COMMENTARY
The Prognostic Value of Self-Assessed Nocturnal Blood Pressure Geoffrey A. Head, BSc, PhD From the Baker IDI Heart and Diabetes Institute, Melbourne, Vic., Australia
The predictive value for cardiovascular risk of nocturnal or sleep blood pressure (BP) levels as well as the absence of nocturnal dipping has long been established and is superior to clinic or even out-of-office daytime BP measurements.1–3 This finding has been made possible largely by the widespread use of ambulatory BP monitoring (ABPM) involving lightweight portable devices introduced in the 1980s with sufficient memory and battery power to make possible multiple measurements per hour (usually two or three) over 24 hours or even several days. ABPM is not only the gold standard for BP measurement but has been adopted by the National Institute for Health and Clinical Excellence in the United Kingdom as the preferred technique for the diagnosis of hypertension.4 A strong case is being made that ABPM is now ready to replace clinic BP for the diagnosis and management of hypertension5 although there are counter arguments.6 The superior prognostic capability of ABPM over clinic BP was perhaps thought to be the result of the accuracy of the large number of recordings during the active and sleep periods, but recent studies suggest that this is not so straightforward. Generally fewer measurements are made during the night to limit the disturbance to sleep7 and yet the best prediction of cardiovascular outcomes appears to be from the nocturnal measurement. Thus, one of the strongest arguments for ABPM over other techniques has been the ability to determine nocturnal asleep BP, which is particularly important for high-risk patients such as those with diabetes or chronic kidney disease.8 A recent finding from the Korean Ambulatory Blood Pressure multicenter observational study suggests that the nocturnal BP level rather than the presence of nondipping predicts left ventricular hypertrophy.9 By contrast, analysis of the Spanish ABPM Registry suggests that nondipping is associated with more advanced disease.10 This discussion is somewhat parallel to the controversy of whether it is the morning BP surge or extreme nocturnal dipping that accounts for the greater number of strokes in the morning, as outlined in a recent article in this Journal.11 These studies highlight the confounding issue that the relatedness of each measure of BP, whether it’s a change in BP at a particular time or a peak or trough makes it very difficult to separate the contribution that each value makes to cardiovascular risk. Thus, the very large population studies that are Address for correspondence: Geoffrey A. Head, BSc, PhD, Baker IDI Heart and Diabetes Institute, PO Box 6492, St Kilda Road, Central, Melbourne, Victoria 8008, Australia E-mail: [email protected] DOI: 10.1111/jch.12502
sufficiently powered to distinguish the exact contribution of all the interrelated day and night measures of systolic and diastolic BP would be very expensive and perhaps prohibitively so using ABPM. While the Spanish ABPM Registry has more than 37,000 patients, others have used a meta-analysis approach to combine international databases. An example is the Hansen study reported in 2007 with more than 7000 patients.12 By comparison, epidemiological studies in specific cancers can contain hundreds of thousands of patients.13 What is limiting the size of hypertension studies in predicting cardiovascular events related to sleep or nocturnal levels is that, currently, ABPM devices are expensive and not widely available. Further, a considerable investment has to be made to implement the skills in general practice required to operate the device and to extract and interpret the findings.14 While technology with apps and smartphones is advancing and simplifying the procedures and reducing training, the high cost of the ABPM device has remained due to robustness of the device required for its continual use in clinical practice. Cost is particularly relevant to underdeveloped countries where such outlays may be prohibitive. Thus, there appears to be a need for a low-cost device such as those used for home BP measurement that will also measure sleep BP sufficiently accurately to be able to provide the full prognostic information currently provided for by ABPM. A major recent development by Ishikawa and colleagues15 has been to develop a home BP measurement (HBPM) device that can be programmed to record multiple measurements during sleep. The device can be programmed to take measurements at 2 AM, 3 AM, and 4 AM, which were considered by the investigators to be the most likely to represent sleep given the differing nocturnal habits of patients. Importantly, the patients were required to do this on as many nights as possible during a 2-week period (average 9).15 The major contribution of this study was to use recordings from 854 patients enrolled in the Japan Morning Surge Home Blood Pressure (J-HOP) trial to show for the first time that nighttime systolic BP measured using a patientcontrolled home device is associated with target organ damage and is a better predictor than even ambulatory nighttime BP. In addition, they found that adding sleep BP to other measures such as clinic or ambulatory BP improved the correlation with target organ damage. A new study by Kario and colleagues16 featured in this issue of The Journal of Clinical Hypertension has considerably extended this work with a new larger analysis of more than 2500 participants also from the J-HOP study. The major findings were that sleepmeasured home systolic BP correlated with all measures The Journal of Clinical Hypertension
