thedinamap 1846sx blood recorder: hawksley zero … · carried out in that subject using both...

J7ournal of Epidemiology and Community, Health 1992; 46: 164-169

The Dinamap 1846SX automated blood pressure

recorder: comparison with the Hawksley randomzero sphygmomanometer under field conditions

Peter H Whincup, Nigel G Bruce, Derek G Cook, A Gerald Shaper

AbstractStudy objective-The aim was to compare

the performance of the Dinamap 1846SXautomated oscillometric blood pressurerecorder with that of the Hawksley randomzero sphygmomanometer during use underfield study conditions.Design-Two independent within subject

measurement comparisons were made, onein adults and one in children, eachconducted in three stages over severalmonths while the Dinamap instrumentswere being used in epidemiological fieldsurveys.Setting-The studies were done in

outpatients clinics (adults) and primaryschools (children).Participants-141 adults (20-85 years) and

152 children (5-7 years) took part.Measurements and main results-In

adults a pair of measurements was madewith each instrument, the order alternatingfor consecutive subjects. In children onemeasurements was made with eachinstrument, in random order. Measure-ments with the Dinamap 1846SX werehigher than those with the random zerosphygmomanometer both in adults (meandifference 8-1 mm Hg; 95% CI 6 5 to 9 7 mmHg) and in children (mean difference 8-3mm Hg; 95% CI 6-9 to 9'7 mm Hg). Diastolicmeasurements were on average verysimilar both in adults and in children. Theresults were consistent at all three stages ofboth studies. The differences in systolicmeasurement were independent of bloodpressure level. However, the extent ofagreement in diastolic pressure dependedon the diastolic blood pressure level; in bothstudies Dinamap diastolic measurementswere higher at low diastolic pressures whilerandom zero diastolic measurements werehigher at high diastolic pressures.Conclusions - Systolic measurements

made with the Dinamap 1846SX instrumentare not directly comparable with thoseof the Hawksley random zero sphygmo-manometer and are unlikely to becomparable with those of earlier Dinamapmodels. These differences have importantimplications for clinical practice andfor comparisons of blood pressuremeasurement between epidemiologicalstudies. However, the consistency ofmeasurement by the Dinamap 1846SX overtime suggests that the instrument may havea place in standardised blood pressuremeasurement in the research setting.

The use of the sphygmomanometer instandardised blood pressure measurement raisesseveral potential problems. Blood pressuremeasurement may vary between observers,' andobserver performance may vary over time,despite observer training.2 3 Modified sphygmo-manometers4 5 may reduce digit preference but donot necessarily eliminate observer bias in bloodpressure measurement. By standardising thetechnical aspects of measurement and recording,automated blood pressure recorders may reducethese variations in blood pressure measurement.However, insufficient information is available onthe performance of many of these instruments.6The Dinamap automated blood pressure recorder(Critikon Inc), which uses the oscillometricmethod,7 is being increasingly used byinvestigators. The earlier Dinamap devices,particularly the 845 and 847 series, have beenextensively studied in comparison with directintra-arterial measurement7-17 and the mercurysphygmomanometer. 18-23 However, relativelylittle attention has been given to the more recentDinamap series.24 25 Moreover, few data areavailable on the accuracy of the instrument atdifferent blood pressure levels26 and on theperformance and reliability of the Dinamap inpopulation based surveys. We report the results oftwo separate studies designed to compare theperformance of the more recent Dinamap 1846SXautomated blood pressure recorder with theHawksley random zero sphygmomanometer.These studies, one in adults and one in children,were both carried out over several months whilethe Dinamap insruments were being used in twolarge population surveys.27 28

MethodsSTUDY IN ADULTS

Subjects aged between 20 and 85 years attending amedical outpatient clinic were invited toparticipate. A total of 154 subjects took part. Thestudy took place in three stages over a total ofseven months. All measurements were made bytwo experienced observers, each of whomexamined approximately half the subjects on eachoccasion. Both observers received training inauscultatory blood pressure measurement2 lessthan a week before the beginning of each stage ofthe study. Observer performance was examinedafter each training session with a standard testtape2; all observers showed an average errorwithin the recommended limits of one second(2 mm Hg) in both systolic and diastolicrecordings throughout the study. All measure-ments were made on the right arm with the subject

