Arterial waveform assessments.
SECONDARY, ARTERIAL STIFFNESS
Central hemodynamics, pulse wave analysis, and PWV were attained in the supine position and estimated noninvasively by an oscillometric cuff-based device (Sphygomocor Xcel, AtCor Medical). To assess central PWV, carotid pulse waves were measured by applanation tonometry, and femoral pulse waves were simultaneously obtained by a partially inflated cuff over the femoral artery at the leg midway between the hip and the knee. The c-f PWV was determined by calculating the ratio of the corrected distance between the pulse-measuring sites to the time delay between the carotid and femoral pulse waves. The distance was measured between (a) the suprasternal notch to the carotid site, (b) femoral artery at the inguinal ligament to the proximal edge of the thigh cuff, and (c) suprasternal notch to the proximal edge of the thigh cuff. Distances a and b were subtracted from distance c and used in the calculation of c-f PWV. Aortic waveform assessments utilized the automatic recording of standard oscillometric brachial BP, followed by partial cuff inflation to subdiastolic pressure levels to capture a brachial artery waveform. The pulse waveform was calibrated to brachial BP, and a validated generalized transfer function was applied to generate the aortic pressure waveform. Pulse wave analysis software was used to compute central BP. Central augmented pressure (AP) was calculated as the difference between the second and the first systolic peaks. AIx, used as an index of aortic wave reflection and a secondary marker of arterial stiffness, was calculated as the ratio of the amplitude of the pressure wave above its systolic shoulder (i.e., the difference between the early and late systolic peaks of the arterial waveform) and the total pulse pressure. AIx values normalized to AIx@HR75 were also reported. All measurements were made in duplicate, and the mean value was used for subsequent analysis.