Vol 17 | No 5 | May 2015
349
Commentary
studied including urinary albumin-creatinine ratio, left ventricular mass index, brachial ankle pulse wave velocity, maximum carotid intima-media thickening, pro–brain-type natriuretic peptide, and cardiac troponin T.16 Interestingly, only urinary albumin-creatinine ratio correlated with sleep diastolic BP. Thus, the multiple linear regression models focused on using sleep systolic BP as the primary measure and then added clinic morning and evening BP into the model, which, in most cases, improved correlations as might be expected. Importantly, after controlling for clinic systolic BP as well as morning and evening BP, the associations between sleep measurements and a majority of the measures of organ damage remain significant. This is a very important study in that it brings the use of home devices into the area that was the domain of ABPM. While the single measurement at hourly intervals for 3 hours during the night does not give as much information as would be obtained with an ambulatory device, the measurement is able to be repeated over many days, which may give a great deal of robustness to the values achieved. This is unlike ABPM, which is mostly used in a single 24-hour period and only occasionally over 48 hours. There is patient resistance to the inconvenience of wearing a device for such long periods and home-type devices are preferred.17 The studies by Kario and colleagues are at the beginning of determining the applicability of this new technology in the management of hypertension. A number of studies still need to be done including ascertaining the ability of sleep BP measurements to predict cardiovascular outcomes and determining whether targeting sleep BP with therapy will prove useful. Clearly the device could also be used to determine whether therapy or other interventions were restoring dipping during sleep. As such, the device could replace many current home devices and provide new sleep BP information for research, particularly when continually repeated over the long term. Such long-term information from clinic visits (visit-to-visit variability) proved to be a very valuable predictor of stroke outcomes only relatively recently.18 Like ABPM, the widespread adoption is directly linked to the affordability of the device. While the current cost of the device is not indicated, the high cost of the ABPM devices is related to the very high quality of the internal machinery required to be used regularly over many years in hundreds of patients. This issue needs some further clarification, but, as the device would be designed for personal use, it would not require anywhere near the degree of robustness as a standard ambulatory recorder and might be made affordable if built in large volumes. One other issue relates to how and why the measurements differ from ABPM. The estimated sleep diastolic BP was similar to an ambulatory assessment but systolic BP was 2 mm Hg to 3 mm Hg higher by the home device.15 Also, I suspect that there will be a trend to increase the number of measurements taken throughout 350
The Journal of Clinical Hypertension
Vol 17 | No 5 | May 2015
the morning, evening, and night driven perhaps to cover gaps in the 24-hour period. If so, would this really differ from the regular ABPM? The advantage of the ABPM is that the patient goes about their normal daily activities, only to remain still during the deflation. By contrast, the accepted home measurement protocols require the patient to sit to take the measurements. Exactly how these different approaches influence the ability to use the information in predictive outcome studies is unclear. In conclusion, the developments in automated home devices that can assess sleep BP in addition to standard home measures mark a major step in providing a convenient method for a more comprehensive assessment of the patient’s true BP. The device may provide a valid alternative for those who are unable or unwilling to wear an ABPM device for 24 hours and offers the potential for better long-term monitoring of high-risk patients with target organ damage. Whether such technology will eventually replace ABPM devices or whether they will merge into a new hybrid device will be an interesting development to follow. Disclosures: No funding of the work was received. GAH is supported by NHMRC Principal Research Fellowship (1002186).
