MEASUREMENT OF BLOOD PRESSURE WITH SPHYGMOMANOMETERS

MEASUREMENT OF BLOOD PRESSURE WITH SPHYGMOMANOMETERS


Brief History of Sphygmomanometer

Hypertension is a 20th century diseases only, because measurement of the arterial blood pressure became conveniently possible when Scipione Rivarocci (1863-1973) perfected an early version of the modern sphygmomanometer in 1896. Stephen Hales, an English clergymen, was the first to measure blood pressure directly – in a mare, in 1733 - and investigators utilizing mercury manometers had measured blood pressure in various ways in the 19th century. Richard Bright ((1789-1858), during the course of his classic studies of the diseases that bears his name, concluded that the thick left ventricle, dilated aorta, and arterial disease could be due to increased resistance to the flow of blood in the blood vessels, but Bright had no method of measuring blood pressure.

At the turn of the century, Rechklinghausen noted the falsely high levels of blood pressure (especially in the obese) that could be obtained with narrow cuffs such as those used by Riva-Rocci; the standard 12.5 cm cuff used today owes its origin to Recklinghausen’s research. Korotkoff in 1905 described the 5 sounds heard over the brachial artery, distal to the cuff, as the pressure in the sphygmomanometer is reduced: Phase I, the abrupt sharp sound as the pressure is reduced just below systolic pressure. Phase II, a prolonged, louder murmuring sound. Phase III, a load clear with only a slight murmur. Phase IV, an abrupt muffling of sounds, thought by some to represent the diastolic pressure. Phase V, the total disappearance of sounds, used usually in the USA to reflect the diastolic pressure.
Mahomed (about 1879) was the first to demonstrate that renal and cardiac disease were complications of hypertension in some patients (and not the reverse, as had been suggested by Bright and by Allbutt).

Types of Sphygmomanometers

At the modern era, there are three types of sphygmomanometers:

1. Digital with manual or automatic inflation. These are electronic, easy to operate, and practical in noisy environments. Many have not been validated for all patient groups, and they can give very inaccurate readings. They measure mean arterial pressure (MAP) and use algorithm to calculate systolic and diastolic values. In this sense, they do not actually measure the blood pressure, but rather derive the readings. Digital oscillometric monitors are also confronted with "special conditions" for which they are not designed to be used: arteriosclerosis; arrhythmia; preeclampsia; pulsus alternans; and pulsus paradoxus. Some wrist cuff blood pressure monitors have been found to be quite accurate, but the monitor has to be at the level of the heart when the reading is taken.
2. Digital portable finger blood pressure monitors with automatic inflation. These are more portable and easy to operate, although less accurate. They are the smallest blood pressure monitors.
3. Manual. Should be operated by a trained person. Mercury manometers are considered to be the "gold standard" of measurement because their measurement is absolute and does not require re-calibration. For this reason they are often required in clinical trials of pharmaceuticals and for clinical evaluations of determining blood pressure for high risk patients including pregnant women. Aneroid, mechanical types are in common use, but they should be calibrated against a mercury manometer. The unit of measurement of blood pressure is millimeters of mercury (mmHg). Blood pressures are usually given as an even number. Manual sphygmomanometers require a stethoscope for auscultation.

Regular Maintenance and Calibration of Sphygmomanometers

The Sphygmomanometer is an essential piece of equipment used daily in general medical practice, and plays a role in many routine consultations. Without regular maintenance and calibration, however, both mercury and aneroid sphygmomanometers are at risk of becoming inaccurate over time. A significant level of inaccuracy may lead to misdiagnosis of hypertension and inhibit its control, thus placing patients at unnecessary risk.

Raouse A and Marshal T (2001) in their study [1]; a researcher trained in the calibration of sphygmomanometers visited 231 general practices in the Birmingham area and calibrated 1462 mercury and aneroid sphygmomanometers. The Practices in Birmingham were asked about what arrangement had been made for maintenance and calibration of their instruments, and, in a small telephone survey, 54 practices across the country were asked the same question. Almost one in 10 of the sphygmomanometers checked gave readings that were inaccurate by more than 5 mmHg (9.2%). None of the practices visited had arrangements in place for the maintenance and calibration of their Sphygmomanometers. Of the 54 practices questioned by telephone, only one had such arrangements in place. The finding has implication for public health, primary care, and medical ethics. Inaccurate sphygmomanometers may result in the prescription of treatment to patient who do not require it.

