Abstract
Objectives. Increased platelet activation plays an important role in the development of atherosclerosis. Mean platelet volume (MPV) is a determinant of platelet activation. In our study, we aimed to determine whether MPV levels are elevated in non-dipper patients compared with dippers and healthy controls. In addition, we tried to find out if MPV levels are correlated with blood pressure measurements in hypertensive patients. Methods. This cross-sectional study included 56 hypertensive patients; 27 age- and sex-matched healthy volunteers were enrolled to study as a control subjects. Ambulatory blood pressure monitoring was performed for all patients. Hypertensive patients were divided into two groups: 28 dipper patients (10 male, mean age 51 ±8 years) and 28 non-dipper patients (11 male, mean age 53±10 years). MPV was measured in a blood sample collected in EDTA tubes and was also used for whole blood counts in all patients. Results. In non-dipper patients, 24-h systolic blood pressure (141.5±10.21 vs 132.3±7.7 mmHg, p<0.001), 24-h diastolic blood pressure (88.2±8.5 vs 81.0±8.2 mmHg, p<0.01) and 24-h average blood pressure (105.7±8.5 vs 97.7±7.4 mmHg, p<0.001) are significantly higher than dippers. Whereas daytime measurements were similar between dippers and non-dippers, there was a significant difference between each group during night-time measurements (night-time systolic 137.1 ±11.0 vs 120.2±8.0 mmHg, p<0.001; night-time diastolic 85.3±8.0 vs 72.8±7.9 mmHg, p<0.001). Non-dipper patients (9.61 ±0.42 fl) demonstrated higher levels of MPV compared with dippers (9.24±0.35 fl) and normotensives (8.87±0.33 fl) (p<0.001 and p<0.001, respectively). There was significant correlation between MPV and ambulatory diastolic and systolic blood pressure in non-dipper hypertensives. Conclusion. Our results suggest that MPV, a determinant of platelet activation, has a positively correlation with blood pressure and elevated in non-dipper compared with dippers and controls. Increased platelet activation could contribute to increase the atherosclerotic risk in non-dipper patients compared with dippers.
Introduction
Blood pressure (BP) shows a circadian rhythm with more than 10% decrease in systolic (SBP) and diastolic blood pressure (DBP) during sleep compared with daytime. However, some hypertensive subjects have not this nocturnal reduction have been termed non-dippers (Citation1).
Many studies have shown that non-dippers carry a high risk of cardiovascular disease such as atherosclerotic events (myocardial or cerebral infarction) and also high incidence of target organ damage compared with dippers (Citation2–Citation4).
As known, increased platelet activation plays an important role in the development of atherosclerosis (Citation5). Increased platelet activity is associated with increased platelet volume. Large platelets that contain more dense granules are metabolically and enzymatically more active than small platelets and higher thrombotic potential (Citation6). Mean platelet volume (MPV), a determinant of platelet activation, has been recognized as an independent risk factor of hypertension, myocardial infarction and stroke (Citation7–11). It is also with poor clinical result among survivors from cardiovascular disease (Citation12,Citation13).
In our study, we aimed to determine whether MPV levels are elevated in non-dipper patients compared with dippers and healthy controls. In addition, we tried to find out if MPV levels are related with BP measurements in hypertensive patients.
Materials and method s
Study population
This crosssectional study included 56 hypertensive patients who admitted to our outpatient clinic of cardiology for routine examination. Twenty-seven healthy volunteers were enrolled to the study as control subjects (16 male, mean age 51±4 years).
According to ambulatory BP monitoring (ABPM), hypertensive patients were divided into two groups: 28 dipper patients (10 male, mean age 51 ±8 years) and 28 non-dipper patients (11 male, mean age 53±10 years). As shown in , in non-dipper patient, 24-h SBP, 24-h DBP and 24-h average BP are significantly higher than dippers. Whereas daytime measurements were similar between dippers and non-dippers, there was a significant difference between each group during night-time measurements (night-time SBP 137.1 ± 11.0 vs 120.2±8.0 mmHg, p<0.001; night-time DBP 85.3±8.0 vs 72.8±7.9 mmHg, p<0.001).
