Interpretation of oscillations in heart rate and blood pressure

Fluctuations of heart rate and blood pressure reflect dynamic control over tonic neuronal activity. A number of confounding factors have to be considered before cardiovascular rhythms can be used as a reliable index of autonomic nervous system integrity. The temporal profile of nonrespiratory oscillations (0.01 to 0.15 Hz with a dominant ≈0.05 Hz rhythm) (NONRF) and oscillations at respiratory frequencies (RF) (0.01 to 0.5 Hz) were analyzed by modified Wigner distribution (WD). Both RF and NONRF were continuously present during supine rest and in the upright position in normal young and elderly subjects. However, the pattern of NONRF oscillations in BP and R-R interval (RRI) becomes unstable in orthostatically intolerant patients, e.g. with vasodepressor syncope or orthostatically intolerant patients. Typically, large transient NONRF oscillations in BP occur after tilt-up and disappear with impending syncope. In patients with severe symptoms of postural tachycardia, both NONRF and RF in RRI are reduced. Loss of rhythmicity over the whole range from 0.01 to 0.5 Hz is associated with severe central lesions (like in brain stem injury). The profile of cardiovascular rhythms provides information about the integrity of the autonomic neural pathways. It could provide insights into the timing and processing of afferent impulses in the brainstem network.