References 1. Verdecchia P, Schillaci G, Borgioni C, et al. Ambulatory pulse pressure a potent predictor of total cardiovascular risk in hypertension. Hypertension. 1998;32:983–988. 2. Verdecchia P, Schillaci G, Guerrieri M, et al. Circadian blood pressure changes and left ventricular hypertrophy in essential hypertension. Circulation. 1990;81:528–536. 3. Boggia J, Li Y, Thijs L, et al. Prognostic accuracy of day versus night ambulatory blood pressure: a cohort study. Lancet. 2007;370:1219– 1229. 4. National Institute for Health and Clinical Excellence. Hypertension: Clinical Management of Primary Hypertension in Adults [Clinical Guideline 127]. London: NICE; 2011. 5. Head GA. Ambulatory BP monitoring is ready to replace clinic BP in the diagnosis of hypertension: pro side of the argument. Hypertension. 2014;64:1175–1181. 6. Redon J, Lurbe E. Ambulatory blood pressure monitoring is ready to replace clinic blood pressure in the diagnosis of hypertension: con side of the argument. Hypertension. 2014;64:1169–1174. 7. Staessen J, Bulpitt CJ, Fagard R, et al. Reference values for ambulatory blood pressure: a population study. J Hypertens Suppl. 1991;9: S320–S321. 8. de la Sierra A, Redon J, Banegas JR, et al. Prevalence and factors associated with circadian blood pressure patterns in hypertensive patients. Hypertension. 2009;53:466–472. 9. Yi JE, Shin J, Ihm SH, et al. Not nondipping but nocturnal blood pressure predicts left ventricular hypertrophy in the essential hypertensive patients: the Korean Ambulatory Blood Pressure multicenter observational study. J Hypertens. 2014;32:1999–2004; discussion. 10. de la Sierra A, Gorostidi M, Banegas JR, et al. Nocturnal hypertension or nondipping: which is better associated with the cardiovascular risk profile? Am J Hypertens. 2014;27:680–687. 11. Cohen DL, Townsend RR. Is it morning blood pressure surge or extreme nocturnal dipping that accounts for the increased stroke risk in the morning waking hours? J Clin Hypertens (Greenwich). 2014;16:847. 12. Hansen TW, Kikuya M, Thijs L, et al. Prognostic superiority of daytime ambulatory over conventional blood pressure in four populations: a meta-analysis of 7,030 individuals. J Hypertens. 2007;25:1554–1564. 13. Albright F, Stephenson RA, Agarwal N, et al. Prostate cancer risk prediction based on complete prostate cancer family history. Prostate. 2015;75:390–398. 14. Bloch MJ, Basile JN. UK guidelines call for routine 24-hour ambulatory blood pressure monitoring in all patients to make the diagnosis of hypertension–not ready for prime time in the United States. J Clin Hypertens (Greenwich). 2011;13:871–872.
Commentary
15. Ishikawa J, Hoshide S, Eguchi K, et al. Nighttime home blood pressure and the risk of hypertensive target organ damage. Hypertension. 2012;60:921–928. 16. Kario K, Hoshide S, Yano Y, et al. Sleep blood pressure self-measured at home as novel determinant of organ damage: Japan Morning Surge Home Blood Pressure (J-HOP) Study. J Clin Hypertens (Greenwich). 2015;17:340–348.
17. Nasothimiou EG, Karpettas N, Dafni MG, Stergiou GS. Patients’ preference for ambulatory versus home blood pressure monitoring. J Hum Hypertens. 2014;28:224–229. 18. Rothwell PM, Howard SC, Dolan E, et al. Prognostic significance of visit-to-visit variability, maximum systolic blood pressure, and episodic hypertension. Lancet. 2010;375:895–905.
