Figure 5. Coherence between systolic pressure and R-R interval in 18 young males during 5 min of supine rest, and of 0.1 Hz oscillatory lower body suction at 10 and 30 mmHg.

The oscillatory suction significantly augments arterial pressure oscillations and cardiac interval oscillations at the Mayer wave frequency; however, the correlation (i.e. coherence) between the oscillations is highly variable, both among subjects and across levels of suction (modified from Hamner et al. 2001).