Department of PublicHealth and PrimaryCare, Royal FreeHospital and Schoolof Medicine, RowlandHill Street, LondonNW3 2PF, UnitedKingdomP H WhincupN G BruceD G CookA G Shaper

Correspondence to:Dr Whincup

Accepted for publicationMay 1991

on March 21, 2021 by guest. P

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Dinamap 1846SX v Hawksley random zero sphygmomanometer

seated after 5 minutes' rest. Four consecutiveblood pressure measurements were taken at oneminute intervals on each participant, two with theDinamap 1846SX and two with the Hawksleyrandom zero sphygmomanometer. The order inwhich the instruments were used was alternatedfor each subject, ensuring that numbers werebalanced for each session. The Dinamap 1846SXhad an initial inflation pressure of 180mm Hg andall results were recorded directly onto a printedoutput. A standard Hawksley random zerosphygmomanometer was used with an initialinflation pressure of 200 mm Hg. Diastolicpressure was recorded at the point ofdisappearance of Korotkow sounds (Phase V).The cuff sizes recommended by the manu-facturer, which conform to the guidelines of theAmerican Heart Association,29 were used on eachoccasion with both instruments.

STUDY IN CHILDRENChildren aged between five and seven years andattending three primary schools were invited totake part in this study. A total of 152 subjects tookpart. The study took place in three stages over aperiod of 10 months. All measurements weremade by two experienced observers, each ofwhom made approximately half of the pairedblood pressure measurements on each occasion.Training and testing in auscultatory bloodpressure measurement was carried out as in theadult study.2 All measurements were made on theright arm with the subject seated after 5 minutes'rest. Two consecutive blood pressure measure-ments were taken one minute apart on eachparticipant, one with a Dinamap 1846SX and onewith a Hawksley random zero sphygmo-manometer. The order of measurement wasrandomly allocated and balanced for each session.Both instruments were distinct from those used inthe adult study. The Dinamap 1846SX was ofidentical specification; the Hawksley random zeroinstrument was fitted with a 20 mm Hg cam,enabling a lower initial inflation pressure of180 mm Hg to be used. Diastolic pressure wasrecorded at the point of muffling of Korotkowsounds (Phase IV) because of the difficulty inrecording Phase V accurately in children.29 Thecuff bladder size used for each instrumentfollowed the recommendations of Prineas andcolleagues,30 closely related to those of theAmerican Heart Association,29 to ensure that cuffbladder length was at least 900/0 of arm

circumference and the cuff bladder width at least120% of arm diameter in every case. Two sizes ofcuffwere available for use with each instrument inthe study; cuff bladder dimensions for theDinamap were 15 cm x 9 cm (child), 22 cm x

12 cm (adult), and for the Hawksley were 18 cm x9 cm (child), 23 cm x 12 cm (adult). In a separatestudy, a systematic difference in blood pressuremeasurement between the two cuffs used witheach instruments was observed, with child cuffsrecording systematically higher blood pressuresthan the adult cuffs.3' Accordingly, all resultswere standardised to the child cuff size asdescribed.32 However, the results presented hereare very similar whether or not suchstandardisation is employed.

USE OF INSTRUMENTS IN FIELD STUDIES

Between the first and third set of comparisonsdescribed here, both Dinamap instruments wereused in epidemiological field surveys, eachinstrument making more than 10 000 bloodpressure measurements and being calibrated dailyduring use against standard mercury columns at0, 50, 100, 150, and 200 mm Hg. No evidence ofdrift in static calibration requiring adjustmentwas detected in either of the two instruments. Inthe adult study, the instrument failed to recordmeasurements in only two subjects out of 2615,while in the child study measurements wereobtained in all but seven of4116 subjects (0- 170%),usually as a result of the child moving. TheHawksley instruments were held specifically forthe comparative studies over this period and madeno other measurements.