The Journal of Clinical Hypertension
Vol 17 | No 5 | May 2015
351
The Prognostic Value of Self-Assessed Nocturnal Blood Pressure Geoffrey A. Head, BSc, PhD From the Baker IDI Heart and Diabetes Institute, Melbourne, Vic., Australia
The predictive value for cardiovascular risk of nocturnal or sleep blood pressure (BP) levels as well as the absence of nocturnal dipping has long been established and is superior to clinic or even out-of-office daytime BP measurements.1–3 This finding has been made possible largely by the widespread use of ambulatory BP monitoring (ABPM) involving lightweight portable devices introduced in the 1980s with sufficient memory and battery power to make possible multiple measurements per hour (usually two or three) over 24 hours or even several days. ABPM is not only the gold standard for BP measurement but has been adopted by the National Institute for Health and Clinical Excellence in the United Kingdom as the preferred technique for the diagnosis of hypertension.4 A strong case is being made that ABPM is now ready to replace clinic BP for the diagnosis and management of hypertension5 although there are counter arguments.6 The superior prognostic capability of ABPM over clinic BP was perhaps thought to be the result of the accuracy of the large number of recordings during the active and sleep periods, but recent studies suggest that this is not so straightforward. Generally fewer measurements are made during the night to limit the disturbance to sleep7 and yet the best prediction of cardiovascular outcomes appears to be from the nocturnal measurement. Thus, one of the strongest arguments for ABPM over other techniques has been the ability to determine nocturnal asleep BP, which is particularly important for high-risk patients such as those with diabetes or chronic kidney disease.8 A recent finding from the Korean Ambulatory Blood Pressure multicenter observational study suggests that the nocturnal BP level rather than the presence of nondipping predicts left ventricular hypertrophy.9 By contrast, analysis of the Spanish ABPM Registry suggests that nondipping is associated with more advanced disease.10 This discussion is somewhat parallel to the controversy of whether it is the morning BP surge or extreme nocturnal dipping that accounts for the greater number of strokes in the morning, as outlined in a recent article in this Journal.11 These studies highlight the confounding issue that the relatedness of each measure of BP, whether it’s a change in BP at a particular time or a peak or trough makes it very difficult to separate the contribution that each value makes to cardiovascular risk. Thus, the very large population studies that are Address for correspondence: Geoffrey A. Head, BSc, PhD, Baker IDI Heart and Diabetes Institute, PO Box 6492, St Kilda Road, Central, Melbourne, Victoria 8008, Australia E-mail: [email protected] DOI: 10.1111/jch.12502
sufficiently powered to distinguish the exact contribution of all the interrelated day and night measures of systolic and diastolic BP would be very expensive and perhaps prohibitively so using ABPM. While the Spanish ABPM Registry has more than 37,000 patients, others have used a meta-analysis approach to combine international databases. An example is the Hansen study reported in 2007 with more than 7000 patients.12 By comparison, epidemiological studies in specific cancers can contain hundreds of thousands of patients.13 What is limiting the size of hypertension studies in predicting cardiovascular events related to sleep or nocturnal levels is that, currently, ABPM devices are expensive and not widely available. Further, a considerable investment has to be made to implement the skills in general practice required to operate the device and to extract and interpret the findings.14 While technology with apps and smartphones is advancing and simplifying the procedures and reducing training, the high cost of the ABPM device has remained due to robustness of the device required for its continual use in clinical practice. Cost is particularly relevant to underdeveloped countries where such outlays may be prohibitive. Thus, there appears to be a need for a low-cost device such as those used for home BP measurement that will also measure sleep BP sufficiently accurately to be able to provide the full prognostic information currently provided for by ABPM. A major recent development by Ishikawa and colleagues15 has been to develop a home BP measurement (HBPM) device that can be programmed to record multiple measurements during sleep. The device can be programmed to take measurements at 2 AM, 3 AM, and 4 AM, which were considered by the investigators to be the most likely to represent sleep given the differing nocturnal habits of patients. Importantly, the patients were required to do this on as many nights as possible during a 2-week period (average 9).15 The major contribution of this study was to use recordings from 854 patients enrolled in the Japan Morning Surge Home Blood Pressure (J-HOP) trial to show for the first time that nighttime systolic BP measured using a patientcontrolled home device is associated with target organ damage and is a better predictor than even ambulatory nighttime BP. In addition, they found that adding sleep BP to other measures such as clinic or ambulatory BP improved the correlation with target organ damage. A new study by Kario and colleagues16 featured in this issue of The Journal of Clinical Hypertension has considerably extended this work with a new larger analysis of more than 2500 participants also from the J-HOP study. The major findings were that sleepmeasured home systolic BP correlated with all measures The Journal of Clinical Hypertension
