Background Key benefits of home-based blood pressure measurements are the potential to reduce the risk of ‘white coat hypertension’, encouraging patients to take ownership of their condition and be more actively involved in their long-term condition care, and to move work out of the doctor’s office.
Aim To assess whether performing 20 resting blood pressure measurements over a 2-day period would provide a reliable, stable representation of patients’ resting systolic and diastolic blood pressure. Following clinician recommendation, each participant completed the Stowhealth home blood pressure monitoring procedure.
Method One thousand and forty-five participants (mean age 66±13 years, 531 women and 514 men) completed the procedure, of 10 resting measurements per day, for 2 days (20 resting systolic and diastolic blood pressure readings in total). All measurements were made using automated oscillometric monitors.
Results Within-patient coefficient of variation for the entire participant cohort was 8% for systolic blood pressure (cohort mean 141±11 mm Hg), and 8% for diastolic blood pressure (cohort mean 79±6 mm Hg). There were no significant differences between the first and second day, for either systolic (142±1vs 141±1 mm Hg, respectively, p>0.05) or diastolic blood pressures (79±1vs 78±1 mm Hg, respectively, p>0.05 in both cases).
Conclusion The overall duration of home blood pressure monitoring may be able to be reduced to just 48 hours. This method would offer meaningful time saving for patients, and financial and time benefits for doctors and their surgery administration.
- general practice
- blood pressure
- home monitoring
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Measuring blood pressure is a very common activity in general practice. Patients diagnosed with hypertension, diabetes, ischaemic heart disease, cerebrovascular disease, chronic kidney disease and peripheral vascular disease all require regular blood pressure monitoring. Patients using oral contraception or hormone replacement therapy also require regular monitoring, and disease-free patients aged 40 years and older have blood pressure checks every 5 years.1 2
In the UK, the Quality and Outcomes Framework (QOF) rewards general practitioners (GPs) for treating these patients to blood pressure targets. In the year prior to 1 April 2016, Stowhealth general practice recorded 6852 blood pressure readings from its list of 18 907 patients. This activity alone places an enormous burden on the primary care team.
Home blood pressure recording is an accepted alternative to practice-based recordings. Key benefits of home-based measurements are the potential to reduce the risk of ‘white coat hypertension’,3 4 encouraging patients to take ownership of their condition and be more actively involved in their long-term condition care,5 and to move work out of the doctor’s office.
The National Institute for Health and Care Excellence (NICE) have outlined a protocol for home blood pressure measurements and monitoring. The recommendation is for twice-daily blood pressure readings, for at least 4 days, and ideally 7 days. The first day’s readings are discarded, and the average of the three to six remaining days’ readings are used for clinical decision-making.1 2
However, given the known diurnal variation in blood pressure,6–8 it is reasonable to doubt the validity and reliability of any representation of ‘resting’ blood pressure when only two measurements are taken twice each day. While a 7-day protocol may help to reduce the impact of physiological or behaviour-induced blood pressure variation, the 7-day duration may place significant strain on patient adherence and certainly places significant financial burden on general practice surgeries due to the purchase or loan of automated, oscillometric measurement devices.
The aim of the study was to assess whether performing 20 resting blood pressure measurements over a 2-day period would provide a reliable, stable representation of patients’ resting systolic and diastolic blood pressure. Following pilot work at the practice, we found that 20 readings (10 per day) were as statistically representative as 30 (15 per day). We hypothesised that the high frequency (10 measurements per day) but low duration (2 days) method would provide a realistic and stable indication of patients’ resting blood pressure. Our hypothesis was based on us capturing diurnal rhythms with 10 measurements per day and verifying repeatability of that variance over the 2 days of measurements.
