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Rapid oscillometric blood pressure measurement compared to
conventional oscillometric measurement
Steven A. Yarowsa, Ketul Patelb and Robert Brooka
Background There have been few reports studying the
necessary interval between blood pressure Oscillometric blood pressure measurement has largely measurements, after the initial rest period.
replaced the auscultatory method in electronic bloodpressure monitors today. Although the measurementmethods are different, the results are clinically equiva- Methods Blood pressure was measured in 50 patients
lent and the devices are easier to manufacturer w1,2x.
using the conventional oscillometric technique ( and the rapid oscillometric technique ( Measurement of blood pressure Ž BP in research studies has used the average of three measurements w3,4x. The Results The difference between COT and ROT was
recommended technique is to have the patient sit for 5 y1.1/y0.1 mmHg, which was not significantly different min and take measurements with 1᎐2 min between the ( p = 0.8/ 1.0 and the pulse difference was y0.8 beats measurements. The recommendation from the Ameri- per minute ( p = can Heart Association to wait 1᎐2 min is based on theauscultatory method of measurement, however this re- Conclusions It is concluded that a 15-second interval
commendation has not been scientifically validated. It is between blood pressure readings is as accurate as a theorized that venous engorgement that occurs with toorapid cuff re-inflation induces measurement errors w x one-minute interval providing that these measurements are started after a 5-minute rest period. Blood Press Unfortunately, these errors are not considered in clinical Monit 6:145– 147 䊚 2001 Lippincott Williams & practice and most clinicians do not use average BP but rather use single blood pressures to make clinical deci-sions and save time w x Blood Pressure Monitoring 2001, 6:145 – 147
Keywords: blood pressure determination, hypertension, oscillometry
The purpose of this study was to determine if, after being seated for 5 min, waiting 15 sec between oscillo- Division of Hypertension, University of Michigan Health System, bCollege of Literature, Science and the Arts, University of Michigan, Ann Arbor, metric blood pressure readings was equivalent to wait- Michigan, USA.
ing 1 min between readings. If the rapid method is as Correspondence and requests for reprints to Steven A. Yarows, MD, effective, this will save time for the busy health care Chelsea Internal Medicine, 128 Van Buren, Chelsea, Michigan 48118,USA.
providers, which may increase the likelihood of repeti- Tel: +1 734 475 8677; fax: +1 734 615 1176; e-mail: syarows@ umich.edu tive blood pressures, which could improve the accuracy Received 05 January 2001 Revised 04 April 2001
of measurement of hypertension.
Accepted 24 April 2001
Methods
Blood pressure was measured in 50 patients of at least
18 years of age using an Omron HEM-705CP automatic
oscillometric device. The experimental protocol and the
process for obtaining consent from the subjects was
approved by the University of Michigan Medical School
Institutional Review Board. The patients were nor-
motensive and hypertensive volunteers from a general
internal medicine practice. Each patient was seated
upright for 5 min before measurement began and was
instructed not to speak during measurement. During
measurement, the patient was seated upright in a chair
with back support. Each subject had three measure-
ments with each technique Žsix measurements total per
subject using the same arm for both the conventionaloscillometric technique Ž COT and the rapid oscillo- metric technique Ž ROT , Figure 1. The COT measured three readings with 1 min between measurements, andthe ROT measured three readings with 15 sec betweenmeasurements. Patients with odd patient numbers had 1359-5237 䊚 2001 Lippincott Williams & Wilkins 146 Blood Pressure Monitoring 2001, Vol 6 No 3
Protocol schematic the COT first, while patients with even patient num- % CI 120.7᎐130.5 r77.0 95% CI 73.8᎐80.1 mmHg bers had the ROT first.
with a pulse of 75.9 Ž95 % CI 72.5᎐79.3bpm. The BP difference was ᎐1.3ry 0.1 mmHg with a pulse differ-ence of ᎐0.5 bpm ps0.72r0.98 and pulse p of 0.83.
