Non-invasive measurement of mechanical properties of arteries in health and disease

Arterial stiffness increases with deteriorating glucose tolerance status: the Hoorn Study

BACKGROUND

Type 2 diabetes (DM-2) and impaired glucose metabolism (IGM) are associated with an increased cardiovascular disease risk. In nondiabetic individuals, increased arterial stiffness is an important cause of cardiovascular disease. Associations between DM-2 and IGM and arterial stiffness have not been systematically investigated.

METHODS AND RESULTS

In a population-based cohort (n=747; 278 with normal glucose metabolism, 168 with IGM, and 301 with DM-2; mean age, 68.5 years), arterial stiffness was ultrasonically estimated by distensibility and compliance of the carotid, femoral, and brachial arteries and by the carotid elastic modulus. After adjustment for age, sex, and mean arterial pressure, DM-2 was associated with increased carotid, femoral, and brachial stiffness, whereas IGM was associated only with increased femoral and brachial stiffness. Carotid but not femoral or brachial stiffness increased from IGM to DM-2. Standardized betas (95% CI) for IGM and DM-2, compared with normal glucose metabolism, were -0.06 (-0.23 to 0.10) and -0.37 (-0.51 to -0.23) for carotid distensibility; -0.02 (-0.18 to 0.18) and -0.25 (-0.40 to -0.09) for carotid compliance; -0.05 (-0.23 to 0.13) and 0.25 (0.10 to 0.40) for carotid elastic modulus; -0.70 (-0.89 to -0.51) and -0.67 (-0.83 to -0.52) for femoral distensibility; and -0.62 (-0.80 to -0.44) and -0.79 (-0.94 to -0.63) for femoral compliance. The brachial artery followed a pattern similar to that of the femoral artery. Increases in stiffness indices were explained by decreases in distension, increases in pulse pressure, an increase in carotid intima-media thickness, and, for the femoral artery, a decrease in diameter. Hyperglycemia or hyperinsulinemia explained only 30% of the arterial changes associated with glucose tolerance. Adjustment for conventional cardiovascular risk factors did not affect these findings.

CONCLUSIONS

IGM and DM-2 are associated with increased arterial stiffness. An important part of the increased stiffness occurs before the onset of DM-2 and is explained neither by conventional cardiovascular risk factors nor by hyperglycemia or hyperinsulinemia.

Strain imaging of internal deformation

A tissue-like gelatin elasticity-flow phantom was examined to develop ultrasonic strain imaging for the detection of internal pulsatile deformations. The same imaging technique was then applied in vivo to monitor deformation in tissues surrounding the normal brachial artery. The results suggest that vascular strain patterns resulting from biologic stimuli are very different from those generated using externally applied stress fields, and are directly related to pressure variations within the vessel. These data suggest a potential role for strain imaging in measuring the relative pressure or vascular elasticity locally and noninvasively.

Assessment of the spatial homogeneity of artery dimension parameters with high frame rate 2-D B-mode

To elicit vessel wall inhomogeneities in diameter and distension along an arterial segment, a 2-D vessel wall-tracking system based on fast B-mode has been developed. The frame rate of a 7.5-MHz linear-array transducer (length 36 mm) is enhanced by increasing the pulse-repetition frequency to 10 kHz, decreasing the number of echo lines per frame from 128 to 64, or increasing the interspacing between echo lines with a factor of two or four. Dedicated software has been developed to extract for each echo-line the end-diastolic diameter from the B-mode image and the 2-D distension waveform from the underlying radiofrequency (RF) information. The method is validated in tubes with various focal lesion sizes. Straight segments of presumably homogeneous common carotid arteries have also been tested. The temporal and spatial SD of diameter or distension reveals inhomogeneities in time or space (i.e., inhomogeneities in artery characteristics). The method can be implemented in echo systems supporting high frame rates and real-time processing of radiofrequency data.