Blood pressure components and stroke in Inner Mongolians — A prospective cohort study

Abstract

Stroke is the leading cause of disability and the second-leading cause of death in the world [1]. It is becoming an ever-increasing public health burden in China [2]. There is a strong association between both systolic blood pressure (SBP) and diastolic blood pressure (DBP) and stroke, but even in cases of normal BP stroke can still occur [3]. This indicates that other risk factors and BP components other than SBP or DBP may play a role in the development of stroke. In addition to SBP and DBP, BP is also characterized by pulse pressure (PP) and mean arterial pressure (MAP). It is notable that the effect of BP components on stroke is controversial and studies are limited in Inner Mongolians. As a result, we sought to analyze the relationship between BP components and stroke in a cohort of Inner Mongolians. This prospective cohort study was conducted from June 2002 to July 2012 in Inner Mongolia, China. After obtaining approval from the Soochow University Ethics Committee, informed, written consent was received from 2589 participants. At baseline examination, participants underwent a physical examination, anthropometry, BP determination, and phlebotomy for vascular risk factors. Up to 2012, 2583 individuals (99.8%) were successfully contacted and who provided comprehensive health information. Additional details on the methods of study participant recruitment and baseline data collection have been detailed elsewhere [4]. For our analysis, stroke incidence during the follow-up period is the primary study outcome. Stroke was defined as the sudden onset of neurological symptoms lasting ≥24 h or by using a cranial computed tomography or magnetic resonance imaging examination [5]. Participants who did not have a stroke, died from other causes, or were lost to follow-up were defined as censored. Trained staff interviewed either the participants or their relatives every two years to find new stroke cases. When a new case was found during follow-up, the staff reviewed the hospital records and completed a standard event form. The questionnaires were sent to a professional review board to determine the participants' stroke diagnosis. In our cohort, there was a total follow-up time of 23,292 person–years; 124 (76 ischemic stroke, 46 hemorrhagic stroke and 2 unknown subtype stroke) individuals developed stroke. Notably, participants who developed stroke had higher BP levels for all components compared to those who did not develop stroke. As shown in Table 1, SBP, DBP, PP and MAP were all significantly associated with an increased risk for stroke, as well as ischemic and hemorrhagic stroke. As shown in Fig. 1, SBP was significantly better than DBP (P = 0.038) and PP (P = 0.005) at predicting stroke. There was no significant difference in the area under the ROC curves between SBP and MAP (P = 0.817). Similarly, SBP and MAP were also the best predictors for ischemic stroke and hemorrhagic stroke. Fig. 1 Receiver operating characteristic curves between each blood pressure component and stroke (A), ischemic stroke (B), and hemorrhagic stroke (C). Panel A shows the discriminatory value of the four blood pressure components for predicting stroke. The areas ... Table 1 Multivariate adjusted relative risk of stroke, ischemic stroke, and hemorrhagic stroke associated with each blood pressure component. The effect of BP components on stroke is controversial. According to a recent study done in a population of Chinese Han women, MAP and DBP may be slightly more informative in predicting stroke mortality [6]. Some other studies found that PP was a major determinant of stroke [7]. In our cohort of Inner Mongolians, SBP was the best predictor of stroke, which is consistent with previous researches [8,9]. MAP was also a strong predictor of stroke in our study, which confirms research conducted in a cohort of middle aged and older Asians [10]. When examining the various BP components, MAP is the steady pressure gradient that transports blood from the heart toward other peripheral tissues. Individuals with hypertension typically have higher SBP and DBP levels, so MAP is generally higher in these individuals as well. In Mongolians, increased MAP is also associated with stroke, though SBP is a slightly better predictor. These results suggest that in addition to SBP, MAP also needs to be monitored in clinical practice and in self-management of hypertension at home.