Understanding short-term blood-pressure-variability phenotypes: from concept to clinical practice

Veerendra Melagireppa Chadachan; Min Tun Ye; Jam Chin Tay; Kannan Subramaniam; Sajita Setia

doi:10.2147/IJGM.S164903

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Review

Understanding short-term blood-pressure-variability phenotypes: from concept to clinical practice

Authors Chadachan VM, Ye MT, Tay JC , Subramaniam K , Setia S

Received 7 February 2018

Accepted for publication 17 April 2018

Published 22 June 2018 Volume 2018:11 Pages 241—254

DOI https://doi.org/10.2147/IJGM.S164903

Checked for plagiarism Yes

Review by Single anonymous peer review

Peer reviewer comments 3

Editor who approved publication: Dr Scott Fraser

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Veerendra Melagireppa Chadachan,¹ Min Tun Ye,² Jam Chin Tay,¹ Kannan Subramaniam,³ Sajita Setia⁴

¹Department of General Medicine, Tang Tock Seng Hospital, ²Department of Pharmacy, National University of Singapore, Singapore; ³Global Medical Affairs, Asia-Pacific Region, Pfizer Australia, Sydney, NSW, Australia; ⁴Medical Affairs, Pfizer, Singapore

Abstract: Clinic blood pressure (BP) is recognized as the gold standard for the screening, diagnosis, and management of hypertension. However, optimal diagnosis and successful management of hypertension cannot be achieved exclusively by a handful of conventionally acquired BP readings. It is critical to estimate the magnitude of BP variability by estimating and quantifying each individual patient’s specific BP variations. Short-term BP variability or exaggerated circadian BP variations that occur within a day are associated with increased cardiovascular events, mortality and target-organ damage. Popular concepts of BP variability, including “white-coat hypertension” and “masked hypertension”, are well recognized in clinical practice. However, nocturnal hypertension, morning surge, and morning hypertension are also important phenotypes of short-term BP variability that warrant attention, especially in the primary-care setting. In this review, we try to theorize and explain these phenotypes to ensure they are better understood and recognized in day-to-day clinical practice.

Keywords: hypertension, BPV, HBPM, ABPM, morning surge, nocturnal dipping

Background

Hypertension, one of the most important preventable causes of death globally, accounts for more than 12.8% of all deaths annually.^1,2 Elevated blood pressure (BP) is one of the major modifiable contributing factors to cardiovascular risk; however, there is often uncertainty as to the “true underlying BP”, as patients often present with discrepant BP readings.³ This is because BP is a continuous variable that fluctuates constantly in response to various changes in physical and mental activities, sleep, and autonomic, humoral, mechanical, myogenic and environmental stimuli.⁴ It is characterized by marked spontaneous oscillations over short- and long-term periods.⁵ As such, clinic BP or home BP (HBP) in an individual at one time can be considerably different from his/her average day and nighttime BP.⁴ This presents a challenge in diagnosing and prescribing treatments for patients correctly.

Physiology of relationship between sleep and BP regulation

Sleep usually involves calmness and detachment from the external environment, and hence generally causes a reduction in BP at night.⁶ This decrease does not occur under conditions of total sleep deprivation. Sleep disturbances, including sleep restriction, sleep apnea, insomnia, and shift work, have also been found to induce stress on the cardiovascular system and play a role in the development of cardiovascular disorders.⁷ The sleep-dependent changes in BP are specific to each sleep state, and result from the integration between cardiovascular reflexes (which modulate heart rate in response to changes in BP) and central autonomic commands to heart and resistance vessels.^6,8 The pathophysiological mechanisms behind these clinical associations probably alter the integration of these cardiovascular reflexes and central autonomic commands.⁶ A positive beneficial association has been found between “close relationships” and BP dipping, while posttraumatic stress disorder and obstructive sleep apnea have been associated with diminished nocturnal BP fall.^9–11

Blood-pressure variability

Even though average clinic BP values remain the gold standard for the diagnosis and treatment of hypertension, recent studies in hypertensive subjects have demonstrated that the assessment and quantification of BP variability (BPV) in addition to normal BP values, is of both physiopathological and prognostic importance.^2,12 For instance, there is strong evidence to show that increased BPV is independently associated with higher risk of target-organ damage, cardiovascular events, and mortality.^2,5,13 It follows that controlling BPV in addition to reducing absolute BP levels may contribute to optimal cardiovascular protection in hypertensive patients.¹⁴

