High blood pressure (BP) is defined as having a persistently high systolic blood pressure (SBP) and/or diastolic blood pressure (DBP) reading. The diagnostic criterion outlined by the American College of Cardiology/American Heart Association Task Force suggest using an average of two or more BP readings obtained on two or more occasions to estimate an individual’s BP.1 This recommendation stems from the fact that BP fluctuates throughout the day based on a variety of factors, including the time of day, waking vs sleeping, changes in activity, body and arm movement, smoking cigarettes, work and environmental stress, driving, use of antihypertensive medications, and other stimuli.2,3 The level of this variation can differ from person to person and based on both genetic and environmental influences.
BP is regulated by various physiologic mechanisms, including the circadian rhythm.4,5 As a result, BP measurements are different at different times of day, with daytime readings normally higher than nighttime readings.5,6 BP readings while asleep usually decrease by at least 10% and then spike in the morning with the increased activity of rising.2,3 One cohort study (n=1,542) examining 24-hour ambulatory BP readings in both normotensive and hypertensive adults found that daytime BP was significantly higher than nighttime BP, with a mean decline of 12.7/15.6 mmHg.4 In the Analysis of the Control of Blood Pressure using Ambulatory Blood Pressure Monitoring (ACAMPA) study, 62.3% (n=53) of those with good BP control and 82.3% (n=187)of those with poor BP control had SBP readings greater than 135 and/or DBP readings greater than 85 during the second hour after waking up.5
Smoking has a significant effect on BP fluctuations. One study (n=40) found that after stratifying by both baseline BP and baseline smoking status, both SBP (p<0.001) and DBP (p<0.001) increased after smoking a cigarette, reaching a peak at 2.5 minutes.7 For both normotensive and hypertensive smokers and nonsmokers, both SBP and DBP increased by 20-30 mmHg after one cigarette and 10 mmHg after subsequent cigarettes.
There is some evidence of a genetic component to the degree of variability in BP throughout the day. In a study of both monozygotic (n=28) and dizygotic (n=16) healthy adult twins, while environmental influences were found to have the greatest effect on 24-hour SBP variation, after analyzing genetic variance, genetics were found to influence 24-hour DBP and heart rate variation.8
In individuals taking antihypertensive medications, the timing of dosing can influence the circadian pattern of BP.9,10 This can be due to fluctuations in the amount of medication found in the blood.
Health Impacts of BP Variability
A 2016 metanalysis that assessed the cardiovascular (CV) significance of BP variability found no significant association between short-term variability, measured by ambulatory BP monitoring, and CV disease events or mortality.11
Sustained volatility in BP, particularly at night, is associated with an increased risk of CV morbidity and mortality. One study following hypertensive patients (n=2649) over 16 years found that greater nocturnal variability in SBP increased risk for cardiac events by 0.38 per 100 person-years (p=0.024).15 Those who experienced cardiac events had a 1.8 mmHg (11.3 vs 13.1) higher standard deviation in nighttime SBP and 0.8 mmHg (9.3 vs 10.1) higher standard deviation in nighttime DBP, representing a 0.27% increase in absolute CV event risk when SBP nighttime variability increased by 1 mmHg and a 0.13% increase in risk for increased DBP variability.
