Blood Pressure Measurement: Should Technique Define Targets?
Phase: NA
Conditions: Hypertension
Sponsor: Ottawa Hospital Research Institute

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Title:  Blood Pressure Measurement: Should Technique Define Targets? 
 
Research team: 
PI: Marcel Ruzicka, Division of Nephrology, The Ottawa Hospital 
Co-PI: Swapnil Hiremath, Division of Nephrology, The Ottawa Hospital 
Co-investigators: 
Cedric Edwards, Division of Nephrology, The Ottawa Hospital 
Tim Ramsay, Methods Centre, OHRI 
 
Study Budget: $45,000 
Funding Body: Physicians Services Incorporated 
Study Duration: September 2017 – Aug 2018 
 
 
 
 
 
 
 
 
 
 
 
 

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Lay Summary 
Hypertension is the single most important risk factor for cardiovascular disease and death. Over 
the last several decades many classes of blood pressure lowering drugs have been discovered. 
These allow physicians to achieve optimal blood pressure and prevent adverse cardiovascular 
outcomes in most patients. However, the optimal blood pressure level has changed over time, 
and most recently has been decreased to 120 mm Hg, on the basis of clinical trials. These trials 
used a specific rigorous method of blood pressure measurement (patient alone in room, 
enforced period of rest, average of multiple readings) that is currently not the standard of 
practice in most clinics. Blood pressure itself is highly influenced by technique and device. In 
particular the length of resting time (if any), and whether it is measured with device requiring 
medical personnel presence in the room or not. For the same individual, the difference 
between blood pressure taken with and without rest could be 10 mmHg, and presence vs 
absence of medical personnel in the room during rest and/or BP assessment could be another 
10 mmHg. Hence, the target blood pressure could vary materially based on BP technique and 
device used. As it is unlikely that all physicians can change their practice overnight and embrace 
blood pressure device allowing for standard resting time and unattended blood assessment, a 
comparative pragmatic study of the blood pressure technique and devices endorsed by 
Hypertension Canada and used in Canada is desirable to avoid either over- or under-treatment 
of Canadian patients with hypertension. In the present study, we will compare 4 different 
methods of measuring blood pressure in the office (casual, resting average of 3 readings with 
nurse present of absent for resting period, and average of 5 readings) as well as a 24 hour 
ambulatory measurement in 90 patients.  
The results of this study will help and enable practicing family physicians and specialists in 
Canada to target BP for their patients based on algorithm and method of assessment of BP they 
use in their offices.  
 
 
 
 
 
 
 

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Background 
Hypertension prevalence 
Hypertension is a chronic disease with a tremendous burden. Its prevalence is estimated 
globally at about 20%, with an increasing trend continuing in the last 15 years(1). Hypertension 
is highly prevalent among adult Canadians (at about 26%). The prevalence of hypertension 
increases from about 4% in young adults (< 30 years of age) to more than 50% among those 60 
years of age and older. Altogether, hypertension is extremely relevant vascular disease among 
adult Canadians.    
Hypertension and Clinical Outcomes 
Hypertension is the single most important risk for adverse vascular outcomes, comprising 
stroke, heart disease, and both cardiovascular and all-cause mortality. The estimated annual 
death rate per 100 000 associated with systolic BP of 140 mm Hg or higher is about 106(1). The 
largest numbers of hypertension related deaths were caused by ischemic heart disease (4.9 
million; 54.5%), hemorrhagic stroke (2.0 million; 58.3%), and ischemic stroke (1.5 million; 
50.0%)(1). Loss of disability-adjusted life-years (DALYs) associated with systolic BP of 140 mm 
Hg or higher are estimated to be about 143.0 million US dollars(1). Treatment of hypertension, 
using randomized controlled trials (RCTs), showing repeatedly that the risk of these adverse 
vascular outcomes is decreased by sustained blood pressure (BP) lowering.  
Advances in Pharmacological Treatment of Hypertension 
Back in 1940, patients diagnosed with hypertension had very limited treatment options: either 
an extreme low salt diet and/or dorsal lumbar sympathectomy, both very radical measures, 
reserved for individuals with malignant hypertension, at what we would now consider 
extremely high blood pressure levels (with target organ damage). Over the last 75 years, more 
than 7 different classes of BP lowering drugs have been discovered. Hence in the modern era, 
almost all patients with hypertension can have BP level decreased to desired numbers. Hence 
the research focus has moved from how blood pressure could be decreased, to how much 
blood pressure should be decreased, and in whom should these targets apply.  
Blood Pressure Treatment Targets 
Targets for BP have been largely established based on results from prospective observational 
studies, which show a progressive rise in adverse cardiovascular outcomes from the levels of 
systolic BP above 120 mmHg with a steep rise with systolic BP above 140 mmHg. RCTs 
confirmed these findings and showed that decreasing BP below 140 mmHg in the general 
populations, 150 mmHg in the very elderly patients, and 130 mmHg in patients with diabetes 
mellitus significantly reduces adverse vascular outcomes such as stroke, chronic heart failure, 
myocardial infarction, and mortality. Recently, new trials tested the hypothesis of whether 
patients with the highest cardiovascular risk benefit from even lower targets of systolic BP(2).  