A total of 1403 participants (mean age 67±13 years, 716 women and 687 men) undertook the Stowhealth home blood pressure monitoring procedure. All participants were patients of Stowhealth practice (Violet Hill Road, Stowmarket, Suffolk, UK; www.stowhealth.com). As of October 2016, Stowhealth had 18 907 registered patients (9660 women, 9247 men). Practice local demographics are presented in figure 1. The total number of patients with a last recorded blood pressure measurement of 150/90 or lower (as per the current QOF) was 2369. Historical context is provided in table 1 and figure 2. Any patient at Stowhealth who qualified for home blood pressure monitoring was invited to use the 2-day protocol. There were no other procedures as an option, and no special inclusion or exclusion criteria were applied.
This is a cross-sectional service evaluation, using anonymised routinely collected data, and as such specific ethical approval is not required. Following clinician recommendation and prior to testing, each participant received a record sheet and written explanation of the home blood pressure monitoring procedures. Following initial participant consent at the point of patient registration with Stowhealth, verbal consent was checked at all appropriate stages of home blood pressure monitoring. Participants represented the diverse nature of National Health Service patient users; the only exclusion criteria applied were patients with known atrial fibrillation and those unable to use an electronic oscillometric blood pressure monitor. All participants completed identical familiarisation appointments with Stowhealth staff, before taking blood pressure devices home to perform measurements.
Procedures and equipment
All participants completed 10 resting blood pressure measurements per day, for 2 days (20 resting systolic and diastolic blood pressure readings in total). All resting blood pressure measurements were made using automated oscillometric blood pressure monitors (upper arm, brachial artery devices). Blood pressure was measured in a seated position, with at least 60 min separating each measurement.
All patients completed a paper record of measurements, and the forms included a time of recording column. Data were not included in the analyses if all 20 readings were not present, with time recorded for each. The procedure asks the patients to take their blood pressure having sat comfortably for a least 2 min, with their measurement arm supported.
Usual practice is for the patient to apply the cuff with their dominant hand to the non-dominant arm. However, it is difficult to be entirely proscriptive as some cases (eg, women post-mastectomy for breast cancer) are told not to use the arm on the operated side due to risk of developing lymphoedema. Therefore, the suggested but not proscriptive cuff placement simply follows real-life practice.
All devices were assessed for accuracy and reliability of measurement, according to standard practice procedures, including annual service and calibration. Cuff size was altered as necessary. While a variety of devices were used, all met the Association for the Advancement of Medical Instrumentation requirements.
All data were assessed for conformity with parametric assumptions, using the D’Agostino and Pearson normality test as recommended by GraphPad Prism V.7 given the data sets included for analysis (GraphPad Software, La Jolla, California, USA). The coefficient of variation was used in order to determine the variance (and reliability) for each individual participant’s 20 repeated systolic and diastolic blood pressure measurements. Average coefficient of variation for all participants was also calculated to represent the typical 20-reading variance/reliability for the entire study cohort (and so typical patient group). To ascertain whether the highest and lowest readings for each participant would exaggerate variance in each sample, analyses were also conducted with the highest and lowest systolic and diastolic readings removed from each patient’s sample.
One-way analysis of variance (ANOVA) was used for the entire participant cohort to assess whether the first day’s measurements differed from the second. Repeated-measures ANOVA assessed for differences across the 20 measurements. An alpha level of <0.05 was set as the threshold for statistical significance, and the Bonferroni post hoc procedure was used to explore any significant differences detected in the repeated-measures ANOVA.
A total of 1045 participants (mean age 66±13 years, 531 women and 514 men) completed the 20 readings, which represents a 75% completion rate based against initial recruitment (1403 participants).
All data were normally distributed. Group mean blood pressure for all 20 resting measures were 141±11 mm Hg for systolic blood pressure and 79±6 mm Hg for diastolic blood pressure. Over the 20 home resting blood pressure monitoring readings, mean within-patient coefficient of variation for the entire participant cohort was 8% for systolic blood pressure (cohort mean 141±11 mm Hg) and 8% for diastolic blood pressure (cohort mean 79±6 mm Hg). Figure 3 illustrates the frequency distribution of individual (within-patient) coefficient of variation values for systolic blood pressure, and figure 4 presents the distribution for diastolic blood pressure.
