Repeatability of the measurement of augmentation index in the clinical assessment of arterial stiffness using radial applanation tonometry

Abstract

Objective. Aortic augmentation index (AIx) measured using applanation tonometry is a non‐invasive indicator of arterial stiffness. The objective of this study was to assess its repeatability when used by nurses with limited experience of the technique. Material and methods. Blood pressure/augmentation index (BP/AIx) was measured 4 times in 20 consecutive ambulant patients (16 male) after they rested supine for 15 min. Two nurses independently and alternately measured BP/AIx using the same equipment (Omron HEM‐757; SphygmoCor with Millar hand‐held tonometer). Nurses were blinded to patient medical records and their colleague's AIx/BP. ‘Within’ and ‘between’ observer differences were assessed using intra‐class correlation coefficients (rI) and 95 % limits of agreement (95 % LoA) derived from Bland‐Altman plots. Results. Mean age was 56 (mean BP 136/79; mean pulse 64). Mean AIx was 24.1 (range 2.8 to 41.0). Both ‘between’ and ‘within’ observer repeatability was very high, with intra‐class correlation coefficients ranging from 0.92 to 0.98. Mean AIx readings ‘between’ observers differed by only 0.68 (95 % CI −0.24 to 1.59) with a high rI (0.98; 95 % CI 0.95 to 0.99) and a narrow 95 % LoA (−3.22 to 4.57). The 95 % LoA for ‘within’ observer repeatability was −6.75 to 7.95. Differences in AIx measurement did not vary over time or with increasing levels of AIx. Conclusions. Even when undertaken by relatively inexperienced operators, both ‘within’ and ‘between’ observer repeatability of AIx measurement is very high. Such non‐invasive assessment of arterial stiffness has the potential to be included in the clinical assessment of ambulant patients.