Table I. Comparison of ambulatory blood pressure monitoring resuls between dippers and non-dippers.
The study population in the control group was investigated for evidence of any diseases that would be exclusion criteria for study, including hypertension by using ABPM; all controls were normotensive and had a dipping profile.
Exclusion criteria for entry into the study were evidence of coronary artery disease, smoking, chronic heart failure, diabetes mellitus, renal or hepatic dysfunction, hematological disease, cancer, thrombocytopenia, autoimmune disease, systemic inflammatory conditions and antithrombotic agents or serotonin reuptake inhibitor drug use. This study complied with the Declaration of Helsinki, was approved by the Ethics Committee and the institutional review board of Erciyes University Medical School, and informed consent was obtained from each patient.
Diagnostic criteria for hypertension and non-dipper
Hypertension was considered to be present if the SBP was > 140 mmHg and/or DBP pressure was >90 mmHg in two or more BP measurements or if the individual was taking antihypertensive medication (Citation10). Ambulatory monitoring was performed to all patients by using Mobil-0-Graph recorder and according to results of measurements; patients with less than 10% decrease in either SBP or DBP were considered non-dippers in this study (Citation1).
Biochemical measurements
Blood samples were drawn in the morning after a 20-min rest following a fasting period of 12 h. Glucose, creatinine and lipid profile were determined by Standard methods. We measured MPV by using Tripotassium EDTA based anticoagulated blood samples that drawn in the morning after a 20-min rest, stored at +4°C and assessed by a Sysmex K-1000 auto analyzer within 30 min of sampling. High-sensitive CRP was measured by using BN2 model nephlometer. The expected values for CRP in our laboratory ranged from 0 to 6 mg/1.
Statistical analysis
The SPSS statistical software (SPSS for Windows 13.0, Inc., Chicago, IL, USA) was used for all statistical calculations. Continuous variables were given as mean±SD, and Categorical variables were defined as percentage. Differences between groups were tested using one-way analysis of variance (ANOVA), Student t-test for unpaired data, ANOVA and %2 test when appropriate. Spearman's correlation was used to evaluate the association between MPV and ambulatory BP. Statistical significance was defined as p<0.05.
Results
The patient characteristics for dipper, non-dipper and normotensive groups are presented in . Age, gender distribution, creatinine, albumin, fasting glucose levels and platelet count were similar among the groups. There were no significant differences in triglyceride levels among groups except total cholesterol. Low-density lipoprotein (LDL) levels are significantly higher in dippers and non-dippers compared with normotensives (p<0.001 and 129.4±26.0 vs p<0.05, respectively). Non-dippers demonstrated a significantly higher high-density lipoprotein (HDL) levels than dippers surprisingly (43.5 vs 37.1, p<0.05). Dipper and non-dipper patients had similar body mass indexes but higher than normotensives (29.5 and 28.4 vs 25.8, p<0.0l)
Table II. Characteristics, blood pressure, and laboratory parameters of study groups.
As expected, clinical BP was significantly higher in dipper and non-dipper patients than normotensives (SBP 144.4±49.3 andl48.2±29.2 vsll6.8±9.7 mmHg; DBP 92.1± 11.3 and 94.4±11.0 vs 65.3±9.2 mmHg, p<0.05, respectively) but was similar between dippers and non-dippers. Non-dippers had significantly higher CRP levels compared with dippers and normotensives (p<0.05). As reported in and , non-dipper patients demonstrated higher levels of MPV compared with dippers and normotensives (9.61 ±0.42 to 9.24±0.35 ü, p<0.00l; 9.61±0.42 to 8.87±0.33 fl , p<0.001, respectively).
Figure 1. Comparison of mean platelet volume (MPV) levels in non-dippers compared with dippers and controls.
In the no-dippers group, nine patients took only one drug, 31 patients took two drugs together and nobody took three drugs. In the dippers group, 13 patients took only one drug, 29 patients took two drugs together and four patients took three drugs. There was no significant difference for antihypertensive medications taken by the dipper and non-dipper groups. Normotensives did not take any medicine.
There was significant positive correlation between MPV and ambulatory DBP and SBP (r=0.503, p=0.006 and r=0.411, p=0.030, respectively) in non-dipper hypertensives, as seen in .
