Noninvasive carotid pressure—diameter loops to identify viscoelastic properties in ageing, hypertension and type 2 diabetes

Objectives: Arterial stiffness as pulse wave velocity (PWV) predicts cardiovascular events independently of blood pressure (BP). PWV does not distinguish between stiffness in systole and diastole. This cross-sectional study aimed to test the hypothesis that viscous and elastic carotid wall properties differ between systole and diastole, distinguishing effects of ageing, hypertension and T2 diabetes (T2DM). Methods: We examined carotid visco-elasticity in 307 people (180 men), with hypertension alone ( n = 69), combined hypertension/T2DM (H-T2DM, n = 99), normotensive (N-T2DM, n = 25) and healthy controls ( n = 114). Diameter ( D )/pressure ( P ) waveforms were measured at right /left common carotid arteries, respectively. Local carotid PWV and distensibility in systole and diastole were evaluated by the D 2 P- loop method, and wall viscosity from hysteresis, the area ( H A ) within the P--D loop, as a dynamic measure of systolic loading and diastolic unloading. Results: Controls’ hysteresis fell quadratically with age ( R 2 = 0.23, P < 0.001). Yet mean H A in hypertensive patients (0.95, 95% CI 0.65–1.23) was six-fold higher than in age-matched controls (0.14, −0.20 to 0.49, P < 0.001) with a 2.5× difference between diastolic ( d Ds ) to systolic ( s Ds) distensibility ( P < 0.05) in hypertensive patients. H A was higher in hypertensive patients and H-T2DMs (0.80, 0.58–1.04) than N-T2DMs (0.20, −0.17 to 0.54, P < 0.05), but similar between controls and N-T2DMs. BP-adjusted carotid diameters in all T2DM were significantly greater compared with controls and hypertensive patients. Conclusion: Higher BP increased wall viscosity, hysteresis and relative difference between systolic and diastolic distensibility across groups. Carotid diameters were increased in all T2DMs, more in H-T2DM, probably altering BP-flow dynamics in T2DM.