Continuing with the theme of a Week of Science sponsored by Just Science, we will highlight some of the key points in: Appelhans BM, Luecken LJ. Heart Rate Variability as an Index of Regulated Emotional Responding. Review of General Psychology. 2006;10:229–240.
Defining Heart Rate Variability
Effective emotional regulation depends on being able to flexibly adjust your physiological response to a changing environment.
“… heart rate variability (HRV) is a measure of the continuous interplay between sympathetic and parasympathetic influences on heart rate that yields information about autonomic flexibility and thereby represents the capacity for regulated emotional responding.”
“HRV reflects the degree to which cardiac activity can be modulated to meet changing situational demands.”
The sympathetic (SNS) and parasympathetic (PNS) branches of the autonomic nervous system (ANS) antagonistically influence the lengths of time between consecutive heartbeats. Faster heart rates, which can be due to increased SNS and/or lower PNS activity, correspond to a shorter interbeat interval while slower heart rates have a longer interbeat interval, which can be attributed to increased PNS and/or decreased SNS activity.
The frequency-based HRV analyses are based on the fact that the variations in heart rate produced by SNS and PNS activity occur at different speeds, or frequencies. SNS is slow acting and mediated by norepinephrine while PNS influence is fast acting and mediated by acetylcholine.
Physiologic Underpinnings of HRV
Breathing air into the lungs temporarily gates off the influence of the parasympathetic influence on heart rate, producing a heart rate increase (see Berntson, Cacioppo, & Quigley, 1993). Breathing air out of the lungs reinstates parasympathetic influence on heart rate, resulting in a heart rate decrease. This rhythmic oscillation in heart rate produced by respiration is called respiratory sinus arrhythmia (Bernardi, Porta, Gabutti, Spicuzza, & Sleight, 2001; Berntson et al., 1993).
The central autonomic network (CAN) assists emotional regulation by adjusting physiological arousal to appropriately match the external and internal environments. The CAN consists of cortical, limbic, and brainstem components. Its output is transmitted to the sinoatrial node of the heart, among other organs.
HRV reflects the moment-to-moment output of the CAN and, by proxy, an individual’s capacity to generate regulated physiological responses in the context of emotional expression (Thayer & Lane, 2000; Thayer & Siegle, 2002).
Psychophysiological Theories of HRV
Two major theories causally relate autonomic flexibility, represented by HRV, and the capacity for regulated emotional responding:
- Polyvagal Theory: an evolutionary explanation that the ANS developed in stages to deal with changes in the environment and respond effectively. The last component developed, the ventral vagus complex, physically connects with the facial muscles, voice production, and other socially important behaviors, which creates a physical connection between the heart and emotional expression.
- Neurovisceral Integration Theory: an integrative explanation that evolutionary forces led to the development of a rapidly responding vagus nerve to support appropriate emotional expression and regulation through connections with the cortex, limbic system, and brainstem. By inhibiting other potential responses through synaptic activity in the brain and vagal activity in the body, the CAN acts as a “neurophysiological command center governing cognitive, behavioral, and physiological elements into regulated emotion states”.
Both theories presented above are similar in that they (a) specify a critical role for parasympathetically mediated inhibition of autonomic arousal in emotional expression and regulation and (b) maintain that HRV measures are informative about individuals’ capacity for this aspect of regulated emotional responding.
Empirical Research With HRV
- Low HRV is an independent risk factor for several negative cardiovascular outcomes
- Low HRV is a proxy for underlying cardiovascular disease processes
- Higher levels of resting HRV have been associated with effective coping strategies
- Attention control is associated with higher HRV
- Patients with generalized anxiety disorder show lower HRV than controls
- Low HRV has been associated with depression
Summary, Future Directions, and Conclusions
“HRV is emerging as an objective measure of individual differences in regulated emotional responding, particularly as it relates to social processes and mental health.”
“Further investigation should attempt to elucidate those contexts in which the autonomic flexibility represented by greater HRV is particularly adaptive, as well as situations in which greater HRV may be maladaptive. Although theorists and researchers have emphasized the importance of parasympathetically mediated HRV in regulated emotional responding, the relative contribution of sympathetic regulation of the heart has not yet been clarified.”
“Potential clinical applications of HRV also exist, as increasing an individual’s capacity for inhibitory emotion regulation through HRV biofeedback (Lehrer et al., 2003) may have therapeutic implications for mood, anxiety, and impulse control disorders.”
“Unlike other psychophysiological variables, HRV provides information regarding both PNS and SNS activity, thereby permitting inferences about both inhibitory and excitatory processes in emotion regulation.”