Why Blood Pressure Is Lower When Measured Again
BMJ. 2001 Apr 21; 322(7292): 981–985.
ABC of hypertension
Blood pressure level measurement
Office I—Sphygmomanometry: factors common to all techniques
Methods of blood pressure measurement
Virtually devices for measuring claret force per unit area are dependent on one common feature, namely, occluding the artery of an extremity (arm, wrist, finger, or leg) with an inflatable cuff to measure claret pressure either oscillometrically, or by detection of Korotkoff sounds. Other techniques, which are non dependent on limb apoplexy, such every bit pulse-waveform analysis, tin can also be used, only these accept petty application in clinical practice. The assortment of techniques available today owe their origins to the conventional technique of auscultatory blood pressure measurement, and these new techniques must indeed exist shown to exist equally accurate as the traditional mercury sphygmomanometer. Since the introduction of sphygmo- manometry, mercury and aneroid sphygmomanometers take been the most pop devices for measuring claret pressures.
Factors affecting claret force per unit area measurement
No matter which device is used to measure blood pressure, it must be recognised that claret pressure level is a variable haemodynamic phenomenon, which is influenced past many factors, not least existence the circumstances of measurement itself. These influences on claret pressure level can be significant, often accounting for rises in systolic blood pressure greater than 20 mm Hg, and if they are ignored, or unrecognised, hypertension will be diagnosed erroneously and inappropriate management instituted. These factors have to be carefully considered in all circumstances of claret force per unit area measurement—self measurement past patients, conventional measurement, measurement with automatic devices whether in a doctor'southward surgery, an ambulance, a pharmacy, or in hospital using sophisticated engineering.1 ,2
Variability of blood pressure
The observer must be enlightened of the considerable variability that may occur in claret pressure level from moment to moment with respiration, emotion, exercise, meals, tobacco, alcohol, temperature, bladder distension, and pain, and that blood force per unit area is also influenced by age, race, and circadian variation. It is usually at its lowest during sleep. It is not always possible to modify these many factors simply nosotros tin can minimise their consequence by taking them into business relationship in reaching a decision equally to the relevance or otherwise of a particular blood force per unit area measurement.one
Insofar as is practical the patient should exist relaxed in a quiet room at a comfy temperature and a brusk period of residual should precede the measurement. When it is non possible to reach optimum conditions, this should be noted with the blood pressure reading—for example, "BP 154/92, R arm, Five phase (patient very nervous)."
"White coat" hypertension
Anxiety raises blood force per unit area, often by as much as 30 mm Hg. This may be regarded equally a physiological reaction, often referred to as the "fight and flying" phenomenon, or "defence" or "alarm" reaction. It is ordinarily seen in the accident and emergency departments of hospitals when patients are frightened and extremely anxious, but it may likewise occur in family doctors' surgeries and in the outpatients section. It may occur in normotensive and hypertensive subjects. The degree of this reaction varies greatly from patient to patient, being absent in many, and information technology is ordinarily reduced or abolished birthday with reassurance and familiarisation with the technique and circumstances of blood pressure level measurement. Its importance in practice is that decisions to lower blood pressure, and especially to administer drugs, should never exist made on the footing of measurements taken in circumstances where the defence reaction is likely to be nowadays.
White coat hypertension is a status in which a normotensive subject becomes hypertensive during claret pressure level measurement, simply pressures then settle to normal exterior the medical environment. It is best demonstrated by ambulatory claret force per unit area measurement (ABPM).
No i group seems to be exempt from the white coat phenomenon; it may affect the young, the elderly, normotensive and hypertensive subjects, and pregnant women. In young subjects with borderline elevation of conventional blood pressure, identification of white glaze hypertension can be of considerable importance in avoiding undue penalties for insurance and employment. Moreover, in that location are no characteristics that allow for the identification of the phenomenon, other than by obtaining claret pressures away from the medical environs, either by self measurement in the abode or with ABPM, which is the technique of choice. Patients diagnosed every bit "hypertensive" with conventional measurement in whom white glaze hypertension is considered a possibility should have ABPM performed earlier they are labelled "hypertensive," and certainly before handling is instigated.