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The Systolic Blood Pressure Intervention Trial (SPRINT) and its relevance for BP target in 
patients with high cardiovascular risk 
In this prospective, randomized controlled trial funded by NIH, patients with high 
cardiovascular risk (Framingham Cardiovascular Risk Score > 15%, average 21%) were 
randomized to standard treatment targeting systolic BP < 140 mmHg or to intensive BP 
lowering regimen targeting systolic BP < 120 mmHg(2). This trial, with 9,361 patients, was 
stopped early after an average follow up period of 3.2 years after patients randomized to the 
intensive BP lowering arm experienced a clinically significant decrease in primary outcome 
(comprising of stroke, acute coronary syndrome, congestive heart failure, and cardiovascular 
death). Following this development, a new target of systolic BP < 120 mm Hg for patients with 
hypertension and high cardiovascular risk has been recommended by major national 
professional organizations including Hypertension Canada/Canadian Hypertension Education 
Program, in their most recent Guidelines on the Diagnosis and Treatment of Hypertension(3). 
However, in the discussion around the benefits and risks of more intensive BP lowering, 
insufficient attention has been focused on the method of BP measurement in SPRINT, and how 
it compares to existing methods(4).   
 
Which BP reading is the most relevant to predict adverse vascular outcomes?  
Over the years it became clear that a single office BP reading provides only a snapshot of the 
overall BP load. As expected, repeated office measurements of BP provide better assessment of 
BP load and overall adverse hypertension related vascular outcomes. 24 hour ambulatory BP 
monitoring (ABPM) provides the ultimate assessment of overall BP load during the daytime and 
nighttime. ABPM allows for identification of white coat effect (out of office BP is lower than 
office BP) and masked effect (out of office BP is higher than office BP). Measurement of the 
diurnal variation also allows for identification of nocturnal blood pressure. The average 
nighttime BP appears to be the single most important predictor of adverse vascular outcomes, 
followed by average daytime BP, and repeated office BP recordings. ABPM is, however, not an 
insured service covered by the provincial health insurance in Ontario, or the rest of Canada. 
Finally, home BP measurements, in combination with repeated office BP readings, have also 
become more commonly used now. But home BP is not used by all patients, there is an 
additional cost involved, and home BP monitors may not be accurate. In the real world, hence, 
office BP readings remain the most commonly method used for diagnosis and the management 
of hypertension. Hence it is crucial that accurate methods are used for office BP measurements. 
 
Automated oscillometric BP devices replaced mercury sphygmomanometry 
Mercury sphygmomanometry was, for nearly 100 years, the most commonly used technique 
for office BP assessment. However, readings using this technique are not as accurate and 
reproducible as one may have thought. Firstly, accuracy is highly dependent on the skills of 

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health care professional, and is not only susceptible to human error and listening skills, but also 
to terminal digit preference (rounding to ‘0’). Secondly, at least 20% of patients display higher 
BP readings with health personnel in the room than in real life (white coat phenomenon). 
Additionally, about 10 - 20% of patients have lower BP readings in the office than in real life 
(masked hypertension). Automated oscillometric BP devices (AOBP) eliminate the human error 
as well as attenuate the white coat effect, since they allow for multiple readings to be taken in 
(un)attended fashion. Observational studies have reported that BP measurements with AOBP 
devices are predictive of cardiovascular events. Because of these two major advantages, 
Hypertension Canada recommends automated oscillometric devices as the method of choice 
for office BP measurement. In the last decade, AOBP devices, which typically provide an 
average of 3-5 measurements, have become widespread for use in specialist clinics, and, 
especially, in general practice.  Several features of automated measurements are noteworthy 
and relevant for further discussion.  
 
