3.1 Clinical and laboratory characteristics
Of the original 202 participants, 12 dropped out of the study and 21 were excluded because of various diseases, leaving 169 participants who were included in this cross-sectional study. Of the 169 participants, 119 were diagnosed with hypertension (70.4%) and 62 were diagnosed with DM (36.7%). There were 150 male participants (88.2%), the mean age was 85.7 ± 0.4 years and the mean BMI was 23.8 ± 0.3 kg/m2. Laboratory parameters, PWV, ABI, and ultrasound parameters are reported in Table 1.
3.2 Comparison of clinical characteristics between hypertension group and normotension group
To identify better method of evaluating arterial stiffness in elderly hypertensive patients, we compared PWV and ABI levels of hypertension group with those of normotension group. As shown in table 2, we observed higher TG concentrations and lower TC concentrations in hypertension group than in normotension group. Compared with normotensive participants, PWV levels of hypertensive patients were slightly higher in left limbs ( 2219 ± 90 cm/s v.s. 1970 ± 66 cm/s, P = 0.090) and significantly higher in right limbs ( 2141 ± 52 cm/s v.s. 1932 ± 67 cm/s, P = 0.023) separately. The ABI levels of right limbs in hypertensive patients were lower than normotensive participants ( 1.00 ± 0.02 v.s. 1.06 ± 0.02, P = 0.049), but no significant different ABI levels were reported in left limbs. The levels of age, BMI, FPG, LDL, HDL, HCT, Creatinine, EF and IMT were not significantly different between hypertension group and normotension group.
3.3 Comparison of clinical characteristics between DM group and non- DM group
To identify better method of evaluating arterial stiffness in elderly DM patients, we compared PWV and ABI levels of DM group with those of non- DM group. FPG concentrations of DM patients were higher, while TC concentrations of DM patients were lower than those of non- DM participants. Compared with non- DM participants, ABI levels of DM patients were significantly lower in left limbs ( 0.96 ± 0.02 v.s. 1.05 ± 0.02, P = 0.002) and slightly lower in right limbs ( 0.99 ± 0.03 v.s. 1.03 ± 0.02, P = 0.071) separately. No difference was observed between PWV levels of DM patients and non- DM participants either in left limbs or in right limbs. TG concentrations were slightly higher and EF levels were slightly lower in DM patients compared to non- DM participants. The levels of age, BMI, FPG, LDL, HDL, HCT, creatinine and IMT were not significantly different between DM group and non- DM group. (Table 3)
3.4 Peripheral expressions of candidate bio-markers for arterial stiffness
For investigating potential bio-markers for arterial stiffness in elderly population, 86 candidates had the tests of serum levels of VCAM, Ang Ⅱ, OPN and GPX. The mean levels of VCAM, Ang Ⅱ, OPN and GPX were 318.8 ± 7.1 ng/ml, 116.2 ± 2.6 pg/ml, 33.8 ± 0.7 ng/ml and 615.7 ± 14.2 U/L, separately. As shown in table 4a, the VCAM concentrations of hypertensive patients were significantly lower than normotensive participants ( 310.3 ± 7.9 ng/ml v.s. 344.9 ± 14.1 ng/ml, P = 0.034). No significant difference of Ang Ⅱ, OPN or GPX was observed between hypertension group and normotension group. However, the Ang Ⅱ levels of DM patients were significantly lower than non- DM participants ( 107.5 ± 4.5 pg/ml v.s. 121.9 ± 2.8 pg/ml, P = 0.005). The levels of VCAM, OPN and GPX of DM patients were not significantly different from those of non- DM participants.
3.5 Correlations between PWV and candidate bio-markers
To investigate the roles of VCAM, Ang Ⅱ, OPN and GPX in arterial stiffness in elderly population, we performed partial correlation analysis between PWV and candidate bio-markers. Both PWV of left limbs (L-PWV) and PWV of right limbs (R-PWV) were negatively correlated to VCAM ( R = - 0.316, P = 0.028; R = - 0.310, P = 0.031, separately) after adjusted for age, BMI, FPG, TC and HCT. OPN was negatively correlated with R-PWV ( R = - 0.278, P = 0.009), but not correlated with L-PWV. Neither Ang Ⅱ nor GPX was found to be correlated to PWV. ( Table 5)
3.6 Correlations between ABI and candidate bio-markers
Partial correlation analysis between ABI and candidate bio-markers was performed. After adjusted for age, BMI, FPG, TC and HCT, ABI of left limbs (L-ABI) was significantly correlated to Ang Ⅱ( R = - 0.381, P = 0.010) , but ABI of right limbs (R-ABI) was only slightly correlated to Ang Ⅱ ( R = - 0.234, P = 0.082). OPN was negatively correlated with R-ABI ( R = - 0.303, P = 0.005), but not correlated with L-ABI. Neither VCAM nor GPX was found to be correlated to ABI. ( Table 6)
3.7 Bio-markers for predicting arterial stiffness in regression models
Since VCAM and OPN were found to be correlated to PWV, linear regression analysis of PWV with variate of age, BMI, FPG, TC, HCT, VCAM and OPN were performed. Only VCAM was included in the regression models of L-PWV and R-PWV ( Beta = - 0.307, P = 0.048; Beta = - 0.358, P = 0.020, separately). Table 7
Linear regression analysis of ABI with variate of age, BMI, FPG, TC, HCT, Ang Ⅱ and OPN were performed. OPN was included both in the regression models of L-ABI and R-ABI ( Beta = - 0.320, P = 0.039; Beta = - 0.290, P = 0.011, separately). In the second model of R-ABI, both OPN and FPG were included. However, Ang Ⅱ was not included in any model of ABI. Table 8