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ORIGINAL ARTICLE

Both body and arm position significantlyinfluence blood pressure measurement

RT Netea, JWM Lenders, P Smits and Th ThienDivision of General Internal Medicine, Department of Medicine, University Hospital Nijmegen, Nijmegen,The Netherlands

The position of both the body and the arm duringindirect blood pressure (BP) measurement is oftenneglected. The aim of the present study was to test theinfluence of the position of the patient on BP readings:(1) sitting with the arms supported precisely at the rightatrium level and (2) supine: (a) with the arms precisely atthe right atrium level and (b) with the arms on the

examination bed. In a first group of 57 hypertensivepatients, two sessions of BP and heart rate (HR)measurements were performed in two positions: sittingand supine with the arms supported precisely at rightatrium level in both positions. BP was measuredsimultaneously at both arms, with a Hawksley RandomZero sphygmomanometer at the right arm, and with anautomated oscillometric device (Bosomat) at the leftarm. BP and HR readings obtained in the two positionswere then compared. In a second group of 25 normo-and hypertensive persons, two sessions of BP and HRreadings were performed in supine with the arms in twodifferent arm positions: (a) the arm placed precisely atright atrium level and (b) the other arm on the exami-nation bed. The measurements were performed at botharms with two automated devices (Bosomat). The read-

ings taken in the two positions were compared. Bothsystolic BP (SBP; by 9.579.0 (standard deviation, s.d.);right arm) and diastolic BP (DBP; by 4.876.0 mmHg;right arm) were significantly higher in the supine than inthe sitting position. When the two different arm posi-tions (body continously supine) were compared in thesecond part of the study, significantly higher SBP (by

4.676.1 mmHg) and DBP (by 3.972.8 mmHg) wereobtained when the arm of the patient was placed onthe bed (below the right atrium level), than when the armwas placed at the level of the right atrium. BP readingsin sitting and supine positions are not the same. Whenaccording to guidelines the arm of the patient ismeticulously placed at the right atrium level in bothpositions, the difference is even greater than when thearm rests on the desk or on the arm support of the chair.Moreover, in the supine position small but significantdifferences in BP are measured between arm on a 5cm-high pillow and arm on the bed. In every studyreporting BP values, the position of both the body andespecially the arm should be precisely mentioned.Journal of Human Hypertension (2003) 17, 459462.doi:10.1038/sj.jhh.1001573

Keywords: blood pressure measurements; hypertension; body and arm position

Introduction

The indirect blood pressure (BP) measurement witha mercury or aneroid sphygmomanometer and astethoscope by a trained observer is widely recom-mended as the cheapest and the most accuratemanner of measuring the BP in the daily routine.

The position of the patient during the measurementis often neglected. The reference point for themeasurement of BP is the right atrium, the so-calledheart level.1 The guidelines of the World HealthOrganisation/International Society of Hypertension(WHO/ISH) recommend that the BP should be

routinely measured with the patient comfortablyseated with the arms supported at heart level.2 Todetect orthostatic hypotension, BP should also bemeasured with the patient first supine and subse-quently in the standing position.2 It has beensuggested that BP readings taken in sitting andsupine positions can be considered equivalent if thepatients arm is placed at heart level (right atrium) inboth positions.3 As a practical approximation of theheart level when sitting or standing, it has beenproposed to take the level of the fourth intercostalspace2 or the level of the midsternum.3 We couldfind only scarce information about the approxima-tion of the heart level in the supine position. Usingcomputerised tomography, it has previously beenshown that the level of the right atrium in the supineposition is situated approximately half way betweenbed surface and sternum.4 A special pillow has beendeveloped to be placed under the arm, in order tosupport it at the right atrium level in the supine

Received 28 September 2002; revised 18 January 2003; accepted18 March 2003

Correspondence: Dr Th Thien, Department of Medicine (541),University Medical Center St Radboud, PO Box 9101, 6500 HBNijmegen, The Netherlands.E-mail: t.thien@aig.umcn.nl

Journal of Human Hyper tension (2003) 17, 459462& 2003 Nature Publishing Group All rights reserved 0950-9240/03$25.00

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Results

Influence of body position on BP readings

The main results are given in Table 1. Both thesystolic (SBP) and the diastolic (DBP) blood pres-

sures were significantly higher in the supine posi-tion regardless of the instrument used (Po0.001 forboth). The HR was slightly, but significantly, higherin the sitting than supine position (63.37 9.0 vs62.27 9.0 bpm respectively;P0.037).

Influence of arm position on supine BP readings

Table 2 presents the BP and HR readings taken in thesupine position with the arm on the examinationbed and with the arm supported at the right atriumlevel. As seen in Table 2, no difference was found inthe initial BP readings between the two arms.

However, significantly higher BP readings wererecorded when the arm was placed on the bed thanwhen the arm was supported at right atrium level.Statistical significance was not reached for the SBPin the right arm but the trend of the results wassimilar to that in the left arm. Irrespective of the armposition, the average BP in the first attendedposition (after the first 5 min of rest) was signifi-cantly lower than the initial BP (start BP). Except fora slightly higher SBP difference at the right armwhen the sequence of positions was arm high/arm

low than arm low/arm high (7.074.3 mmHg vs2.376.7 mmHg, P0.048), no significant effect ofthe sequence of the two positions was detected onthe BP differences. With respect to the HR, after aninitial small decrease in the first 5 min of rest itremained unchanged during the procedure.