Relevance of human error and presence of medical personnel for BP readings 
Even trained medical personnel are prone to round up or down actual BP readings to the 
closest zero (5, 6). Automated oscillometric BP devices eliminate this error(7, 8). In addition, 
they mitigate a risk for human error related to variable training, and hearing deficit (6-8).  
Furthermore, the presence of medical personnel during BP readings imposes a positive bias on 
BP, the ‘white coat effect’. This effect may differ from person to person, likely related to varying 
susceptibility for white coat effect between patients (4, 9). By contrast, automated oscillometric 
devices allow for BP assessment in an unattended fashion. Not surprisingly, the differences 
between office BP readings taken by automated oscillometric devices and mercury 
sphygmomanometers can be relatively large. For example, Myers et al reported a positive bias 
for BP readings taken by manual measurement of 13.9 mm Hg, compared to the automated 
oscillometric device(10). Other studies, including those by our group, concur with this 
important degree of positive bias imposed by human error and presence of medical personnel 
in the room during BP readings (11, 12). Finally, casual BP readings taken immediately after 
patient arrival to the office, without prior resting, are also materially higher compared to those 
taken after a rest period. In the recent study by Agarwal, systolic BP readings by using the 
technique and the same device employed in SPRINT were 12.7 mmHg lower as compared to 
single office non-resting office BP reading taken by another oscillometric device, in the 
presence of a medical personnel (13). Indeed, the presence of another person who is talking 
has been reported to result in a positive bias ranging from 4 – 19 mm Hg in systolic BP (6). In 
addition, just the presence of a health personnel (who is not talking) as well as the hospital 
environment itself are the major component of the white coat effect (14). The automated 
devices attenuate this effect by virtue of allowing (a) unattended BP measurement and (b) 
taking an average of multiple readings.  

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Method 
Device  
Details  
Comments 
Difference 
BP trend 
1 
Casual blood 
pressure 
Oscillometric 
device, rarely 
mercury 
First BP 
measured as 
patients walks 
into the clinic 
Can be 
artificially 
high (white 
coat effect) 
Reference 
Higher 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Lower 
 
Resting Blood pressure methods 
2 
BPTru 
BPTru device 
No extra period 
of rest 
1st reading by 
Nurse, who 
leaves room 
5 additional 
readings 1-2 
minutes apart,  
output = 
average of 5 
Reduces 
white coat 
effect 
Associated 
with CV 
outcomes. 
Commonest 
method used 
in Canada 
~ 5-8 mm 
Hg lower 
3 
Omron HEM 
907XL, partly 
attended 
OMRON HEM 
907XL 
5 minutes of 
unattended 
rest, 
Nurse enters 
room 
3 BP readings, 
output = 
average  
Method used 
in SPRINT   
~ 12 – 13 
mm Hg 
lower 
4 
Omron HEM 
907XL, 
unattended 
OMRON HEM 
907XL 
5 minutes of 
unattended 
rest, 
3 BP readings, 
output = 
average 
Patient alone in 
room 
throughout 
 
Not known,  
? 15 mm Hg  
 
 
Ambulatory Blood pressure 
 
5 
ABPM 
Many devices, 
eg Spacelabs 
Oscillometric 
device; left on 
for 24 hours.  
Records every 
30 minutes 
while awake, 60 
minutes when 
asleep 
Linked to CV 
outcomes; 
diagnosis of 
white coat 
and masked 
effect; shows 
diurnal 
variation in 
BP 
~ 5 mm Hg 
lower 
 