Vol 17 | No 5 | May 2015
349
Commentary
studied including urinary albumin-creatinine ratio, left ventricular mass index, brachial ankle pulse wave velocity, maximum carotid intima-media thickening, pro–brain-type natriuretic peptide, and cardiac troponin T.16 Interestingly, only urinary albumin-creatinine ratio correlated with sleep diastolic BP. Thus, the multiple linear regression models focused on using sleep systolic BP as the primary measure and then added clinic morning and evening BP into the model, which, in most cases, improved correlations as might be expected. Importantly, after controlling for clinic systolic BP as well as morning and evening BP, the associations between sleep measurements and a majority of the measures of organ damage remain significant. This is a very important study in that it brings the use of home devices into the area that was the domain of ABPM. While the single measurement at hourly intervals for 3 hours during the night does not give as much information as would be obtained with an ambulatory device, the measurement is able to be repeated over many days, which may give a great deal of robustness to the values achieved. This is unlike ABPM, which is mostly used in a single 24-hour period and only occasionally over 48 hours. There is patient resistance to the inconvenience of wearing a device for such long periods and home-type devices are preferred.17 The studies by Kario and colleagues are at the beginning of determining the applicability of this new technology in the management of hypertension. A number of studies still need to be done including ascertaining the ability of sleep BP measurements to predict cardiovascular outcomes and determining whether targeting sleep BP with therapy will prove useful. Clearly the device could also be used to determine whether therapy or other interventions were restoring dipping during sleep. As such, the device could replace many current home devices and provide new sleep BP information for research, particularly when continually repeated over the long term. Such long-term information from clinic visits (visit-to-visit variability) proved to be a very valuable predictor of stroke outcomes only relatively recently.18 Like ABPM, the widespread adoption is directly linked to the affordability of the device. While the current cost of the device is not indicated, the high cost of the ABPM devices is related to the very high quality of the internal machinery required to be used regularly over many years in hundreds of patients. This issue needs some further clarification, but, as the device would be designed for personal use, it would not require anywhere near the degree of robustness as a standard ambulatory recorder and might be made affordable if built in large volumes. One other issue relates to how and why the measurements differ from ABPM. The estimated sleep diastolic BP was similar to an ambulatory assessment but systolic BP was 2 mm Hg to 3 mm Hg higher by the home device.15 Also, I suspect that there will be a trend to increase the number of measurements taken throughout 350
The Journal of Clinical Hypertension
Vol 17 | No 5 | May 2015
the morning, evening, and night driven perhaps to cover gaps in the 24-hour period. If so, would this really differ from the regular ABPM? The advantage of the ABPM is that the patient goes about their normal daily activities, only to remain still during the deflation. By contrast, the accepted home measurement protocols require the patient to sit to take the measurements. Exactly how these different approaches influence the ability to use the information in predictive outcome studies is unclear. In conclusion, the developments in automated home devices that can assess sleep BP in addition to standard home measures mark a major step in providing a convenient method for a more comprehensive assessment of the patient’s true BP. The device may provide a valid alternative for those who are unable or unwilling to wear an ABPM device for 24 hours and offers the potential for better long-term monitoring of high-risk patients with target organ damage. Whether such technology will eventually replace ABPM devices or whether they will merge into a new hybrid device will be an interesting development to follow. Disclosures: No funding of the work was received. GAH is supported by NHMRC Principal Research Fellowship (1002186).
