Calculation of arterial path length for carotid-femoral pulse wave velocity determination using an established formula: relevance of left and right side measurements

Objective: Despite being established as the gold standard for quantifying large artery stiffness and its additive value beyond traditional risk factors in the prognosis of hypertension, carotid-femoral pulse wave velocity (cfPWV) is not recommended for routine clinical practice in the current guidelines due, in part, to practical limitations with its measurement. A formula was recently developed (Weir-McCall et al. Hypertension. 2018;71 (5):937–945) for calculation of both left- and right-side arterial path length for cfPWV determination using routinely collected clinical parameters (gender, age, weight, height, heart rate, diastolic blood pressure). However, only the right-side formula was validated. This study aimed to determine the validity of the left-side formula and whether accounting for side of cfPWV measurement would improve the agreement between formula-calculated and measured cfPWV. Design and method: Arterial path length was re-calculated in 127 subjects (aged 65 ± 12 years, 51 females) using the left- (n = 71) and right-side (n = 56) formula according to the side on which their cfPWV was previously measured. The formula-calculated distances were then used to re-calculate cfPWV. Arterial path length and cfPWV were also re-calculated in all 127 subjects using only either the left- or right-side formula. Results: Mean differences between formula-calculated and measured arterial path length and cfPWV were 29.5 ± 42.5 mm (mean ± SD, P < 0.001), 0.03 ± 1.0 m/s (P = 0.775) and 5.1 ± 35.4 mm (P = 0.286), 0.8 ± 0.7 m/s (P < 0.001) for left- and right-side, respectively, giving an average difference of 18.7 ± 41.2 mm (P < 0.001), 0.4 ± 0.9 m/s (P < 0.001). When only the left-side arterial length formula was used, the mean differences were 34.2 ± 40.9 mm (P < 0.001), 0.7 ± 0.9 m/s (P < 0.001). When only the right arterial path length formula was used, the mean differences were −0.21 ± 39.6 mm (P = 0.953), 0.1 ± 0.9 m/s (P = 0.378). Conclusions: Whilst the left-side formula resulted in a larger bias in arterial path length compared with the right-side formula, the resulting cfPWV had a better agreement with measured values. On a sample population level, the best agreement was achieved when only the right-side formula was used. These findings demonstrate that if a formula for path length is used, the left-side and right-side formulae result in different ranges of cfPWV differences in individual measurements and in population studies.