Table 3.

Methods used to derive BRS in the selected papers

Measures	Derivation of BRS
BRS sequence method [34, 36, 42, 45, 47, 49]	Identifying sequences of at least three consecutive beats, where both SBP and RRI either increase or decrease, and then calculating the average slope of the identified sequences within a defined time frame
BRS spectral method [38–41, 43, 45, 49]	Calculating the modulus or gain of the transfer function at a frequency of 0.1 Hz using the formula: $\mathrm{BRS}[\text{ms}/\text{mmHg}]=\frac{Gxy(f)}{Gxx(f)}$ Gxy(f): cross-spectral density between SBP and RRI; Gxx(f): power spectral density of SBP
BRSf [39, 40, 45]	Using the same formula as BRS spectral method, calculating the modulus at 0.1 Hz using the instantaneous values of the heart rate (in Hz) and SBP $\mathrm{BRS}[\text{Hz}/\text{mmHg}]=\frac{Gxy(f)}{Gxx(f)}$ Gxy(f): cross-spectral density between HR and RRI; Gxx(f): power spectral density of SBP
BRS alpha-index [36, 44]	Calculating the square root of the ratio of the spectral powers of RRI and SBP within a band of a particular frequency. In [36], alpha-index for LF band (0.04–0.15 Hz) was considered. In [44], both LF and HF band (0.20–0.35 Hz) were considered and combined alpha-index was calculated: 0.5 × [LF alpha-index + HF alpha-index]

BRS baroreflex sensitivity, HF high frequency, LF low frequency, RRI RR-interval, SBP systolic blood pressure