Continuous intra-arterial BP recordings are used to assess very short-term beat-to-beat changes in BPV, whereas continuous monitoring systems, such as ambulatory BP monitoring (ABPM), are used for assessing short-term BP fluctuations within a day (24 hours). On the other hand, home BP monitoring (HBPM) or office BP monitoring (OBPM) over lengthy time periods are used to detect long-term changes in BP stretching over days or visits.^2,15

Some studies have observed that the extent of BPV is directly proportional to mean BP values, and hence BPV is generally higher in hypertensive subjects compared to normotensive subjects.¹⁶ It is also noted that a reduction in mean BP values leads to a proportional reduction in BPV, and thus it has been suggested that employment of longer-acting BP-lowering drugs might be particularly beneficial in controlling BPV in addition to BP control.¹⁶ However, setting the optimal therapeutic target for BPV control with antihypertensive therapy remains a challenge.¹⁴

Different types of BPV

Popular concepts of BPV, such as “white-coat hypertension” and “masked hypertension”, are well recognized in clinical practice, and have been studied extensively for their prognostic relevance.¹³ White-coat hypertension or isolated office hypertension is characterized by elevated office BP (OBP) with normal ambulatory BP (ABP) or HBP, and might be caused by anxiety or in response to an unusual clinical setting.^17,18 Masked hypertension, on the other hand, is characterized by normal OBP, even though ABP or HBP levels are elevated.¹⁹ However, it is important to recognize that BPV is a complex phenomenon that expands beyond such popular concepts, and is influenced by fluctuations in both the short term, ranging from seconds to hours, and the long term, ranging from days to months.^2,5,14 In general, BPV can be divided into three different types, based on the time frame it occurs: very short-term BPV, short-term BPV and long-term BPV.^2,15 Depending on the method and time interval considered for its assessment, the clinical significance and prognostic implications of a given measure of BPV differ.^2,14

Very short-term BPV

Very short-term BPV refers to beat-to-beat fluctuations in BP due to the interplay of different cardiovascular control systems, such as the baroreceptor reflex, the renin–angiotensin system, the vascular myogenic response, and the release of nitric oxide from the endothelium, as well as changes in behavioral and emotional mechanisms.^2,5,20 It is usually assessed in a laboratory via intra-arterial recording or under ambulatory conditions by noninvasive finger cuffs that continuously track finger-BP levels through infrared photoplethysmography.^2,15 Standard deviations of BP values or fluctuations in BP obtained from spectral analyses at various frequency bands are often used as the main indices for assessing very short-term BPV.²

Even though its usefulness and reliability in practical usage is questionable, very short-term BPV has been used as a tool in diagnosing and treating patients with cardiovascular disease, as well as to study the mechanism of action of antihypertensive drugs.^2,20–22 Detecting changes in beat-to-beat BPV can also help in rationally selecting antihypertensive drugs.⁵ For instance, hypertensive patients with elevated low-frequency BPV may present with enhanced sympathetic modulation of vascular tone, and hence may respond well to sympatholytic antihypertensive drugs.²⁰

Short-term BPV

Short-term BPV refers to the BP changes that occur within a day (24 hours), and is characterized by normal circadian variations, such as nocturnal BP dipping and morning BP surge.^2,14,15,23 It is mainly influenced by central neural factors, reflex autonomic modulation, and changes in the elastic properties of arteries and humoral systems and rheological and mechanical factors.^15,24–29 However, all these factors are often inextricably intertwined with each other.¹⁴ Various studies have demonstrated that higher 24-hour BPV independently of mean BP values is clinically important, as this can increase cardiovascular (CV) events, mortality, and target-organ damage.^30–37

Short-term BPV can be measured in two ways: using either ABPM to measure BP every 15–30 minutes over a 24-hour period or special HBPM devices that can measure BP while sleeping.^2,14,38,39 Some common indices of measurement for short-term BPV include standard standard deviation (SD) of BP values measured over the whole 24-hour period, waking hours, or sleeping hours.² Other indices include coefficient of variation (CoV), 24-hour weighted SD, and average real variability (ARV).^2,40–42 These indices are covered in detail in “Understanding indices of short-term BPV” section. The main advantages of short-term BPV monitoring are that it can provide extensive information on BP changes over a day and detect important circadian BP changes, such as morning BP surge and nocturnal dipping, that may have important prognostic implications.^43–47