Posture of subject
Posture affects claret force per unit area, with a general tendency for it to increment from the lying to the sitting or standing position. However, in most people posture is unlikely to lead to pregnant mistake in blood pressure measurement provided the arm is supported at heart level. None the less, it is advisable to standardise posture for individual patients and in exercise blood pressure is usually measured in the sitting position. Patients should be comfortable whatever their position. No information is available on the optimal time that a subject field should remain in a particular position before a measurement, but three minutes is suggested for the lying and sitting positions and 1 infinitesimal continuing. Some antihypertensive drugs cause postural hypotension, and when this is expected claret pressure should be measured both lying and standing.1
Arm support
If the arm in which measurement is being made is unsupported, every bit tends to happen if the subject is sitting or continuing, isometric exercise is performed raising blood pressure level and heart rate. Diastolic claret pressure may be raised by equally much every bit 10% past having the arm extended and unsupported during claret pressure measurement. The result of isometric practice is greater in hypertensive patients and in those taking β blockers. It is essential, therefore that the arm is supported during blood pressure measurement and this is best achieved in exercise by having the observer hold the subject's arm at the elbow, although in research the utilize of an arm support on a stand up has much to commend it.i
Arm position
The arm must too exist horizontal at the level of the eye equally denoted by the midsternal level. Dependency of the arm below heart level leads to an overestimation of systolic and diastolic pressures and raising the arm above eye level leads to underestimation. The magnitude of this error can be every bit great as 10 mm Hg for systolic and diastolic pressures. This source of error becomes specially important in the sitting and standing positions, when the arm is probable to be dependent by the subject's side. However, it has been demonstrated that fifty-fifty in the supine position an fault of 5 mm Hg for diastolic pressure level may occur if the arm is not supported at heart level.1 ,two Arm position has go an important issue for cocky measurement of blood force per unit area with the industry of devices for measuring blood force per unit area at the wrist, which are proving very popular because of the ease of measurement. Many of these devices are inherently inaccurate, only measurement is extremely inaccurate if the wrist is not held at heart level during measurement.
Which arm
This topic remains controversial every bit some studies, only not all, using simultaneous measurement have demonstrated significant differences between arms.ane Nevertheless, the fact that blood pressure differences betwixt arms are variable makes the issue even more problematical. A reasonable policy is to measure blood pressure in both artillery at the initial examination, and if differences greater than 20 mm Hg for systolic or 10 mm Hg for diastolic pressure are nowadays on three consecutive readings the patient should be referred to a cardiovascular centre for further evaluation.
The cuff and bladder
The cuff is an inelastic textile that encircles the arm and encloses the inflatable rubber bladder. It is secured around the arm nearly commonly by means of Velcro on the adjoining surfaces of the cuff, occasionally by wrapping a tapering terminate into the encircling gage, and rarely by hooks. Velcro surfaces must be effective, and when they lose their grip the cuff should be discarded. It should be possible to remove the bladder from the cuff so that the latter can exist done from time to time.i
"Cuff hypertension"
Still sophisticated a blood pressure measuring device may be, if it is dependent on cuff occlusion of the arm (as are the majority of devices), information technology will and then be prone to the inaccuracy induced by miscuffing, whereby a cuff containing a bladder that is either too long or too curt relative to arm circumference is used.
A review of the literature on the century-old controversy relating to the mistake that may be introduced to blood pressure measurement by using a cuff with a bladder of inappropriate dimensions for the arm for which information technology is intended has shown that miscuffing is a serious source of mistake, which must inevitably atomic number 82 to wrong diagnosis in practice and erroneous conclusions in hypertension research.3 There is unequivocal evidence that either too narrow or also brusk a float (undercuffing) will cause overestimation of blood pressure, so called "gage hypertension," and at that place is growing evidence that too broad or too long a bladder (overcuffing) may cause underestimation of claret force per unit area. Undercuffing has the outcome in clinical practice of overdiagnosing hypertension and overcuffing leads to hypertensive subjects being diagnosed as normotensive. Either eventuality has serious implications for the epidemiology of hypertension and clinical practice.
A review of the literature shows that a number of approaches accept been used over the years to cope with the difficulty of mismatching and none has been ideal. These take included application of correction factors, a range of cuffs, cuffs containing a variety of bladders, and a gage for the majority of artillery.
Blood force per unit area measurement in special subjects
Certain groups of people merit special consideration for blood pressure measurement, either because of age, body habitus, or disturbances of blood force per unit area related to haemodynamic alterations in other parts of the cardiovascular system. Although in that location is prove that many subgroups of the hypertensive population may have peculiarities affecting the accurateness of measurement, such as patients with renal disease, patients with diabetes mellitus, women with pre-eclampsia, and youths with "spurious" hypertension, discussion will be confined to children, the elderly, obese subjects, and significant women.
Children
Blood pressure measurement in children presents a number of difficulties and variability of claret pressure is greater than in adults, and thus whatever one reading is less probable to represent the true blood pressure. Too increased variability confers a greater trend for regression towards the mean. Conventional sphygmomanometry is recommended for general use, but systolic pressure is preferred to diastolic pressure considering of greater accurateness and reproducibility. Gage dimensions are most important and three cuffs with bladders measuring 4×13 cm, 10×18 cm, and the adult dimensions 12×26 cm are required for the range of arm sizes probable to exist encountered in the age range 0-14 years. The widest gage practicable should be used. Korotkoff sounds are not reliably audible in all children under one twelvemonth and in many under 5 years of age. In such cases conventional sphygmomanometry is incommunicable and more sensitive methods of detection such as Doppler, ultrasound, or oscillometry must exist used.four
Elderly people
In epidemiological and interventional studies blood pressure level predicts morbidity and mortality in elderly people every bit effectively as in the young.five The extent to which blood pressure predicts outcome may be influenced by various factors that affect the accurateness of blood force per unit area measurement and the extent to which coincidental blood pressure represents the claret pressure level load on the center and circulation.6
The elderly are subject field to considerable blood force per unit area variability, which can lead to a number of circadian blood pressure patterns that are best identified using ambulatory blood force per unit area measurement. The practical clinical consequence of these variable patterns in the elderly is that blood pressure measuring techniques tin can be inaccurate and/or misleading.
