Cardiovascular periodicities in healthy humans in the absence of breathing and under reduced chemical drive of respiration.

In 20 healthy human subjects (aged 20-24 years) power density spectra in 1-min time series were computed by modified MATLAB procedures from inter-beat heart intervals and systolic and diastolic finger blood pressure. High- (HF), mid- (MF) and low-frequency (LF) peaks (0.16-0.37 Hz, 0.08-0.12 Hz and 0.02-0.05 Hz, respectively) were distinguished in power density spectra (PDS). During 1-min voluntary apneas MF and LF power increased and in 18 out of 20 subjects HF peaks disappeared in PDS. Breath holding performed in hyperoxia or in hyperoxia accompanied by 1-min hyperventilation preceding apnea augmented power at MF and LF range and abolished marginal HF peaks present in the spectrum in two subjects. It is concluded that apneic PDS is characterized by augmented power of MF and LF rhythms, and represents endogenous free running cardiovascular periodicities released from feed-back mechanical, reflex and feed-forward central entrainment to respiratory rhythm.