DIABETES TECHNOLOGY & THERAPEUTICS Volume 14, Number 6, 2012 ª Mary Ann Liebert, Inc. DOI: 10.1089/dia.2012.0006
ORIGINAL ARTICLE
Ambulatory Tonometric Blood Pressure Measurements in Patients with Diabetes Simone Theilade, M.D., Christel Joergensen, M.D., Frederik Persson, M.D., Maria Lajer, Ph.D., and Peter Rossing, DmSc
Abstract Background: Arterial tonometry is a novel technique for measuring ambulatory blood pressure (AMBP). The watch-like device BPro (HealthSTATS International, Singapore) captures radial pulsewave reflection and calculates brachial blood pressure (BP). In this study we investigate if arterial tonometry is applicable and reliable in patients with diabetes. Subjects and Methods: We compared tonometric (BPro) to cuff-based oscillometric and auscultatoric BPs (Takeda model TM2421, A&D Medical, Tokyo, Japan) in 25 Caucasian patients with type 1 or type 2 diabetes. Patients were seen twice within 2 weeks. At visit 1, a 15-min rest was followed by the recording of three cuff-based BPs and 2-min continuous tonometric BPs. At both visits 24-h AMBP measurements were recorded with the BPro device. Results: At Visit 1, auscultatoric BP (mean – SD) was 136 – 19/72 – 8 mm Hg versus 138 – 19/78 – 8 mm Hg with the tonometric device. Visit 1 AMBP was 131 – 20/76 – 9 mm Hg versus 131 – 12/75 – 9 mm Hg at Visit 2. Mean 24-h AMBP, daytime BP, nighttime BP, and dipping at the two visits were similar (P > 0.40). Linear and intraclass correlations coefficients between auscultatoric and tonometric systolic and diastolic BP were r = 0.86 and 0.65, respectively (P < 0.001 for both), and r = 0.83 and 0.77, respectively (P < 0.001 for both). The mean differences between devices were 1.9 – 10 and 5.5 – 6.6 mm Hg for systolic and diastolic BP, respectively. Conclusions: In patients with diabetes tonometric and cuff-based BPs are comparable, and tonometric AMBPs are reproducible and feasible.
Introduction
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lood pressure (BP) control is paramount in prevention of complications to diabetes, and hypertension significantly increases macro- and microvascular complications.1,2 A BP of ‡ 130 mm Hg defines hypertension in diabetes.3 Conventionally, BP has been measured with sphygmomanometry, using a device consisting of an inflatable cuff for occlusion of blood flow and a manometer for measuring pressure.4 In recent years arterial tonometry has emerged as an alternative way of indirect BP measuring. A tonometric device captures pulsewaves from arterial surfaces (e.g., the radial artery) and translate wave characteristics to BPs.5 Oscillometric devices are less accurate in measuring BP in persons with increased arterial stiffness.6 It is possible that increased arterial stiffness also impair the accuracy of tonometric BP measurements. Patients with diabetes have in-
creased arterial stiffness,7 and with this study we aimed to investigate if tonometry is applicable and reliable in BP measuring in patients with diabetes. Some of these data have been previously published in abstract form.8 Subjects and Methods The study design is cross-sectional, including 25 patients: 17 with type 1 and eight with type 2 diabetes. All were Caucasian. Patients were 59.6 – 7.8 years old, with a duration of diabetes of 24.5 – 14.3 years, and 18 (72%) men. Nine patients had normoalbuminuria, defined as persistent normoalbuminuria with a urinary albumin excretion rate of < 30 mg/24-h period. Two and 14 patients had micro- and macroalbuminuria, respectively, defined as a urinary albumin excretion rate between 30 and 300 mg/24-h period and > 300 mg/24-h period in two out of three consecutive measurements. Glomerular
Steno Diabetes Center, Gentofte, Denmark. Data were previously presented in abstract form at the 2011 meeting of the European Association for the Study of Diabetes and the 2011 meeting of the Danish Society of Hypertension.
