Heart period sensitivity to forced oscillations in ventilatory pressure

Heart rate variability analysis is a dynamic method to estimate the autonomic control over the cardiac cycle. Although dysfunction in this control system may appear spontaneously, other deficits may require provocation of the system. In this article we describe a non-invasive method to perturb the autonomic influences on the cardiac cycle. We recorded the ECG and respiratory pressure of ten healthy volunteers while introducing a random forced oscillation pressure wave onto spontaneous respiration. The heart period time series was determined and the power spectra for the 0.05-0.15, 0.15-0.3 and 0.05-0.4 Hz bands were calculated. The random input did not alter mean heart rate. However, the segments with the forced oscillation input demonstrated, on average, a tenfold increase in spectral power averaged across all subjects, with a maximum observed effect of 100-fold increase in power. This increase in power correlated with the respiratory frequency. This study demonstrates that random noise ventilation, such as used in respiratory forced oscillation impedance estimates, significantly alters the autonomic input to cardiac cycle variability in wake subjects.