Arterial stiffness, endothelial function and microcirculatory reactivity in healthy young males.

Large (C1) and small (C2) arterial stiffness has been suggested to parallel endothelial reactivity and has led researchers to suggest parameters of arterial stiffness may be alternative measures to brachial sonographic assessments of flow-mediated dilatation (FMD). However, past studies comparing these measures can be criticized. In addition to %FMD responses, we recorded concurrent hyperaemic responses of the microcirculation and both were compared with C1 and C2. Twenty-nine subjects 18-30 years of age were investigated. Radial blood pressure was recorded with a tonometer. Pulse waveform analysis was performed to calculate C1 and C2. These were compared with %FMD responses and responses of finger flux measured by laser Doppler fluxmetry (LDF); pulsatile finger volume measured by photoplethysmography (PPG); and palm skin temperature measured by infrared thermography (Tpalm) (i.e. microcirculatory responses). Responses were determined as % changes from control. We only found weak relationships between C1 and %FMD (r=0.4, P=0.04); C2 and %PPG (r=0.38, P=0.07); and C2 and %LDFdorsal (r=-0.38; P=0.04). Responses of %FMD weakly parallel those of C1. Neither C2 nor C1 are viable indicators of endothelial or microcirculatory reactivity (i.e. hyperaemic or venous constriction) in healthy, resting young males. These findings refute the claims that C1 and C2 are substitute measures to sonographic assessments of brachial FMD.