy of the anaeroid devices andhave shown significant inaccuracies.102,103,104 The few studies that have been conducted with anaeroid devices have focused on the accuracy of the pressure registeringsystem as opposed to the degree of observer error, which is likely to be higher with the small dials used in many of thedevices.

III) Hybrid sphygmomanometer

Devices have been developed that combine some of the featuresof both electronic and auscultatory devices, and are referredto as "hybrid" sphygmomanometers. The key feature is that themercury column is replaced by an electronic pressure gauge,such as are used in

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oscillometric devices. Blood pressure istaken in the same way as with a mercury or anaeroid device byan observer using a stethoscope and listening for the Korotkoffsounds. The cuff pressure can be displayed as a simulated mercurycolumn, as a digital readout, or as a simulated anaeroid display.In one version, the cuff is deflated in the normal way, andwhen systolic and diastolic pressure are heard a button nextto the deflation knob is pressed, which freezes the digitaldisplay to show systolic and diastolic pressures. This has thepotential of minimizing terminal digit preference, which isa major source of error with mercury and anaeroid devices. Thehybrid sphygmomanometer has the potential to become a replacement for mercury, because it combines some of the best features ofboth mercury and electronic devices at any rate until the latterbecome accurate enough to be used without individual validation.¹⁰⁵