Purpose: The frequency of breathing influences the spectral powers of heart rate variability (HRV) as well as the magnitudes of heart rate deceleration capacity (DC) and acceleration capacity (AC). We compared the strength of their relationships under different breathing frequencies.
Methods: We studied 14 healthy young adults who breathed spontaneously and controlled their breathing rates to 0.1, 0.2, 0.3 and 0.4 Hz in a supine position. A 5-min R-R interval time series without movement artefacts or ectopic beats was obtained for each study period. Spectral indices were defined as the square roots of spectral powers in the very low frequency (0.01-0.04 Hz), low frequency (0.04-0.15 Hz), high frequency (0.15-0.4 Hz) and respiratory frequency bands. We also combined these frequency bands into LHF (0.04-0.4 Hz) and VLHF (0.01-0.4 Hz). DC and AC were obtained using phase rectified signal averaging.
Results: DC and AC were significantly correlated with all indices of HRV. The within-subject correlation coefficients for the LHF index had the greatest absolute values (0.953 and -0.919, respectively). DC and AC had different strength of relationships with the LHF index, but became comparable (0.954 vs. -0.943) when the data obtained under 0.1-Hz breathing were excluded.
Conclusion: DC is strongly correlated with the spectral index of the LHF band, indicating that they are controlled by similar influences under the conditions used in this study. AC is less related to the LHF index due to the fact that its magnitude deceases during 0.1-Hz breathing.
Keywords: Acceleration; Deceleration; Heart rate; Respiration; Spectral analysis.