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 delve into this relationship, we applied low (10 mmHg) and moderate (30 mmHg) lower body negative pressure (LBNP) in 10-s cycles to 18 healthy young male subjects. They showed no change in average blood pressure with this oscillatory 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-frequency blood pressure oscillations in a graded response to oscillatory LBNP level (P < 0.05) while significantly increasing low-frequency R-R interval 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 basal conditions (n = 17), only seven subjects maintained significant coherence during both levels of LBNP. These results suggest that a complex interaction of regulatory mechanisms determines the link between low-frequency oscillations and the responses to even low levels of LBNP.