Time domain, geometrical and frequency domain analysis of cardiac vagal outflow: effects of various respiratory patterns

Abstract

The purpose of this study was to compare the applicability of four different measures of heart rate variability (HRV) in the assessment of cardiac vagal outflow, with special reference to the effect of breathing pattern. The anticholinergic effects of an intravenous glycopyrrolate infusion (5 microg x kg(-1) x h(-1) for 2 h) during spontaneous and controlled (15 min(-1)) breathing rate were investigated in eight volunteers, and the effects of different fixed breathing rates (6-15-24 min(-1)) and hyperventilation in 12 subjects. Cardiac vagal activity was assessed by ECG recordings in which the following measures of HRV were computed: the high-frequency (HF) spectral component, the instantaneous RR interval (RRI) variability (SD1) analysed from the Poincaré plots, the percentage of differences between successive RRIs greater than 50 ms (pNN50), and the square root of the mean squared differences of successive RRIs (RMSSD). On average, glycopyrrolate reduced the HF spectral component by 99.8%, SD1 by 91.3%, pNN50 by 100% and RMSSD by 97.0%. The change of breathing pattern from controlled to spontaneous decreased significantly the HF component and pNN50, but did not affect SD1 or RMSSD. Rapid breathing rate (24 min(-1)) decreased the HF component, but had no effects on the other measures. A controlled breathing rate is needed for a reliable assessment of cardiac vagal outflow by the spectral analysis technique. The quantitative geometrical analysis of short-term RRI variability from the Poincaré plots and the time domain measure RMSSD were not significantly affected by changes in the breathing rate, suggesting that these indices are more suitable for the measurement of cardiac vagal outflow during the 'free-running' ambulatory conditions.

The effect of short-term intermittent hypoxic exposure on heart rate variability in a sedentary population

“…Given that there can be substantial individual variation in the hypoxic ventilatory response (11), the change in breathing frequency with hypoxic exposure may be responsible for the decrease in rMSSD, rather than autonomic change. However, while Penttilä et al (18) did note a decrease in rMSSD with increased breathing frequency, these differences were not statistically significant, and therefore the decrease in rMSSD during hypoxic exposure in our study is likely to predominantly reflect vagal withdrawal, rather than change in respiration. In addition to the high level of autonomic variation between participants, there was also a wide variation in the nature of the subjective reponses in the participants which were collected in session by session comment books.…”

“…To measure heart rate variability, the root mean square of successive differences in the RR interval (rMSSD) and RR interval were used to provide an indication of vagal outflow. These measures are more resistant to breathing artefact than alternative analyses (18). However, to provide a more complete dataset, and to enable greater comparability with other research, the standard deviation of N-N intervals (SDNN) and high frequency (HF: 0.15 -0.4 Hz) measurements were also reported.…”

Heart rate variability and critical flicker fusion frequency changes during and after parachute jumping in experienced skydivers

“…Jumping from a plane at 4000 m of height may cause changes in the respiration rate and depth (Fenz and Epstein 1967;Roth et al 1996). These in turn can affect HRV (Penttila et al 2001;Brown et al 1993;Kitney et al 1985), and subsequently increase the parasympathetic contribution (HF) by a shift from LF to HF, potentially masking the LF increase that should coincide with the rise of the sympathetic tone during the jump. Thus, correct interpretation of HRV measures by frequency domain has to account for possible changes in the respiration rate during the time course of data collection.…”

“…This vagal input reduction is not clearly shown in the frequency domain. This can be explained by the fact that the non-linear domain is much less affected by the RSA (Lewis and Short 2007;Penttila et al 2001). Previous studies have indeed shown that the SD1 component is not influenced by any modified breathing patterns (Penttila et al 2001).…”

“…This can be explained by the fact that the non-linear domain is much less affected by the RSA (Lewis and Short 2007;Penttila et al 2001). Previous studies have indeed shown that the SD1 component is not influenced by any modified breathing patterns (Penttila et al 2001). This supports the idea of the influence of the RSA on the frequency domain results at the time of the jump since the HF component did not decrease at this moment.…”