Amplification of the pressure pulse between central and peripheral arteries renders pressure values in the upper limb an inaccurate measure of ascending aortic (AA) pressure. Accuracy could be improved by allowance for such amplification.
Transfer functions (TF) for pressures between AA and brachial artery (BA): (BATF) and between AA and radial artery (RA): (RATF) were derived from high-fidelity pressure recordings obtained at cardiac catheterization in 14 patients under control conditions, and after sublingual nitroglycerine 0.3 mg. There was no significant difference in BATF under control conditions and with nitroglycerine; hence results were pooled. Control and nitroglycerine results were also pooled to obtain a single RATF. BATF and RATF moduli peaked at 5 Hz and 4 Hz, reaching 2.5 and 2.8 times the value at zero frequency respectively. Frequency-dependent changes in modulus and phase of BATF and RATF were attributable to wave travel and reflection in the upper limb. BATF and RATF were compared to published transfer functions and those derived from analysis of aortic and brachial or radial pressure waves in previous publications. Results were similar. Our BATF and RATF were used to synthesize AA pressure waves from published peripheral pulses. Correspondence was close, especially for systolic pressure which d by 2.4 ± 1.0 (mean ± SEM) mmHg, whereas recorded systolic pressure differed by 20.4 ± 2.6 (mean ± SEM) mmHg between central and peripheral sites.
Results indicate that in adult humans a single generalized TF can be used with acceptable accuracy to determine central from peripheral pressure under different conditions. While this process is capable of refinement, it represents an advance on the present practice of assuming that central and peripheral pressures are identical.