STATISTICAL METHODSMean differences between instruments-In theadult study results are based on the means of thepairs of readings carried out with each instrumentin each subject; in the study of children, resultsare based on single readings. The comparisonsbetween instruments reported are all based onwithin subject differences, presented as Dinamapmeasurement minus Hawksley measurementthroughout.Bloodpressure level-Blood pressure level for eachsubject is calculated as the mean of all readingscarried out in that subject using both Dinamapand Hawksley instruments. Adjustments for theorder in which the machines were used for eachsubject were made because blood pressure tendsto fall with succesive measurements. Relation-ships between the difference between measure-ments by the two instruments and the meanrecorded blood pressure were examined usingstandard multiple linear regression techniques.Comparisons of measurements at differentsessions were examined using a one way analysisof variance.

ResultsResults are presented for all 152 subjects in thechildren's study. In the adult study results arepresented for 141 (93%) subjects. Thirteensubjects with incomplete data have beenexcluded. The characteristics ofsubjects allocatedto different order ofmeasurement are presented inthe table. In the adult study there was a differencein the age and sex distribution of the two groups,with subjects measured first with the Hawksley

Characteristics ofsubjects by order ofmeasurement. Valuesare mean (SE).

Dinamap first Hawksley firstAdult study

Number 71 70Age (years) 51-8 (1-9) 57-0 (2 0)Sex (qO male) 45 59Observer (°h each) 51/49 56/44SBP (mean of both readings) 135-9 (3-0) 135-8 (2-6)DBP (mean of both readings) 78-4 (1-6) 76-4 (1 5)

Child studyNumber 74 78Age (years) 6-32 (0-08) 6-31 (0-08)Sex (%1 male) 52 54Observer (00 each) 50/50 47/53SBP (mean of both readings) 96-4 (1-2) 96-4 (1-1)DBP (mean of both readings) 58-2 (0-8) 57-1 (0-7)SBP= systolic blood pressure; DBP = diastolic blood pressure

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being older and having a greater predominance ofmales. However, adjustment for these factors hadno important effect on the measurement

differences between the instruments. Thecharacteristics of the randomised groups in thestudy of children are very similar. All results wereexamined for each observer separately. Noimportant differences between observers were

found and results are therefore presented withoutobserver adjustment.

MEAN SYSTOLIC PRESSURE DIFFERENCES BETWEENINSTRUMENTS AND THEIR RELATIONSHIPS TOSYSTOLIC BLOOD PRESSURE LEVEL

Systolic blood pressure measurements were

markedly higher with the Dinamap instrumentthan the Hawksley instrument both in adults(mean difference 8-1 mm Hg; 950° CI 6 5 to9 7 mm Hg; p<0 0001) and in children (meandifference 8-3 mm Hg; 950o CI 6-9 to 9 7 mm Hg;p < 0001).The relationships between these systolic blood

pressure differences between instruments andsystolic blood pressure level are presented infigure 1. Systolic differences between instrumentsare not importantly influenced by blood pressurelevel either in adults or in children; regressioncoefficients, representing the change in systolicblood pressure difference between instruments inmmHg for each 1 mm Hg change in systolic bloodpressure level, are 0-046 (standard error 0 035,p=0 20) for adults and 0-013 (standard error

0-072, p=O085) for children.

MEAN DIASTOLIC PRESSURE DIFFERENCES BETWEEN

INSTRUMENTS AND THEIR RELATIONSHIPS TO

DIASTOLIC BLOOD PRESSURE LEVEL

Mean differences in diastolic pressure betweenthe Dinamap and Hawksley instruments are verysmall, both in adults (mean difference 0-2mm Hg;95% CI 1-2 to 1-6 mm Hg) and in children (meandifference -0.2 mm Hg; 95% CI 1-8 to 1-4 mm

60-

I

E 40Ea)0C

CD 20-

O

-20-

Children1 Systolic

Hg), suggesting a high level of overall agreementin diastolic pressure between the instruments.The relationships between diastolic differencesbetween instruments and diastolic blood presurelevel are presented in figure 1. There appears to bea negative relationship between blood pressure

level and blood pressure difference betweeninstruments; at high diastolic pressure levelsDinamap readings are lower than Hawksleyreadings, whereas at low diastolic pressure levelsthe reverse is true. This appears to be the case inboth the study of adults and the study of children.Regression coefficients, which represent thechange in diastolic blood pressure differencebetween instruments (mm Hg) for each mm Hgchange in diastolic blood pressure level, are