Long-term BPV

Long-term BPV refers to day-to-day, visit-to-visit, and season-to-season BP changes.^2,15 Factors contributing to long-term BPV remain relatively unclear.² Long-term BPV could be a consequence of poor BP control in treated patients, such as inadequate treatment by the physician, poor patient adherence, or improper BP-measurement methods.^2,15 It may also be influenced by behavioral changes in an individual, as well as environmental factors, such as outdoor temperature and daylight-hour differences between different seasons.^2,4,15 For instance, BPV was found to be greater during winter than in summer, possibly due to increased sodium retention and vascular resistance caused by augmented sympathetic activity.⁴ Some studies have also suggested that increased arterial stiffness contributes to the pathogenesis of long-term BPV.^5,48

Day-to-day BPV can be assessed by ABPM over 48 hours or HBPM data collected over several days, weeks, or months, while visit-to-visit BPV is usually assessed by ABPM or OBPM that is usually spaced by visits over weeks, months, and years.^2,15 However, the reliability of using OBPM to assess long-term BPV has been questioned, as it does not take into account the patient’s normal activities and requires frequent visits to the physician for BP measurements.^2,15 A recent single-center cross-sectional study showed significant differences between single OBPM and means of consecutive BP measurements.⁴⁹ In-office measurements are also sometimes inaccurate, mainly because of the white-coat effect, inadequate or uncalibrated devices, and suboptimal measurement techniques (eg, incorrect cuff size, no rest before measurement).^50,51 Although a large number of recommendations on correct OBPM techniques have been published (Table 1), these guidelines are generally not translated into primary-care practice.^51,52

Table 1 Recommendations for OBP monitoring from key guidelines on hypertension

Abbreviations: OBP, office blood pressure; JSH, Japanese Society of Hypertension; NICE, National Institute for Health and Care Excellence; ESH, European Society of Hypertension; ESC, European Society of Cardiology; CHEP, Canadian Hypertension Education Program; AHA, American Heart Association; OBPM, OBP monitoring; AOBP, automated OBP.

There is strong evidence to suggest that increased long-term BPV is associated with higher risk of stroke, cardiovascular events, and mortality, including all-cause mortality.^53–⁵⁷ Therefore, measuring long-term BPV might be clinically important, as it can provide useful insights into the long-term control of the patient’s BP and effectiveness of the patient’s current antihypertensive therapy.²

Understanding short-term BP variability

Nocturnal dipping and nocturnal hypertension

BP generally dips about 10%–20% during sleep in normotensive patients, due to a phenomenon known as nocturnal dipping.^14,15 However, in hypertensive patients, the extent of BP dipping can differ significantly, and individuals can be categorized into four groups based on the extent of fall in nighttime BP. These include extreme dippers, dippers, nondippers, and reverse dippers.¹⁵ In general, individuals whose BP falls in the range of 10%–20% are known as dippers.⁵⁸ Those who dip >20% are known as extreme dippers, while those exhibit <10% dip in BP are called nondippers. On the other hand, those who have an increase in nocturnal BP, instead of a fall, are known as “risers” or “reverse dippers”.⁵⁸ Various causes for the absence of dipping have been proposed including sleep disturbance, depression, obesity, obstructive sleep apnea, orthostatic hypotension, autonomic dysfunction, chronic kidney disease, diabetic neuropathy, and old age.^23,59–61

There is strong evidence indicating that such circadian variations have prognostic significance in both hypertensive and normotensive patients. For instance, blunted or reverse nocturnal BP dipping and exaggerated morning BP surge are independently associated with increased cardiovascular events, stroke, and target-organ damage.^{4,37,43,62–}⁷⁷ These circadian variations within 24 hours can also give rise to other phenotypes of short-term BP variations, such as nocturnal hypertension and morning hypertension.^78,79

