Stroke Risk of Blood Pressure Indices Determined by Home Blood Pressure Measurement
The Ohasama Study
Background and Purpose—The purpose of this prospective cohort study was to investigate associations between stroke and blood pressure (BP) indices (systolic BP [SBP], diastolic BP [DBP], mean BP, and pulse pressure [PP]) determined by home BP measurement.
Methods—Associations between stroke and BP indices were examined in a rural Japanese population. Home BP data of 2369 subjects (40% men) ≥35 years of age (mean, 59 years) without a history of stroke were obtained. Associations between stroke and each index were determined using Cox proportional hazards regression and the likelihood ratio (LR) test.
Results—During follow-up (mean, 11.7 years), 238 strokes occurred. The LR test showed that SBP and mean BP were significantly more strongly associated with total and ischemic stroke than DBP and PP (LR χ2 ≥9.3, P<0.01 for SBP/mean BP, LR χ2 ≤3.8, P≥0.05 for DBP/PP). SBP tended to be more strongly associated with total/ischemic stroke than mean BP (LR χ2=3.8, P=0.05 for SBP, LR χ2 ≤0.2, P>0.6 for mean BP). PP tended to be slightly more strongly associated with ischemic stroke than DBP (LR χ2=7.5, P<0.01 for DBP, LR χ2=9.3, P<0.01 for PP), whereas DBP was significantly more strongly associated with hemorrhagic stroke than PP (LR χ2=9.2, P<0.01 for DBP, LR χ2=2.5, P=0.01 for PP).
Conclusion—PP obtained from home BP measurements was weakly associated with stroke, whereas SBP showed the strongest association. Additionally, DBP and PP may be associated with different stroke types.
- diastolic blood pressure
- home blood pressure measurement
- mean blood pressure
- pulse pressure
- systolic blood pressure
Recently, pulse pressure (PP) was reported to be associated with coronary heart disease.1,2 However, several studies showed that PP is not strongly associated with stroke when compared with other blood pressure (BP) indices.3,4 These studies were based on casual-screening BP (CBP). Thus, the present study evaluated associations between stroke and systolic BP (SBP), diastolic BP (DBP), mean BP (MBP), and PP obtained from home BP (HBP) measurement, which has been demonstrated to predict cardiovascular diseases more accurately than CBP.5
The present study is part of a longitudinal observational cohort study of subjects who have been participating in our HBP measurement project in Ohasama, Japan. The socioeconomic and demographic characteristics of Ohasama, the selection procedure of the study populations, the HBP and CBP measurement procedures, and the data collection procedures have been described previously.5–7 The present study population consisted of 2369 individuals (40% men), ≥35 years of age (mean, 59.2 years), without a history of stroke and with ≥3 days of morning HBP and a CBP.6
The subjects were followed from the dates of HBP measurement (approximately 1992) until December 31, 2004. The procedures for diagnosing stroke were described previously.7,8 Cerebral infarction (International Classification of Diseases, 10th Revision code I63) was defined as ischemic stroke, and intracerebral hemorrhage (I61) and subarachnoid hemorrhage (I60) were defined as hemorrhagic stroke.
The relative hazard and 95% CI were estimated for a 1-SD difference for each index using Cox proportional hazards regression, adjusted for age, sex, smoking status, use of antihypertensive medication, and history of heart disease, diabetes mellitus, or hypercholesterolemia. The likelihood ratio (LR) χ2 value was used as a measure of the improvement of goodness of fit9 between the model containing a single BP index (and confounding factors) and the model containing 2 indices. A significant LR χ2 indicates that the index represents a significantly stronger association with stroke.9
During follow-up (mean, 11.7 years), 238 strokes occurred (169 ischemic, 69 hemorrhagic).
All baseline BP indices were significantly higher in subjects who developed stroke than in those who did not (Table 1).
Figure A shows relative hazards for total stroke. Of the HBP indices, SBP and MBP were strongly associated with total stroke followed by DBP. The association between total stroke and PP was relatively weak. Associations between stroke and the CBP indices were generally weak. Table 2 shows the LR χ2 values when 2 HBP indices were analyzed simultaneously. For total stroke, the LR χ2 values of SBP and MBP (LR χ2 ≥11.8, P<0.01) were significantly higher than those of DBP and PP (LR χ2 ≤3.8, P≥0.05). The LR χ2 value of SBP tended to be larger than that of MBP, although the difference was not significant. The LR χ2 values of DBP and PP were not significantly different when DBP and PP were compared.
Figure B shows the relative hazards for ischemic stroke. The association between ischemic stroke and SBP was the strongest followed by MBP. Associations between ischemic stroke and DBP and PP were relatively weak. As shown in Table 2, the LR χ2 of SBP tended to be larger than that of MBP when SBP was compared with MBP, but there were no significant differences. The LR χ2 values of SBP and MBP were significantly stronger than those of DBP and PP when SBP and MBP were compared with DBP and PP. The LR χ2 values of DBP and PP were not significantly different when DBP and PP were compared, although that of PP tended to be larger than that of DBP.
Figure C shows the relative hazards for hemorrhagic stroke. SBP, DBP, and MBP were similarly associated with hemorrhagic stroke, and PP was not significantly associated. No significant differences were observed when the LR χ2 values of SBP, DBP, and MBP were compared; these values were also significantly larger than that of PP (Table 2). These results did not change for the analysis of intracerebral hemorrhage alone.
Recent studies using CBP3,4 and ambulatory BP,8 which investigated associations between stroke and BP indices, showed that PP was not very strongly associated with stroke. In the present study using HBP, like in these previous studies, PP was not strongly associated with stroke. LR tests showed that SBP and MBP were significantly more strongly associated with total or ischemic stroke than DBP and PP. SBP, MBP, and DBP were all significantly more strongly associated with hemorrhagic stroke than PP. Thus, PP may not be important for predicting stroke. However, PP tended to be slightly more strongly associated with ischemic stroke than DBP, suggesting that different BP indices are specifically associated with different stroke types.
SBP tended to be more strongly associated with total and ischemic stroke than MBP, although the differences were not significant. Considering that MBP has to be calculated from the formula as an approximation, SBP may be the most useful index to follow in daily medical practice.
In conclusion, PP obtained from HBP measurements was not strongly associated with stroke. SBP showed a strong association with stroke and appears to be a useful index. DBP and PP may be associated with different stroke types.
Sources of Funding
This study was supported in part by Grants for Scientific Research (15790293, 16590433, 17790381, 18390192, 18590587, 19590929, and 19790423) from the Ministry of Education, Culture, Sports, Science and Technology, Japan; Grants-in-Aid (H17-Kenkou-007, H18-Junkankitou [Seishuu]-Ippan-012, and H20-Junkankitou [Seishuu]-Ippan-009, 013) from the Ministry of Health, Labour and Welfare, Health and Labor Sciences Research Grants, Japan; Grants-in-Aid for Japan Society for the Promotion of Science (JSPS) fellows (16.54041, 18.54042, 19.7152, 20.7198, 20.7477, and 20.54043); Health Science Research Grants and Medical Technology Evaluation Research Grants from the Ministry of Health, Labour and Welfare, Japan; the Japan Atherosclerosis Prevention Fund; Uehara Memorial Foundation; Takeda Medical Research Foundation; National Cardiovascular Research Grants; and Biomedical Innovation Grants.
- Received December 28, 2008.
- Revision received February 22, 2009.
- Accepted March 12, 2009.
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