-0-189 (SE 0-051, p=0 0003) for adults and-0-324 (SE 0-102, p=0 002) for children. Thestrengths of these relationships suggest that a 10mm Hg rise in diastolic blood pressure level isaccompanied by a fall in Dinamap-Hawksleydifferences of 1 9 mm Hg for adults and 3-1 mmHg for children. The slopes of these relationshipsbetween blood pressure level and measurementdifferences are not markedly different in the twostudies (test for difference between slopes,p = 0-25). However, the positions of these slopesare quite different, as indicated by the differencebetween the two studies in the diastolic bloodpressure level at which there is completeagreement between instruments, 79mm Hg in theadult study and 57mm Hg in the child study. Thisdifference is highly statistically significant(p< OOl).

BLOOD PRESSURE DIFFERENCES BETWEEN

INSTRUMENTS OVER TIME

The differences in blood pressure measurementbetween the Dinamap and Hawksley instrumentsat each of the three examination sessions are

presented in fig 2. Variations in measurementdifferences between sessions were more marked

601 Systolic

40-

70 80 90g 100 110 120 130Systolic blood pressure level (mm Hg)

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Figure 1 Blood pressurelevel and differences inblood pressuremeasurement betweenDinamap 1846SX andHawksley instruments.Systolic and diastolicdifferences (Dinamap-Hawksley) are presentedfor individual subjects inboth adult and childstudies. SBP=s stolicblood pressure; DBPdiastolic blood pressure.

20-

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-40-.5 .O .5 56 .5 60 d5 iO 7'5

Diastolic blood pressure level (mm Hg)80

Diastolic blood pressure level (mm Hg)



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Children

Figure 2 Differences inblood pressuremeasurement betweenDinamap 1846SX andHawksley instruments(Dinamap-Hawksley) bysession of examination.Means and 95,confidence intervals areshown. SBP=systolicblood pressure;DBP= diastolic bloodpressure.

Figure 3 Review ofpublished comparisons ofsystolic and diastolic bloodpressure measurementbetween Dinamap oscillo-metric recorders andsphygmomanometers. Thename of the first author,the number of theDinamap model, and thetype of sphygmo-manometer(SS= standard mercurysphygmomanometer;RZ= random zerosphygmomanometer;MM= mercury mano-meter) are given in eachcase. The mean Dinamap-sphygmomanometerdifference, with 95%confidence intervals wherepossible, is shown for eachstudy. ch=child;ad= adult.

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for systolic than for diastolic pressure in bothadults and children. In the case of adults, meanDinamap-Hawksley systolic differences increasedby a total of2-8mmHg between the first and thirdsessions. However, these changes could easily bedue to chance (p = 0 42). There was also anincrease in systolic differences between the firstand third stages of the children's study (by 3 5mm Hg) but although the difference approachedthe conventional level of statistical significance(p = 0-064) there was no indication of a consistenttrend. For diastolic pressure the agreement ofDinamap and Hawksley measurements wasextremely consistent over the period ofexamination in both adult and child studies.

DiscussionThis report is among the first describing theperformance of a contemporary automatedoscillometric blood pressure recorder, theDinamap 1846SX, under field survey conditions.The populations studied encompass a wide rangeof ages and blood pressure levels, with over 10%of adult subjects being hypertensive (systolicblood pressure>, 160 mm Hg or diastolic bloodpressure .95 mm Hg).