Nocturnal hypertension is defined as having an average of nocturnal BP values of ≥ 120/70 mmHg and is generally caused by a failure in nocturnal dipping and hence usually observed in nondippers or reverse dippers.⁵⁹ It is especially important to control nocturnal BP, as it is more likely to represent the patient’s actual BP more closely, as it is often not influenced by the pressor effects of physical, emotional, and other environmental factors that occur during the day.¹⁴ Moreover, patients with nocturnal hypertension have been found to be at significantly higher risk of organ damage and cardiovascular events, independently of OBP or morning BP values.^{59,64,80–82} Nocturnal BP has also been found to be a superior predictor of cardiovascular disease than daytime BP.^45,83 Previously, nocturnal hypertension was able to be detected only by ABPM. However, development of novel semiautomatic HBPM devices that can intermittently measure BP during sleep have allowed HBPM to monitor nocturnal BP accurately.^59,84–87 Nocturnal HBP values obtained by such devices are comparable to nocturnal BP values obtained by traditional ABPM.^59,85

Morning surge and morning hypertension

BP tends to surge higher in the morning, and this is considered a normal physiological process, but exaggerated morning BP surge has been observed in some hypertensive patients.²³ Early-morning BP is also viewed as a missed therapeutic target, since the timing of the trough plasma-drug level and the lowest pharmacological effect may coincide with early-morning rise in BP, especially for antihypertensives taken once daily in the morning.⁸⁸

Morning hypertension is diagnosed if morning BP values are ≥135/85 mmHg using out-of-office BP monitoring or ≥140/90 mmHg using OBPM in the morning.⁸⁹ It can also be defined as having a morning–evening BP difference of >15 mmHg or a morning–nocturnal BP difference of >35–55 mmHg.^59,90 It is recommended to take two to three BP readings every morning for 5–7 days, and the average of these BP readings should be used for evaluation.⁸⁹ There are two types of morning hypertension that can be detected by HBPM: one is caused by extreme morning BP surge, whereas the other is caused by prolonged nocturnal hypertension that extends into the morning.^59,66,79,91 In the latter case, persistent nocturnal hypertension overlaps partially with morning hypertension, and it is often observed in patients with nondipping or reverse nocturnal dipping patterns.^78,91

The morning surge observed by ABPM has been found to be unreproducible.⁹⁰ Also, a threshold above which the morning surge in BP becomes pathological remains elusive, and there is still no consensus on a clear definition and assessment of this parameter.^14,23 Morning BP, however, may be regarded as a therapeutic target for preventing target-organ damage and subsequent cardiovascular events in hypertension. Morning hypertension is best monitored through HBPM under fixed conditions at the same time in the morning and evening (or during sleep if possible) over a long period.⁷⁸ Japanese Society of Hypertension guidelines recommend morning HBP be measured within 1 hour of waking and after urination, but before medications or meals, while evening HBP should be measured just before going to bed (Figure 1).^92,93

Figure 1 Measurement of home blood pressure (BP).

Note: Image created as per recommendations from JSH³⁹ and NICE¹⁴² guidelines.

Abbreviations: JSH, Japanese Society of Hypertension; NICE, National Institute for Health and Care Excellence.

Measurement of short-term BPV

There is increasing evidence to show that conventional OBPM to diagnose and monitor a patient’s response to antihypertensive treatment may not be effective.^14,23,49 OBP measurements have some serious limitations, such as their inability to assess the dynamic characteristics of BP and collect data in the patient’s usual daily setting.¹⁴ They also rely heavily on the technique of the operator, and thus may give rise to observer bias.¹⁴ Lastly, white-coat hypertension and masked hypertension are also commonly associated with BP readings taken in a clinical setting, which may lead to an inaccurate diagnosis of hypertension.^2,14,18 HBPM and ABPM, on the other hand, are recommended in clinical practice to diagnose white-coat hypertension and masked hypertension and can estimate increased BPV, since they are able to detect various changes in BP associated with such conditions.^23,94

A major advantage of out-of-office BP monitoring is that it can provide a large number of BP measurements away from the medical environment. Evidence is growing that such out-of-office measurements can also have better prognostic values for cardiovascular events, and these are now widely considered as significantly superior to OBPM readings.^{14,23,73,95–100} As such, out-of-office measurements, such as ABPM and HBPM, are increasingly recommended by major guidelines to complement conventional OBP measurements in clinical practice (Table 2).^101–104

Table 2 Recommendations on out-of-office BP measurements from key international guidelines on hypertension

Abbreviations: BP, blood pressure; JSH, Japanese Society of Hypertension; NICE, National Institute for Health and Care Excellence; ESH, European Society of Hypertension; ESC, European Society of Cardiology; CHEP, Canadian Hypertension Education Program; AHA, American Heart Association; BPV, BP variability; OBP, office BP; OBPM, office BP monitoring; HBP, home BP; HBPM, HBP monitoring; ABP, ambulatory BP; ABPM, ABP monitoring; AOBP, automated OBP; CV, cardiovascular; CVD, cardiovascular disease; CKD, chronic kidney disease.

