The reproducibility of central aortic blood pressure measurements in healthy subjects using applanation tonometry and sphygmocardiography

Aim: Sphygmocardiography via applanation tonometry is a non-invasive, bedside technology which utilises tonometric analysis of the radial artery pulse wave and measurement of peripheral arterial blood pressure (BP) to derive a central arterial pulse wave, central arterial BP and related indices. The present study was designed to determine: (1) the inter-operator variability in measurements obtained using this technique; (2) the relationship between measured peripheral arterial BP and derived central arterial BP. Method: Multiple measurements were made from 25 healthy subjects (15 male), mean age 33 (s.d. 10.3) years, mean arterial BP 90 (s.d. 12) mm Hg by two trained observers at the same time of day on three separate occasions. Results: The mean inter-operator difference was 0.1 (s.d. 1.7) mm Hg for derived systolic aortic BP and 0.1 (s.d. 0.7) mm Hg for derived diastolic aortic BP (Bland and Altman analysis). Pulse wave Augmentation Index (AIx) values, ranged from -22% to +40%, with the inter-operator measurement difference being only 0.4 (s.d. 6.4)%. Buckberg ratio measurements ranged from 119% to 254%, with the inter-operator measurement difference being only 2.7 (s.d. 15.4)%. The relationship between derived central systolic BP and peripheral systolic BP readings in individual patients was not constant and showed significant variance when compared on different days (ANOVA, P = 0.03). This was not explained by any significant variance in heart rate (ANOVA, P = 0.39). Conclusion: Applanation tonometry has excellent interobserver reproducibility when used by trained observers. Moreover, the inconsistency in the relationship between peripheral and central aortic BP suggests that the former is not a perfect surrogate for the latter. Further prospective studies are required to define whether derived central aortic BP may be a better predictor of cardiovascular morbidity and mortality and the impact of different antihypertensive therapies on the relationship between peripheral and central arterial BP.