The first readings for each subject were always after 5 min of rest. The first reading was alternated with con- 161r104 mmHg and in the ROT group 170r101 mmHg.
secutive subjects between the COT and the ROT to The minimum BP in the COT group was 90r55 mmHg avoid bias from the initial 5 min of relaxation. The first and in the ROT group 87r54 mmHg.
readings from each of the methods were not included inthe analysis to avoid skewing the results due to the5-min initial baseline rest before the first of the six The measurements were analysed according to con- readings per subject. Thus, the analysis only included ventional systolic BP ranges - 110, 110᎐139, and measurements that allowed 15 sec Ž )139 mmHg. The greatest difference was seen in the COT between readings.
conventional systolic BP Ž SBP - 100 mmHg in which the ROT under-measured the systolic by 2.3mmHg.
The diastolic and pulse in this range and all the mea- Microsoft Excel 97 was used for analysis of the data.
surements for the other blood pressure ranges all de- The student's t-test with two-tail distribution and two- monstrated differences of less than 1.6 mmHg between sample equal variance was used to determine any sig- the techniques and these differences for systolic, dias- nificance in the relationship between blood pressure tolic, and pulse differences were not significant Ž p ) and pulse. 50 subjects were calculated to have the 80% 0.05. 8 percent of the ROT group was misclassified power to detect a 3mmHg difference Ž p fidence intervals were calculated with an alpha of 0.05.
-110 mmHg. 12 percent was misclassified within theconventional SBP range of 110᎐139 mmHg, whereas 5%misclassified within the )139 mmHg range.
Results
50 subjects volunteered for the study. The average age
was 50
Figure 2 shows the Bland᎐Altman plot indicating a lack " 17 years old range 18᎐97 with 55% of the subjects being male. The average blood pressure in the of difference in the measurement techniques based on COT group was 123.4 conventional systolic and diastolic pressures. Most of % CI 120.0᎐126.9 r76.4 95% the readings were within two standard deviations. The ᎐78.6 mmHg and in the ROT group was 124.5 COT pulse was slightly greater than the ROT pulse at % CI 121.0᎐128.1 r76.5 95% CI 74.3᎐78.6 mmHg higher pulses and less than ROT at lower pulses, how- % CI 72.7᎐77.8 and 76.1 95% CI ever this difference was slight and most of the readings ᎐78.6 beats per min bpm , respectively. The dif- ference between COT and ROT was y1.1ry were within two standard deviations.
0.0 mmHg, which was not significantly different Ž p s0.8 r1.0 and the pulse difference was y0.8 bpm ps One patient had a 21 mmHg systolic difference between 0.8. Including the first measurements with the second the techniques and this patient had a rapid 24 mmHg and third measurements produced similar results. The decrease in systolic BP over the first 8 min including COT average was 124.0 Ž95 % CI 119.5᎐129.1 r76.9 the 5-min waiting period. This suggests that the usual % CI 73.9᎐79.9 mmHg with a pulse of 75.4 95% CI 5-min waiting period was not adequate for this patient.
᎐78.9 bpm. The ROT group average was 125.6 Another patient had a 33 bpm change in heart rate ROT measurement compared to COT measurement Yarows et al. 147
mended that 1᎐2 min should elapse between measure-ments to allow the release of blood trapped in the veinsbefore further determinations are made, although evi-dence supporting this was not cited w x 5 . Ischemia in an arm distal to the measurement will lower BP by5r15 mmHg if the ischaemia is 20 mmHg above thesystolic BP Ž SBP for 90 sec, however it raises the BP slightly if the ischaemia is sustained for only 30 sec w x Since proper technique is to inflate the 20 mmHg abovethe SBP and use a deflation rate of 2 mmHgrsecond,ischaemia above the SBP would only last 10 sec and itis unlikely to change the measurement of the BP.
There was a non-significant Ž -1.1 mmHg difference between the rapid and conventional BP measurementtechniques for systolic, diastolic and pulse readings.
The rapid technique had the greatest difference com-pared to the conventional technique between systolicBP 90᎐109 mmHg based on the conventional tech-nique, however this difference was also not significantŽ p Conclusion
Blood pressure readings may be repeated after 15 sec
without affecting the accuracy of the measurements.
The proper technique is to have the patient seated for
five minutes and perform 2᎐3measurements with 15
sec between readings.
Acknowledgements
We are grateful to Andrew Zweifler, MD, John Amer-
ena, MD, and Osamu Shirasaki for their assistance in
this manuscript.
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Discussion
There is little experimental evidence to indicate the
proper interval between BP measurements. The Ameri-
can Heart Association Committee in 1980 recom-

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