BAROREFLEX SENSITIVITY DURING NOXIOUS-STIMULATION IN VASOVAGAL REACTORS TO BLOOD DONATION

Baroreflex sensitivity was assessed at rest and during constrictive pa in in healthy males with and without a history of vasovagal reactions to blood donation. Continuous recordings of cardiac inter-beat interva l and finger arterial pressure were obtained at rest and during repeat ed presentations of constrictive thigh-cuff stimulation. Baroreflex se nsitivity (in msec/mm Hg) was computed according to the spontaneous se quence analysis method. Results indicated that vasovagal reactors exhi bited significantly lower descending baroreflex sensitivity across all periods, and significantly lower ascending baroreflex sensitivity at rest. Baseline differences in ascending baroreflex sensitivity were el iminated during thigh-cuff stimulation, as vasovagal reactors exhibite d increases in ascending baroreflex sensitivity while non-reactors exh ibited decreases. These findings suggest that susceptibility to vasova gal reactions may be associated with individual differences in baroref lex sensitivity.