HBPM is defined as regular measurement of BP at home by the patient outside any clinical setting.³ Despite the widespread use of HBPM, there is no standardized protocol for its measurement, and this might result in an inaccurate assessment of BP. Therefore, it is vital to adopt a standardized protocol that has been validated.³ HBPM is recommended to be measured as such:

BP measurement should be taken in a quiet room in a seated position using a validated automatic BP device with correct arm-cuff size^3,103,105
the patient should be seated with their back supported and feet flat on the floor with legs uncrossed, while the measuring arm should be relaxed and supported at heart level^3,105
the patient should be in a comfortable and calm state while the measurement is made, and should have at least 1–5 minutes of seated rest before the measurement^39,105,106
measurement should be taken before medication, food, or vigorous exercise and after micturition^{3,105,107–110}
stimulants containing such products as coffee and cigarettes should not be consumed for 30 minutes before BP measurement.^3,105

Two measurements should be conducted, 1 minute apart, in the morning, as well as in the evening, for a total of 7 days (at least 5 days).^{94,105,111–113} Measurements should be taken at around the same time while maintaining similar conditions throughout the measuring period to minimize the BPV around the true mean BP value.¹¹⁴ HBP is then calculated by averaging systolic and diastolic BP recorded over the period after excluding the first day’s readings.³ In general, HBP higher than 135/85 mmHg is accepted as the criterion for diagnosis of hypertension by various guidelines (Table 3).^{3,92,93,101,103,104,115} However, it has been found that many physicians may not follow this BP-cutoff point for diagnosis of hypertension, but instead use a higher BP cutoff (>140/90 mmHg) to diagnose hypertension based on HBPM recordings.^116–118

Table 3 Recommendations from key international guidelines on diagnosis of hypertension using OBP and out-of-office BP monitoring

Notes: ^aAverage of BP readings taken while patient is awake; ^baverage of BP readings taken while patient is asleep; ^caverage of BP readings taken over a whole day (24 hours).

The consensus target HBP for antihypertensive treatment remains controversial. The recent American Heart Association guidelines now recommend HBP of 135/85 mmHg as target for treatment in hypertensive patients and 130/80 mmHg in high-risk patients.¹¹⁵ Japanese Society of Hypertension guidelines, on the other hand, recommend HBP of 125/80 mmHg as target for treatment in young and middle-aged persons and 135/85 mmHg in the elderly.^93,119

ABPM is defined as the method of measuring BP readings noninvasively at short intervals over a 24-hour period with the aid of an automated BP device while the patient is going about their daily routine.^39,105,120 An ABPM device automatically takes BP readings every 15 minutes during the day and 30 minutes at night over a 24-hour period.²³ Daytime for ABPM is defined as 9:00–21:00 while the patient is normally awake. On the other hand, nighttime is defined as 1:00–6:00 while the patient is asleep. A total of at least 20 valid readings when awake and seven valid readings while asleep (about 70% of total readings) are needed to confirm the results at the end of the 24-hour ABPM. The ABPM device automatically provides the user with unique data, such as 24-hour average BP, daytime (awake hours) BP, nighttime (sleeping) BP, dipping status, early-morning BP surge, BP load, trough:peak ratio, and smoothness index. The actual diagnosis of hypertension depends on the time frame of ABPM used.^23,94 In general, patients with greater-than-average BP of 130/80 mmHg measured over a 24-hour period are considered hypertensive.⁹⁴ In addition, a daytime average >135/85 mmHg or a nighttime average >120/70 mmHg are also considered hypertensive.⁹⁴

Understanding indices of short-term BPV

There are a few different methods to represent short-term BPV.¹⁵ SD of 24-hour average ABP values is one of the most commonly used parameters in measuring short-term BPV, but it is sometimes expressed as the weighted mean of daytime and nighttime BP levels to take into account the fall in BP during sleep.^15,41,121 However, the validity of SD has been questioned as an appropriate index of short-term BPV, considering that it reflects only the dispersion of values around the mean, does not account for the order in which BP measurements are obtained, and is sensitive to the low sampling frequency of ABPM.¹²²

