Baroreflex sensitivity during noxious stimulation in vasovagal reactors to blood donation.

Baroreflex sensitivity was assessed at rest and during constrictive pain in healthy males with and without a history of vasovagal reactions to blood donation. Continuous recordings of cardiac inter-beat interval and finger arterial pressure were obtained at rest and during repeated presentations of constrictive thigh-cuff stimulation. Baroreflex sensitivity (in msec/mm Hg) was computed according to the spontaneous sequence analysis method. Results indicated that vasovagal reactors exhibited significantly lower descending baroreflex sensitivity across all periods, and significantly lower ascending baroreflex sensitivity at rest. Baseline differences in ascending baroreflex sensitivity were eliminated during thigh-cuff stimulation, as vasovagal reactors exhibited increases in ascending baroreflex sensitivity while non-reactors exhibited decreases. These findings suggest that susceptibility to vasovagal reactions may be associated with individual differences in baroreflex sensitivity.