Comparison of heart and respiratory rate variability measures using an intermittent incremental submaximal exercise model

Abstract

To better understand the alterations in cardiorespiratory variability during exercise, the present study characterized the patterns of change in heart rate variability (HRV), respiratory rate variability (RRV), and combined cardiorespiratory variability (HRV-RRV) during an intermittent incremental submaximal exercise model. Six males and six females completed a submaximal exercise protocol consisting of an initial baseline resting period followed by three 10-min bouts of exercise at 20%, 40%, and 60% of maximal aerobic capacity (V̇O2max). The R-R interval and interbreath interval variability were measured at baseline rest and throughout the submaximal exercise. A group of 93 HRV, 83 RRV, and 28 HRV-RRV measures of variability were tracked over time through a windowed analysis using a 5-min window size and 30-s window step. A total of 91 HRV measures were able to detect the presence of exercise, whereas only 46 RRV and 3 HRV-RRV measures were able to detect the same stimulus. Moreover, there was a loss of overall HRV and RRV, loss of complexity of HRV and RRV, and loss of parasympathetic modulation of HRV (up to 40% V̇O2max) with exercise. Conflicting changes in scale-invariant structure of HRV and RRV with increases in exercise intensity were also observed. In summary, in this simultaneous evaluation of HRV and RRV, we found more consistent changes across HRV metrics compared with RRV and HRV-RRV.

Do physiological and pathological stresses produce different changes in heart rate variability?

“…Standard deviation decreased during both sepsis and exercise, possibly confirming the hypothesis that it represents the level of cardiopulmonary reserve of the body (i.e., the lowest the measure, the more the body is toward its maximal capacity). LF/HF ratio, measure of sympathovagal modulation, was reduced during exercise, rather than increasing as shown in Barrera-Ramirez et al (2013). Furthermore, despite the increase in HR, no significant change of LF/HF was detected during sepsis.…”

“…The physiological interpretation of each measure in lights of the physiological dimensions of (Barrera-Ramirez et al, 2013) is instead more challenging. Standard deviation decreased during both sepsis and exercise, possibly confirming the hypothesis that it represents the level of cardiopulmonary reserve of the body (i.e., the lowest the measure, the more the body is toward its maximal capacity).…”

“…With a larger dataset in the future, it may be possible to better relate changes in HRV to the current theories about the nature of variability in physiological systems (Seely and Macklem, 2012; Barrera-Ramirez et al, 2013). It is worth noticing also the need to characterize the sensitivity of each measure of variability to non-stationarity.…”

“…The underlying hypothesis was that physiological and pathological stresses produce different effects on the body, and therefore their effects on HRV should differ. To test this hypothesis, we studied the changes in mean heart rate (HR), as well as four measures of variability belonging to different domains (Bravi et al, 2011), and associated to distinct physiological dimensions (Barrera-Ramirez et al, 2013). Each domain of variability highlights the mathematical nature of a measure of variability, while the physiological dimensions are supposed to provide a physiological rationale to the changes in variability.…”

Variability is adaptability…also during weaning!

“…During exercise, the patterns of change in heart rate variability, respiratory rate variability, and combined cardiorespiratory variability have been studied simultaneously. Measures of heart rate variability were found to be more frequently able to detect the presence of exercise, with more consistent changes across their metrics compared with breathing variables [9]. However, it is possible that, during a specific situation such as weaning from mechanical ventilation, heart rate variability and breathing pattern variability could be combined in the future to better describe the global response of the cardiorespiratory system and help the clinician in a difficult decision-making process.…”