Differential contribution of forward and backward pressure to carotid pressure waveform in fibromuscular dysplasia compared to essential hypertension

Background: Fibromuscular dysplasia (FMD) is a non-atherosclerotic, multi-arterial disease with unknown aetiology that usually presents with hypertension. Alterations in the elastic and geometric properties of carotid and radial arteries have been reported in FMD (1) which may differentially affect wave morphology compared to essential hypertension (HTN) and healthy subjects (HS).

Methods: Left and Right carotid pressure waveforms measured using tonometry and blood flow velocity from ultrasound in patients with FMD (n = 17), HTN (n = 24) and age-matched HS (n = 21) were used for wave separation analysis. Forward (Pf) and backward (Pb) pressure wave amplitude, reflection magnitude (RM=Pb/Pf) and reflection index (RI=Pb/(Pf+Pb)) were derived.

Results: Age was comparable between groups (FMD vs HTN vs HS; 52.1±15.9 vs 53.0±14.8 vs 52.0±13.8years, p = 0.97). Pulse pressure was comparable between FMD and HTN but significantly higher in FMD than HS (43.7±15.1 vs 41.3±10.9 vs 35.3±9.23mmHg, p =0.01). After correcting for measurement sites and height, Pf was significantly higher in FMD (n = 33) and Pb was significantly higher in essential HTN (n =49) compared to controls (n = 43) (Pf: 40.8±15.1 vs 35.5±9.08 vs
32.6±8.78mmHg, p = 0.007 and Pb: 13.7±5.49 vs 14.2±4.00 vs 11.7±4.12mmHg, p = 0.044). RM and RI were higher in HTN compared to FMD (RM: 0.35±0.10 vs 0.41±0.11 vs 0.37±0.11, p =0.036, RI: 0.25±0.06 vs 0.28±0.05 vs 0.26±0.06, p =0.032).

Conclusion: Despite similar pulse pressure, there is a differential contribution of forward and
backward pressure (Figure 1) to the carotid pressure waveform in FMD and HTN.