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

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.