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filtration rate (GFR) in patients with macroalbuminuria was 73.6 – 34.2 mL/min/1.73 m2. All patients were followed up at Steno Diabetes Center, Gentofte, Denmark. They were randomly selected from the outpatient clinic without regard for sex, age, type of diabetes, or kidney function. The number of participants included in the study was based on power calculations. One patient was excluded from the validation analysis because of missing sphygmomanometric measurements. Another patient only had one valid 24-h ambulatory BP (AMBP) measurement and was not included in the reproducibility analysis. Sphygmomanometric BPs were recorded with a Takeda device (TM2421, version 7, A&D Medical, Tokyo, Japan) and tonometric measurements with the BPro (HealthSTATS International, Singapore) device (Fig. 1). Both Takeda and BPro measurements were recorded on the left arm on all patients. The Takeda device is currently used for AMBP measurements at Steno Diabetes Center and was therefore chosen for comparison with the BPro device. Measurements of both cuff-based and tonometric BPs were performed by trained laboratory technicians. The cuff-based Takeda device obtains auscultatoric and oscillometric BP measurements simultaneously. Auscultatoric systolic BP (SBP) and diastolic BP (DBP) measurements are recorded at the appearance of the first and by the disappearance of the last Korotkoff sound, when entering the fifth Korotkoff’s phase, respectively. The transducer records oscillations equivalent to mean arterial pressure (MAP) and calculates oscillometric BPs based on accepted algorithms. Auscultatoric SBPs are typically lower, whereas DBPs are higher, than oscillometric measurements.4 The BPro is a watch-like device that captures radial pulsewave reflection and calculates brachial AMBP. A brachial AMBP can be recorded for every 10 s of pulsewave measurements. The BPro has previously been validated and meets
European Society of Hypertension and Association for the Advancement of Medical Instrumentation standards.9 In this study, the BPro device was calibrated with an oscillometric device (model UA 787, A&D Medical) prior to BP measuring, and every other year the device is serviced by the manufacturer (HealthSTATS). At Visit 1, patients were placed supine in a resting position for 15 min. A cuff of appropriate size was placed on the right arm. The stethoscope for auscultatoric and the transducer for oscillometric measurements were both placed above the brachial artery. Three separate Takeda measurements were obtained, and subsequently 2-min continuous BPro measurements were recorded. At both visits AMBP was recorded with BPro. AMBP recordings were performed every 15 min during daytime and nighttime. Daytime AMBP was from 7 a.m. to 11 p.m., whereas nighttime AMBP was 11 p.m. to 7 a.m. The BPro device also calculated dipping, which refers to the percentage decline in BP from daytime to nighttime. Mean AMBP was calculated as the average of all measurements obtained during the 24-h period. Statistical analysis is performed using SPSS version 15.0 for Windows (SPSS Inc., Chicago, IL). Variables are given as mean – SD values. Correlations between devices are calculated by linear regression equations and intraclass correlation. Mean differences between devices are calculated and visualized in a Bland–Altman plot, and 95% limits of agreement are calculated. Paired Student’s t tests compare AMBPs, and independent-samples t test compares groups. A two-tailed P value of < 0.05 is considered statistically significant. The study conformed to the Declaration of Helsinki, and all patients gave informed consent.
Results Validation
FIG. 1.
Photograph of the BPro.
Auscultatoric, oscillometric, and tonometric BPs (mean – SD) were 136 – 19/72 – 8, 137 – 16/77 – 9, and 138 – 19/78 – 8 mm Hg, respectively. Respective linear correlation coefficients between auscultatoric and tonometric SBP and DBP were r = 0.86 and 0.65 (P < 0.001 for both) (Fig. 2a), with intraclass correlations coefficients of r = 0.83 and 0.77 (P < 0.001 for both). Respective linear correlation coefficients between oscillometric and tonometric SBP and DBP were r = 0.89 and 0.82 (P < 0.001 for both), with intraclass correlation coefficients of r = 0.94 and 0.90 (P < 0.001 for both). Respective linear correlation coefficients between auscultatoric and oscillometric SBP and DBP were r = 0.91 and 0.77 (P < 0.001 for both), with intraclass correlation coefficients of r = 0.86 and 0.87 (P < 0.001 for both). Mean differences between tonometric and auscultatoric SBP and DBP were 1.9 – 10 and 5.5 – 6.6 mm Hg, respectively, with 95% limits of agreement of - 17.7 to 21.5 and - 7.4 to 18.4 mm Hg, respectively (Fig. 2b). Mean differences between tonometric and oscillometric SBP and DBP were 1.9 – 8.6 and 0.0 – 5.1 mm Hg, respectively, with 95% limits of agreement of - 15.0 to 18.8 and - 10 to 10 mm Hg, respectively. Mean differences between auscultatoric and oscillometric SBP and DBP were 0.2 – 8.0 and 5.6 – 5.8 mm Hg, respectively, with 95% limits of agreement of - 15.5 to 15.9 and - 5.8 to 17.0 mm Hg, respectively.
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FIG. 2. (a) Correlations plot and (b) Bland–Altman plot for systolic blood pressure (SBP) measured with sphygmomanometry (auscultatoric) (Takeda) versus tonometry (BPro).
