Hybrid reservoir-wave models assume that the measured arterial pressure can be separated into two additive components, reservoir/windkessel and excess/wave pressure waveforms. Therefore, the effect of the reservoir volume should be excluded to properly quantify the effects of forward/backward-travelling waves on blood pressure. However, there is no consensus on the value of the asymptotic diastolic pressure decay (P∞) which is required for the calculation of the reservoir pressure. The aim of this study was to examine the effects of varying the value of P∞ on the calculation of reservoir and excess components of the measured pressure and velocity waveforms. Common carotid pressure and flow velocity were measured using appalanation tonometery and Doppler ultrasound, respectively, in 1037 healthy humans aged 35–55 years; a subset of the Asklepios population. Wave speed was determined using the PU-loop method, and used to separate the reservoir and wave pressures. Wave intensity analysis was performed and its parameters have been analysed with varying P∞ between −75% to +75% of its initial calculated value. The underestimation (up to −75%) of P∞ (with respect to a reference value of 48.6 ± 21 mmHg) did not result in any substantial change in either hemodynamic or wave intensity parameters, whereas its overestimation (from +25% to +100%) brought unrealistic increases of the studied parameters and large standard deviations. Nevertheless, reservoir pressure features and wave speed seemed insensitive to changes in P∞. We conclude that underestimation and overestimation of P∞ produce different hemodynamic effects; no change and substantially unrealistic change, respectively on wave intensity parameters. The reservoir pressure features and wave speed are independent of changes in P∞, and could be considered more reliable diagnostic indicators than other hemodynamic parameters, which are affected by changes in P∞.