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Resting time and Blood Pressure levels 
Ideally, BP measurement should be done after a 5 minute period of rest, as per 
recommendations and best practices. Indeed, insufficient rest period can result in a positive 
bias ranging from + 4.2 to + 11.6 mm Hg(6). Unfortunately, in the real world setting, proper 
resting is rare, and results ‘routine’ BP measurement were reported to be higher by 5.3 mm Hg 
compared to properly done resting BP(15). Importantly, the longer the rest, it appears, the 
lower the BP readings, even beyond the normally recommended 5 minutes. In this regards, 
Nikolic et al compared BP readings taken by automated oscillometric BP device after 5 and 10 
minutes of rest (16). Readings after an additional 5 minutes of rest were lower -4.2 mm Hg. This 
study indicates that the number of minutes of rest prior to BP readings could indeed have a 
clinically meaningful impact on the result, above and beyond the ‘normal’ resting period of 5 
minutes. Until recently, it was left up to medical personnel to assure that BP readings were 
taken after 5 minutes of rest. While there are no studies on quality assurance in this regard, it 
seems reasonable to assume that readings taken by medical personnel are taken with widely 
varying degrees of rest, thereby seriously undermining the clinical interpretation of the 
result(15). The Omron HEM 907 XL, used in SPRINT, is the first automated oscillometric BP 
device that allows for a pre-set defined resting period of 5 minutes, in accordance with 
guidelines on BP measurement by national professional organizations. This device thus allows 
for the removal of the other element of human error, an inadequate resting period. 
Additionally, based on the results of SPRINT, this device does have strong data in terms of its 
use for BP measurement and management and reduction in clinical outcomes. However, this 
device and method is not yet in widespread use in clinical practice.  
 
Barriers to Implementation of BP methods from SPRINT into routine clinical practice 
An enforced 5 minutes of rest and 3 BP readings taken about 1 minute apart (with about 20 
seconds per reading) results in an additional 9 minutes of time. Incorporating this method of BP 
measurement will result in a significant increase in time spent for a routine clinic visit both for 
the patient and for the provider office. The logistics involved may thus require not just the 
additional cost of purchasing new devices, but also additional space, such as a separate room to 
allow for patient flow. These barriers are still very important to surmount, given the fact that 
using this method results in more accurate data, and can result in improved outcomes. Given 
that the BPTru automated devices (which provide no pre-set rest, average of 5 readings) are 
already in widespread use, data on the comparability of these two methods would thus be very 
useful. However, comparative data on automated oscillometric devices with and without pre-
set resting period preceding BP assessment, are however lacking at this time.  
 
 
 

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Translational knowledge gap 
The above data clearly indicate, that there is a significant gap after the SPRINT and that is 
whether and to what extent office BP technique determines the target for systolic BP. Use of 
currently practiced methods (eg casual BP, automated BP with BPTru) for BP measurement, 
while using targets derived from SPRINT may result  in undertreatment or overtreatment of 
hypertensive patients, putting them at risk for cardiovascular outcomes, or exposing them to 
risk of unnecessary adverse events, respectively. As we outlined in our review, taking into 
account the lack of comparative data on differences between BP methods and devices used in 
clinical practice and their effect on BP, comparative studies of casual, attended vs non-attended 
BP readings with and without rest, and daytime BP averages from 24-hour ambulatory BP 
monitoring devices will be important to guide individualized hypertension care (see Appendix,  
“Precision medicine for hypertension management in chronic kidney disease: Relevance of 
SPRINT for therapeutic targets in non-diabetic renal disease” Ruzicka M., et al Can J Cardiol, 
2017, in press). This is exactly the knowledge gap which this study aims to address.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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References 
 