Discussion

In our group of hypertensive patients, in an out-patient setting, we found significantly lower BPreadings in the sitting than in the supine positionwhen the patients arms were supported at the rightatrium level as exactly as possible in both positions.This confirms previous observations in normo-tensive subjects.4,7

The BP measurement in sitting position is mostoften used in the general physicians office, whereasin some hospitals BP is often measured in supineposition. Both diagnostic and therapeutic decisionsare based on BP readings taken sometimes in sittingand sometimes in supine positions, since they areoften regarded as equivalent. The differences wefound using the Hawksley Random Zero sphygmo-manometer are sustained by those found with theautomatic instrument. The explanation of the slightdifferences in results between the two instrumentscould be the different measurement principle. Oneshould realise that with the oscillometric methodthe mean arterial pressure is determined by themaximal amplitude of the oscillations, and SBP andDBP are subsequently computed from this value.With the mercury sphygmomanometer, however,

both SBP and DBP are separately measured.Another factor that is often neglected during BPmeasurement is the position of the arm of thepatient. We and others79 have shown that thisinduces a consistent difference between BP readingstaken with the arm in different positions. In patientswith a length of 190 cm, we measured differences aslarge as 25 cm between the level of the arm supportof a common chair and the mid-sternum level. Suchdifferences may result in large errors in BP readingsthat could obscure or even inverse the difference in

Table 1 Systolic blood pressure (SBP), diastolic blood pressures(DBP) in mmHg, and heart rate (HR) in bpm, in the 57 patients inthe sitting and supine positions. Results are given as means7 s.d.

Sitting Supine Difference P-value

Hawksley Random ZeroSBP 135.5724.0 145.0723.2 9.579.0 o0.001

DBP 79.279.7 84.179.0 4.876.0 o0.001HR 63.379.0 62.279.0 1.173.8 0.037Automatic oscillometric

SBP 135.7724.8 141.3725.5 5.678.3 o0.001DBP 79.579.7 84.6710.5 5.175.3 o0.001HR 63.379.7 62.579.7 0.873.8 0.128

Table 2 Supine systolic (SBP), diastolic (DBP) blood pressure in mmHg, and heart rate (HR) readings in bpm, in 25 subjects with thearms supported at the heart level and with the arms on the bed; the sequence of the two positions was randomized. Results are given asmean7 s.d.

Starta (arm on the bed) Arm high (at heart level) Arm low (arm on the bed) Difference P-value

Right armSBP 153.07 33.6 138.3729.2 140.2729.4 1.976.3 0.105DBP 85.07 15.6 77.8713.7 80.6714.1 2.872.7 o0.0001HR 69.77 19.2 67.3716.0 67.5717.0 0.272.6 0.57

Left armSBP 151.07 31.6 137.4729.0 142.1728.0 4.676.1 0.0009DBP 86.77 14.2 78.2714.4 82.1713.4 3.972.8 o0.0001HR 70.07 19.4 67.4716.7 67.1716.0 0.273.5 0.638

aThe start readings represent the initial control readings to exclude leftright differences.

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BP readings between the sitting and supine position.The effect of the arm position on BP readings in thesupine position was especially observed duringnocturnal BP registration in ambulatory BP mea-surement (ABPM) studies1013 and in pregnantwomen,1416 when the BP was measured in thelateral recumbent position. The BP values recorded

when the arm was placed above the heart level weresignificantly lower than those recorded when thearm was situated below the heart level. When thepatient is lying on the examination bed, oneassumes that the arms of the patient rest at the levelof the right atrium.5 However, Ljungvall et al 4

demonstrate that even in this case the arms of thepatient are situated clearly below the right atriumlevel. Our results in a group of patients with a widerange of BP values, show that even such a smallvariation in the arm position can result in significantBP differences. To obtain a double control of theresults and to avoid observer bias, we used auto-mated devices, and we performed simultaneousreadings in both arms and for each arm in bothsequences of the two positions. The results showedsimilar trends in both arms and were independent ofthe sequence of the two positions and of the BPlevel. The magnitude of differences we obtainedwas slightly smaller (ranging from 2.8 to 4.6 mmHg)than in the study of Ljungvall et al (5.5 mmHg).A possible explanation for the difference betweenthese two studies could be the fact that oscillometricinstruments were used in the present study, whereasstandard mercury sphygmomanometers were usedin the study of Ljungvall et al .4 However, thedifferences we obtained are closer to those theoreti-

cally expected, when one considers the effects ofhydrostatic forces as a major determinant of thedifferences in BP between the two positions.17

Differences of 34 mmHg may be small as absolutevalue, but are still important in epidemiologicalterms.

In conclusion, the present study shows that theassumption that blood pressure in sitting and supineposition can be considered similar is incorrect evenwhen the arm of the patient is placed at the correctright atrium level in both positions, as officiallyrecommended.

Supporting the arm of the patient on the armsupport of a common chair in the sitting positioncould partially correct and potentially reverse thedifferences between sitting and supine positions.However, this introduces a new source of variationin BP measurement: the various distances betweenthe heart level and the arm support of the chair,which can be as large as 25 cm in tall patients. In

consequence, such practice is incorrect and shouldbe discouraged.

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