Temporal changes in the spectroscopic parameters of the 129Xe gas, barrier, and RBC resonances in a subject with IPF (Subject 13) during inhalation, breath-hold (gray bar), and exhalation. All amplitudes are normalized to the maximum barrier-phase 129Xe signal. Unlike the healthy volunteer, the RBC resonance exhibits notable oscillations at the heart rate not only in amplitude but also in chemical shift and phase, as indicated by the black bar. The oscillation frequency is consistent with a heart rate of 71 bpm