How to measure arterial stiffness independently of blood pressure: the QKD method

OBJECTIVE: Arterial stiffness, an important predictor of cardiovascular event, has two components: one linked to the nonlinear elastic behaviour of the arterial wall and dependent of the blood pressure (BP) at the time of measurement, and the other linked to the structural modifications of the arterial wall as the consequences of the long-term effects of all cardiovascular risk factors, including BP. This second component is certainly the most important one and can be assessed with 24-h ambulatory monitoring of cardio-arm pulse transmission time (QKD method). METHODS: The working hypothesis of this study is that QKD100-60, the value of the QKD for a 100 mmHg SBP and 60 bpm heart rate is independent of 24-h SBP in both normotensive volunteers and treated hypertensive patients, in whom the long-term influence of BP is limited, whereas QKD100-60 is not independent of 24-h SBP in untreated hypertensive patients in whom high BP was able to damage the arterial wall on the long term. So we studied the relationships of QKD100-60 with 24-h BP and heart rate together with age, sex, height in multivariate regression analysis in three groups of patients; normal, untreated and treated hypertensive patients. QKD was measured with Novacor devices. RESULTS: In the normal population (n = 323, aged 29 ± 10 years) and in the treated hypertensive population (n = 425, aged 58 ± 13 years) the QKD100-60 was indeed not significantly related to 24-h SBP. In the untreated hypertensive population (n = 614, aged 51 ± 13 years) the QKD100-60 was weakly but significantly related to 24-h SBP (r = 0.249, P < 0.0001). CONCLUSION: Ambulatory monitoring of QKD provides indices of arterial stiffness independent of BP level at the time of measurement and most interestingly of 24-h BP with the potential to refine risk in patients with low traditional risk scores.