1. 
Forouzanfar MH, Liu P, Roth GA, Ng M, Biryukov S, Marczak L, et al. Global Burden of 
Hypertension and Systolic Blood Pressure of at Least 110 to 115 mm Hg, 1990-2015. JAMA. 2017 Jan 
10;317(2):165-82. 
2. 
Wright JT, Jr., Williamson JD, Whelton PK, Snyder JK, Sink KM, Rocco MV, et al. A Randomized 
Trial of Intensive versus Standard Blood-Pressure Control. N Engl J Med. 2015 Nov 26;373(22):2103-16. 
3. 
Leung AA, Nerenberg K, Daskalopoulou SS, McBrien K, Zarnke KB, Dasgupta K, et al. 
Hypertension Canada's 2016 Canadian Hypertension Education Program Guidelines for Blood Pressure 
Measurement, Diagnosis, Assessment of Risk, Prevention, and Treatment of Hypertension. Can J Cardiol. 
2016 May;32(5):569-88. 
4. 
McCormick BB, Hiremath S, Ruzicka M. A Randomized Trial of Intensive versus Standard Blood-
Pressure Control. N Engl J Med. 2016 Jun 9;374(23):2291-2. 
5. 
Nietert PJ, Wessell AM, Feifer C, Ornstein SM. Effect of terminal digit preference on blood 
pressure measurement and treatment in primary care. Am J Hypertens. 2006 Feb;19(2):147-52. 
6. 
Kallioinen N, Hill A, Horswill MS, Ward HE, Watson MO. Sources of inaccuracy in the 
measurement of adult patients' resting blood pressure in clinical settings: a systematic review. J 
Hypertens. 2017 Mar;35(3):421-41. 
7. 
Myers MG. Eliminating the human factor in office blood pressure measurement. J Clin 
Hypertens (Greenwich). 2014 Feb;16(2):83-6. 
8. 
Myers MG, Godwin M. Automated office blood pressure. Can J Cardiol. 2012 May;28(3):341-6. 
9. 
Myers MG, Godwin M, Dawes M, Kiss A, Tobe SW, Kaczorowski J. The conventional versus 
automated measurement of blood pressure in the office (CAMBO) trial: masked hypertension sub-study. 
J Hypertens. 2012 Oct;30(10):1937-41. 
10. 
Myers MG, Godwin M, Dawes M, Kiss A, Tobe SW, Grant FC, et al. Conventional versus 
automated measurement of blood pressure in primary care patients with systolic hypertension: 
randomised parallel design controlled trial. BMJ. 2011;342:d286. 
11. 
Edwards C, Hiremath S, Gupta A, McCormick BB, Ruzicka M. BpTRUth: do automated blood 
pressure monitors outperform mercury? J Am Soc Hypertens. 2013 Nov-Dec;7(6):448-53. 
12. 
Myers MG, Godwin M, Dawes M, Kiss A, Tobe SW, Kaczorowski J. Conventional versus 
automated measurement of blood pressure in the office (CAMBO) trial. Fam Pract. 2012 Aug;29(4):376-
82. 
13. 
Agarwal R. Implications of Blood Pressure Measurement Technique for Implementation of 
Systolic Blood Pressure Intervention Trial (SPRINT). J Am Heart Assoc. 2017 Feb 03;6(2). 
14. 
Adiyaman A, Aksoy I, Deinum J, Staessen JA, Thien T. Influence of the hospital environment and 
presence of the physician on the white-coat effect. J Hypertens. 2015 Nov;33(11):2245-9. 
15. 
Sewell K, Halanych JH, Russell LB, Andreae SJ, Cherrington AL, Martin MY, et al. Blood Pressure 
Measurement Biases in Clinical Settings, Alabama, 2010-2011. Prev Chronic Dis. 2016 Jan 07;13:E01. 

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16. 
Nikolic SB, Abhayaratna WP, Leano R, Stowasser M, Sharman JE. Waiting a few extra minutes 
before measuring blood pressure has potentially important clinical and research ramifications. J Hum 
Hypertens. 2014 Jan;28(1):56-61. 
 
 
Project Design, Methodology and Analysis 
In this study, we propose to compare the two commonly used automated oscillometric BP 
devices (ie BPTru, most commonly used in Canada and OMRON HEM 907XL, used in SPRINT) as 
well as ambulatory blood pressure monitoring (ABPM) with the most commonly used ‘casual’ 
blood pressure (BP) (see table below for details about the different BP methods). In addition, 
the measurements with the Omron HEM 907XL will be conducted in two different ways, with 
the nurse present after the quiet resting period, but during the BP measurement (ie partially 
attended), or the patient being completely alone (unattended). This will allow us to determine 
the effects of extra time, the difference between devices and being partially attended or 
completely unattended. 
Study Design 
We propose to perform a prospective, randomized, cross-over study to compare two different 
blood pressure (BP) BP measurement methods (see figure 1 for study flow).  
Study Population 
This is a low risk trial where the only `intervention' is additional BP measurements, and office 
visits for the same.  
Inclusion criteria 
All patients being followed in the Renal Hypertension Clinic will be eligible for 
enrolment.  
Exclusion criteria  
These will be focused on those patients for whom oscillometric measurements may be 
difficult  
(1) inability to do oscillometric measurements (eg arrhythmias, pain, device reporting 
error)  
(2) inability to consent the patient 
 
 
 
 
 
 
 
 

