CARDIAC BAROREFLEX FUNCTION DURING POSTURAL CHANGE ASSESSED USING NONINVASIVE SPONTANEOUS SEQUENCE-ANALYSIS IN YOUNG MEN

Study objective - The aim was to assess the value of baroreflex sensitivity estimates calculated from analyses of spontaneous systolic blood pressure and pulse interval sequences derived from continuous non-invasive finger blood pressure recordings during sitting and active standing.Design - Continuous recordings of digital systolic blood pressure and pulse interval were obtained non-invasively using a Finapres FD5 during 5 min trials of sitting and standing.Subjects - Subjects were healthy males aged 19-28, divided into those with "high" normal (n = 18) and "low" normal (n = 17) blood pressure.Measurements and main results - Recordings were scanned for spontaneous sequences of three or more cardiac cycles over which systolic blood pressure increased progressively in conjunction with prolonged pulse interval, or decreased while pulse interval became shorter. Regressions between blood pressure and pulse interval (r≥0.80) provided estimates of cardiac baroreceptor reflex control. Computations were carried out with concurrent blood pressure and pulse interval measurements, and with a delay or lag of one and two cycles between the two variables. Pulse interval was reduced from an average 870.3 ms sitting to 571.3 ms on standing. Mean baroreflex sensitivity while sitting averaged 17.5 ms·mm Hg-1 at a delay of one cycle, falling to 7.65 ms·mm Hg-1 with standing. The decrease in sensitivity was correlated with the change in pulse interval between trials. The number of sequences was also significantly reduced with standing as opposed to sitting. Three cycle sequences were most frequent, with a lesser number of sequences involving 4,5, and 6 or more cycles. No significant differences between "high" and "low" normal blood pressure groups were observed.Conclusions - The analysis of spontaneous sequences from non-invasive recordings may provide useful information concerning cardiac baroreflex control in different postural and behavioural states. A lag of one cycle between systolic blood pressure and pulse interval may provide the most representative estimates of baroreflex sensitivity.