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Heart rate complexity: A novel approach to assessing cardiac stress reactivity
Ryan C Brindle1, Annie T Ginty2, Anna C Phillips1
1School of Sport, Exercise, and Rehabilitation Sciences, University of Birmingham, Birmingham, UK.
Insights
Correlation dimension (D2), a measure of heart rate complexity, independently predicts heart rate reactivity during mental stress. This finding suggests D2 offers unique insights beyond traditional autonomic measures for assessing cardiac stress responses.
Area of Science:
- Cardiology
- Psychophysiology
- Complexity Science
Background:
- Heart rate (HR) complexity, measured by correlation dimension (D2), decreases with acute mental stress.
- Reduced D2 is linked to adverse cardiovascular health outcomes.
- The precise relationship between stress-induced D2 changes and HR reactivity requires further elucidation.
Purpose of the Study:
- To systematically assess the relationship between stress-induced changes in D2 and HR reactivity.
- To determine if D2 provides unique predictive information for HR reactivity, independent of autonomic nervous system activity.
- To investigate this relationship while controlling for respiration and autonomic modulations.
Main Methods:
- Two studies were conducted, with sample sizes of 25 (Study 1) and 162 (Study 2).
- Correlation dimension (D2) was calculated from heart rate variability data during mental stress tasks.
- Hierarchical linear models were used to assess D2 as a predictor of HR reactivity, controlling for respiration rate, cardiac vagal tone, and cardiac sympathetic activity.
Main Results:
- In both studies, D2 decreased significantly during acute mental stress.
- Study 1 demonstrated that D2 predicted HR reactivity even after adjusting for respiration rate and cardiac vagal tone.
- Study 2 confirmed D2 as an independent predictor of HR reactivity within a comprehensive model including parasympathetic and sympathetic activity.
Conclusions:
- Correlation dimension (D2) offers valuable information regarding cardiac stress reactivity.
- D2 provides incremental predictive value for heart rate reactivity beyond traditional measures of cardiac autonomic function.
- These findings highlight the potential utility of D2 in understanding cardiovascular responses to stress.
Abstract:
Correlation dimension (D2), a measure of heart rate (HR) complexity, has been shown to decrease in response to acute mental stress and relate to adverse cardiovascular health. However, the relationship between stress-induced changes in D2 and HR has yet to be established. The present studies aimed to assess this relationship systematically while controlling for changes in respiration and autonomic activity. In Study 1 (N = 25) D2 decreased during stress and predicted HR reactivity even after adjusting for changes in respiration rate, and cardiac vagal tone. This result was replicated in Study 2 (N = 162) and extended by including a measure of cardiac sympathetic activity; correlation dimension remained an independent predictor of HR reactivity in a hierarchical linear model containing measures of cardiac parasympathetic and sympathetic activity and their interaction. These results suggest that correlation dimension may provide additional information regarding cardiac stress reactivity above that provided by traditional measures of cardiac autonomic function.
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