Correlations of Arterial Stiffness and Augmentation Index With Metabolic Risk Factors in Patients With Type 2 Diabetes

To the Editor:

We read the recent article by Pikilidou and colleagues1 with great interest. They studied arterial stiffness and augmentation index (AIx) in patients with sickle cell disease (SCD). In their study, AIx was significantly higher in SCD patients compared with healthy controls; however, pulse wave velocity (PWV) was comparable between two groups,1 suggesting the existence of different determinants of AIx and PWV. Patients with type 2 diabetes have increased arterial stiffness. However, the association of PWV and AIx with metabolic risk factors in type 2 diabetes is poorly understood.

We studied correlations of AIx and PWV with metabolic risk factors at baseline, and also examined correlations of changes in AIx and PWV after 3 and 6 months with changes in metabolic risk factors after 3 and 6 months in 54 patients with type 2 diabetes (32 men and 22 women) (Table). At baseline, the mean±standard deviation of age, duration of diabetes, height, weight, body mass index, systolic and diastolic blood pressures, fasting plasma glucose, and glycated hemoglobin in patients were 65.3±11.1 years, 8.8±9.7 years, 159.7±8.7 cm, 65.5±14.1 kg, 25.6±4.9 kg/m², 140.8±20.6 mm Hg, 80.0±11.3 mm Hg, 134.9±27.7 mg/dL, and 6.8±0.9%, respectively.

Table 1.

Correlations of AIx and PWV With Metabolic Parameters in Patients With Type 2 Diabetes

	AIx						PWV
	Baseline		∆AIx vs ∆Parameters After 3 Months		∆AIx vs ∆Parameters After 6 Months		Baseline		∆PWV vs ∆Parameters After 3 Months		∆PWV vs ∆Parameters After 6 Months
	r	P Value	r	P Value	r	P Value	r	P Value	r	P Value	r	P Value
Age	0.338	.013	–	–	–	–	0.626	<.0001	–	–	–	–
Duration of diabetes	0.099	.477	–	–	–	–	0.378	.005	–	–	–	–
Body mass index	−0.148	.286	–	–	–	–	−0.248	.071	–	–	–	–
Systolic blood pressure	0.401	.003	0.533	<.0001	0.321	.028	0.391	.003	0.34	.012	0.238	.107
Diastolic blood pressure	0.024	.861	0.401	.003	0.083	.58	−0.101	.465	0.238	.083	0.385	.007
Fasting plasma glucose	0.025	.855	−0.184	.184	−0.284	.053	0.079	.57	−0.203	.142	−0.151	.309
Glycated hemoglobin	−0.087	.532	−0.015	.916	−0.181	.223	0.066	.638	−0.081	.559	−0.033	.828
Triglycerides	−0.25	.069	0.079	.572	−0.082	.583	−0.195	.157	−0.138	.319	0.074	.622
LDL cholesterol	0.157	.258	0.027	.845	0.131	.379	−0.087	.531	0.349	.01	0.194	.192
HDL cholesterol	0.001	.996	−0.18	.194	−0.053	.723	−0.036	.794	0.158	.253	−0.101	.499
Oxidized LDL	0.008	.956	0.016	.907	−0.115	.441	−0.088	.528	0.109	.434	0.116	.437
Small dense LDL	−0.144	.3	−0.168	.226	−0.198	.183	−0.147	.287	0.079	.571	−0.05	.736
hs‐CRP	0.104	.456	0.092	.507	−0.14	.35	−0.01	.942	−0.183	.185	0.161	.279
UACR	0.26	.058	−0.023	.869	−0.233	.116	0.597	<.0001	0.34	.012	0.401	.005
C‐peptide	−0.295	.03	−0.252	.066	−0.357	.014	−0.347	.01	−0.125	.366	−0.07	.638

Abbreviations: AIx, augmentation index; HDL, high‐density lipoprotein; hs‐CRP, high‐sensitivity C‐reactive protein; LDL, low‐density lipoprotein; PWV, pulse wave velocity; UACR, urine albumin to creatinine ratio. r indicates Spearman's rank correlation coefficient; ∆, change.

Age was positively and significantly correlated with both AIx and PWV at baseline. PWV was positively correlated with duration of diabetes, however, which was not correlated with AIx. Systolic blood pressure was significantly correlated with both AIx and PWV at baseline, and changes in systolic and diastolic blood pressure were significantly correlated with changes in AIx and PWV. The change in low‐density lipoprotein (LDL) cholesterol after 3 months was positively correlated with the change in PWV after 3 months, but not with the change in AIx. Fasting serum C‐peptide level was significantly and negatively correlated with both AIx and PWV at baseline. Although there were no correlations between urine albumin to creatinine ratio (UACR) and AIx, PWV at baseline and changes in PWV after 3 and 6 months were positively and significantly correlated with UACR at baseline and changes in UACR after 3 and 6 months, respectively.

AIx and PWV are considered to be markers for arterial stiffness and seem to be closely correlated. However, they are not identical, having different units of measurement. In our study, AIx was not correlated with PWV (r=0.168, P=.224 by Spearman's rank correlation) at baseline, and changes in AIx after 3 and 6 months were not correlated with changes in PWV after 3 (r=0.067, P=.631) and 6 (r=0.009, P=.951) months, respectively.

Both AIx and PWV were significantly associated with age and peripheral blood pressure in our study, as in the previous study.2 Duration of diabetes was significantly correlated with PWV but not with AIx. UACR as the marker for diabetic microvascular complication was also significantly associated with PWV but not with AIx. The change in LDL cholesterol was positively correlated with the change in PWV. These results may suggest that the status of diabetes and/or lipid profile induce more effects on PWV than AIx. Both AIx and PWV were significantly and negatively correlated with fasting serum C‐peptide level. Fasting serum C‐peptide level was significantly and negatively correlated with age (r=−0.29, P=.034) and duration of diabetes (r=−0.307, P=.024). Aging and duration of diabetes may explain the association between AIx/PWV and fasting serum C‐peptide.

In addition to the study by Pikilidou and colleagues, Zhang and colleagues3 reported ethnic disparity in AIx and PWV and their determinants among Asian patient with type 2 diabetes. Our study presented different determinants for AIx and PWV in Japanese patients with type 2 diabetes. Further, Vyssoulis and colleagues4 reported a differential impact of metabolic syndrome on PWV and AIx. Briefly, PWV is increased in patients with the metabolic syndrome; however, metabolic syndrome has no effect on AIx,4 supporting our result.

We have to mention the limitation of our study. The number of patients was small. To elucidate our hypothesis, further studies, preferably with larger numbers of participants, will be needed.

In conclusion, our study showed that age, peripheral blood pressure, and fasting serum C‐peptide were determinants for both AIx and PWV, and duration of diabetes, LDL cholesterol, and UACR were determinants for only PWV in Japanese patients with type 2 diabetes.