Figure 2. Correlations between mean platelet volume (MPV) and ambulatory diastolic (A) and systolic (B) blood pressure.
Discussion
To our knowledge, this is the first study to evaluate MPV levels in non-dippers. We found that the MPV levels were significantly higher in the non-dipper group than in the dipper and healthy groups.
MPV is a well-known determinant of platelet activation and has become a prognostic factor in coronary heart disease (Citation14). The MPV correlates closely with platelet size and activity. Hemostatically activated platelets mean larger platelets have more granules and adhesion receptors that have resulted in increased platelet volumes (Citation15). Eventually, increased MPV levels means activated platelets.
According to the many studies investigating the role of platelets in atherosclerosis, many of the mole-cules involved belong to activated platelets. In one of animal studies, P-selectin is determined as an adhesion molecule of activated platelets, leading to prolonged contact with endothelial cells that activate monocytes and aggravate atherosclerotic lesions in mice (Citation16). The strong proinflammatory mediator interleukin-1 is secreted by activated platelets and has an impact on atherosclerosis that induces alterations of the adhesive and chemotactic properties of endothelial cells (Citation17). Primarily described proatherogenic chemokine MCP-1 is also found in activated platelets. The involvement of glycoprotein Ib (GPIb) in activated platelets may encompass binding to von Willebrand factor to support platelet adhesion or to leukocyte Mac-1 to support platelet/leukocyte aggregates (Citation18).
There are some studies about the MPV and hypertension relationship. Nadar et al. (Citation19) found that MPV in patients with hypertension was significantly higher than in normotensive control subjects, and within the hypertensive group, those with larger platelets had greater mass than those without target organ damage. Previous studies showed that the MPV in patients with gestational hypertension was significantly higher than in normal pregnant women (Citation20,Citation21). Coban et al. (Citation22) found that MPV was positive correlated with ambulatory DBP in essential hypertension and white coat hypertension groups, and Tavil et al. (Citation23) reported that MPV in patients with metabolic syndrome (some of patients with pre-hypertension or hypertension) is associated with coronary artery disease.
Different from these previous studies, the present study demonstrates, for the first time, the significant positive correlation between MPV and BP measurements in hypertensive patients. To our knowledge, the first step in thrombus formation is platelet activation by complex interaction, which may be started by some factors like high BP leading to endothelial damage, which initiate thrombosis. This process involves thrombus formation, which contributes to increased platelet activation. A rise in BP was found to be coincident with morning stroke and myocardial infarction (Citation24–Citation28).
One of the limitations of this study may be method of MPV measurement. Tripotassium EDTA-based anticoagulated blood samples were used to measure MPV levels in our study. Most laboratories use EDTA for anticoagulation of whole blood prior to automated cell counting but because of platelet swelling, MPV values may increase with its use. Dastjerdi et al. (Citation16) found that MPV can be measured accurately by using anticoagulation, EDTA and citrate if the analysis is performed within 1 h of sampling. Macey et al. (Citation17) also showed the changes in MPV, which reflect platelet sphering and swelling, were greatest after between 30 and 60 min in blood stored at ambient temperature, whereas in our study, blood samples were drawn in the morning after a 20-min rest, stored at +4°C and measurement performed within 30 min. So, we were adequately confidence about results in our study. Moreover, we did not offer a cut-off value for MPV; we compared groups between each other in the terms of MPV levels, which were determined by using same methodology for all patients. The other limitation of this study is absence of clinical follow-up for non-dipper patients with elevated MPV levels, but our data determined MPV as a useful parameter and suggested a possible explanation for the high incidence of ath-erosclerotic events in non-dippers, and may inspire further prospective studies.
Conclusion
Our results suggest that MPV, a determinant of platelet activation, has a positively correlation with BP and is elevated in non-dippers compared with dippers and controls. Increased platelet activation could contribute to increase the atherosclerotic risk in non-dipper patients compared with dippers.
Declaration of interest: This study is related to our previous study already published in Blood Pressure. The relation between serotonin levels and insufficient blood pressure decrease during night-time in hypertensive patients, Blood Pressure. 2009; 18: 367–371.
Related Research Data
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