Therefore, other indices, eg, 24-hour weighted SD, CoV, and ARV, are also used to overcome the limitations of traditional SD values and provide more accurate assessment better to predict target-organ damage and cardiovascular risk:^2,40–42

24-hour SD can also be divided by the corresponding mean BP and multiplied by 100 to be expressed as a CoV;² CoV has been observed to have greater prognostic ability than SD, as it can pinpoint individuals whose BPV falls outside its anticipated range⁴
24-hour weighted SD is the average of daytime and nighttime BP that has been adjusted for the duration of the day and night period to account for day–night BP changes.⁴¹
ARV is another index that is the average of the absolute differences between consecutive BP measurements, and some studies have shown it to be more reliable prognostic indicator compared to SD, as it is more sensitive to the individual BP-measurement sequence and less sensitive to low sampling frequency.^4,2,40,123

ABPM vs HBPM for assessment of short-term BPV

ABPM monitors changes in BP at many time points throughout the day in an unrestricted manner, whereas HBPM detects BP fluctuations under standardized conditions over a longer period.⁷⁸ Multiple readings of ABPM obtained within 24 hours allow for more detailed analyses of both night- and daytime readings, making ABPM more suitable than HBPM for monitoring of intraday BP fluctuations.^14,23 As such, ABPM may provide several advantages over HBPM in providing more extensive information on BP changes throughout the day.²³

Even though ABPM can provide extensive information, such as average day and night readings, BPV, morning BP surge, and BP load, ABPM still faces many issues regarding practicality, reproducibility, and long-term usage.^{2,3,23,78,124} Previously, only ABPM had the ability to record nocturnal BP values, which are superior to daytime values in predicting mortality.^{43,77,83,124–126} With recent developments and newer HBPM devices with the ability to record accurate nocturnal recordings, HBPM might offer a reliable alternative to ABPM for monitoring short-term BPV within a day.⁹⁵

HBPM is also highly practical and more affordable and accessible to patients compared with ABPM.¹²⁷ HBPM can also be easily repeated over prolonged periods (days to months) in the patient’s own environment, making it more suitable for the monitoring of longer-term BPV in day-to-day or visit-to-visit parameters.^{2,23,95,104,128,129} As such, HBPM was found to be the more common tool used by physicians to diagnose hypertension, even though ABPM was ranked the more valuable tool for assessing hypertension.^78,116 Moreover, mean BP values from HBPM are stable and highly reproducible, since they are obtained under fixed conditions and not easily influenced by changes in daily activities.⁷⁸ In addition, HBPM is easily available to the general public, and can thus be used in both normotensive and hypertensive individuals.^78,130

HBPM can also provide instant feedback directly to the health-care professional regarding the diagnosis and treatment of hypertension, while there is usually a delay in ABPM in relaying the information.^78,131–134 However, HBPM is prone to patient-recording errors and improper BP-recording techniques, which may compromise the accuracy and reliability of the data.^78,135,136 Therefore, it is useful to use a device with integrated memory, and patients should be properly trained on the method for its use.^{2,23,78,105,137–139} On balance, HBPM has been suggested as the method of choice to monitor BPV over the long term in clinical practice by many guidelines, even though it may not provide insights as extensive as ABPM.^{2,58,92,93,103,104,140,141}

Conclusion

Short-term BPV within 24-hours is heavily influenced by circadian variations, resulting in many important phenotypes, such as morning BP surge, morning hypertension, nocturnal dipping, and nocturnal hypertension. Such variations in short-term BPV are only captured and reflected through out-of-office BP measurements like 24-hour ABPM or HBPM. As such, it is important to have a good understanding of proper use of these out-of-office measurements in a clinically validated manner. Both physicians and patients should be strongly encouraged to use ABPM and/or HBPM for monitoring BP, as a reduction in nocturnal hypertension and exaggerated morning BP surge are vital for the effective management of hypertension, rather than simply controlling average BP levels.

Acknowledgment

The authors would like to thank Ms. Tanaya Bharatan, Pfizer, for her editorial support with this manuscript.

Author contributions

All authors were involved in the conception, design, and analysis and interpretation of data. All authors were also involved in preparation of the manuscript, revising it for scientific content and final approval before its submission for publication.

Disclosure

KS and SS are employees of Pfizer. MTY underwent indirect patient-care pharmacy training for 3 months at Pfizer, Singapore. The other authors report no conflicts of interest in this work.

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