Study

Whincup (ch)Whincup (ad)MaheswaranOrnsteinEllisonSilasPessenhoferUndenJenner

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1 846/RZ1 846/RZ1 846/RZ81 00/SS845/SS i

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OVERALL DIFFERENCES BETWEEN DINAMAP AND

HAWSKLEY INSTRUMENTSThe Dinamap 1846SX recorded systolicpressures consistently higher than those obtainedby the Hawksley instrument in both adults andchildren. Diastolic pressures, by contrast, showeda high level of overall agreement betweeninstruments. Although these results are based onstudies using a single instrument in each case, theobservations of the two studies are strikinglyconsistent. Placed in the context of previousreported comparisons between Dinamap andauscultatory instruments (fig 3), the results are inclose agreement with the one previous studyinvolving the Dinamap 1846SX,25 and also withthe results of a study of the Dinamap 8100, aclosely related model.'8 The most striking featureof this figure is that whereas systolicmeasurements made by the earlier Dinamap 845model match auscultatory measurements closely,those ofthe 8100 and 1846SX exceed auscultatorymeasurements by several millimetres. Differentreference sphygmomanometers were used inthese studies, with some using the standardmercury instrument and others the Hawksleyrandom zero instrument. However, the

StudyWhincup (ch)Whincup (ad)MaheswaranOrnsteinEllisonSilasPessenhoferUndenJenner

15

1846/RZ1 846/RZ1 846/RZ8100/RZ845/SS845/RZ845/MM845/SS845/RZ

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differences shown in fig 3 appear to beindependent of the type of reference sphygmo-manometer used and the findings are thereforeunlikely to be explained by the differences inblood pressure measurement between thestandard and random zero instruments whichhave been reported.32-34 The most likelyexplanation of the findings in fig 3 is that systolicmeasurement by the Dinamap 1846SX and 8100models is not comparable with that of the earlier845 model, possibly as a result of changes inprogramming in the newer models. For diastolicpressure, by contrast, measurements made by allDinamap models agree closely with those ofsphygmomanometers (fig 3). The relationshipbetween Dinamap 1846SX measurement anddirect intra-arterial measurements remainsuncertain. Only one study, conducted inpremature neonates, has compared Dinamap1846SX measurements with direct intra-arterialmeasurement.24 In that study, the Dinamap1846SX underestimated directly measured systolicpressure by an average of 4 9 mm Hg, a findingwhich contrasts with earlier reports on the 845and 847 models, which showed good agreementwith direct intra-arterial measurement.9-11 Thesecontradictory findings emphasise the need forfurther evaluation of the Dinamap 1846 SX,particularly in relation to direct intra-arterialpressure measurement.

INSTRUMENT DIFFERENCES IN BLOOD PRESSURE

MEASUREMENT AND THEIR RELATIONSHIP TO BLOOD

PRESSURE LEVEL

A negative relationship between diastolic pressurelevel and diastolic differences between the twoinstruments was observed in both adult and childstudies. This has not previously been reportedwith the Dinamap 1846SX,25 although an earlierstudy suggested that the Dinamap 845 mightoverestimate pressures at low blood pressurelevels. 17 The basis for the finding remainsuncertain, but it seems unlikely that diastolicblood pressure level per se is responsible. Themarked difference in the position of the slopesrelating diastolic blood pressure level andinstrument differences in the adult and childhoodstudies argues strongly against a uniformrelationship between blood pressure level andinstrument differences. This suggests that a factorother than blood pressure level is responsible forthe relationship.

CONSISTENCY OF DINAMAP PERFORMANCE OVER

TIMEThe Dinamp instrument proved robust, with nomechanical or electronic component failuresdespite frequent dismantling and removal.However, the condition of the rubber 0-ringssealing the pressure hose junctions coulddeteriorate quite rapidly with repeated cuffchanges and dismantling of the instrument andcareful monitoring was required to ensure thatthese remained in satisfactory condition. Thestatic calibration testing of both instrumentsremained stable throughout the periods of study.Moreover, the studies described in this reportprovide no strong evidence of drift in bloodpressure measurement with either instrument,

despite extensive use, an experience consistentwith that of Ellison et al with the Dinamap 845.19