BP Monitor Variability
In addition to true changes in BP, shortcomings in the accuracy of oscillometric measurement devices are another possible cause of differences in BP readings throughout the day. In a study of 755 people referred to an outpatient hypertension clinic, 18% were found to have a discrepancy of more than 10 mmHg (either systolic or diastolic) between simultaneous measurements using a professional oscillometric device and a mercury sphygmomanometer.17 Women and individuals with smaller arm circumference have an increased likelihood of getting an inaccurate reading from an oscillometric measurement device. While this unreliability is recognized, there is unfortunately no consensus on how to account for inaccuracies in a manner that is practical or efficient enough for clinically feasible implementation.18 asdad
References
- Whelton PK, Carey RM, Aronow WS, et al. 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA Guideline for the Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults: Executive Summary: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. Hypertension. Jun 2018;71(6):1269-1324. doi:10.1161/HYP.0000000000000066
- O'Brien E, Parati G, Stergiou G, et al. European Society of Hypertension position paper on ambulatory blood pressure monitoring. Journal of hypertension. Sep 2013;31(9):1731-68. doi:10.1097/HJH.0b013e328363e964
- Parati G, Stergiou G, O'Brien E, et al. European Society of Hypertension practice guidelines for ambulatory blood pressure monitoring. Journal of hypertension. Jul 2014;32(7):1359-66. doi:10.1097/HJH.0000000000000221
- Ohkubo T, Hozawa A, Yamaguchi J, et al. Prognostic significance of the nocturnal decline in blood pressure in individuals with and without high 24-h blood pressure: the Ohasama study. J Hypertens. Nov 2002;20(11):2183-9. doi:10.1097/00004872-200211000-00017
- Redon J, Roca-Cusachs A, Mora-Macia J. Uncontrolled early morning blood pressure in medicated patients: the ACAMPA study. Analysis of the Control of Blood Pressure using Abulatory Blood Pressure Monitoring. Blood Press Monit. Apr 2002;7(2):111-6. doi:10.1097/00126097-200204000-00004
- Parati G, Stergiou GS, Asmar R, et al. European Society of Hypertension guidelines for blood pressure monitoring at home: a summary report of the Second International Consensus Conference on Home Blood Pressure Monitoring. J Hypertens. Aug 2008;26(8):1505-26. doi:10.1097/HJH.0b013e328308da66
- De Cesaris R, Ranieri G, Filitti V, Bonfantino MV, Andriani A. Cardiovascular effects of cigarette smoking. Cardiology. 1992;81(4-5):233-7. doi:10.1159/000175809
- Degaute JP, Van Cauter E, van de Borne P, Linkowski P. Twenty-four-hour blood pressure and heart rate profiles in humans. A twin study. Hypertension. Feb 1994;23(2):244-53. doi:10.1161/01.hyp.23.2.244
- Hermida RC, Ayala DE, Fernandez JR, Calvo C. Chronotherapy improves blood pressure control and reverts the nondipper pattern in patients with resistant hypertension. Hypertension. Jan 2008;51(1):69-76. doi:10.1161/HYPERTENSIONAHA.107.096933
- Hermida RC, Ayala DE. Chronotherapy with the angiotensin-converting enzyme inhibitor ramipril in essential hypertension: improved blood pressure control with bedtime dosing. Hypertension. Jul 2009;54(1):40-6. doi:10.1161/HYPERTENSIONAHA.109.130203
- Stevens SL, Wood S, Koshiaris C, et al. Blood pressure variability and cardiovascular disease: systematic review and meta-analysis. BMJ (Clinical research ed). Aug 9 2016;354:i4098. doi:10.1136/bmj.i4098
- Chadachan VM, Ye MT, Tay JC, Subramaniam K, Setia S. Understanding short-term blood-pressure-variability phenotypes: from concept to clinical practice. Int J Gen Med. 2018;11:241-254. doi:10.2147/IJGM.S164903
- Mena LJ, Felix VG, Melgarejo JD, Maestre GE. 24-Hour Blood Pressure Variability Assessed by Average Real Variability: A Systematic Review and Meta-Analysis. J Am Heart Assoc. Oct 19 2017;6(10)doi:10.1161/JAHA.117.006895
- Portaluppi F, Montanari L, Ferlini M, et al. Consistent changes in the circadian rhythms of blood pressure and atrial natriuretic peptide in congestive heart failure. Chronobiol Int. 1991;8(5):432-9. doi:10.3109/07420529109059178
- Verdecchia P, Angeli F, Gattobigio R, Rapicetta C, Reboldi G. Impact of blood pressure variability on cardiac and cerebrovascular complications in hypertension. American journal of hypertension. Feb 2007;20(2):154-61. doi:10.1016/j.amjhyper.2006.07.017
- Mancia G, Bombelli M, Facchetti R, et al. Long-term prognostic value of blood pressure variability in the general population: results of the Pressioni Arteriose Monitorate e Loro Associazioni Study. Hypertension. Jun 2007;49(6):1265-70. doi:10.1161/HYPERTENSIONAHA.107.088708
- Stergiou GS, Lourida P, Tzamouranis D, Baibas NM. Unreliable oscillometric blood pressure measurement: prevalence, repeatability and characteristics of the phenomenon. J Hum Hypertens. Dec 2009;23(12):794-800. doi:10.1038/jhh.2009.20
- Padwal R, Campbell NRC, Schutte AE, et al. Optimizing observer performance of clinic blood pressure measurement: a position statement from the Lancet Commission on Hypertension Group. J Hypertens. Sep 2019;37(9):1737-1745. doi:10.1097/HJH.0000000000002112
