Relationship between blood viscosity and existence and severity of carotid artery plaque.

Background: Accumulating evidence shows that the increase in blood viscosity (BV) is an independent risk factor for atherosclerosis and its related diseases, but as far as we know, there are few studies on the relationship between blood viscosity and carotid plaque severity. Therefore, we aimed to investigate the relationship between blood viscosity and the presence of carotid plaques, and further explore its relationship with the severity of carotid plaques.

Methods: We retrospectively analyzed the data of consecutive subjects in the physical examination center of the Affiliated Hospital of Ningbo University Medical College from January 2022 to May 2022.The parameters of blood viscosity include the whole blood viscosity (WBV) at high, middle, and low shear rate, plasma viscosity (PV), hematocrit (HCT), rigidity "k", rigidity index (RI), aggregation index (AI) and electrophoresis rate (ER), and standardized BV calculated by Quemada's equation were included in the study. Carotid plaque score (CPS) was used to measure the severity of carotid artery disease, and participants were divided into mild, moderate, and severe groups according to the quartile of the score. Independent samples t-test and one-way ANOVA were used to compare normally distributed continuous variables between two or more independent groups, respectively. Binary logistic regression was used to evaluate the risk factors of carotid plaque.

Results: 314 men were enrolled in the study, of which 165 participants were diagnosed with Carotid artery plaque (CAP) (66.9%). Compared with the CAP- group, the WBV and PV of the CAP+group decreased, but the difference only existed in the PV (p = 0.001). However, standardized BV values (HCT set at 0.45) were higher in the CAP+group than in the CAP- group (3.8643±0.35431vs 3.9542±0.64871, p = 0.188). Regarding the rigidity and aggregation of RBC, the parameters including rigidity "k", RI, AI and ER increased in the CAP+group compared with the CAP- group. The difference was statistically significant in k and ER (p = 0.04, p = 0.009). To assess the severity of carotid plaque, we divided the participants into mild, moderate, and severe groups by using the tertile of CPS value. The mild group was defined as CPS≤0.5 (n = 108), the moderate group as 0.5 < CPS≤1.7 (n = 105), and the severe group as CPS > 1.7 (n = 101). It was found that WBV and PV decreased with the increase of plaque severity, but the difference among the three groups was significant in PV (F = 8.073, p < 0.0001). In addition, with the severity of plaque from mild to severe, standardized BV gradually increased, which were 3.8611±0.34845, 3.8757±0.36637, 3.9007±0.38353 respectively. The difference between the groups was close to statistically significant (F = 2.438, p = 0.089). The values of parameters describing erythrocyte aggregation and rigidity increased among the mild, moderate, and severe groups. The difference was statistically significant in RBC rigidity "k" and ER of RBC (F = 3.863, p = 0.022; F = 5.897, p = 0.003, respectively).

Conclusion: Increased blood viscosity is a risk factor for carotid plaque, but its increase may be hidden by decreased hematocrit. Therefore, it is necessary to comprehensively analyze various parameters of blood viscosity, such as the standardized BV calculated by Quemada's equation, which may provide more useful reference value.