Inconsistent link between low-frequency oscillations: R-R interval responses to augmented Mayer waves

Low-frequency oscillations in arterial blood pressure (Mayer waves) and R-R interval are thought to be linked through the arterial baroreflex. To delv e into this relationship, we applied low (10 mmHg) and moderate (30 mmHg) l ower body negative pressure (LBNP) in 10-s cycles to 18 healthy young male subjects. They showed no change in average blood pressure with this oscilla tory stimulus but did show a significant decrease in R-R interval (P < 0.05 ) during both levels of LBNP. In addition, we succeeded in augmenting low-f requency blood pressure oscillations in a graded response to oscillatory LB NP level (P < 0.05) while significantly increasing low-frequency R-R interv al oscillations (P < 0.05). However, cross-spectral coherence between these increased oscillations was highly variable across individuals and stimulus level. Although nearly all subjects showed significant coherence during ba sal conditions (n = 17), only seven subjects maintained significant coheren ce during both levels of LBNP. These results suggest that a complex interac tion of regulatory mechanisms determines the link between low-frequency osc illations and the responses to even low levels of LBNP.