Spontaneous baroreflex analysis
The sequence method was used to evaluate baroreflex function over the
physiological range of fluctuations in arterial pressure without any
pharmacological manipulation. For this purpose, the beat-to-beat values
of systolic arterial pressure (SAP) and pulse interval (PI) were
analysed using CardioSeries v2 software (Lataro, Silva, Silva, Salgado,
& Fazan, 2017). The SAP time series were evaluated to find SAP
elevations of 4 or more beats that were accompanied by a progressive
increase in the R-R interval, which are called UP ramps. DOWN ramps are
the opposite and consist of SAP reductions of four or more beats that
are accompanied by a progressive decrease in the R-R interval.
Spontaneous baroreflex activity was assessed based on the slope
(ms/mmHg) of the linear regression between the SAP and PI for UP, DOWN
and average (i.e., mean of UP and DOWN sequences) sequences (Di Rienzo
et al., 2001). For this experiment, we used a correlation coefficient
(r) greater than 0.80. The baroreflex effectiveness index (BEI) was also
calculated as the ratio between the number of SAP ramps followed by the
reflex PI response and the total number of SAP ramps (Di Rienzo et al.,
2001).