Session S22.1

High Frequency Component of HRV-Respiratory Frequency Continuous Relationship during Postural Change

S Carrasco-Sosa, A Guillén-Mandujano*, P Coello-Caballero

Universidad Autonoma Metropolitana
Mexico City, Mexico

The high frequency component (HF) of the heart rate variability (HRV) spectrum results from the interplay of respiratory and non-respiratory modulating factors. Controlled breathing at a single frequency is used to keep the respiratory factor constant to make the HF changes less ambiguous. However, the HF component is a complex function of the respiratory frequency (RF). The aims of the present study were to obtain a continuous HF-RF relationship during a brief chirp-patterned breathing maneuver and to evaluate its ability to indicate the vagal withdrawal produced by the change from sitting to standing position. ECG and lung volume were registered and acquired from 30 healthy young volunteers during the breathing maneuver executed in sitting and standing positions. Subjects performed a 90-s continuous and linear respiratory frequency increase from 0.05 to 0.8 Hz at constant tidal volume, visually guided by an electronic device. Since the time series of interest are nonstationary, their time-varying power spectra were estimated using the smoothed pseudo Wigner-Ville transform to compute the HF component of HRV and the instantaneous frequency of the respiratory signal, from which the HF-RF relationships were formed. In all cases the HF-RF relationship depicted a continuous, non linear and inverse curve. After logarithmic transformation their linear regressions and correlations could be computed. Mean correlations were r=-0.88±0.03 in sitting and r=-0.89±0.04 in standing. With the change from sitting to standing the ln-regression intercept decreased from 7.6±1.1 to 7.0±1.0 ln-ms2 (p<0.001) and the slope increased from -0.74±0.58 to -0.95±0.60 ln-ms2Hz-1 (p<0.009). Our brief chirp-patterned breathing procedure allows to obtain a continuous HF-RF relationship over a very wide range of RF without fatiguing the subjects, and to be superimposed on a different maneuver. The intercept decrease and the slope increase correctly and clearly measure the vagal withdrawal induced by the postural change. Thus our findings demonstrate that the postural change effect can be assessed separately from the RF influence; this ability improves the reliability of HF as a vagal index.

(Abstract Control Number: 133)