There were no significant differences in agreement between devices when comparing normo- versus micro- and macroalbuminuric patients, men versus women, or patients with type 1 versus type 2 diabetes (P > 0.05) (data not shown). Evaluation of repeated measurements of AMBP Mean BP values from the two visits were similar. Mean AMBP was 131 – 20/76 – 9 mm Hg versus 132 – 12/75 – 9 mm Hg (P = 0.917 and P = 0.954, respectively), mean daytime BP was 136 – 22/78 – 9 mm Hg versus 136 – 13/78 – 10 mm Hg (P = 0.385 and P = 0.972, respectively), mean nighttime BP was 124 – 20/71 – 9 mm Hg versus 124 – 13/71 – 8 mm Hg (P = 0.935 and P = 0.984, respectively), and mean dipping was 9.3 – 5.7% versus 9.1 – 4.8% (P = 0.871). Patient satisfaction and AMBP completion Only one patient (4%) declined to repeat the AMBP. For the remaining patients the discomfort associated with the tonometric AMBP was acceptable, and AMBP measurements were successful according to present guidelines.10 Discussion In this study on patients with diabetes, we found tonometric and cuff-based BPs to be comparable and tonometric AMBPs to be reproducible. The BPro values correlated better with oscillometric than with auscultatoric values, which could be explained by the BPro device being calibrated with an oscillometric device. We obtained lower SBP and DBP auscultatoric than oscillometric values, despite oscillometric values typically overestimating SBP and underestimating DBP. This could be caused by our cohort having increased arterial stiffness secondary to diabetes,7 leading to overestimation of both SBP and DBP oscillometric values and underestimation of auscultatoric SBP.4,6
We did not find any significant difference in agreement between devices when subdividing patients according to albuminuria status, sex or type of diabetes. However, this finding may be due to lack of power. Aside from brachial arterial BP, the BPro device measures various indices of arterial stiffness including augmentation index, central BP, and MAP. Brachial arterial BP is an inferior risk marker of cardiovascular outcome compared with markers of arterial stiffness.11 As patients with diabetes have increased arterial stiffness,7 measuring indices of arterial stiffness rather than peripheral BP may prove to be a better risk marker as well as a better treatment target for management of hypertension in patients with diabetes. Therefore the BPro possess potentially advantageous qualities for the purpose of measurements of both BP and arterial stiffness, although we did not investigate arterial stiffness in the current study. A great advantage of the BPro is the smaller size and more accessible position of the device, causing less discomfort both during and between BP measurements. The absence of an inflatable cuff and the inaudibility of the device prevent anticipation rise of BP and nighttime awakening in connection with measurements. This allows for more frequent and undisturbed measuring and possibly a more accurate AMBP. Our study has some limitations. The small number of participants does not allow for scrutinizing patient data when dividing patients according to kidney function, gender, or type of diabetes. However, we did not see any association between patient characteristics and reliability of tonometric BPs. We only performed tonometric AMBPs. Concurrent AMBP measurements with both cuff-based and tonometric devices would have been interesting. However, as both devices would have had to be strapped on to the same arm, faulty measurements were likely to be obtained. Furthermore, the application of two devices concurrently probably would have been bothersome to patients, thereby affecting measurements.
456 In conclusion, we find that the manufacturer-validated BPro device recorded reliable and reproducible tonometric BP measurements in patients with diabetes. The BPro device offers frequent and undisturbed BP measurements, along with additional information on arterial state. Furthermore, tonometric measurements appear to be feasible and possibly more convenient for the patients. We therefore propose that in patients with diabetes tonometric BPs may be preferable to sphygmomanometric measurements. However, larger studies with sufficient follow-up are needed to establish the role of tonometric BP measurements in diabetes, in particular for the purpose of evaluating the value of parameters of arterial stiffness.
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Author Disclosure Statement No competing financial interests exist. References 1. Adler AI, Stratton IM, Neil HA, Yudkin JS, Matthews DR, Cull CA, Wright AD, Turner RC, Holman RR: Association of systolic blood pressure with macrovascular and microvascular complications of type 2 diabetes (UKPDS 36): prospective observational study. BMJ 2000;321:412–419. 2. Chen G, McAlister FA, Walker RL, Hemmelgarn BR, Campbell NR: Cardiovascular outcomes in Framingham participants with diabetes: the importance of blood pressure. Hypertension 2011;57:891–897. 3. American Diabetes Association: Standards of medical care in diabetes—2010. Diabetes Care 2010;33(Suppl 1):S11–S61. 4. Pickering TG, Hall JE, Appel LJ, Falkner BE, Graves J, Hill MN, Jones DW, Kurtz T, Sheps SG, Roccella EJ: Recommendations for blood pressure measurement in humans and experimental animals: Part 1: Blood pressure measurement in humans: a statement for professionals from the Subcommittee of Professional and Public Education of the American Heart Association Council on High Blood Pressure Research. Circulation 2005;111:697–716. 5. Chen CH, Nevo E, Fetics B, Pak PH, Yin FC, Maughan WL, Kass DA: Estimation of central aortic pressure waveform by mathematical transformation of radial tonometry pressure.
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Address correspondence to: Simone Theilade, M.D. Steno Diabetes Center Niels Steensens Vej 2, NLC 2.07 DK-2820 Gentofte, Denmark E-mail:
[email protected] 