IMPLICATIONS FOR USE OF THE DINAMAP 1846SXINSTRUMENTThe large systematic difference in systolicmeasurement between the Dinamap 1846SX andthe random zero sphygmomanometer, exceedingthe 5 mm Hg limits advocated by the Associationfor the Advancement of Medical Instrumen-tation,35 could lead to the overdiagnosis of hyper-tension if systolic criteria based on auscultatorymeasurements are applied to measurements madeby the Dinamap 1846SX. The results of this studytherefore suggest that the Dinamap 1846SX isunsuitable as a direct substitute for thesphygmomanometer in a clinical setting. In theresearch setting (both in population studies andclinical trials), the ability to make consistentmeasurements in all circumstances is particularlyimportant. Our data suggest that the Dinamap1846SX fulfils this criterion. Systematicdifferences in blood pressure measurement fromthe standard sphygmomanometer are of lessimportance in the research context because themain outcome of a research investigation willnormally be based on blood pressure comparisonsconducted within the study. However,comparisons between studies using the Dinamap1846SX and other instruments are inadvisableunless differences in measurement between theseinstruments are taken into account.

Addendum-Since this paper was prepared,another report has provided evidence ofsystematic differences in systolic blood pressuremeasurement (and possibly also diastolicmeasurement) between the Dinamap 1846SX andausculatory instruments.36

We thank the patients, parents and children whoparticipated in this study. The contributions ofCatherine Bond RGN, Sarah Burke RGN RM,Stephanie Kershaw RGN, Madeleine St Clair RGN,Dave Macfarlane BA and Andy Thomson BA aregratefully acknowledged.The studies were supported by grants from the MedicalResearch Council, British Heart Foundation, WellcomeTrust, and Scottish Hospital Endowment ResearchTrust.

1 Rose GA, Blackburn H, Gillum RF, Prineas RJ.Cardiovascular survey methods. Geneva: World HealthOrganization, 1982: 78-88.

2 Rose G. Standardisation of observers in blood pressuremeasurement. Lancet 1965; i: 673-4.

3 Bruce NG, Shaper AG, Wannamethee G, Walker M.Observer bias in blood pressure studies. J Hypertens 1988;6: 375-80.

4 Garrow JS. A zero muddler for unprejudiced sphygmo-manometry. Lancet 1963; ii: 1205.

5 Rose GA, Holland WW, Crowley EA. A sphygmo-manometer for epidemiologists. Lancet 1964, ii: 296-200.

6 O'Brien E, Petrie JC, Littler WA, de Swiet M. Standards forblood pressure measuring devices. BMJ 1987; 294: 1245-6.

7 Ramsey M. Non-invasive automatic determinants of meanarterial pressure. Med Biol Eng Comput 1979; 17: 11-18.

8 Park MK, Menard SM. Accuracy of blood pressuremeasurement by the Dinamap monitor in infants andchildren. Pediatrics 1987; 79: 907-14.

9 Pellegrini-Caliumi G, Agostino R, Naderi G, et al.Evaluation of an anterior oscillometric method and ofvarious cuffs for the measurement of arterial blood pressurein the neonate. Acta Paediatr Scand 1982; 71: 791-7.

10 Colan S, Fujii A, Borow K, et al. Non-invasivedetermination of systolic, diastolic and end-systolic bloodpressure in neonates, infants and young children:comparisons with central aortic pressure measurements.Amn _7 Cardiol 1983; 52: 867-75.

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11 Borow KM, Newburger JW. Non-invasive estimation ofcentral aortic pressure using the oscillometric method foranalysing systemic artery pulsatile flow: comparative studyof indirect systolic, diastolic and mean arterial pressurewith simultaneous direct central aortic pressuremeasurements. Am Heart J 1982; 103: 879-86.

12 Kimble KJ, Darnall RAJ, Yelderman M, Ariagno RL, ReamAK. An automated oscillometric technique for estimatingarterial pressure in critically ill newborns. Anesthesiology1981; 54: 423-5.

13 Yelderman M, Ream AK. Indirect measurements of meanblood pressure in the anaesthesized patient. Anesthesiology1979; 50: 253-6.

14 Hutton P, Dye J, Prys-Roberts C. An assessment of theDinamap 845. Anaesthesia 1984; 39: 261-7.

15 Rutten AJ, Ilsley AH, Skowronski GA, Runciman WB. Acomparative study of the measurement of mean arterialblood pressure using automatic oscillometers, arterialcannulation and auscultation. Anaesth Intensive Care 1986;14: 58-65.