Pseudohypertension
It has been postulated that as a event of the decrease in arterial compliance and arterial stiffening with ageing, indirect sphygmomanometry becomes inaccurate. This has led to the concept of "pseudohypertension" to describe patients with a large discrepancy between cuff and direct blood force per unit area measurement.vii The significance of this miracle has been disputed,8 but in elderly patients in whom blood pressure measured with the conventional technique seems to be out of proportion to the clinical findings, referral to a specialist cardiovascular heart for further investigation may be appropriate.
Overweight people
The association betwixt obesity and hypertension has been known since 1923. The link has been confirmed in many epidemiological studies, and has at least two components.9 Firstly, there appears to be a pathophysiological connectedness and it may well be that in some cases the two conditions are causally linked, and secondly, if not taken into account, it may result in inaccurate blood pressure level values being obtained by indirect measurement techniques.
Obesity may bear upon the accuracy of blood pressure measurement in children, young people, the elderly, and significant women.
The relationship of arm circumference and float dimensions has been discussed above. If the bladder is too short, claret pressure will be overestimated—"cuff hypertension"—and, if too long, blood pressure may be underestimated.3
Arrhythmias
The difficulty in measuring claret pressure in patients with arrhythmias is that when cardiac rhythm is irregular there is a big variation in blood pressure from beat to beat. Thus in arrhythmias, such equally atrial fibrillation, stroke book and as a consequence claret pressure vary, depending on the preceding pulse interval. Secondly, in such circumstances, there is no generally accepted method of determining auscultatory endpoints. Furthermore claret force per unit area measuring devices vary greatly in their ability to accurately record blood pressure in patients with atrial fibrillation, indicating that devices should be validated independently in patients with arrhythmias.10
In bradyarrhythmias in that location may exist two sources of fault. Firstly, if the rhythm is irregular the same bug equally with atrial fibrillation volition apply. Secondly, when the middle rate is extremely slow, for example 40 beats per minute, information technology is important that the deflation charge per unit used is less than for normal heart rates as too rapid deflation volition atomic number 82 to underestimation of systolic and overestimation of diastolic pressure.
Pregnancy
Clinically relevant hypertension occurs in more than x% of pregnant women in most populations, and in a significant number of these raised claret force per unit area is a key factor in medical decision making in the pregnancy. Particular attention must be paid to blood pressure measurement in pregnancy because of the of import implications for patient direction, equally well every bit the fact that it presents some special problems.11
At that place has been much controversy as to whether the muffling or disappearance of sounds should be taken for diastolic claret pressure. The general consensus from obstetricians based on careful assay of the testify is that disappearance of sounds (5th phase) is the most authentic measurement of diastolic pressure, with the proviso that in those rare instances in which sounds persist to zero the 4th phase of muffling of sounds should be used.12 ,thirteen
Case of a normal ambulatory blood pressure pattern plotted by the DABL® Programme showing a marked variability of blood pressure
Patient in standard seated position
Arm support in standing position
Mean systolic (top) and diastolic (bottom) blood pressures of boys and girls from nativity to xviii years. Diastolic blood pressure reflects the utilize of phase IV Korotkov sounds. Reproduced with permission from de Swiet M, Dillon MJ, Littler W, O'Brien E, Padfield PL, Petrie JC. Measurement of blood pressure in children. Recommendations of a working party of the British Hypertension Society. BMJ 1989;299:469-70
Epidemiological graph for the risk of hypertension in the elderly. Reproduced with permission from Dahloff B, Lindholm LH, Hansson L, Schersten B, Ekbom T, Wester PO. Morbidity and mortality in the Swedish Trial in Quondam Patients with Hypertension (STOP-Hypertension). Lancet 1991;394:405-12
Recommended bladder length
Blood pressure in atrial fibrillation
Taking blood force per unit area of a meaning adult female
Table
Recommended bladder dimensions. Data reproduced from O'Brien E, Petrie J, Littler WA et al. Claret Pressure Measurement: Recommendations of the British Hypertension Society. London: BMJ Books, 1997
| Dimensions (cm) | Subject area | Maximum arm circumference (cm) |
|---|---|---|
| 4×thirteen | Small children | 17 |
| 10×18 | Medium sized children | |
| Lean adults | 26 | |
| 12×26 | Majority of adult arms | 33 |
| 12×40 | Obese adults | 50 |
References
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Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1120141/
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