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Study Procedures 
Eligible patients will be randomized to three groups, to have BP assessed on 2 different visits as 
follows (also see figure 1). All patients will have casual BP taken at baseline.  
Group 1: 
Visit # 1: Patients will have oscillometric device, BpTru (method 2 from table) applied to the 
arm with the higher BP. This will allow assessment with the commonest used Canadian device, 
which provides an average after 5 unattended readings. This assessment will be followed by 24-
hour ABPM.  
Visit# 2: Upon returning 24-hr ABPM device, the patient will have the Omron HEM 907XL 
applied to same arm as BPTru above. There will be 5 minutes of quiet rest (patient alone) and 3 
readings subsequently (patient still alone) with the average being noted (method 4 from table). 
This measurement will be compared to casual BP for primary outcome.  
Group 2  
They will undergo same process as group 1, in the reverse order (see figure 1, below).  
Group 3 
Visit # 1: Patients will have the Omron HEM 907 XL applied to the arm with the higher BP. There 
will be 5 minutes of quiet rest (patient alone) and 3 readings subsequently, but with the nurse 
entering the room (ie partially attended), with the average being noted (method 3 from table). 
This was the method most likely to have been used in SPRINT(1). This assessment will be 
followed by 24-hour ABPM.  
Visit# 2: Upon returning 24-hr ABPM device, patient will have the Omron HEM 907XL applied to 
same arm as before. There will be 5 minutes of quiet rest (patient alone) and 3 readings 
subsequently (patient still alone) with the average being noted (method 4 from table).  
 

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 Outcome Measures 
Primary outcome measure 
The effect of unattended 5-minute rest preceding unattended systolic BP assessment will be 
derived from the difference between casual BP and average resting unattended SBP pressure 
measured with the Omron HEM 907XL (ie methods 1 and 4 in table 1).  
 We will also report three secondary outcome measures  
1/ difference between average SBP measured with BPTru and Omron HEM907 XL (methods 2 
and 4 in table 1) will allow us to report the effect of the additional 5 minutes of rest, 
2/difference between SBP at 10 minutes between the two visits in Group 3 (ie methods 3 and 4 
in table 1) will address an issue of unattended versus partially attended resting SBP,  
3/we will report the difference between the average unattended SBP and daytime average BP 
from 24-hr ABPM (ie methods 4 and 5 in table 1).  
 Analytic Plan 
 We will report descriptive statistics for variables of interest. We will report continuous 
variables as mean and standard deviation and categorical variables as proportions. For the 
outcome comparisons, we will use the student's t-test. See details for sample size estimation 
below. However, the mean differences are measures of average bias and not accuracy, or 

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precision. For the latter, plotting the difference between methods against the mean of the two 
methods, as suggested by Bland and Altman, are necessary(2). Hence, Bland-Altman scatter 
plots will be used to display the BP measurement data with the various methods, and we will 
also report the 95% limits of agreement as suggested by Bland and Altman. Lastly, we will carry 
out exploratory analysis to assess the effect of certain key covariates (eg age, sex, diabetes, 
presence of white coat or masked effect) on the mean bias between effects. 
Rationale for the proposed sample size and power 
The magnitude of the difference between casual and unattended average of 3 oscillometric 
readings after 5 minutes rest appears to be about 12.7 mmHg (3). Our review of the literature 
identified a range of possible standard deviations from 5 to 16 mm Hg. To be conservative, we 
will assume a standard deviation of 16 mm Hg. Hence, a sample size of 55 will give 90% power 
with a t-test at an alpha of 0.05. We anticipate little loss to follow up given the short nature of 
the study (2 visits 1 day apart). In addition, we will enrol an additional 30 patients in whom we 
will compare the effect of partially attended versus completely unattended blood pressures. 
We assume that a maximum of 5 patients may have errors with BP measurements with 
oscillometric methods. Hence we will plan to enrol 90 patients in this trial. 
Team, Expertise and Resources 
This study will be managed by the Kidney Research Centre in Ottawa, which has dedicated 
administrative staff and experienced clinical research coordinators, and conducts several 
clinical trials. Hypertension Specialists/Nephrologists, Drs. Marcel Ruzicka, Cedric Edwards, 
Swapnil Hiremath will oversee patient recruitment, and all described investigations, and will be 
responsible for collection and evaluation of all data. A dedicated and experienced staff nurse at 
Renal Hypertension clinic will perform all BP assessments. The nurses at this clinic are all 
certified RN, with additional certification in nephrology (C Neph), with additional experience in 
BP measurement. The data analysis will be conducted by Swapnil Hiremath, nephrologist and 
epidemiologist and Tim Ramsay, senior biostatistician and director of the Methods centre in 
Ottawa.  
Timelines and Deliverable 
Upon successful application for funding of this proposal, a clinical research coordinator within 
the Kidney Research Centre will be identified, and requisite devices purchased. We assume 
completion of recruitment 6 months as about 100 patients with hypertension are seen every 
week in the hypertension clinic every week, and the inclusion criteria for this study are very 
broad, with only 2 extra visits, above the standard of care. See table below for anticipated 
timeline of completion of project.  
 