There were no significant differences between the first and second day of home-monitored resting blood pressure for either systolic (142±1 vs 141±1 mm Hg, respectively, P>0.05) or diastolic blood pressures (79±1 vs 78±1 mm Hg, respectively, P>0.05 in both cases). However, individually, the first measurement of systolic (146±18 mm Hg) and diastolic (82±13 mm Hg) blood pressure was higher than all the following 19 measurements for each (P<0.001 in all cases). Table 2 presents the 20 systolic and diastolic blood pressure readings, as group mean values across the 48-hour period.
Despite there being statistically significant higher readings for both systolic and diastolic blood pressure on the first of 20 measurements, after removing the highest and lowest measurements from all 20, the coefficient of variation was not appreciably different for either systolic (6% vs 8% for all 20 readings) or diastolic blood pressure (7% vs 8% for all 20 readings). Using the overall group mean values of systolic and diastolic blood pressure as an example, this would equate to 9 vs 11 mm Hg variance for systolic pressure (6% vs 8% of 141 mm Hg) and an identical 6 mm Hg for diastolic pressure (7% vs 8% of 79 mm Hg; using zero decimal place diastolic values).
The results of this study have shown that 2 days of 10 resting blood pressure readings (20 in total) can provide a stable and pragmatic approach to home blood pressure monitoring. Therefore, we believe it is appropriate to open debate as to whether this protocol could provide an alternative to the current NICE guidance.
The typical within-patient variance presented in figures 3 and 4 are considered entirely acceptable within the context of primary care management of hypertension. Stowhealth GP practice has 10 years of clinical experience of decision-making algorithms using a home blood pressure monitoring protocol. Anecdotally, they have proved acceptable to both patients and clinicians. Our results provide evidence that home blood pressure monitoring generates reliable readings for clinical decision-making, and in just 2 days of home measurement.
Physiologically, it is reasonable to suggest that 10 measurements per day are likely to be more clinically valid than the existing 2-measurements-per- day recommendation.1 2 Given the average within-patient coefficient of variance of 9 to 11 mm Hg for systolic pressure, and 6 mm Hg for diastolic pressure, our 10-measurements-per-day protocol is more likely to show some diurnal variation and circadian rhythm. Conversely, the current NICE average of two measurements, twice-per-day protocol might be more easily skewed by this normal variance. Indeed, the well-established 24-hour variance in both systolic and diastolic pressure9 10 is known to be increased in hypertensive patients compared with normotensive individuals.11 Therefore, a more frequent measurement protocol is likely to be of benefit to all patient groups.
Even though there were no differences between day 1 and 2, it is still reasonable to suggest a 2-day protocol. Analysis from previous work has shown that the reading mean varies within the accuracy of the machine after 12 data points, suggesting this would be the minimum number of readings. Two days is a pragmatic compromise. Outside of the study, some patients do not manage to complete 10 readings in 1 day; a 2-day protocol allows enough data for a meaningful mean value.
Comparison with existing literature
The 10-measurements-per-day protocol (each separated by at least 60 min) is far more likely to incorporate the myriad of factors known to affect blood pressure. Behaviour-induced factors such as sleep, diet, exercise, cigarette smoking and psychosocial stress will be better covered by more frequent measurements. Neural and mechanical/neural (baroreflex) mechanisms will make adjustments to resting blood pressure throughout any given 24-hour period, as well as specific vasomotor tone,12 renin–angiotensin regulation13 14 and catecholamine release factors.13 15–17 Recording just two measurements, twice daily, may be more likely to miss these exogenous and endogenous factors.
Strengths and limitations
Of course, these complex and autonomous factors are the reason for some to champion the use of ambulatory 24-hour blood pressure monitors. For example, it is widely believed the 24-hour monitors are helpful for demonstrating the presence or otherwise of day–night dipping and morning surge, which is a useful prognostic indicator.18–20 However, the within-patient variance reported in this study would suggest some or a good deal of diurnal variance and circadian rhythm has been detected.