References 1. Verdecchia P, Schillaci G, Borgioni C, et al. Ambulatory pulse pressure a potent predictor of total cardiovascular risk in hypertension. Hypertension. 1998;32:983–988. 2. Verdecchia P, Schillaci G, Guerrieri M, et al. Circadian blood pressure changes and left ventricular hypertrophy in essential hypertension. Circulation. 1990;81:528–536. 3. Boggia J, Li Y, Thijs L, et al. Prognostic accuracy of day versus night ambulatory blood pressure: a cohort study. Lancet. 2007;370:1219– 1229. 4. National Institute for Health and Clinical Excellence. Hypertension: Clinical Management of Primary Hypertension in Adults [Clinical Guideline 127]. London: NICE; 2011. 5. Head GA. Ambulatory BP monitoring is ready to replace clinic BP in the diagnosis of hypertension: pro side of the argument. Hypertension. 2014;64:1175–1181. 6. Redon J, Lurbe E. Ambulatory blood pressure monitoring is ready to replace clinic blood pressure in the diagnosis of hypertension: con side of the argument. Hypertension. 2014;64:1169–1174. 7. Staessen J, Bulpitt CJ, Fagard R, et al. Reference values for ambulatory blood pressure: a population study. J Hypertens Suppl. 1991;9: S320–S321. 8. de la Sierra A, Redon J, Banegas JR, et al. Prevalence and factors associated with circadian blood pressure patterns in hypertensive patients. Hypertension. 2009;53:466–472. 9. Yi JE, Shin J, Ihm SH, et al. Not nondipping but nocturnal blood pressure predicts left ventricular hypertrophy in the essential hypertensive patients: the Korean Ambulatory Blood Pressure multicenter observational study. J Hypertens. 2014;32:1999–2004; discussion. 10. de la Sierra A, Gorostidi M, Banegas JR, et al. Nocturnal hypertension or nondipping: which is better associated with the cardiovascular risk profile? Am J Hypertens. 2014;27:680–687. 11. Cohen DL, Townsend RR. Is it morning blood pressure surge or extreme nocturnal dipping that accounts for the increased stroke risk in the morning waking hours? J Clin Hypertens (Greenwich). 2014;16:847. 12. Hansen TW, Kikuya M, Thijs L, et al. Prognostic superiority of daytime ambulatory over conventional blood pressure in four populations: a meta-analysis of 7,030 individuals. J Hypertens. 2007;25:1554–1564. 13. Albright F, Stephenson RA, Agarwal N, et al. Prostate cancer risk prediction based on complete prostate cancer family history. Prostate. 2015;75:390–398. 14. Bloch MJ, Basile JN. UK guidelines call for routine 24-hour ambulatory blood pressure monitoring in all patients to make the diagnosis of hypertension–not ready for prime time in the United States. J Clin Hypertens (Greenwich). 2011;13:871–872.
Commentary
15. Ishikawa J, Hoshide S, Eguchi K, et al. Nighttime home blood pressure and the risk of hypertensive target organ damage. Hypertension. 2012;60:921–928. 16. Kario K, Hoshide S, Yano Y, et al. Sleep blood pressure self-measured at home as novel determinant of organ damage: Japan Morning Surge Home Blood Pressure (J-HOP) Study. J Clin Hypertens (Greenwich). 2015;17:340–348.
17. Nasothimiou EG, Karpettas N, Dafni MG, Stergiou GS. Patients’ preference for ambulatory versus home blood pressure monitoring. J Hum Hypertens. 2014;28:224–229. 18. Rothwell PM, Howard SC, Dolan E, et al. Prognostic significance of visit-to-visit variability, maximum systolic blood pressure, and episodic hypertension. Lancet. 2010;375:895–905.
The Journal of Clinical Hypertension
Vol 17 | No 5 | May 2015
351
