Arterial stiffness measurement
AS was evaluated, according to the guidelines, using the gold standard carotid-femoral pulse wave velocity by the Sphygmocor (SphygmoCor Cardiovascular Management System software version 1.3; AtCor Medical Pty. Ltd., Sydney Australia). Participants were studied in the morning in the supine position after resting for 5–10 minutes in a quiet and temperature-controlled room. According to the instructions of the device, SphygmoCor XCEL PWA uses a standard brachial cuff to measure brachial systolic and diastolic pressures, and capture a brachial waveform. The brachial waveform is then analyzed by SphygmoCor to provide a central aortic waveform. Central BP measurements such as central aortic systolic BP, central pulse pressure, and an augmentation index were also reported. To conduct a carotid-femoral PWV measurement, a cuff placed around the femoral artery of the patient to capture the femoral waveform, and a tonometer was used to capture the carotid waveform. The distance in millimeters from the patient’s carotid artery to their sternal notch (Carotid to Sternal Notch) and also the distance from their sternal notch to the top edge of the femoral cuff (Sternal Notch to Cuff) is measured, and the velocity automatically determined by dividing the distance by the pulse transit time. After 10 seconds of simultaneous valid carotid tonometer signal, The SphygmoCor software derives the ascending aortic pressure wave, substantially equivalent to the pressure wave measured by an invasive catheter. From the aortic pressure wave, the number of valuable cardiovascular measurements is determined, including central aortic systolic pressure, aortic augmentation index and central pulse pressure. The PWV was calculated using the distance and mean time difference between the two recorded points.
The central augmented pressure calculated as the difference between the maximum systolic peak on the aortic pulse wave and the inflection point. The latter is defined as the merging point for the incident and reflected wave. The cAIx indicates as the augmented pressure divided by pulse pressure (PP) ×100.