It should be made clear we do not present a control condition using the NICE protocol in this data set. Stowhealth has been using home monitoring for approximately 15 years, previously having a 3-day, 30-reading protocol that was modified in the light of previous work.
However, it is relatively easy to make comparisons with oscillometric, 7-day protocols or 24-hour ambulatory recording. For instance, in an influential paper, coefficient of variance across 808 patients for conventional oscillometric blood pressure recordings can be seen to be 6% for systolic (173.3±10.8 mm Hg) and 7% for diastolic (86.0±5.8 mm Hg), completed as a mean of six readings, two each on three clinic visits, each separate by 1 month.21 Also, in those same 808 participants, it was 11% for both systolic and diastolic using ambulatory methods (145.8±15.6 and 79.3±8.9 mm Hg, respectively).21 Given the individual participant variance shown in figures 3 and 4, it is reasonable to suggest this 48-hour protocol might provide clinically useful readings in a short time period.
Furthermore, home oscillatory monitors are significantly less expensive than 24-hour blood pressure monitors, and the continuous wearing and inflation of the cuff may cause annoyance to patient users during ambulatory measurements. At the time of writing, a typical 24-hour monitor is circa £1200, whereas a typical validated oscillometric device used in this study is circa £55. Finally, it was not the aim of this paper, and so we do not attempt to identify or discuss any confounding factors (age, heart rate variability, etc). Power calculations were not performed before the data were analysed, as this was a service evaluation, using anonymised routinely collected data.
Implications for research and/or practice
Crucially, by requesting 10 measurements per day, the results show we are able to reduce the overall duration of home blood pressure monitoring to just 48 hours. This 2-day method would offer meaningful time saving for patients, and financial and time benefits for doctors and their surgery administration. The oscillometric home monitors lent to patients by practices can be used for more patient management episodes, compared against 4-day to 7-day protocols.
Importantly, the 25% procedure incompletion rate reported in this manuscript will be greatly exaggerated compared with real practice. Many participant data sets were not included for this research analysis, which may have been used for patient care; reasons included patient names and dates of birth not being clearly written. Also, only complete, 20-measurement paper records were included for this analysis. This was because an independent researcher entered and reviewed all blood pressure data sets. This exclusion criterion would almost certainly not need to exist when a healthcare practitioner works with a patient on a one-to-one basis. Therefore, it is very likely the useful recording sets in practice. Stowhealth report very high patient acceptability of the 2-day methodology.
Importantly, this paper is not attempting to alter current guidance and/or practice by itself. It is instead attempting to offer evidence that suggests there may be a more cost-effective means of capturing the variance in blood pressure reported in the currently preferred ambulatory monitoring technique. At the very least, there may be alternatives to current recommendations, which is important given that patients appear to appreciate a flexible approach to home blood pressure monitoring.22
All authors would like to thank patients at Stowhealth and members of the Primary Healthcare Team for their support with home blood pressure monitoring work.
Contributors GD: guarantor, lead author responsible for data analysis, statistical methodology and writing of the paper. DG, FF, PB: result research and initial data entry. NM, SR: developers of Stowhealth blood pressure protocols, study design, GP clinical input and help with writing the paper.
Funding This work was funded through normal practice review processes at Stowhealth and an existing research relationship with the University of Suffolk.
Competing interests None declared.
Patient consent Detail has been removed from this case description/these case descriptions to ensure anonymity. The editors and reviewers have seen the detailed information available and are satisfied that the information backs up the case the authors are making.
Ethics approval This is a service evaluation using anonymised routinely collected data, and as such, specific ethical approval is not required. Ethical approval to publish findings were registered by the Faculty of Health, Science and Technology at the University of Suffolk.
Provenance and peer review Not commissioned; externally peer reviewed.
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