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Startup, 
Obtain 
devices, 
REB 
approval      
Recruitment 
Complete 
follow up 
Data analysis, 
Interpretation,  
preparation of 
manuscript 
0-3 months 
  
  
  
  
3-9 months 
  
  
  
  
9 - 12 
months 
  
  
  
  
 
Anticipated results and Interpretation 
We anticipate three possible results with this study. It is possible that the results show a tight, 
precise, bias between casual and unattended OMRON HEM 907 XL readings (primary outcome). 
This bias would then allow for calibration of results such that it would be possible to have 
different targets based on method of BP measurement. It is also somewhat possible, that 
though we might find an average bias that is significant, that this may not be precise, ie with a 
lot of scatter seen in the Bland Altman plot. In this case, it would be useful to examine if there 
are reasons for higher or lower bias (ie association of covariates with the bias) to allow for 
adjustment/calibration based on the population. Indeed, it may be that there are no such 
factors, in which case, the outcome could be that casual BP measurements should be 
abandoned completely, especially if considering intensive BP targets such as in SPRINT. The 
other additional BP measurements would also allow us to make similar inferences, apart from 
the scientific aspect of being able to tease out the effect of waiting additional time, and the 
presence of a nurse.   
Knowledge Translation 
The results of the study will be presented at national and international conferences (Canadian 
hypertension Congress, and American Heart Association – Council for High Blood Pressure). In 
addition, publication of full results will be done in a peer reviewed journal. We will also use 
social media, such as Twitter and Youtube, for dissemination of the results to a wider audience. 
In collaboration with the Office for CME of the University of Ottawa, Drs. Edwards will oversee 
development and delivery of teaching modules on BP targets for Canadian patients with 
hypertension using difference BP techniques for family physicians and other primary care 
providers. Drs. Marcel Ruzicka and Swapnil Hiremath are members of the Recommendations 

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Task Force (RTF) for the Hypertension Canada guidelines, and will present the results to the 
same for possible incorporation in the next iteration of the guidelines, as appropriate.  
Potential Challenges and Mitigation 
Recruitment 
Recruitment is always a challenge for prospective studies. However, we work in a centre with a 
large catchment area, and the hypertension clinic receives ~ 200 new referrals every year, and 
about 1100 patients are being currently followed up in the clinic. Also, we perform 20-30 ABPM 
procedures every week. In addition, the inclusion/exclusion criteria are very broad, thus most 
patients will be eligible for participation in this study. Lastly, the design for an individual 
participant is rather simple, with no invasive procedures, and only two additional visits.  
Loss to Follow up 
The study has only a 24 hour follow up, when participants return the ABPM device, hence we 
anticipate very little loss to follow up.  
Inadequate/errors in BP measurement 
It is indeed true that oscillometric devices do not always capture the correct blood pressure. 
Hence as part of the exclusion criteria, we will exclude patients in whom this happens, 
irrespective of the reason (eg arrhythymia, pain etc). In addition, we have increased the sample 
size by 5 to account for additional error that may occur in the eligible patients.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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References 
 
1. 
Bakris GL. The Implications of Blood Pressure Measurement Methods on Treatment Targets 
for Blood Pressure. Circulation. 2016 Sep 27;134(13):904-5. 
2. 
Bland JM, Altman DG. Comparing methods of measurement: why plotting difference against 
standard method is misleading. Lancet. 1995 Oct 21;346(8982):1085-7. 
3. 
Agarwal R. Implications of Blood Pressure Measurement Technique for Implementation of 
Systolic Blood Pressure Intervention Trial (SPRINT). J Am Heart Assoc. 2017 Feb 03;6(2).