16 Friesen RH, Lichtor JL. Indirect measurement of bloodpressure in neonates and infants utilizing an automaticnon-invasive oscillometric monitor. Anesth Anaig 1981; 60:742-5.

17 Johnson CJH, Kerr JH. Automatic blood pressure monitors.A clinical evaluation of five models in adults. Anaesthesia1985; 40: 471-8.

18 Ornstein S, Markert G, Litchfield L, Zemp L. Evaluation ofthe Dinamap blood pressure monitor in an ambulatoryprimary care setting. Jf Fam Pract 1988; 26: 517-21.

19 Ellison RC, Gamble WJ, Taft DS. A device for theautomatic measurement of blood pressure in epidemiologicstudies. Am J Epidemiol 1984; 120: 542-9.

20 Silas JH, Barker AT, Ramsay LE. Clinical evaluation ofDinamap 845 automated blood pressure recorder. Br HeartJ 1980; 43: 202-5.

21 Pessonhofer H. Single cuff comparison of two methods forindirect measurement of arterial blood pressure: standardauscultatory method versus automatic oscillometricmethod. Basic Res Cardiol 1986; 781: 101-9.

22 Linden W, Wright JM. Lack of comparability of twoautomated blood pressure monitors in a hypertensivepopulation. Clin Invest Med 1986; 9: 71-5.

23 Jenner DA, Beilin LJ, Vandogen R. A comparison of bloodpressure measurements obtained with the Dinamap845XT, the standard mercury sphygmomanometer and theLondon School ofHygiene device. Clin Exp Hypertens (A)1988; 10: 575-88.

24 Wareham JA, Haugh LD, Yeager SB, Horbar JD.Predicition of arterial blood pressure in the prematureneonate using the oscillometric method. Am J Dis Child1987; 141: 1108-10.

25 Maheswaran R, Zezulka AV, Gill JS, Beevers M, Davies P,Beevers DG. Clinical evaluation of the Copal UA-251 andthe Dinamap 1846SX automatic blood pressure monitors.J7Med Eng Technol 1988; 12: 160-3.

26 Bland JM, Altman DG. Statistical methods for assessingagreement between two methods of clinical measurement.Lancet 1986; i: 307-10.

27 Whincup PH, Cook DG, Shaper AG, Macfarlane DJ,Walker M. Blood pressure in British children: associationswith adult blood pressure and cardiovascular mortality.Lancet 1988; ii: 890-3.

28 Bruce NG, Cook DG, Shaper AG, Thomson AG.Geographical variation in blood pressure in British menand women. J Clin Epidemiol 1990; 43: 385-98.

29 Frohlich ED, Grim C, Labarthe DR, et al.Recommendations for human blood pressuredeterminations by sphygmomanometers. Report of aspecial task force appointed by the Steering Committee,American Heart Association. Circulation 1988; 77: 502-14A.

30 Prineas RJ, Gillum RF, Hirobe H, Hannan PJ. TheMinneapolis children's blood pressure study. Part 1:standards of measurement for children's blood pressure.Hypertension 1980; 2 (suppl 1): 18-24.

31 Whincup PH, Cook DG, Shaper AG. Blood pressuremeasurement in children: the importance of cuff size. JHypertens 1989; 7: 845-50.

32 O'Brien E, Mee F, Atkins N, O'Malley K. Inaccuracy of theHawksley random zero sphygmomanometer. Lancet 1991;336: 1465-8.

33 De Gaudemaris R, Folsam AR, Prineas RJ, Leupker RV.The random-zero versus the standard mercurysphygmomanometer: a systematic blood pressuredifference. Am J Epidemiol 1985; 121: 282-90.

34 Evans JG, Prior IAM. Experience with the random-zerosphygmomanometer. Br J Prev Soc Med 1970; 24: 10-15.

35 Association for the Advancment of MedicalInstrumentation. Recommendations for electronic orautomated sphygmomanometers. Arlington, Virginia:AAMI, 1987.

36 Weaver MG, Park MK, Lee D-H. Differences in bloodpressure level obtained by ausculatory and oscillometricmethods. AmJDis Child 1990; 144: 911-4.

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