In the other study by Mion D and Pierin AMG, 1998 [2]; was to assess the accuracy and reliability of mercury and aneroid sphygmomanometers. Measurement of accuracy of calibration and evaluation of physical conditions were carried out in 524 sphygmomanometers, 351 from a hospital setting, and 173 from private medical offices. Mercury sphygmomanometers were considered inaccurate if the meniscus was not ‘0’ at rest. Aneroid sphygmomanometers were tested against a properly calibrated mercury manometer, and were considered calibrated when the error was <3 mm Hg. Both types of sphygmomamometers were evaluated for conditions of cuff/bladder, bulb, pump and valve.

In this study; of the mercury sphygmomanometers tested 21% were found to be inaccurate. Of this group, unreliability was noted due to: excessive bouncing (14%), illegibility of the gauge (7%), blockage of the filter (6%), and lack of mercury in the reservoir (3%). Bladder damage was noted in 10% of the hospital devices and in 6% of private medical practices. Rubber aging occurred in 34% and 25%, leaks/holes in 19% and 18%, and leaks in the pump bulb in 16% and 30% of hospital devices and private practice devices, respectively. Of the aneroid sphygmomanometers tested, 44% in the hospital setting and 61% in private medical practices were found to be inaccurate. Of these, the magnitude of inaccuracy was 4–6 mm Hg in 32%, 7–12 mm Hg in 19% and . 13 mm Hg in 7%. In summary, most of the mercury and aneroid sphygmomanometers showed inaccuracy (21% vs 58%) and unreliability (64% vs 70%).

Additionally, home blood pressure readings may be more representative than those obtained in the clinicians's office. The prevalence of home sphygmomanometers in the general population is currently undocumented. The prevalence of ownership (7.5 per cent) and the accuracy of home sphygmomanometers were determined in a population-based survey in the Minneapolis-St. Paul metropolitan area. A study by Hahn LP and Folsom AR (1987) [3]; Prevalence and Accuracy of Home Sphygmomanometers
in an Urban Population. Sixty-four per cent of home sphygmomanometers were accurate within ±2 mm Hg of a calibrating sphygmomanometer; another 26 per cent were within ±3-6 mm Hg. These results suggest that although many home sphygmomanometers are accurate, some are very inaccurate. Health care providers should advise regular calibration when home sphygmomanometers are used for therapeutic self-management of hypertension.

As conclusion, the present studies showed a high incidence of inaccuracy in both aneroid and mercury sphygmomanometers, and in both hospital and private medical practice based settings. These results reinforce the recommendations made by The American Heart Association and The British Hypertension Society that aneroid and mercury sphygmomanometers must be checked regularly in order to avoid errors in blood pressure measurement and consequently the diagnosis and treatment of hypertension.

Andi Surya Amal
email : suryaamal88@gmail.com

Reference :

1. Rouse A, Marshal T (2001), The Extent and Implication of Sphygmomanometer Calibration Error in Primary Care, Journal of Human Hypertension; 15[9]:587-591
2. Mion D and Pierin AMG (1998), How accurate are sphygmomanometers?, Journal of Human Hypertension; 12, 245–248
3. Hahn LP and Folsom AR et al (1987), Prevalence and Accuracy of Home Sphygmomanometers in an Urban Population, American Journal of Public Health, Vol. 77, No. 11, 77:1459-1461
4. Markandu NK, Whitcher F, Arnold A, Carney C (2000), The Mercury sphygmomanometer should be abandoned before it is prescribed. Journal of Human Hypertension 14(1): 31-6.
5. Sokolow M and Mcllroy MB (1979), Clinical Cardiology, 2nd Ed., Lange Medical Publications, 208-209
6. Jones DW, Frohlich ED (2001), Mercury Sphygmomanometers Should Not be Abandoned: An Advisory Statement From the Council for High Blood Pressure Research, American Heart Association, Hypertension;37:185